README 1.7 03/02/21 1997 Jul 24 17:03:17 - Introduction Output from ag includes eight files, including this README file. The LOG file contains a blank line followed by a single 159-character string. An example is 1997-08-18 HNPT 34.24 0.07 4.63 0.17 -57.48 0.41 nev|1997-08-18 HNPT 288 88.8 0.353 -0.143 1700 35 1689 10 57 57 The fields are as follows: field value in example comment _____ ________________ ______________________________________ date 1997-08-18 year-month-day site HNPT uppercase north 34.24 deviation from nominal in north, cm d north 0.07 formal error, cm east 4.63 deviation from nominal in east, cm d east 0.17 formal error, cm vertical -57.48 deviation from nominal in vertical, cm d vertical 0.41 formal error, cm separator nev| separator date 1997-08-18 repeat site HNPT repeat number 288 number of points for which a valid receiver clock solution exists noise 88.8 rms deviation from straight line of clock solution (ns) drift 0.353 drift of clock solution (parts per trillion) clock -0.143 clock solution (usec) at start of day prn meas 1700 number of pseudorange measurements prn rms 35 rms (cm) of pseudorange measurements phase meas 1689 number of phase measurements phase rms 10 rms (mm) of phase measurements initial breaks 57 number of initial phase breaks final breaks 57 number of final phase breaks - Naming convention Except for the LOG and README files, the filename convention is yyyy-mm-dd.site..Z where yyyy-mm-dd is the date of the data (e.g., 1997-07-23 for July 23, 1997); site is the 4-character ID (always forced to uppercase by ag); is the file type (to be discussed); .Z indicates the file is Unix compressed. - Estimated coordinates Your "gd" file should look similar to the following: zcat 1997-07-09.METS.gd.Z METS LAT 97JUL09 60.217471154 +- .0009 .041701 -.120684 METS LON 97JUL09 24.395317576 +- .0017 -.007703 METS RAD 97JUL09 94.6265 +- .0043 The site "METS" is estimated to be at 60.217471154 degrees latitude, 24.39531757 degrees longitude, and 94.6265 meters elevation (WGS84 reference ellipsoid). The corresponding 1-sigma formal errors are 0.9 mm, 1.7 mm, and 4.3 mm. (The formal errors in the file are expressed in meters, to 0.1-mm precision.) The correlation between latitude and longitude is 0.041701, between latitude and height is -0.120684, and between longitude and height is -0.007703. (The formal errors reflect assumed data noise of 1 cm in phase and 1 m in pseudorange, data every 5 minutes. They do _not_ account for GPS orbit or clock errors, or for any mismodeling. Based on observed daily repeatabilities, real uncertainties in estimated coordinates are probably factors of two to five higher.) The ITRF Cartesian components can be found in the "stacvx" file. (The "stacov" file gives the Cartesian components in a loosely-defined reference frame, and is supplied only for completeness.) An example of a stacvx file is: 3 PARAMETERS ON 97JUL09. 1 METS STA X .289257094452427E+07 +- .226127368484964E-02 2 METS STA Y .131184334996079E+07 +- .178279367506613E-02 3 METS STA Z .551263409074963E+07 +- .371525386305951E-02 2 1 .244303003012567E+00 3 1 .860052835059401E+00 3 2 .491679565793214E+00 METS ANTENNA LC 0.0000 0.0000 0.0000 !up north east (m) ! transformed to ITRF94 with apply using flags -r -t -s The coordinates ("STA X", "STA Y", "STA Z") and 1-sigma formal errors are in meters. For example, the estimate of METS's X component is 2892570.94452427 meters plus-or-minus about 2.3 mm. The correlation between estimates of X and Z is about 0.860. The line with "METS ANTENNA LC" indicates that these coordinates refer to the antenna phase center, since all three values are zero. Note that ag _always_ uses this convention, regardless of what may or may not be in the header of the RINEX file! - Other estimated parameters One other file that contains parameter estimates and formal errors is the "tdp" file. Each record in a tdp file has four fields. The first is time in GPS seconds past J2000. Next is the a priori value, followed by the estimated value, and 1-sigma formal error of the estimate. The last field contains the name of the parameter. The estimated parameters include wet troposphere zenith delay ("WETZTROPsite"), phase biases (for example, "PB GPS15 site"), receiver clock ("STA BIASsite"), and station coordinates ("STA X site", similar for Y and Z). All numbers in this file are in kilometers, except for the troposphere parameters, which are in meters. - Postfit residuals The "pfr" file contains information on the quality of the fit. Post-fit residuals for each measurement are given. Each record in a pfr file has nine fields. They are (1) site name, (2) satellite, (3) data type (120 means phase, 110 means pseudorange), (4) date, (5) time (date and time are UTC), (6) seconds past first measurement, (7) post-fit residual in cm, (8) elevation angle in degrees from receiver to satellite, and (9) azimuth angle, degrees. - Gipsy "qregres namelist" The last file will be of interest only if you know about Gipsy. It is the qregres namelist that was used in the analysis.