12. 540 Principles of the Global Positioning System Lecture 20 Prof. Thomas Herring 04/3003 12540Lec20 Processing Software Examine basic features of processing software and methods Files needed General overview of the mit gamit/globk suite of programs
04/30/03 12.540 Lec 20 1 12.540 Principles of the Global Positioning System Lecture 20 04/30/03 12.540 Lec 20 2 – Files needed – General overview of the MIT GAMIT/GLOBK suite of programs Prof. Thomas Herring Processing Software • Examine basic features of processing software and methods 1
Primary research programs Geophysical research GPS analysis packages GAMIT (GPS at MIT): Uses double differences GYPSY: Jet Propulsion Laboratory (JPL) processing packages: Uses one-way observables and explicitly estimates clocks Bernese: Developed at Astronomical Institute University of Bern, Switzerland. Also referred to as BPE ( Bernese Processing Engine). Double differences Files needed for precise geodesy For all programs the basic class of files needed to accurately compute the apriori models of the delays and phas Table of satellite types. Since the PRn numbers are re-used (1-32), there could be ambiguity about the mass, size and hase center position of the satellites. There is a unique sv number for each satellite. Latest is 54 Ephemeredes of Sun and Moon. Needed for tidal forces or satellite. Can be in tabular form(most common; Harvard Smithsonian Center for Astrophysics and JPL produce these) or in analytic form(accuracy problems ). Ephemeredes can also be used for eart
04/30/03 12.540 Lec 20 3 Primary research programs packages: – – GYPSY: Jet Propulsion Laboratory (JPL) and explicitly estimates clocks – University of Bern, Switzerland. Also referred to as BPE (Bernese Processing Engine). Double differences. 04/30/03 12.540 Lec 20 4 Files needed for precise geodesy • For all programs the basic class of files needed to accurately compute the apriori models of the delays and phase: Since the PRN numbers are re-used (1-32), there could be ambiguity about the mass, size and phase center position of the satellites. There is a unique SV number for each satellite. Latest is 54. Needed for tidal forces on satellite. Smithsonian Center for Astrophysics and JPL produce these) or in analytic form (accuracy problems). Ephemeredes can also be used for Earth tide calculations. • Geophysical research GPS analysis GAMIT (GPS at MIT): Uses double differences processing packages: Uses one-way observables Bernese: Developed at Astronomical Institute – Table of satellite types. – Ephemeredes of Sun and Moon. Can be in tabular form (most common; Harvard- 2
Files needed of earths b arth fixed frame(not common Leap second table. Allows conversion from gPS time to UTC d in broadcast ephem Polar motion/uT1 earth-fixed orbits used not strictly necessary. Ocean tide loading model tables. Either in the form of station id that is 深 our averaged site:mmga would be expected 4/3003 12540Lec20 Files needed Antenna phase center model tables. Give the deviations of the phase as a function of elevation angle(and possibly azimuth) relative to a fixed point on the antenna(the ARP-antenna reference point). If the same type of antenna used in a small area, then not strictly needed but with mixed antenna types or large extent networks(such that satellites are seen at different elevation angles) then needed. May also need a file that translates names of antennas in rineX files into standard names(IGs maintains list of standard names for antennas)
04/30/03 12.540 Lec 20 5 Files needed Needed for transforming orbits integrated in inertial space integrated in Earth fixed frame (not common). Allows conversion from GPS time to UTC. Offset included in broadcast ephemeris so not strictly needed if broadcast ephemeris used. Leap seconds are announced by the IERS Needed in the transformation from inertial to earth fixed frame. Available through the IERS. If earth-fixed orbits used not strictly necessary. Either in the form of station dependent values or in a grid that is interpolated. Recent addition. Signals are diurnal and semidiurnal mainly but alias through 24-hour averaged site positions more effectively than would be expected. 04/30/03 12.540 Lec 20 6 Files needed – Antenna phase center model tables. Give the deviations of the phase as a function of elevation angle (and possibly azimuth) relative to a fixed point on the antenna (the ARP-antenna reference point). If the same type of antenna used in a small area, then not strictly needed but with mixed antenna types or large extent networks (such that satellites are seen at different elevation angles) then needed. May also need a file that translates names of antennas in RINEX files into standard names (IGS maintains list of standard names for antennas). – Nutation tables: Give position of Earth’s body axis in space. back to Earth fixed frame or to compute the coriolis forces if – Leap second table. – Polar motion/UT1 tables. – Ocean tide loading model tables. 3
Files needed Station information that gives position of ARP relative to ground mark. Strictly this should be in RINEX file header but is often incorrect. Getting this information correct is often the biggest problem in campaign GPS processing. Information is ecorded on paper log sheets that need to be transcribed correctly. Often referred to as meta-data for RINEX file priori coordinates and velocities for sites(can extract position from RINEX header but these are often not very Apriori orbit information for satellites. If working near real-time than maybe use"yesterdays"orbit extrapolated forward Atmospheric and water loadi available although some grou a local press when comp results) Specific programs The files before are generic that all programs need. Specific programs use other files to control them We will examine gamit which the mit developed GPS program. There are two basic modules: GaMit and gloBK
04/30/03 12.540 Lec 20 7 Files needed ground mark. Strictly this should be in RINEX file header but is often incorrect. Getting this information correct is often the biggest problem in campaign GPS processing. Information is recorded on paper log sheets that need to be transcribed correctly. Often referred to as meta-data for RINEX file. position from RINEX header but these are often not very good) If working near real-time Not normally used or available although some groups use a local pressure admittance model (need to be careful when comparing results). 04/30/03 12.540 Lec 20 8 Specific programs need. – Station information that gives position of ARP relative to – Apriori coordinates and velocities for sites (can extract – Apriori orbit information for satellites. than maybe use “yesterdays” orbit extrapolated forward. – Atmospheric and water loading. • The files before are generic that all programs Specific programs use other files to control them. • We will examine GAMIT which the MIT developed GPS program. There are two basic modules: GAMIT and GLOBK 4
Basic framework: gamit GAMIT: Series of programs that process GPS hase data · Parameters estimated Station positions Satellite orbits parameters Initial conditions Radiation parameters Earth orientation parameters(EOP) Atmospheric delay parameters Time dependent Zenith delays and gradients Carrier phase ambiguities Basic framework: GLOBK GLOBK: Uses parameter estimates and full covariance matrices from different sources to combine results Inputs from gPs, sLr, VLbI and sineX files Used to estimate quantities such as Site velocities from series of measurements Satellite orbit improvement EOP parameter Other derived parameters
04/30/03 12.540 Lec 20 9 – Station positions – Satellite orbits parameters • Initial conditions • • Phase center offsets – Earth orientation parameters (EOP) – Atmospheric delay parameters • Time dependent Zenith delays and gradients – Basic framework: GAMIT • GAMIT: Series of programs that process GPS phase data • Parameters estimated: Radiation parameters Carrier phase ambiguities 04/30/03 12.540 Lec 20 10 Basic framework: GLOBK – Site velocities from series of measurements – Satellite orbit improvement – EOP parameters – Other derived parameters • GLOBK: Uses parameter estimates and full covariance matrices from different sources to combine results • Inputs from GPS, SLR, VLBI and SINEX files • Used to estimate quantities such as: 5
GAMIT Structure History Data types Steps needed in processing Files needed for processing 04/3003 12540Lec20 GAMIT History Development started in late 1970s when MIT was building GPs receivers Code derived from 1960-1970 Planetary ephemeris and Vlbi software Ported to unix in 1987 Start of IGs in 1992 prompted development of automatic processing schemes Fully automatic processing mid-1990s including continuous stations and campaign GPS measurements
04/30/03 12.540 Lec 20 11 GAMIT Structure • History • Data types • Steps needed in processing • Files needed for processing 04/30/03 12.540 Lec 20 12 GAMIT History • Development started in late 1970s when MIT was building GPS receivers • and VLBI software • Ported to Unix in 1987 • Start of IGS in 1992 prompted development of automatic processing schemes • continuous stations and campaign GPS measurements Code derived from 1960-1970 Planetary ephemeris Fully automatic processing mid-1990s including 6
Current GAMIT Status · Automation features FTPing of data and other files Extraction of information from rineX files Automatic directory creation Status/arning files generated to monitor proces Largest automatic run Southern California Earthquake center campaign data set from 19922002. 04/3003 12540Lec20 Data Type L1 and l2 phase used for parameter estimation P1 and P2 range measurements Cleaning data Receiver clock error estimates(tolerance 1 microsecond=300m) L1 and l2 combined to form ionospheric-free observable lc ionospheric delay called lg Melbourne-Wibena widelane wl
04/30/03 12.540 Lec 20 13 – – Extraction of information from RINEX files – Automatic directory creation – 1992-2002. Current GAMIT Status • Automation features: FTP'ing of data and other files Status/Warning files generated to monitor process • Largest automatic run: Southern California Earthquake Center Campaign Data set from 04/30/03 12.540 Lec 20 14 estimation – Cleaning data – Receiver clock error estimates (tolerance 1 microsecond=300m) Data Types • L1 and L2 phase used for parameter • P1 and P2 range measurements: • L1 and L2 combined to form ionospheric-free observable LC • Ionospheric delay called LG • Melbourne-Wibena Widelane WL 7
Processing steps-Major GPS satellite orbit integration(arc) Modeling phase and partial derivative generation(model) GPS data cleaning and cycle slip repair (autcln Least-squares estimator(solve) 04/3003 12540Lec20 Processing steps- Minor Yaw table generation for gPs satellites Ocean tide loading coefficient generation Explicit site values Interpolation of gridded values Estimation of satellite and ground receiver clock models Display of phase residuals
04/30/03 12.540 Lec 20 15 (autcln) 04/30/03 12.540 Lec 20 16 – – Processing steps - Major • GPS satellite orbit integration (arc) • Modeling phase and partial derivative generation (model) • GPS data cleaning and cycle slip repair • Least-squares estimator (solve) Processing steps - Minor • Yaw table generation for GPS satellites • Ocean tide loading coefficient generation Explicit site values Interpolation of gridded values • Estimation of satellite and ground receiver clock models • Display of phase residuals 8
Files needed for processing Initial orbit information Sources Broadcast ephemeris from receivers SP3 orbit files from IGs GAMIT g-files Earth Orientation Parameters(EOP)files Orbit integration in inertial space Satellite clock files (j-files) Ocean tide files 04/3003 12540Lec20 Files continued Moon and Sun ephemeredes orbit integration solid earth tid leap-second file(Utc versus AT Satellite information files GPS antenna information(phase center) Information about stations(coordinates receiver/antenna types and heights) Control files for GAMIT. Two major ones are caller sestbl which controls the type of run and sittbl controls how stations are treated(e.g, sigmas of apriori coordinates)
04/30/03 12.540 Lec 20 17 Files needed for processing – Broadcast ephemeris from receivers – SP3 orbit files from IGS – GAMIT g-files ) files: • Initial orbit information: Sources • Earth Orientation Parameters (EOP Orbit integration in inertial space • Satellite clock files (j-files) • Ocean tide files 04/30/03 12.540 Lec 20 18 Files continued • Moon and Sun ephemeredes • leap-second file (UTC versus AT) • Satellite information files • GPS antenna information (phase center) • Information about stations (coordinates, • Control files for GAMIT. Two major ones are called apriori coordinates). – orbit integration – solid Earth tides receiver/antenna types and heights) sestbl. which controls the type of run and sittbl. Which controls how stations are treated (e.g, sigmas of 9
Data Files Raw receiver files: UNAVCO teqc program used to convert to rinex files RiNEX files Gamit converts to own format x- files Data files can be local or ftp'd from international archives 04/3003 12540Lec20 GAMIT File summary GAMIT uses many files Many of these files are standard and automatically created Automatic processing scripts either link or ftp these Some files should be updated from MiT ftp site (bowie. mit. edu) The satellite information files needs to be updated when new satellites are launched GAMIT can be downloaded at http://www-gpsg.mitedu/simon/gtgk
04/30/03 12.540 Lec 20 19 Data Files files • Raw receiver files: UNAVCO teqc program used to convert to RINEX files • RINEX files: GAMIT converts to own format x- • Data files can be local or ftp'd from international archives GAMIT File summary • GAMIT uses many files: Many of these files are standard and automatically created • Automatic processing scripts either link or ftp these files. • Some files should be updated from MIT ftp site (bowie.mit.edu) • The satellite information files needs to be updated when new satellites are launched • GAMIT can be downloaded at: http://www-gpsg.mit.edu/~simon/gtgk 04/30/03 12.540 Lec 20 20 10
