High Rate GPS Solutions

Transcription

1 High Rate GPS Solutions High rate GPS data (1 Hz or higher) Network solution Fixed a local reference clock Bias fixed Sub daily position estimates solutions Position becomes stochastic parameter Fairly standard models for processing May have to iterate on solutions to estimate the troposphere May have to account for multipath

2 GPS the Seismometer Elo segui, et al, 2006 Larson, K. M., P. Boden, and J. Gomberg (2003), Using 1 Hz GPS data to measure deformations caused by the Denali fault earthquake, Science, 300, P. Elo segui, J. L. Davis, D. Oberlander, R. Baena, and G. Ekstro m, Accuracy of high rate GPS for seismology, GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L11308, doi: /2006gl026065, 2006

3 Multiple rate GPS solutions for studying different fault processes Preliminary 1hz soln for JRGN vert vert east east Goals: Daily solutions for coseismic offset and long term postseismic response Sub daily solutions using 15 sec data for coseismic offset, immediate postseismic 1 and 5 Hz solutions for dynamic response, coseismic offset, immediate postseismic north north First, test strategies on 15 second data Runs faster Data exists for all stations, all days

4 Point positioning vs. Baseline east north vert JRGN, Point positioned Baseline (ATJN JRGN) Point positioning: gd2p orbits and clocks fixed no antenna maps, ambiguity resolution Baseline: longarc strategy from Bruce Haines estimate all participating clocks (excepting ATJN reference clock) antenna maps, ambiguity resolution Both: 1 min position solns using 15 sec data, troposphere parameters estimated

5 Effect of phase center maps, regional solution JRGN, vertical JRGN, east Red no maps Green with maps Red single baseline Green regional soln Blue reg. soln, amb res Effect of antenna phase center maps Small difference in all 3 components ATJN and JRGN have same antenna type, effect might be larger with mixed antennas Effect of using regional solution very few ambiguities resolved for ATJN JRGN baseline (~450 km) added nearby sites to solution, resolved more ambiguities

6 Real or imaginary pre earthquake transient? Seen on east component on multiple stations

7 Real or imaginary pre earthquake transient? But pattern repeats every day, shifted by 4 minutes

8 More motivation for sidereal filtering Zooming in, see higher frequency scatter also repeating every day, shifted by 4 minutes

9 Modified Sidereal Filter (MSF) Remove site specific multi path effects through stacking residuals offset by orbit period of each satellite Similar to MSF technique of K. Larson, (Univ. of Colorado) Except applied to phase data and not to 1 Hz solutions MSF correction determined by Stacking phase residuals for +/ 5 days around target day offset by orbit repeat period Apply mean as a correction to the phase Re point position

10 Orbit repeat periods are not quite sidereal

11 Example of MSF correction

12 Modified Sidereal Filtering for Tocopilla Changes from prior sidereal filtering scripts: Use longarc residuals to generate phase & pseudorange corrections Only use days prior to earthquake Want to downweight or not use at all residuals from day of earthquake vert east north SRGD Filtered SRGD For stations with smaller coseismic offsets, sidereal filtering is critical to estimate coseismic offset

13 Summary of 15 second analysis tests Significant improvements seen from: Baseline solutions compared to point positioning Regional solutions with shorter baselines (allows for ambiguities to be fixed) Sidereal filtering Small/no effect seen from: Antenna phase center variation maps Iterating solution Multiday solution

14 1Hz solutions: Changing the position update interval mid solution Desired result: 10 minute updates prior to earthquake epoch by epoch updates at the time of the earthquake 1 2 minute updates for postseismic time period vert east north JRGN

15 1Hz solutions: Changing the position update interval mid solution Method: 1. Edit stochastic parameters in wash.nml file 2. Run preprefilter and prefilter to generate batch.txt file 3. Remove multiple station parameter listings from top of batch.txt file 4. Run wash script, starting from filter vert east north JRGN JRGN

16 1Hz solutions: Dynamic coseismic motion CDLC VLZL CTLR MCLA JRGN

17 1Hz solutions: Constrain Epicenter CDLC CTLR MCLA

18 5hz solutions:jrgn east north vert

19 5hz solutions:ctlr north east vert

20 Improving Tropo Modeling: GMF Niell Mapping Function Based on 1 year of radiosonde data from Northern Hemisphere Global Mapping Function Based on data from global ECMWF numerical weather model Coefficients obtained from expansion of Vienna Mapping Function (VMF1) VMF1 has 6 hourly values

21 Improved Tropo modeling: GMF Mean height changes (in mm) when using the hydrostatic GMF instead of NMF for January (upper plot) and July (lower plot). From Boehm et al., GRL 2006

22 New Analysis Strategies Using Global Mapping Function for troposphere (Boehm et al., 2006) May 7, 2009

23 May 7, 2009 Effects of GMF on Time Series