ILRS Fall 2005 Workshop Eastbourne, 3 – 7 October 2005 SLR towards mm accuracy Stanisław Schillak e-mail: firstname.lastname@example.org Space Research Centre of the Polish Academy of Sciences Astrogeodynamic Observatory Borowiec
Atmosphere 5 – 10 mm Is the Marini-Murray atmospheric model enough accurate for 1 mm ranging accuracy? Why not? model is fixed and depend only on latitude and geodetic height, model is true only for short distance about 10 km, model don’t include changes of refraction coefficient from local conditions (winds, rapidly temperature and pressure changes etc.) Are other better models? How we can to control error value? Is it really several mm? How we can to correct this error? two-color ranging – we need to know distance between two colors for each measurement with accuracy several picoseconds, is detector for it? determination of the seasonal correction from orbital analysis? are the other methods?
Satellite Center of Mass 2 – 4 mm How we can to eliminate this error? 1 new Lageos type satellite with prisms like in Larets or Westpac (returns only from one cube corner) additional advantage: more normal points for stations coordinates determination 2 strong signal – return will be from the nearest prism 3 determination corrections from a model of satellite signature 4 kHz lasers – identification of corner cubes, is it possible?
Detector – stop signal strength variation 1.Width of the laser pulse uncertainty of the photons distribution before detector for low signal: 100 ps 15 mm 40 ps 6 mm 10 ps 1.5 mm is this effect important? new lasers with pulse width below 10 ps are necessary? short laser pulses are also important for spatial error 2.Detector delay is a model of Time Walk enough accurate for one mm accuracy? level of calibration is really the same as a mean level of satelliteobservation? how we can to control it? 3. Stability of stop pulse amplitude and shape discriminator problem 30 ps - 4.5 mm single photoelectron level?
Systematic deviations per month (LAGEOS satellites) ERRORS SOURCES THE BEST SLR SYSTEM IN 2004 (mm) BOROWIEC SLR SYSTEM IN 2004(mm) ENVIROMENTAL ERRORS • ATMOSPHERIC PROPAGATION (MODEL) ~5 ~5 • ATMOSPHERIC PROPAGATION (METEO) <1 <1 • SATELLITE CENTER OF MASS 2 2 • REFERENCE POINT POSITION 1 3 SLR SYTEM ERRORS • CALIBRATION PATH (SURVEY) 1 1 • CALIBRATION PATH (METEO) <1 <1 • SIGNAL STRENGTH VARIATION 2 5 • TEMPORAL VARIATION 1 2 • SPATIAL VARIATION 1 2 • MOUNT ECCENTRICITIES 1 1 • TIMER 1 4 • STANDARD FREQUENCY (RANGE) <1 <1 • SOFTWARE ERRORS <1 <1 TIMING ERRORS • UTC TIME SCALE 10ns 10ns • STANDARD FREQUENCY (EPOCH) 100ns 100ns • EPOCH REGISTRATION 100ns 100ns TOTAL 6 9
ERRORS SOURCES THE BEST SLR SYSTEM IN 2004 BOROWIEC SLR SYSTEM IN 2004 PARAMETER s (mm) PARAMETER s (mm) STABILITY OF „STOP” PULSE Discriminator 30 ps 4.5 Discriminator 30 ps 4.5 DETECTOR’S TTS 25 ps 2.9 160 ps 12.4 LASER PULSE WIDTH 30 ps 1.9 40 ps 2.6 STABILITY OF „START” PULSE Discriminator <1 Discriminator <1 ELECTRONIC’S PRECISION ET 5 ps 0.7 TIC 25 ps 3.8 FREQUENCY JITTER Cesium <1 Cesium <1 EPOCH REGISTRATION 100 ns 0 100 ns 0 SATELLITE - LAGEOS CC 4.0 4.0 TOTAL – SINGLE SHOT 6.9 14.6 TOTAL – NORMAL POINT 100 pts/NP 0.7 20 pts/NP 3.3 Random errors - LAGEOS satellites (single photoelectron)
BOROWIEC SLR (7811) Single shot precision of LAGEOS-1 and LAGEOS-2 passes in the period 1993.5 – 2003.5 Orbital RMS of normal points of LAGEOS-1 and LAGEOS-2 passes in the period 1993.5 – 2000.5
What is important for improvement of the station coordinates determination? STATION number of normal points per station Precision of stations coordinates determination vs. number of normal points per orbital arc data quality (single shot RMS, NP RMS, Range Bias, Time Bias) continuity of observations rejection of normal points and passes
What is important for improvement of the station coordinates determination? ANALYSIS CENTER rejection of normal points and passes new models of the Earth gravity field: GRACE, GOCE long term gravity variations polar motion coordinates, below 1 day? new stations coordinates: ITRF2004 geocenter motion satellite-station perturbations (improvement or new effects) new model of atmosphere new precession-nutation model (IAU2000) new celestial and terrestrial reference system (IAU2000) near-real time monitoring of stations coordinates