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