LIST OF ABSTRACTS

Session 4: "Network and Station Performance"

Attempts to separate apparent observational range bias from true geodetic signals

Graham Appleby (1), Matthew Wilkinson (1), Vincenza Luceri (2), Philip Gibbs (1), Victoria Smith (1)
(1) NERC Space Geodesy Facility, UK
(2) e-GEOS, Italy
E-mail: gapp@nerc.ac.uk

Orbital solutions that include laser range bias naturally produce results that are highly correlated with station height variations that may be driven by various geophysical processes. In this paper we investigate features of a long time-series of Herstmonceux LAGEOS and LAGEOS-II range bias solutions derived by the ILRS Primary Combination Centre at ASI. We discuss time-of-flight counter effects apparent in the results as well as attempting to separate bias and height signals using other on-site geodetic techniques including GNSS and absolute gravity.

Development of quality control tools for the MLRO

G. Bianco(1), V. Luceri(2), D. Iacovone(3)
(1) ASI Centro di Geodesia Spaziale "G. Colombo", Italy
(2) e-GEOS SpA, Italy
(3) Sistematica SpA, Italy
E-mail: giuseppe.bianco@asi.it

Starting from the need to trace and correct the unmodeled range bias which arose in the MLRO data during last year, we have developed a control infrastructure and a web based information system which enables us to constantly monitor the system parameters and alert the station operators and data analysists for possible anomalies in quasi real time. This presentation gives a thorough description of what has been done so far.

NGSLR Performance in High and Low Energy Operation

Peter Dunn, Christopher Clarke, Mark Torrence
Raytheon/GSFC, USA
E-mail: Peter.J.Dunn@Raytheon.com

The Next Generation Satellite Laser Ranging System (NGSLR) has been designed to track targets at lunar distance as well as Earth-orbiting retroreflector-equipped satellites. NGSLR's eye-safe, single photon, high frequency observations of the closer targets exhibit characteristics of system and satellite signature which must be considered in an effective orbit determination in combination with data collected by other observatories in the global SLR network. To help isolate these features, observations taken by the instrument as the receiver in a two-station configuration with MOBLAS-7 at Goddard Geophysical and Astronomical Observatory (GGAO) have been used to calibrate the NGSLR event timer and processor. High energy returns from available Earth orbiting satellites have now been used to calibrate the longer-pulse transmit system built into NGSLR to support the up-coming Lunar Reconnaissance Orbiter (LRO) Mission. Special efforts by stations in the tracking network will provide the timing required to construct the lunar observations from signals received at LRO. We will show the results of a continuing analysis of the accuracy and precision of each of the two NGSLR systems observing returns from geodetic satellites ranging in altitude from Larets to Etalon.

TRF datum and ILRS network geometry

V. Luceri(1), G. Bianco(2), C. Sciarretta(3), M. Virelli (2)
(1) e-GEOS SpA, CGS-Matera, Italy
(2) Agenzia Spaziale Italiana, CGS-Matera, Italy
(3) Telespazio SpA, Roma, Italy

The definition of the ITRF datum is one of the key element to assure a stable reference frame without internal distorsion. The last geodetic reference system ITRF2005 was constructed by combining time series from all the space geodesy techniques. The orientation was constrained to the ITRF2000 orientation at epoch 2000.0 and null orientation rates between the two, the translation and its rate were fixed to the SLR solutions and scale and its rate to the VLBI solutions. The SLR time series was not considered in the scale definition mainly for its discontinuity in the time series. The SLR network geometry has been identified as a candidate to explain the discontinuity and this presentation will investigate possible evidences of the network effect.

Assessing Tracking Performance of High Satellites at Mt Stromlo SLR Station

Christopher Moore
EOS Space Systems, Australia
E-mail: cmoore@eos-aus.com

An analysis of changes to tracking productivity of high satellites following the 2007 laser power upgrade at Mt Stromlo SLR Station is presented. This analysis uses data obtained from tracking Giove A and other satellites during June-August 2008 and contrasts the results with similar data obtained during May-August 2006. The results show that the increase in power level has subsequently allowed the station to operate unmanned in all weather conditions and still maintain productivity levels.

Multi-Satellite Daily Bias Report: How to Read and Handle it

Toshimichi Otsubo, Mihoko Kobayashi ^*,Tadahiro Gotoh, Toshihiro Kubo-oka^**
* Hitotsubashi University
** NICT
E-mail : t.otsubo@srv.cc.hit-u.ac.jp

A quality control system for the ILRS global network has been developed utilizing the precise orbit determination technique. Laser-range observation data for as many as 15 satellites are being processed every day within 24 to 48 hours after ranging observations, and the quality control numerical tables are available via web, ftp and email. The analysis reports, formerly provided by National Institute of Information and Communications Technology and currently by Hitotsubashi University, are widely used for detecting and alerting various kinds of problems. A quick guide to interpret the daily report will be presented.

Improved Modeling Approaches Towards the mm SLR

E.C. Pavlis, M. Kuzmicz-Cieslak, and P. M. Hinkey
Joint Center for Earth Systems Technology (JCET), USA
E-mail: epavlis@umbc.edu

Accuracy requirements for the International Terrestrial Reference Frame (ITRF) are becoming increasingly more stringent, especially with regards to its origin definition and its scale stability. Satellite Laser Ranging (SLR) contributes unique information on the origin, and along with VLBI, for its absolute scale. Advances in our understanding of the coupling between the sub-components of system Earth require that we revisit our current modeling used in the reduction of SLR data. Over the past few years, the inclusion (or not) in our models of high frequency effects of the temporal gravity signals due to mass redistribution in the terrestrial system, has been a topic of heated discussions at venues such the EGU, AGU and various workshops. With the recent release of numerous products from global circulation models and, satellite and terrestrial observations, we are able now to examine the effect of such improved modeling in the analysis of several years of SLR data. We will present results from such analyses and compare them to our nominal results, based on the currently accepted ILRS standards. Depending on the outcome of these tests, we anticipate that in the near future, ILRS will formulate a proposal to IERS for modification of the analysis standards related to the products contributing to the establishment of the future ITRFxx.

Challenges of the TerraSAR-X/TanDEM-X formation

Krzysztof Snopek, Ludwig Grunwaldt, Rolf Koenig
GFZ German Research Centre for Geosciences, Germany
E-mail: snopek@gfz-potsdam.de

In September 2009 TanDEM-X will be launched to fly with TerraSAR-X in a very close formation called helix. The helix means distances of the two spacecrafts of approximately 200 meters at one time in along-track direction, at another time in radial direction. Orbit predictions for both spacecrafts will exhibit the usual accuracy of 2 to 3 m radialy and something below 10 ms in along-track within 8 hours after release. Due to the very close formation, the stations need to distinguish between the two targets. We will present the formation scenario and highlight the parts where the constellation exhibits extrem positions for tracking. From this, conclusions are drawn on the difficult situations and possible remedies for the various station types.

State of the SLR in Russia

Burmistrov V. B., Glotov V.D., Parkhomenko N.N., Sadovnikov M.A., Shargorodsky V.D.,  Vasiliev V.P.
IPIE, Russia
E-mail: natalia.n@g23.relcom.ru

During a long period, the Russian SLR stations were unable to deliver measurement data to the ILRS. Currently, in accordance with a recent decision of the State Administration, it is permitted to deliver measurement data from two Russian stations (Altay and Baikonur) to the ILRS, as well as to resume data delivery from the Komsomolsk station.
The Altay SLR station has been recently upgraded: a new laser has been installed with a pulse repetition rate of 300 Hz, and a higher average output power. The measurement data from this station will be soon delivered the ILRS.
A description is provided of the Altay and Baikounur SLR stations, as well as their basic parameters.
Information will be also provided concerning the new Russian space missions where the use of SLR is expected.

Sub-centimeter SLR precision with the SLRF2005/LPOD2005 network

N.P. Zelensky, F.G. Lemoine, D.D. Rowlands, S.B. Luthcke, D.S. Chinn, J.W. Beall, B.D. Beckley, S.M. Klosko, P. Willis, V. Luceri
NASA GSFC / SGT, USA
E-mail: nzelensky@sgt-inc.com

Satellite Laser Ranging (SLR) offers the only unambiguous sub-centimeter range measurement to orbiting satellites. This capability finds many applications in addition to precision orbit determination (POD), which include a unique absolute measure of orbit accuracy, accurate altimeter range calibration, accurate definition of the Earth's center of mass, the most accurate definition of the geocentric gravitational coefficient (GM) and scale of a terrestrial reference network. Achieving sub-centimeter precision requires appropriate modeling of the satellite laser retro-reflector array (LRA) coupled in some cases with appropriate modeling of the satellite-dependant station detector characteristics, a highly accurate terrestrial reference frame, and appropriate attention to possible bias modeling of individual stations. We have processed Jason1, Lageos1/2, and TOPEX SLR tracking using the latest and most accurate POD models which include a GRACE-based static gravity, time varying gravity, and the highly accurate ILRS update of the rescaled ITRF2005 SLR complement, SLRF2005. SLRF2005 has been again updated with subsequent recommendations for the rescaled ITRF2005, LPOD2005. Our analysis evaluates individual SLR station performance and systematic signals as observed from all four satellites. Several baseline stations are identified having significant biases, which if untreated could lead to degradation in current levels of POD accuracy, and possibly bias the results for other applications of the SLR measurement.

Assessment of SLR observation performance using LAGEOS data

Gang ZHAO, You ZHAO, Mingguo SUN, Huanhuan YU
Changchun Observatory, NAOC, CAS, China,
E-mail : zhaog@cho.ac.cn

From the beginning of 2008, Changchun Observatory has carried out routine short-arc (3-day) orbit determination and station residual analysis on LAGEOS SLR data. Meanwhile, we commenced analysis in some aspects of related issues. In this report, the satellite precise orbit determination results and its preliminary applications are presented. The analysis is on the basis of 1200-day LAGOES-1/2 SLR data from March of 2005 to June of 2008. Influences of gravity models--JGM-3, EGM96, GGM02C--were checked and compared. We found these models are nearly equivalent for mm-level orbit determination with maximum difference less than 3%. Results of short-arc orbit determination which showed our orbit determination accuracy is around 1.2cm with moderate discrepancy are presented. Such accuracy could guarantee the development of our future work to a certain extent. After comparison of SLR stations' observation precision, the TB and RB analysis on some high performance stations and some stations we concerned are presented in detail. We expected such analysis will build a bridge between our theoretical research and observational work.