Session 1

  1.1 Pending  
NAMEZhang Zhongping 
EMAILzzp@shao.ac.cn 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ADDRESSThe Progress and developments of Shanghai SLR station
Zhang Zhongping , Zhang Haifeng, Deng Huarong, Tang Kai ,Wu Zhibo, Qin Si 
(Shanghai Astronomical Observatory of Chinese Academy of Sciences)
zzp@shao.ac.cn
Abstract: Through technical researches and system improvements, the performance of Shanghai kHz repetition rate SLR system has been greatly enhanced. The SLR data quality has been improved persistently, which reaches ILRS guidelines at the field of long and short stability since 2015 and the efforts for further strengthening SLR data stability are still made in order to establish the top-level SLR system. Updating 1kHz laser system, the 4kHz repetition rate laser pulse is setup and applied in the routine SLR measurements, which has increased the amount of laser data and the precision of normal points and make more positive impacts on measuring the spin parameters of laser spherical satellites. At the aspect of laser tracking space debris and the technical analysis of higher stability laser time transfer, the propulsive achievements has been made based on Shanghai SLR system. For further widening the applications of SLR system and improving system performance, the development and experiments of new technologies and novel devices are underway at Shanghai SLR station, including near infrared wavelength (1.064um) SLR technology, methods for increasing detection ability based on multi-telescopes and Superconducting Nanowire Single Photon Detector (SNSPD) with high performance.
 
  1.2 Pending
NAMEWu Zhibo 
EMAILwzb@shao.ac.cn 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ADDRESSSatellite Laser Ranging with 4 kHz Repetition Rate and Its Application
Wuzhi Bo, Zhang Haifeng, Deng Huarong, Tang Kai ,Li Pu, Zhang Zhongping,
(Shanghai Astronomical Observatory of Chinese Academy of Sciences)
wzb@shao.ac.cn
Abstract: There is a technological tendency for improving the performance of SLR system by increasing the working frequency. In 2013, Shanghai Astronomical Observatory (SHAO) breakthrough SLR technology to realize 10 kHz repetition rate laser ranging in the first time. For balancing the detection capability and performances, SHAO put forward and established a routine 4 kHz SLR system by using a civil laser with power of about 2.5 watts, 50ps pulse width and M2 of ~1.2 since 20th of July this year. For the new 4 kHz SLR system, precision of calibration ground target is about 5-8mm, and all the ILRS satellites had been successfully measured with higher precision of NPTs and high data density per pass by comparing with our 1 kHz SLR system. The paper also showed the exciting result of measuring rotation rate of satellites by applying 4 kHz laser data.
 
  1.3  Pending  
NAMEKrzysztof Sośnica, Grzegorz Bury, Radosław Zajdel, Kamil Kaźmierski, Dariusz Strugałek, Mateusz Drożdżewski, Tomasz Hadaś 
EMAILkrzysztof.sosnica@igig.up.<wbr />wroc.pl 
SESSIONSession 2(1): satellite tracking and scheduling 
TYPEPresentation 
ADDRESSCombined multi-GNSS+LAGEOS solutions with the focus on SLR station coordinates, Earth rotation parameters, geocenter and the scale of the reference frame. Results from the ILRS intensive GNSS tracking campaigns.


All satellites of new GNSS systems are equipped with laser retro-reflectors dedicated to SLR tracking. Between 2014 and 2017, the ILRS initiated three intensive SLR tracking campaigns devoted to all GNSS satellites, four Galileo, and one GLONASS campaign. As a result, the number of tracked GNSS satellites and the number of SLR observations have dramatically increased allowing for determining GNSS orbits, SLR station coordinates, geocenter coordinates, and Earth rotation parameters. This paper provides the results from the GNSS intensive tracking campaigns and shows the contribution of SLR tracking of multi-GNSS constellation to improved SLR-derived reference frame and scientific products.
We show a solution strategy with estimating satellite orbits, SLR station coordinates, geocenter coordinates, and Earth rotation parameters using SLR observations to 2 LAGEOS and 55 GNSS satellites: 1 GPS, 31 GLONASS, 18 Galileo, 3 BeiDou IGSO, 1 BeiDou MEO, and 1 QZSS satellite for the period 2014.0-2017.5. We compare the SLR station coordinate repeatability and Earth rotation parameters derived from a combined ‘SLR to GNSS+LAGEOS’ solution to the classical LAGEOS-only solution. We found that the repeatability of SLR station coordinates improves by 6.9, 6.4, and 15.7%, for the North, East, and Up component, respectively, when adding SLR observations to GNSS. Due to a large number of GNSS observations, the number of weekly solutions for some SLR stations, e.g., Arkhyz, Komsomolsk, Altay, Brasilia, Wettzell, is larger up to 41% in the LAGEOS+GNSS solution as compared to LAGEOS-only solution. The RMS of differences of the length-of-day parameter w.r.t. IERS-C04-14 series is reduced from 132 μs to 43 μs when adding SLR observations to multi-GNSS. Finally, we show that the SLR observations to GNSS can transfer the orientation of the reference frame from GNSS to SLR solutions. As a result, the pole coordinates and length-of-day estimates become more stable, whereas the SLR and GNSS solutions become more consistent with each other.
   1.4 Pending  

 

 

NAME

Grzegorz Bury, Krzysztof Sośnica, Radosław Zajdel 
EMAILgrzegorz.bury@igig.up.wroc.pl 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ADDRESSHow many SLR observations and how many stations are needed for deriving high-quality multi-GNSS orbits?


Multi-GNSS Experiment (MGEX) was initiated by the International GNSS Service (IGS) due to emerging of both, new navigation satellite systems, i.e., Galileo, BeiDou, QZSS, NavIC, and modernized GPS and GLONASS. All new navigation satellites are equipped with Laser retroreflectors for Satellite Laser Ranging (SLR). The growth of the number of multi-GNSS constellation induces the International Laser Ranging Service (ILRS) to provide a support in the form of special SLR-GNSS tracking campaigns and the priority list for SLR station to track. This work summarizes three special tracking campaigns which took place in the period: 2014.0-2017.0.

Range measurements to multi-GNSS constellation typically are employed for the validation of microwave products. However, SLR observations can also be used for the multi-GNSS orbit determination. In this work, we aim at addressing the following questions: (1) How many SLR observations to multi-GNSS satellites are necessary to provide multi-GNSS orbits of a decent quality using solely SLR data? (2) What is an optimal geometry of observations and how many stations are needed to determine a high-quality GNSS orbit? 

Moreover, we test 3-, 5-, 7- and 9-day GNSS orbital arcs based on SLR data and we develop a common strategy for multi-GNSS orbit determination in order to both, increase the number of SLR observations and not allow orbit parameters to obsolete. We consider the whole GLONASS constellation, all active Galileo satellites, four BeiDou spacecraft (1 MEO, 3 IGSO) and the first QZSS satellite, QZS-1. In order to be as consistent as possible with MGEX, we use official MGEX products from the Center for Orbit Determination in Europe (CODE). CODE’s orbits serve as both, a priori data and as a reference microwave orbits. Orbit quality is assessed as a difference between reference CODE products and calculated SLR orbits in the radial, along-track and cross-track directions. 

For all MEO satellites we obtain orbits with the accuracy at the level of 4, 10 and 18 cm in the radial, along-track and cross-track direction, respectively when compared to microwave orbits, from just 60 SLR observation gathered in a 3-day period. With the increase of the number of observation to 100, the accuracy grows to 2, 8 and 11 cm for the radial, along-track, and cross-track direction, respectively. The minimum number of SLR tracking stations is 5 for the orbit quality at sub-meter level. The solution obtained from 10 stations results in orbit at the level of 5, 10 and 20 cm in the radial, along-track and cross-track direction, respectively. Calculating 3-day arcs leads to an insufficient quality of multi-GNSS orbits when using solely SLR data for most of the GNSS satellites. The compromise between the quality and efficiency in calculations are 5- and 7-day arcs. 9-day arcs lead to the degradation in orbit quality in the along-track direction. 

The best orbit solution was obtained for the GLONASS R07 spacecraft on 15 July 2015. The 5-day solution was calculated using 129 SLR observations provided by 12 homogeneously distributed SLR stations. During the 5-day period the satellite R07 was tracked by 2 stations from North America, 3 from Asia, 2 from Australia, and 5 from Europe, all of which provided an even and supreme geometry of observations. The RMS of differences between microwave-based and SLR-based orbits for the best 5-day solution of GLONASS R07 equals 8, 24, 19 mm in the radial, along-track and cross-track direction, respectively.  
   1.5 Pending  
NAMEJohann Eckl 
EMAILeckl@fs.wettzell.de 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ADDRESSGround station requirements for the ELT experiment

When is comes to precise orbit determination in geodesy, Satellite Laser
Ranging is the state of the art technology. Therefore, the geometrical
reference point of the ground stations is well defined in space. Upgarding
these systems with highly accurate clocks in combination with a good
definition and stability of the local reference points in time would
enable this technique for highly accurate and precise optical time
transfer between space and ground. As a consequence the stations will
become reference points in time as well. We report on the requirements for
ground stations, which participate in the ELT experiment and the
performance that can be expected. 
   1.6 Pending  
NAMEDavid Lucchesi 
EMAILdavid.lucchesi@iaps.inaf.it 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ADDRESSSatellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) are two very important techniques, among the others, of the observational space geodesy. Indeed, Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), together with SLR and LLR constitute the Global Geodetic Observing System (GGOS) and contribute to the definition of the Interna-
tional Terrestrial Reference Frame. Obviously, in the context of the GGOS, improvements in technology and in modelling will produce advances in geodesy and geophysics as well as in GR measurements. Therefore, these two important research fields, space geodesy and GR, are not independent, but tightly related to each other. In the near future it is expected, within the GGOS activities, an improvement of one order of magnitude in global accuracies in the observational as well as the theoretical components of space geodesy. This implies improvements in measuring accuracies, in reference frames realization, in modelling, in the stations network geometry and, consequently, into the accuracies involved when doing fundamental physics measurements using space geodesy techniques.
In the field of fundamental physics, LLR has provided very accurate tests of both the Einstein Equivalence Principle (EEP) and of the Strong Equivalence Principle (SEP) and, consequently, of the Nordtvedt parameter η. LLR has also provided a significant limit to the Parameterized Post-Newtonian (PPN) parameters β, α1 and α2, to the geodetic precession Kgp , to the time
variation of the gravitational constant Gdot/G, as well as to possible deviations to the inverse square law in case of very weak long–range gravity interactions parameterized by a Yukawa-likepotential.
Conversely, SLR has provided the first direct test of the gravitomagnetic field of GR produced by mass-currents by measuring the precession of the combined nodes (and also perigee) of the two LAGEOS satellites (also known as frame–dragging effect). More recently, also the SLR measurements of LARES have been added to those of the two LAGEOS, and two new precise measurements of the Earth’s gravitomagnetic effect have been obtained. Other significant
results obtained through the SLR technique have been the first measurement of the combination, in the field of the Earth, of the PPN parameters β and γ, with consequent meaningful constraints to a number of alternative theories of gravity and to the strength α of a possible Yukawa long-range interaction with a range of about 1 Earth radius. Moreover, it has been possible to measure separately the PPN parameters β and γ by their direct estimate from the equations of motions as solve-for parameters.
The LAser RAnged Satellites Experiment (LARASE) aims to provide an original contribution in testing and verifying relativistic physics — in the weak-field and slow-motion limit of GR — by means of the SLR technique together with a precise orbit determination (POD) of a set of passive laser-ranged satellites, namely the two LAGEOS and LARES. However, although the final goal of LARASE is to perform new measurements of gravitational physics and to test the
validity of the predictions of Einstein’s GR with respect to those of other metric and non-metric theories for the gravitational interaction, the activities performed to reach such objective, such as the improvements needed to the dynamical model of the cited satellites, represent a bridge that naturally links, as said previously, fundamental physics measurements with geophysics and space geodesy.
The results obtained so far by LARASE in term of relativistic measurements and dynamical models improvements will be presented and discussed in relationship with the importance of a continuous tracking of the two LAGEOS and LARES satellites. 
    1.7 Pending  
NAMEJaime Fernández, Carlos Fernández, Pierre Féménias, Heike Peter 
EMAILjfernandez@gmv.comheike.peter@positim.com 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPoster 
ADDRESSThe Copernicus Sentinel-3 mission

Sentinel-3A, the first satellite of the Copernicus Sentinel-3 mission, was launched on 16 February 2016. The mission is jointly operated by ESA and EUMETSAT to deliver operational ocean and land observation services within the Copernicus project. 
In addition to the main payloads namely the SAR Radar Altimeter, the Ocean and Land Colour Instrument, the Microwave Radiometer and the Sea and Land Surface Temperature Radiometer the satellite carries a couple of GPS receivers, a Laser Retro Reflector (LRR), and a DORIS receiver for Precise Orbit Determination. Observations from all three techniques are equally important to fulfil the stringent orbit accuracy requirements of 2-3 cm in radial direction. 
The Copernicus Precise Orbit Determination (POD) Service, a GMV-led consortium being in charge of generating precise orbital products and auxiliary data files not only for Sentinel-3 but also Sentinel-1 and -2, is in charge of computing and delivering the CPF orbit files to the ILRS community and is a main user of the Satellite Laser Ranging (SLR) measurements to compute the precise orbital products of Sentinel-3.
SLR is a key technique to calibrate the GPS and DORIS instrument and the overall POD processing chain. On ESA request Sentinel-3A advanced in the ILRS tracking priority list on 31 January 2017. The importance of the demanding accuracies of the altimetry mission is reflected by this step. A decent amount of SLR tracking data is needed for the entire mission life-time to perform regular checks of the biases that could exist between different tracking techniques.
The SLR measurements confirm a Sentinel-3A orbit accuracy below 2 cm RMS. However, to be able to identify biases between different tracking techniques it has to be assured that the SLR observations themselves do not have biases. Therefore, the SLR data of the 25 SLR stations providing more or less frequently observations to Sentinel-3A are regularly checked for their quality.
Status and performance of the Sentinel-3A SLR processing are presented in particular focussing on the station quality assessment. More than one year of data in the satellite’s operational phase have been analysed. The excellent quality of the Sentinel-3A orbits from the Copernicus POD Service will be shown as well as the evolution of the tracking in terms of number of stations and number of passes and normal points. 
  1.8 Pending  
NAMEJaime Fernández, Carlos Fernández, Pierre Féménias, Constantin Mavrocordatos, Bernd Seitz, Heike Peter 
EMAILjfernandez@gmv.comheike.peter@positim.com 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPoster 
ADDRESSThe tandem constellation of Sentinel-3A and -3B

Sentinel-3B, the second satellite of the Copernicus Sentinel-3 mission, is planned to be launched in spring 2018. During the commissioning phase of the satellite it will be flying only 30 sec apart from Sentinel-3A. The tandem constellation will be hold for about 4-5 months. It shall guarantee a proper calibration of the instruments, mainly the SAR altimeter. After the tandem phase Sentinel-3B will be moved to its long-term orbit at a 140o phase shift with respect to Sentinel-3A. 
Sentinel-3B is identical to Sentinel-3A. Additionally to the main payloads it will also carry a couple of GPS receivers, a DORIS receiver, and a laser retro reflector for Satellite Laser Ranging (SLR).
The mission support from ILRS is again very important and very much appreciated as well. 
The SLR tracking will be equally important for Sentinel-3B as for Sentinel-3A. In particular during the tandem phase it is of utmost importance to get evenly distributed tracking data for the two satellites.
The Sentinel-3 project will send a request to ILRS for an interleaved tracking of the two satellites from those SLR stations able to do so. Other stations are requested to alternate the tracking evenly between Sentinel-3A and Sentinel-3B. The tracking scenarios will be similar to those from Jason-2 and Jason-3 during their tandem phase.
The poster will present information and details about the commissioning phase of Sentinel-3B and the planned tandem phase of the two Sentinel-3 satellites. 
  1.9 Pending Moved to session 2 as 2.12      1.10  Pending  
NAMEM.Medvedskyy,V.Pap, Yu.Hluschenko.  
EMAILmmmedvedsky@gmail.com 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTInformation on the development of new equipment for the control of the laser station 1824 - Golosiiv-Kyiv. The structure of the developed equipment includes the following parts:
- Telescope control module;
- time base module
- time synchronization module
- time gate module for event timer A31
- communication modules with PC
- the module for generating START and STOP signals.
The development status and test results of individual modules are presented.
  1.11 Pending
NAMEChristian Schwatke 
EMAILchristian.schwatke@tum.de 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPoster 
ABSTRACTEUROLAS Data Center (EDC) - Updated Procedure for Station History Logs and Site Logs 

Within the ILRS, automation and uniform standards have become more and more important in recent years. Especially for SLR analysts, complete and up-to-date descriptions of ILRS sites are required. Also, station upgrades such as laser repair, etc. have to be precisely documented. Both information are stored in the site log and station history log which are available on the FTP of the EUROLAS Data Center (EDC) and the Crustal Dynamics Data Information System (CDDIS).

In the last years, the procedure of submitting log files to the data centers was purely based on e-mail transfer without additional validation checks. The management of the log files was performed more or less manually.
In 2017, the procedure of submitting station history logs and site logs was updated and automated. In this poster, the new procedure is demonstrated in detail. Now, all site logs and station history logs are stored in a database at EDC. Station managers can easily update the log files using the EDC website. After logging in on the EDC website, updated site log and station history log files can be uploaded or modified directly. All performed changes are followed by a validation check which provides feedback to the station manager about errors immediately. Finally, when site logs and station history logs are updated successfully on the EDC website, they are transferred to CDDIS and stored on both FTPs automatically. 
  1.12 Pending   
NAMEPeiyuan Wang 
EMAILpeiyuan.wang@oeaw.ac.at 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTTitle:COTS reflectors application on Technosat 

Abstract:
Technosat is a nanosatellite mission of Technical University of Berlin, which was launched on July 14, 2017 and has been tracked successfully by several ILRS stations. Across the 10 surfaces of the 8-edge prism satellite 14 small (10mm diameter) COTS (Commercial off-the-shelf) laser retroreflectors are distributed.
Unlike specially designed retro-reflectors for usual missions, it shall evaluate the suitability of commercial low-cost reflectors for a typical 600 km orbit. SLR measurements will be applied mainly to determine attitude and attitude motion – during and after operational phase. 
The COTS retro-reflectors have been measured by GFZ Potsdam; Graz characterized and simulated several different distributions of these retro-reflectors to optimize identification of satellite attitude, and to determine spin parameters after its operational / stabilized phase.
On a small mountain about 32 km southwest of Graz station we placed a wire grid model of the satellite – with various numbers and distributions of retro-reflectors - on a tripod; this satellite model was rotated by stepper motors, simulating attitude motions while we measured the distance with our 2 kHz SLR system. Simulations and these ground measurement are compared.
Basing on tracked SLR data, Graz continues studying changes and strategies of the attitudes of this mission.
 
  1.13 Pending  
NAMEFlorian Andritsch 
EMAILflorian.andritsch@aiub.unibe.<wbr />ch 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTFlorian Andritsch, Andrea Grahsl, Rolf Dach, Adrian Jäggi
Studying different tracking strategies to LAGEOS and Etalon with respect to the weekly ILRS solution
A tool for simulating realistic Satellite Laser Ranging (SLR) observation scenarios was developed at the Astronomical Institute of the University of Bern (AIUB). Analyzing the available measurements, a profile for each station regarding tracking density, maintenance outages, weather conditions on one hand and specific noise behavior for the different targets on the other hand was established. Unlike other studies, we focus on the tracking capabilities of the International Laser Ranging Service (ILRS) network as it is today and simulate realistic, synthetic observation scenarios considering the tracking capacity of each station. 
The operational ILRS standard solution, which is computed week, contains station and geocenter coordinates, as well as Earth rotation parameters (ERPs) and orbits for LAGEOS and Etalon. Based on these solution types also the contribution to the International Terrestrial Reference Frame (ITRF) is computed. Today, the solution is only based on observations to the LAGEOS and Etalon satellites with about ten times the number of LAGEOS observations compared to Etalon.
The purpose of this study is to analyze the effect of different numbers of normal points to LAGEOS and Etalon satellites on the main parameters of the ILRS standard solution. We show that in our simulation experiments that a reduction of LAGEOS observations by up to 20% does not significantly impact the quality of results. Using this spared LAGEOS tracking capability for example to increase the amount of Etalon normal points in the combined solution leads to an improvement of almost 10% in the recovery of the ERPs considering even the higher noise level and potential systematic effects in the Etalon measurements. 
  1.14 Pending  
NAMEDavid A. Arnold 
EMAILdavid-arnold@earthlink.net 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTTransfer Function of the Lares-2 satellite
David A. Arnold, Smithsonian Astrophysical Observatory, Cambridge, MA (retired)

The design proposed for LARES-2 uses 1.0 inch uncoated COTS cube corners with no intentional dihedral angle offset. The cubes are held in a floating mount that virtually eliminates conductive heat transfer to the cubes. This design minimizes the effect of thermal gradients and manufacturing errors in the dihedral angle offsets. The isothermal transfer function should be very close to the actual performance in orbit. Testing of a set of 10 COTS cubes shows good optical performance. The cubes are inexpensive and are manufactured in bulk. Simulations show that the systematic range errors should be on the order of a half millimeter. 
  1.15 Pending  
NAMEJames Bennett 
EMAILjamesbennett@serc.org.au 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTAn analysis of the close approach between Jason 2 and Topex/Poseidon

On June 20 2017 at 04:40 UTC there was a close approach between Jason 2 and Topex/Poseidon (T/P). The calculated miss distance was 365 metres with a relative velocity of 80 m/s. 

An analysis of the close approach is presented for two datasets. A comparison is made between the close approach calculations resulting from TLE propagation with SGP4 and orbit predictions fitting the ILRS Space Debris Study Group satellite laser ranging data. It is found that the TLE results and the SLR orbit fit results agree well with the miss distance between the two methods, agreeing to within 50 metres.

This near-miss is a stark reminder of the hazards of space debris and the importance of conjunction risk assessments for the ILRS. 
 
  1.16 Pending
NAMEMarkus Rothacher 
EMAILmarkus.rothacher@ethz.ch 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTGlobal navigation satellite systems (GNSS) are nowadays one of the
standard techniques for orbit determination. With the increasing
popularity of small satellites like, e.g., the CubeSat standard,
the need for an adapted small orbit determination payload
increases. Therefore, we have developed a small-sized versatile
GNSS payload board based on commercial-of-the-shelf GNSS receivers
minimizing weight, power consumption and costs. These
single-frequency GNSS receivers are unique, as they are capable of
tracking 5 different GNSS, namely GPS, GLONASS, Galileo, Beidou and
QZSS. The payload board features two separate antenna connectors
and four GNSS receivers — two per antenna. This redundancy lowers
the risk of total payload failure in case one receiver should
malfunction. As the receivers are initially not intended to be used
in space applications, they have been tested for vacuum,
temperature variations and irradiation. Apart from the GNSS
receivers, the payload also consists of three corner cubes with a
diameter of 10 mm each. These corner cubes will allow the
assessment of the orbit determination accuracy of the real-time and
the post-processing solutions. In view of the importance of the SLR
validation to reach the mission goals, a request for SLR tracking
will be submitted to the ILRS.

We present details on the developed payload board, the setup of the
corner cube and their performance as well as the results from
various test scenarios. Based on extensive GNSS signal simulator
tests and on SLR simulations, we show the satellite operations
planned for SLR validation and the general suitability of these
low-cost receivers for orbit determination in space applications. 
  1.17 Pending  
NAMEM. A. Sadovnikov, V. D. Shargorodskiy 
EMAILmsadovnikov@gmail.com 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTMethods to increase the ranging performance and accuracy implemented in the Russian new generation laser station «Tochka»

M. A. Sadovnikov[1], V. D. Shargorodskiy[1]

[1] Joint-stock Company «Research-and-Production Corporation
«Precision Systems and Instruments», JC «RPC «PSI»
new generation station «Tochka» is designed to perform ranging to geodetic and navigation satellites at a submillimeter level of accuracy, as well as to take laser and radio-frequency pseudoranging measurements to the navigation satellites equipped with laser pulse re-ception modules at a subnanosecond level of accuracy.
By now the station «Tochka» has been developed, produced and has successfully passed the initial bench tests. Installation of the station at an operating site will be completed at the end of 2017, followed by its further tests under natural conditions.
The report addresses key methods to increase the ranging performance and accuracy imple-mented in the Russian new generation laser station «Tochka», including:
- methods for high-accuracy control over a laser beam in space and high-accuracy laser beam pointing at space objects;
- methods for automatic laser beam pointing control and monitoring over coaxial alignment of transmit-receive optical paths;
- methods for detection and processing of single-electron laser pulses reflected by on-board retroreflectors under night and daytime tracking conditions;
- methods to achieve a submillimeter accuracy of the systematic measurement error;
- methods to achieve a submillimeter measurement error of normal point generation;
- methods for station activity automation and increase of ranging performance under mostly cloudy conditions.
The report also represents key results of the initial bench tests the laser station «Tochka» has been put to.
  1.18 Pending  
NAMEChristoph Bamann 
EMAILchristoph.bamann@tum.de 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPoster 
ABSTRACTVisibility Aspects of Station Locations for Space Debris Laser Ranging 

Christoph Bamann, Urs Hugentobler, Jennifer Kriese

Recent developments in laser ranging of space debris facilitated its successful application to orbit determination in various studies. This work studies potential locations for future debris laser ranging stations in view of these great achievements. In doing so, it deals with visibility aspects of trackable objects from the USSTRATCOM catalogue rather than with mathematical observability properties. Object visibility durations are computed as a function of geometric visibility (mean pass duration and mean revisit frequency), illumination conditions (twilight zone), and average cloud coverage. These three factors are analyzed both individually and in combination for different sets of objects corresponding to different orbit regimes. Eventually, some favorable station locations are discussed with und without the additional requirement of maximum station separation. 
  1.19 Pending  
NAMEM.Medvedskyy,V.Pap, Yu.Hluschenko.  
EMAILmmmedvedsky@gmail.com 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPoster 
ABSTRACTDevelopment of new equipment for laser stations 1824 

Information on the development of new equipment for the control of the laser station 1824 - Golosiiv-Kyiv. The structure of the developed equipment includes the following parts:
- Telescope control module;
- time base module
- time synchronization module
- time gate module for event timer A31
- communication modules with PC
- the module for generating START and STOP signals.
The development status and test results of individual modules are presented.
 
  1.20 Pending  
NAMEErricos C. Pavlis and Magdalena Kuzmicz-Cieslak 
EMAILepavlis@umbc.edu 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTSLR Requirements for the Development of the ITRF

Erricos C. Pavlis and Magdalena Kuzmicz-Cieslak

JCET/UMBC, Baltimore, Maryland, USA

For nearly four decades Satellite Laser Ranging (SLR) data have been used to derive tracking station coordinates and velocities for the global network. Since the launch of the BTS, the precursor of the International Terrestrial Reference Frame (ITRF), the SLR contribution has played a unique and fundamental role in the realization of the frame’s origin, and shared with VLBI the definition of its scale. The ITRF development is based on an inter-technique combination of the geodetic solutions obtained from an intra-technique combination strategy performed at each IAG Technique Centre. It is the responsibility of each technique to determine and assure the quality and quantity of data that are required in this process, to ensure the accuracy and stability goal of the model.
In recent years, simulations have determined the minimum size of a future network that will deliver the quantity and quality data to support the future requirements of the ITRF accuracy and stability: 1 mm and 1 mm/decade. We will briefly review these findings and compare them to the present level of data products that the ILRS requires from its member stations.
SLR is also used to calibrate, scale and center the GNSS orbits which are the main distributors of the ITRF to the user community. We will review results of simulations that helped set minimum requirements of tracking to assure the delivery of the ITRF to the users with its intrinsic accuracy uncompromised.
 
  1.21  
NAMEK. Matsuo, T. Otsubo, M. Bloßfeld, A. Kehm, H. Müller 
EMAILt.otsubo@r.hit-u.ac.jp 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTSLR contributions to time-variable gravity field and thermospheric neutral density estimates

Besides the ability of SLR to determine the Earth's figure and orientation, it is also possible to accurately estimate the Earth's time-varying gravity field. Moreover, for low Earth orbiting satellites, the neutral thermospheric density plays a crucial role due to the large perturbing (drag) acceleration. If multiple satellites (inclinations) are combined, various parameters can be estimated simultaneously in one common adjustment. In this study, we present the results of an Earth's gravity field solution purely based on SLR data. Using 6 or more satellites (LAGEOS-1, 2, Ajisai, Starlette, Stella and LARES, ...), it is possible (and reasonable) to solve for selected Stokes coefficients up to degree 6. The obtained results are compared to other SLR and GRACE solutions. The observations reveal a long-term ice gain/loss in high latitude regions even before the launch of GRACE. It is pointed out that especially the low altitude satellites are important for gravitational research.
In a second part, the ability of SLR to determine the thermospheric neurtal density is discussed. Here, multiple density models are calibrated with an SLR multi-satellite solution. The obtained scaling factors are discussed and put into context to recent thermospheric density studies. We found that SLR observations to very low orbiting satellites (less than 300km altitude) are most valuable for thermosperic research.
  1.22  
NAMEKeith Evans , Magdalena Kuzmicz-Cieslak and Erricos C. Pavlis 
EMAILepavlis@umbc.edu 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPoster 
ABSTRACTILRS Site Configuration Project: 2015 Questionnaire Summary

Keith Evans , Magdalena Kuzmicz-Cieslak and Erricos C. Pavlis
JCET/University of Maryland Baltimore County, Baltimore, MD 21250, USA

In late 2015 the ILRS developed a questionnaire that was distributed to all ILRS stations at that time. The purpose of the questionnaire was to assess the network’s future-plans, near- and long-term. 
The tracking-load for the ILRS network is expanding with a large influx of new GNSS satellites and new LEO satellites with special requirements. Although this is exciting, it comes with a challenge. In another ten years, we could have more than one hundred GNSS and GEO satellites; and this is also true of LEO satellites. GNSS tracking will be a major topic for the coming decades.
The GNSS campaigns that we have conducted so far have given us a baseline of expectations for the current network. It is very unlikely that all stations will be able to track all the satellites during the same period with sufficient data density to satisfy every mission. We recognize that we need to categorize different stations based on capabilities and availabilities.
There are simulations underway to try to evaluate some options that might help us optimize our tracking activities. These simulations depend of course on the capabilities that we can expect from the stations in the future; we are considering projections for 5 and 10 years into the future. We understand that none of us can project with certainty for the long term, but we would like to find out from the stations what you think your situation will be.
This poster is an attempt to summarize the replies received to date. It took several reminders until we received a credible number of replies for the process to be considered successful. We thank all the stations that took the time to complete and return promptly the questionnaire and we hope that those who did not yet do that, as well as the new stations that recently joined the network, will do so in the near-future.
 
  1.23  
NAMEMagdalena Kuzmicz-Cieslak and Erricos C. Pavlis 
EMAILepavlis@umbc.edu 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPoster 
ABSTRACTILRS Tracking Data Requirements Survey 2017

Magdalena Kuzmicz-Cieslak and Erricos C. Pavlis
JCET/University of Maryland Baltimore County, Baltimore, MD 21250, USA

Many stations in the ILRS network are nearly saturated in their tracking schedule. The ILRS decided to re-assess its tracking needs in hopes of maximizing its utility. To ensure that the needs of those using its services will be fully considered, a questionnaire was designed to collect information from all individuals and agencies that depend in any way on ILRS data and products. The questionnaire was distributed in March 2017 requesting replies by April 15, 2017. Eventually the deadline was extended and several reminder messages were sent out until a reasonable number of responses were received. Using the results of this survey, the ILRS plans to make revisions in its tracking list based on the stated users’ needs. 
This poster summarizes the replies received to date. We thank all the users that took the time to complete and return promptly the survey and we hope that those who did not yet do that, as well as new users that recently joined the ILRS community, will do so in the near-future.
 
  1.24  
NAMEV. Pasinkov, V. Shargorodskiy, A. Ipatov 
EMAILspp@npk-spp.ru 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTReport on completion of the ILRS GNSS LARGE-4 pilot project campaign covering the period of January 15, 2017 to April 15, 2017

ILRS GNSS LARGE-4 pilot project campaign covered the period of January 15, 2017 to April 15, 2017. What makes this campaign unique is that it was carried out in parallel with the Russian pilot project aimed at obtaining GLONASS SC measurements through the VLBI technique.
As a result, the GLONASS system became a collocated one which can simultaneously collect measurements by means of three different techniques: GNSS, SLR and VLBI.
At the same time, all three stations of the IAA RAS VLBI-network are also co-located and each of these stations features at least three types of measuring techniques.
 

Session 2

2.1 Pending
NAMEXiaoya Wang*,Fan Shao,Jing Zhang 
EMAILwxy@shao.ac.cn 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ADDRESSModel Comparisons and Optimizations of SLR Data Processing

SLR is one of an important space geodesy for geodetic and geophysical research as well as IERS products such as International Terrestrial Reference Frame (ITRF) and Earth Orientation Parameters (EOP). In order to obtain better and more consistent results with other space geodetic techniques SLR observation and dynamical models should be checked and better models should be applied. Therefore, we firstly checked and compared CoM correction models, Tidal models including ocean tidal models and atmosphere loading correction, atmosphere delay correction, relativistic corrections, gravity models and so on in our SLR data processing software. After comparisons we chose the better models as input and applied a fuzzy-logic method with an enhanced probability function for weighting the SLR station observations. It shows the RMS of the orbit and the individual station becomes smaller. Then we reprocessed SLR data and compared the modified tropospheric delay with other techniques. It shows there are a big difference. We added the tropospheric zenith wet delay estimation and horizontal gradient estimation in our SLR data processing. It improved the precision of the global precise orbit determination (POD) solution. Finally, by comparing our SINEX result with other ACs’ solutions we checked and analyzed these models again.
  2.2 Pending  
NAMED. Ampatzidis, D. Thaller, A. Sušnik, R. Dach 
EMAILdaniela.thaller@bkg.bund.de 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTThe SLR observations to GNSS satellites with improved modelling: Preliminary results and open questions


In this study the results of the long-term processing of SLR observations to GNSS satellites (both for GPS and GLONASS satellites) will be presented, using the Bernese GNSS Software (SLR development version). The aim of the study is to investigate the associated SLR range biases, defined as the differences between: (a) the observed SLR ranges and (b) the computed spatial distances between the ground stations and the GNSS (precise) orbits. For both, i.e., station positions as well as satellite orbits, we used the latest products: SLRF2014 station positions and Center for Orbit Determination in Europe (CODE) reprocessed orbits applying the improved CODE orbit modelling. With this basis it is assumed that the SLR residuals are reduced compared to earlier investigations. The biases are estimated for the entire period of SLR processing, taking into account inter alia, the non-tidal loading corrections and the Atmospheric Ocean De-aliasing (AOD) effect. The results indicate different biases for the GPS and GLONASS satellites and show remarkable variability among the ground stations. 
   2.3 Pending
NAMEGang Zhao, Xuhua Zhou, Kai Li 
EMAILzhaogangbuaa@sina.com 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTTitle:
Orbit determination and SLR evaluation of China's space laboratory
Asbstrct:
SLR has been taken as an important tracking technique for satellite engineering in China such as Beidou navigation constellation in GEO/MEO, Haiyang-2A oceanographic satellite and APOD experimental satellites in LEO, and has also been included in a series of follow-up planning. China's space laboratory has also incorporated into Chinese regional SLR scheduling. Dynamic and reduced dynamic orbit determination strategies of China's space laboratory based on space-borne GPS are presented. The role of SLR in orbit accuracy validation and the performance evaluation of regional SLR tracking network are discussed.
 
  2.4 Pending  
NAMEJosé Rodríguez 
EMAILjosrod@nerc.ac.uk 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTVariability of LAGEOS normal point sampling: causes and mitigation.

Residual analysis of LAGEOS normal point data shows, for a number of SLR stations, a strong correlation between residual values and normal point precision. Although the dispersion of the distributions of range observations collected by SLR stations to derive normal points should ideally be perfectly stable, several factors introduce variability in the data. We performed ray-tracing computations of laser pulses reflected off satellite LAGEOS at different incidence angles to simulate the returned signals for individual normal points. The results indicate that partial sampling of the retroreflector array is a significant, unavoidable source of variability. Excluding return rate fluctuations, this effect, plus purely random sampling and the presence of variable levels of background noise explain most of the observed dispersion in the normal point data, as well as the correlation with residual values in the orbital dynamics results. We discuss these sources of normal point variability and, using both simulated and empirical data, compare the performance of different screening methods in terms of their success to cope with it and ability to define a stable reference point. 
  2.5 Pending  
NAMEMr. Joseph O'Leary 
EMAILjoseph.oleary@mymail.unisa.<wbr />edu.au 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTJoseph O'Leary
University of South Australia, School of Information Technology and Mathematical Sciences, Australia.
Space Environment Research Centre, SERC, Mount Stromlo, Australia.

Title: Improved general relativistic equations of motion in geodesy and astronomy.

Abstract: The field equations of General Relativity (GR) represent a system of ten independent, coupled, non-linear partial differential equations. Known solutions exhibit high degrees of symmetry making the modelling of realistic astrophysical problems a formidable task. The Post-Newtonian (PN) approximation has been successfully developed to approximate solutions of the field equations of GR and is relied upon in both geodesy and astronomy where precise orbit knowledge is required. 

The general relativistic equations of motion recommended by the International Earth Rotation and Reference system Service (IERS) are obtained using the first PN approximation. However, the currently recommended equations of motion model the acceleration of a near-Earth satellite in a spherically symmetric gravitational field. In this talk, we look at improved general relativistic equations of motion which extend the current equations of motion to include non-spherical bodies and present an overview of methods which can be employed to test their validity.  
    2.6 Pending  
NAMEHorst Mueller 
EMAILhorst.mueller@tum.de 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTEvaluation of the present SLR tracking stations


For the spherical satellites we looked into data quality, by analysing range biases. The results from various test, like range, elevationa or azimuth dependency. The influence of nontidal loading and center of mass corrections is also taken into account. And we have looked into the longterm stability of the stations and the station coordinates and velocities.  
    2.7 Pending  
NAMEQuirin Funke 
EMAILquirin.funke@esa.int 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTTitle: Required Improvements of Debris Laser Ranging to Support Collision Avoidance
Authors: Benedikt Reihs, Quirin Funke, Tim Flohrer

Debris laser ranging is highly interesting for collision avoidance as it has the
potential to improve the uncertainties on the chaser object orbit, at a
significantly lower price than radar measurements. This is especially the case
for small debris objects, where the available orbit is of poor quality usually.

With more laser ranging stations building up debris ranging capabilities,
operational support for collision avoidance is getting in reach. It is the goal
of this paper, to investigate on the current capabilities and readiness for this
task.

High risk close approaches of ESA satellites since 2009 have been analysed for
the potential of debris laser ranging support. This takes into account current
and planned stations with debris laser ranging capabilities and their
limitations. Weak points are identified and improvements suggested.
  2.8 Pending  
NAMEToshimichi Otsubo 
EMAILt.otsubo@r.hit-u.ac.jp 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTSLR error sources in the kHz repetition era: How should we improve the range measurement and the products?

We present various error sources in SLR and its behaviour in orbit determination analyses. In particular, we focus on what the laser ranging community should do to improve the normal-point accuracy in both conventional and kHz systems. Random error will cancel out if one obtains large number of observations, but systematic error remains and easily maps the geodetic products. Based on a quality check analysis of the last 12 months, we discuss what component causes what sort of error, and we hope to exchange ideas with the audience.
  2.9 Pending  
NAMEDaniel Koenig, Daniela Thaller 
EMAILdaniel.koenig@bkg.bund.de 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTAccording to the guidelines of the ILRS Pilot Project on Systematic Errors a reprocessing has been carried out at BKG. Besides the time span of 2005-2008 required by ILRS the whole reprocessing covers the years 2000-2012 yielding LAGEOS-only solutions of weekly station positions and Range Biases as well as daily Earth Rotation Parameters. The time series of the parameters obtained are presented and their quality evaluated. Additionally alternative solutions are produced and compared to the standard solution of the pilot project
  2.10 Pending  
NAMEThomas Varghese 
EMAILtv@cybioms.com 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACT
Transitioning the NASA SLR network of seven stations from the Time Interval Mode to the Event Timing Mode

Thomas Varghese 
NASA SLR program & Cybioms Corporation


Abstract:
Seven of the SLR stations in the NASA network has been using the HP 5370 time interval units (TIU) for the time of flight measurements for the last 25+ years. This product has been obsolete since the early 2000. Consequently, maintaining this product for network operations has become extremely hard and in some cases have impacted data quality. Event timer is widely used and proven in the ILRS community and is the natural successor to the TIU. For a SLR network with global coverage, transitioning to any replacement device requires significant scrutiny and long term validation. Long term measurement, however, has the potential for interrupting the station's operational data flow to the ILRS due to quarantine. An operationally non-invasive concurrent data taking strategy was devised for the new and old hardware to perform simultaneous measurements. This unconventional concurrent data, although quarantined, also forced an ILRS procedural change for a station's upgrade. This paper describes the rigorous process employed for the measurement, analysis, operational deployment as well as the comparison characteristics.
  2.11 Pending  
NAMEKoenig, R., Glaser, S., Balidakis, K., Neumayer, H.K., Nilsson, T., Heinkelmann, R. Flechtner, F., Schuh, H. 
EMAILrolf.koenig@gfz-potsdam.de 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTSimulation of Multi-Technique Terrestrial Reference Frames with Focus on Benefits from Enhanced SLR Networks


The requirements of the Global Geodetic Observing System (GGOS) on the quality of global Terrestrial Reference Frames (TRFs), i.e. 1 mm accuracy and 0.1mm/yr stability, have not been met by the available state-of-the-art TRFs. In order to adress this issue we simulate the observations of all four space geodetic techniques contributing to the TRF in the time span 2008-2014. The simulations are carried out as realistically as possible following the tracking record of the stations and the accuracies achieved in that time span. At the time being we have succeeded in combining the simulated GPS, SLR, and VLBI networks and assessing the requirements on local ties and the potential of the planned VLBI network enhancements to reach the GGOS goals.

Here we investigate the benefits of enhancing the SLR network by foreseeable upgrades and re-locations of current sites and by probable new sites. For the network enhancements we selected 14 sites, the simulations of their observations are based on a global cloud atlas that allows to better predict possible tracking records. We then assess the benefits of each new site with respect to the old situation in terms of improvement of mean coordinate and Earth orientation parameter precision. 
  2.12 ( 1.9)  Pending  
NAMERadosław Zajdel, Krzysztof Sośnica, Grzegorz Bury 
EMAILradoslaw.zajdel@igig.up.wroc.<wbr />pl 
SESSIONSession 1: satellite tracking and scheduling 
TYPEPresentation 
ABSTRACTTitle: GOVUS – a new on-line tool for the evaluation of SLR observations to GPS, GLONASS, Galileo, BeiDou and QZSS
Authors: Radosław Zajdel, Krzysztof Sośnica, Grzegorz Bury

In the last decade, we have been witnessing a radical development of the new GNSS constellations. Besides the well-known GPS and GLONASS systems, newly developed systems such as Galileo, BeiDou and QZSS, become increasingly important. Thanks to adapting of the new generations of GNSS satellites to the SLR requirements, SLR became a valuable source of data. On the other hand, the constantly increasing number of the SLR targets imposes a great challenge for the ILRS tracking stations. In March 2017 a new ILRS Associated Analysis Center (ACC) was established with the main focus on the identification of systematic errors in SLR observations to new GNSS constellations, as well as for the assessment of the quality of multi-GNSS orbit products. The main service offered by the new ILRS ACC is the multi-GNSS Orbit Validation Visualizer Using SLR (GOVUS). The system performs a near real-time SLR validation of multi-GNSS microwave-based precise orbit products delivered by the Center for Orbit Determination in Europe (CODE) in the framework of the IGS MGEX project and covers five different GNSS systems: GPS, GLONASS, Galileo, QZSS, BeiDou MEO and IGSO. GOVUS allows for analyzing and visualizing the validation results using the dedicated on-line applications. The computational algorithms make use of the modified Bernese GNSS Software and provide fully automatic validation of new orbit products as a daily routine. 
GOVUS system is a useful tool for the both, the ILRS and multi-GNSS community. The dataset of nearly half a million archival SLR residuals, which covers the time span since 2012, is being updated every day. The current and the past performance of the 40 ILRS stations, in terms of quantity and quality of data, can be easily investigated in the aspect of the GNSS tracking and finding systematic biases. Moreover, the validation results of 61 GNSS satellites from 5 systems, can be analyzed on the web browser without installation of any additional software. We present a comprehensive overview of the functionality and the structure of the developed system, as well as examples of analyses performed using the service modules. The analysis of the laser stations’ performance reveals a heterogeneity of the SLR dataset in the context of the accuracy, the station systematics and compliance with the ILRS priorities list. The dependencies between the SLR residuals and particular stations’ equipment will also be examined, e.g., the single and multi-photon mode of signal detection, differences between event and interval timers, 10Hz and kHz stations’ performance. 
  2.13 Pending  
NAMEErricos C. Pavlis, Magdalena Kuzmicz-Cieslak and Keith Evans 
EMAILepavlis@umbc.edu 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTJCET Tools for the Assessment of the ILRS Stations’ Performance

Erricos C. Pavlis, Magdalena Kuzmicz-Cieslak and Keith Evans
JCET/University of Maryland Baltimore County, Baltimore, MD 21250, USA

We will discuss and demonstrate web-accessed tools developed at JCET using the products of the ILRS Analysis and Associate Analysis Centers (AC & AAC) to aid stations assess their performance. The ILRS generates a wealth of analysis products that can be used to evaluate the performance of the systems providing the SLR data from which the products themselves are derived. Of interest to SLR data users and station operators are the time series of station position evolution (detecting unexpected discontinuities), offsets from the current ITRF model (monitoring consistent stability at each site), and systematic measurement error time series (the stability and smallness of magnitude of which characterizes the best stations). This presentation will highlight the various ways that JCET uses these products, and it will introduce the web portals from which users can access these diagnostic tools. Detailed examples can be demonstrated to interested users during the workshop.
 
  2.14  
NAMEDavid Arnold 
EMAILdavid-arnold@earthlink.net 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACT“Effect of pulse length, rise time, signal strength, and type of detection system
on the range correction for LAGEOS-2”

David Arnold, Smithsonian Astrophysical Observatory, Cambridge MA (retired)

The pulse shape seen by the detector consists of the sum of a discrete number of photoelectrons. This pulse shape can vary significantly from the shape of the electric field in the return from Lageos. The pulse seen by the detector is a function of transmitted pulse length, rise time of the receiver, number of photoelectrons, and type of detection system. For LAGEOS-2 the centroid of the return is around 242 millimeters. However, the leading edge of the pulse is at around 256 millimeters. This is a difference of 14 millimeters. The range correction can be anywhere between the centroid and the leading edge. This greatly exceeds the one millimeter accuracy goal for geodetic studies.
 
  2.15
NAMET. Otsubo, H. Mueller, E. Pavlis, C. Schwatke 
EMAILt.otsubo@r.hit-u.ac.jp 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTThe ILRS Rapid Service Mail a tool to inform stations quickly about
potential problems.

During the 17th International Workshop on Laser Ranging in Bad Kötzting,
Germany, ILRS has decided to set up a service to allow better communication
between stations and analysts. The Rapid Service Mail is a unique address
for the 5 quality control centres to contact stations in case of unexpected
biases or erratic behaviour and informs in parallel other analysts on that
problem. Stations are asked to analyse the reason for that problem and
respond to that email. There are about 25 emails yearly with different
responses. In 2017 the number of alerts has decreased to 5, all with a
positive stations reaction
 
    2.16
NAMEV. Luceri, M. Pirri, G. Bianco 
EMAILcinzia.luceri@e-geos.it 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTThe ILRS ASC Pilot Project on systematic error estimation

The estimation of systematic errors is under debate since years within the ILRS Analysis Standing Committee (ASC). A pilot project was started to investigate an alternative approach that could improve the analysis results. 
The approach of the pilot project allows the simultaneous estimation of site coordinates and range bias for each station regardless of correlation with events at the station that could have introduced systematic errors in the observations. 
The first results confirmed a significant effect on the realization of the TRF, in particular on its scale.
The current status of the pilot project is presented. Future procedures for handling systematic errors will be based on the outcome and analysis of the current investigations.
    2.17  
NAMEAlexandre Belli ; Pierre Exertier ; Erricos C. Pavlis ; Frank G. Lemoine 
EMAILbelli@geoazur.unice.fr 
SESSIONSession 2: Performance evaluation 
TYPEPresentation 
ABSTRACTFrom Time Transfer by Laser Ranging to space geodetic products


Since June 2008, the Time Transfer by Laser Link (T2L2) experiment on-board the satellite Jason-2 provided many time transfer data from the current International Laser Ranging network managed by ILRS. The Full Rate laser ranging data from 25 to 32 stations in addition to the on-board recording of the one-way short laser shots provided the basic tools to establish the time synchronization between the ground reference clocks of the laser network. As a result of this wide expertise of the actual time & frequency statement of the network many systematic time biases were identified at a level of several hundreds of nanoseconds (ns) relative to UTC/TAI exceeding thus the current requirement of 100. In order to provide our community with time series of time biases being a priori values of some systematism affecting the integrity of laser ranging measurements to many targeted satellites including geodetics we digitized information over the 2008-2016 period. 
We show here the result of this work and illustrate the behavior of some time & frequency systems on the long term that need to be included in many geodetic analysis involving laser ranging as the weekly geodetic products of ILRS Analysis Centers and the precise orbit determination of altimeter satellites like Jason and above all lower orbits as e.g. SARAL. 

Session 3

3.1 Pending
NAMEGrzegorz Bury, Krzysztof Sośnica 
EMAILgrzegorz.bury@igig.up.wroc.pl 
SESSIONSession 3: Accuracy and scheduling 
TYPEPoster 
ADDRESSImpact of atmospheric pressure loading on SLR-derived station coordinates using range measurements to multi-GNSS satellites 


The current requirements imposed by the Global Geodetic Observing System (GGOS) demand an integrated, stable in time, and accurate at the level of 1 mm, reference frame. Due to that fact, the solutions based on several space techniques should be as consistent as possible. 

Satellite Laser Ranging (SLR) is a precise space technique that provides range measurements to artificial satellites equipped with laser retroreflectors. SLR contributes to GGOS to a great extent i.e., provides the origin of the International Terrestrial Reference Frame, the global scale, satellite orbits, gravity field parameters, and station coordinates. The Multi-GNSS Experiment (MGEX) was initiated, because of the emerging of new navigation system i.e., Galileo, BeiDou, QZSS, and NavIC and modernized GPS and GLONASS. SLR measurements are performed to new GNSS, because all new active multi-GNSS satellites are equipped with Laser Retroreflector Arrays. As a result, SLR became an independent tool for investigation of systematic errors that microwave solutions suffer from, as well as for the SLR-GNSS co-location in space. 

Displacements of the Earth’s crust caused by tidal and non-tidal forces play a crucial role in precise space geodesy. The omission of atmospheric pressure loading models during SLR data processing may lead to inconsistency between microwave (GNSS) and optical (SLR) solutions. SLR observations can be performed only during cloudless conditions, which coincide with high values of air pressure. High atmospheric pressure deforms the Earth’s crust. The systematic shift of the stations heights is called the Blue-sky effect. 

The goal of this study is to determine the value of the Blue-sky effect for particular SLR stations using range measurements to multi-GNSS satellites. Predictably, the highest value of the Blue-sky effect is observed for the inland stations i.e., 2.3 mm for Svetloe, 2.0 mm for Potsdam and Baikonur, and 1.9 mm for Altay. For the coastal stations, the effect is exiguous i.e., 0.3 mm for Yarragadee and 0.0 mm for Tahiti. 

Applying the Blue-sky effect calculated basing on range measurements to multi-GNSS satellites improves the consistency between SLR and GNSS solution thus it should be performed by SLR Analysis Centers. Even a sub-millimeters values of systematic shift should be taken into consideration if we want to fulfill the 1-mm requirements imposed by GGOS.
 
  3.2 Pending   Transitioning the NASA SLR network from the Time Interval Mode to Event Timing Mode with improved Data quality and quantity    Thomas Varghese1, David McCormick2  1Cybioms Corporation and NASA SLR program 2NASA Goddard Space Flight Center   Abstract: Seven of the SLR stations in the NASA network has been using the HP 5370 time interval counters for time of flight measurements for the last 25+ years. This product has been obsolete since the early 2000 and maintaining this product for network operations has become extremely hard or impossible. Event timer is widely used in the ILRS community for range measurements and is a natural successor. Despite this, for a network with global impact, transitioning to any replacement device requires significant scrutiny and long term validation. Long term measurement, however, has the potential for interrupting station operational data flow to ILRS through quarantine and hence a non-invasive concurrent strategy was devised for the new and old hardware to perform simultaneous phased measurements across multiple stations to bring about a robust transition. The unconventional concurrent data, although quarantined, forced an ILRS procedural change for the station upgrade.  This paper describes the process for the measurement and analysis as well as the steps towards the transition   3.3 Pending  

 

NAME

Mateusz Drożdżewski, Krzysztof Sośnica 
EMAILmateusz.drozdzewski@igig.up.<wbr />wroc.pl 
SESSIONSession 3: Accuracy and scheduling 
TYPEPoster 
ADDRESSTitle: Sensitivity of SLR observations to horizontal gradients of the tropospheric delay


Satellite laser ranging is only the one space geodetic technique which currently does not consider horizontal gradients of the troposphere delay. This neglect may have a negative impact on SLR products. SLR observations are sensitive mainly to the hydrostatic part of troposphere delay. In comparison to microwave-based space observation techniques, the variability of the impact of non-hydrostatic delay is very small and does not require estimating additional parameters in case of SLR. This paper shows the potential of SLR for the recovery and validation of atmospheric asymmetry above SLR stations. We use observations to passive geodetic satellites: LAGEOS-1 and LAGEOS-2. The horizontal gradients are estimated as additional parameters in standard SLR solution with the North and East components using Chen-Herring mapping function. We compare new products of SLR solutions with Linear Horizontal Gradients (LHG) derived from the European Centre of Medium Range Weather Forecast (ECMWF) and GNSS horizontal gradients obtained from the solutions provided by the Center for Orbit Determination in Europe (CODE) for SLR-GNSS co-located stations. SLR provides observation only under cloudless weather conditions, which results in a much smaller number of observations when compared, e.g., to GNSS. Due to a limited number of SLR observations we estimate horizontal gradient parameters once per 7 days. The long-term analysis of SLR horizontal gradients shows a moderate agreement with GNSS, a good agreement with hydrostatic part of LHG and a moderate agreement with non-hydrostatic part of LHG at the level of: 47 %, 74 %, 54 %, respectively. In a result, the SLR horizontal gradients can be used as a tool for the validation and extraction of long-term horizontal gradients of the troposphere delay as well as for the assessment of the atmosphere asymmetry over SLR stations.
   3.4 Pending  
NAMEDaniel Kucharski 
EMAILdanielkucharski@serc.org.au 
SESSIONSession 3: Accuracy and scheduling 
TYPEPresentation 
ADDRESSOptical quality of Ajisai mirrors measured by Graz Single Photon Counting System for laser time transfer experiment

Daniel Kucharski (1*), Georg Kirchner (2), Toshimichi Otsubo (3), Franz Koidl (2), Peiyuan Wang (2), Hiroo Kunimori (4), James C. Bennett (1), Krzysztof Sośnica (5), Francesco Vespe (6)

1. Space Environment Research Centre, SERC, Mount Stromlo, Australia 
*) danielkucharski@serc.org.au
2. Space Research Institute, Austrian Academy of Sciences, Graz, Austria
3. Hitotsubashi University, Tokyo, Japan
4. NICT, Tokyo, Japan
5. Institute of Geodesy and Geoinformatics, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
6. Agenzia Spaziale Italiana, Centro di Geodesia Spaziale "G. Colombo", Matera, Italy

Abstract 

The JAXA’s Experimental Geodetic Payload Ajisai is equipped with 1436 corner cube reflectors for Satellite Laser Ranging (SLR) and also with 318 mirrors initially used to determine the direction to the satellite. Since the mirrors cover more than 80% of the satellite surface it has been proposed to use Ajisai as a passive transponder to reflect laser pulses between the ground SLR systems for the time scale comparison (Kunimori et al., 1992, Otsubo et al., 2006). While the previous concepts treat Ajisai as a single reflection point, we propose a new approach based on the method that predicts the inertial attitude of the single mirrors and allows mapping their surface reflectivity with the Single Photon Counting System developed at Graz SLR station (Kirchner et al., 2015).

Ajisai was launched with an initial spin of 1.5 s in order to keep the inertial orientation aligned with the Earth’s rotational axis. The satellite spin parameters are routinely measured by the high repetition rate SLR systems (Kucharski et al., 2016) and change slightly over time due to the spacecraft interaction with the Earth’s magnetic field and solar irradiation. The SLR-derived spin model allows referring the satellite brightness measurements to the specific mirror surface area that the solar flux is reflected from. This method makes it possible to map the optical reflectivity over the satellite surface area and select the best mirrors to be used in the laser time transfer experiment. 

This presentation will demonstrate the advantage of merging the SLR and photometry techniques to deliver highly accurate inertial attitude models and reflectivity maps of Ajisai mirrors for the laser time transfer application. 


References

Kirchner G., Koidl F., Steindorfer M., Peiyuan W., 2015. Light Curve Measurements with Single Photon Counters at Graz SLR. ILRS Technical Workshop, Matera, Italy, October 2015.

Kucharski D., Kirchner G., Otsubo T., Lim H.-C., Bennett J., Koidl F., Kim Y.-R., Hwang J.-Y. Confirmation of gravitationally induced attitude drift of spinning satellite Ajisai with Graz high repetition rate SLR data. Adv. Space Res., vol. 57 (4), pp. 983-990, doi:10.1016/j.asr.2015.12.010, February 2016.

Kunimori H., Takahashi F., Itabe T., Yamamoto A., 1992. Laser ranging application to time transfer using geodetic satellite and to other Japanese space programs. In: Proc. 8th Int. Workshop on Laser Ranging Instrumentation, Annapolis, USA, May 1992.

Otsubo T., Kunimori H., Gotoh T., 2006. New Application for kHz Laser Ranging: Time Transfer via Ajisai. In: Proc. 15th Int. Workshop on Laser Ranging Instrumentation, Canberra, Australia, October 2006. 
   3.5 Pending  
NAMEUlrich Schreiber 
EMAILschreiber@fs.wettzell.de 
SESSIONSession 3: Accuracy and scheduling 
TYPEPresentation 
ADDRESSDelay compensated Optical Time and Frequency Distribution for Space Geodesy

In order to achieve a delay compensated time and frequency distribution, we have designed 
an all optical two-way system, which allows the campus synchronization of a distributed 
set of geodetic measurement systems in time and frequency with an accuracy of 1 ps. The 
goal is to make it possible to eventually use time as an observable and not as an 
adjustment parameter in a non-linear fitting process. With a centralized fs- pulse laser 
and a star like fiber network it is possible to reference all measurements to the same 
time scale and to control system biases. This opens the door to accurate closure 
measurements of system delays within each geodetic measurement technique and from one 
technique to the next (e.g. from SLR to VLBI). 
  3.6 Pending  
NAMEMichael Steindorfer 
EMAILmichael.steindorfer@oeaw.ac.at<wbr /> 
SESSIONSession 3: Accuracy and scheduling 
TYPEPresentation 
ABSTRACTSimultaneous space debris laser ranging and light curve measurements of a large re-entering upper stage

The upper stage of the long march 3B rocket body (NORAD 38253) reentered in August 2017. One month before reentry, light curves were recorded by using single photon avalanche diodes while simultaneously doing distance measurements via space debris laser ranging. Based on a simple cylindrical model of the upper stage simulated light curves and SLR range residuals were calculated. A comparison of the experimental results with the simulations allows to draw conclusions on the rotation parameters of the rocket body. 
  3.7 Pending   
NAMEBauer, S., Steinborn, J., Grunwaldt, L. 
EMAILsven.bauer@gfz-potsdam.de 
SESSIONSession 3: Accuracy and scheduling 
TYPEPresentation 
ABSTRACTSLR station operation relies to a large extend on the quality of the required satellite position predictions. Poor predictions with large time and range biases increase the target acquisition time and thus reduce the performance of stations and the network as a whole. This is relevant for low flying satellites, in particular if they carry out maneuvers. Despite the relevance of the prediction accuracy, there is currently no established process to evaluate their quality. We present a method for such a process that uses normal point data uploaded to data centers by ILRS stations worldwide. First analysis results showed systematic trends over time for most targets and prediction providers. Furthermore we used these trends to predict real time correction values for the time bias. We also present a service prototype that provides these correction values for the latest predictions of relevant satellites and providers in real time. Using these correction values during tracking allowed for faster target acquisition and thus a better tracking performance of low flying satellites at GFZ Potsdam SLR station.
  3.8 Pending  
NAMEJohn J. Degnan 
EMAILjohn.degnan@sigmaspace.com 
SESSIONSession 3: Accuracy and scheduling 
TYPEPresentation 
ABSTRACTChallenges to Achieving Millimeter Accuracy Normal Points in Conventional Multiphoton and kHz Single Photon SLR Systems
John J. Degnan
Sigma Space Corporation, Lanham, MD 20706 USA

ABSTRACT
The GGOS challenge to achieve 1 mm accuracy normal points is complicated by many factors, one of which is the way the SLR community traditionally measures pulse time of flight. The Probability Distribution Function (PDF) for the photon time of arrival is given by the convolution of the laser pulse profile, the satellite impulse response, and the detector impulse response. On the transmit/start side, things are simpler due to a stable pulse amplitude and no satellite impulse response to contend with. However, the PDFs for the start and stop pulses are not the same. 
In conventional multiphoton lidars, a Constant Fraction Discriminator (CDF) is often used in both the start and stop receiver channels to largely eliminate variable range biases caused by signal strength variations but, due to the different start and stop PDFs, the range measurement is not bias free. Furthermore, the bias varies with different satellite retroreflector geometries, and, for non-spherically symmetric satellites (e.g. GNSS flat panels) , the relevant receive PDF can even take on different shapes during a pass which can in turn introduce time dependent range biases.
In kHz Single Photon SLR systems, the observed signal strength can vary over a wide range due to satellite altitude, elevation angle, atmospheric conditions, etc. Most kHz stations tend to operate with low return rates of 10% or less in order to avoid “first photon” range bias effects. Unfortunately, this greatly increases the time required to generate a 1mm RMS normal point, resulting in much longer orbital arcs associated with each satellite normal point and fewer satellite tracking opportunities overall. 
First photon bias effects can be avoided in both conventional and kHz SLR systems by abandoning current threshold based detection and instead recording all of the available start and stop photons in a receiver designed to detect the centroid of the pulses. Although such techniques have been used by radar engineers, SLR implementation would require use of optical detectors capable of detecting and combining all of the individual photon events into a single waveform. MicroChannel Plate Photomultiplier Tubes and Silicon Photomultipliers would qualify because they permit a large number of of near simultaneous photons to be detected, amplified and output to a single anode. Following the radar approach, the observed waveform would be input to an integrator, whose output would be split with one half input to an inverting integrator and then summed with the other half and input to a zero-crossing detector which yields the time centroid of the pulse plus a constant which is determined during ground calibrations. The input and output centroids would then be used to compute an “unbiased” range. Centroid detection can be easily implemented in most conventional or kHz single photon systems employing single start and stop timing channels, and can even be adapted to SGSLR’s Multifunctional 45 pixel Receiver. Nevertheless, the efficacy of centroid detection in a low signal-to-noise environment needs to be studied. 
    3.9 Pending  
NAMEJorge del Pino, Raja-Halli Arrtu, Kalvis Salmins, Jyri Naranen 
EMAILjorge.delpino@lu.lvarttu.raja-halli@<wbr />maanmittauslaitos.fi 
SESSIONSession 3: Accuracy and scheduling 
TYPEPresentation 
ABSTRACTSky Clarity Comparison between Riga and Metsahovi SLR Stations
Jorge del Pino[1], Raja-Halli Arrtu[2], Kalvis Salmins[1], Jyri Naranen [2]

Jorge.delpino@lu.lvarttu.raja-halli@<wbr />maanmittauslaitos.fi
[1]Institute of Astronomy, Latvijas Universitate, Riga, Latvia 
[2]Metsähovi Research Station, Finnish Geospatial Research Institute, FGI


In this paper we present the preliminary work on comparing the satellite sky clarity conditions for two close (~320 km) SLR stations: 1884 Riga (Latvia) and Metsahovi (Finland).
Sky clarity measurements are now done on regular basis in both stations by Aurora Cloud Sensor III (Riga) and Boltwood Cloud Sensor II (Metsahovi), complemented by all-sky cameras.
We plan to do a long term evaluation about the feasibility of optimizing the work load and in particular about future multi-static Space Debris observations. 
Sky clarity values are compared with images from all-sky cameras and from visibility values from web services as MeteoBlue astronomical seeing prognosis (https://www.meteoblue.com/en/<wbr />weather/forecast/seeing/riga_<wbr />latvia_456172 and https://www.meteoblue.com/en/<wbr />weather/forecast/seeing/<wbr />veikkola_finland_632024)
  3.10 Pending  
NAMEJulie Horvath / Christopher Clarke 
EMAILjulie.horvath@kbrwyle.com 
SESSIONSession 3: Accuracy and scheduling 
TYPEPoster 
ABSTRACTOver a decade ago, Honeywell Technology Solutions Inc (HTSI, now KBRwyle) developed an intelligent SLR scheduling software package during the development of the Matera Laser Ranging Observatory. This package offered a broad advanced capability to produce prioritized SLR schedules using multiple optimizations, including evolving satellite priority based on mission data requirements. HTSI further developed this software package for NASA and installed it at the NASA Data Operation Center to be used for all routine scheduling for participating NASA operational stations and the NGSLR. Although a number of the software’s capabilities were used in scheduling the NASA stations, much of the broader capability, including coordinated Network scheduling, was left unused due to of the lack of system automation as well as the lack of satellite scheduling interferences. As the satellite roster continues to increase with the launch of multiple navigation constellations, experimental satellites, and Earth observers, it is important to work toward scheduling networks rather than individual stations, in order to fully meet the ILRS performance requirements. In addition, with the increased automation of SLR stations, the ability to make full use of this scheduling capability is finally being realized. NASA and KBRwyle plan to further develop this Network scheduling tool to intelligently schedule the next generation Space Geodesy Satellite Laser Ranging (SGSLR) Network. This poster will explore the current NASA scheduling capabilities as well as our vision for the future of the SGSLR Network scheduling. 

Session 4