About GAMIT

GAMIT and GLOBK are a comprehensive suite of programs developed by MIT for analyzing GPS measurements primarily to study crustal deformation, generating orbit/EOP products, and establishing and maintaining the reference frame.

GAMIT home page

The SOPAC data archive GAMIT directory contains all of the setup files listed here.

Global list

Regional list

Reference Frame Definition and Date Specific a priori Coordinates

The International Terrestrial Reference Frame (ITRF) is defined by IERS and is updated every few years. The most recent reference frame is ITRF2020. The previous two frames were ITRF2014 and ITRF2008.

Based on ITRF2020, the International GNSS Service (IGS) created a frame specific for GNSS technology, known as IGB20.

The derivation of ITRF is based on multiple modern space geodetic techniques, namely GNSS, SLR, VLBI, and DORIS.

Based on ITRF2020, the International GNSS Service (IGS) created a frame specific for GNSS technology, known as IGb20.

The current SOPAC data analysis, since 1992-06-13 (GPS week 648), is based on the IGb20 reference frame. IGb20 is derived from the analysis of GNSS only solutions contributed by IGS Data Analysis Centers while the core stations are constrained onto ITRF2020 defined stations. Therefore, its positions/velocities are completely consistent with IGS published orbits/clocks and earth orientation parameters (EOP), as well as all the physical models and model corrections, such as the antenna phase center model for receivers and satellites, the differential code biases (DCB), and various tidal loading displacements etc. SOPAC routinely processes a large volume of GPS data (about 3500 sites) collected from both global and regional networks, with a focus on tectonic plate boundaries.

The a priori coordinates used in SOPAC data processing come from three sources:

1. IGb20 definition (major offsets caused by large earthquakes are considered);
2. SOPAC multi-year solutions (if velocities are estimated);
3. Most recent SOPAC weekly solutions (if velocities have not been estimated or affected by earthquakes).

The true of date a priori files containing the above mentioned a priori coordinates are date sensitive. Daily files are updated weekly. An example of an  a prior file for  YYYY=2025 and DOY=003

Differential Code Biases

dcb.dat.code.rinex.G html

dcb.dat.code.rinex.R html

dcb.dat.code.rinex html