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pages

Program for Adjustment of GPS Ephemerides

Overview

pages is the newest generation orbit/baseline estimation software. Using double-differenced phase as its observable, pages should be suitable for a variety of projects requiring the highest accuracy. A variety of parameter types can be estimated including tropo corrections, station coordinates and linear velocities, satellite state vectors and polar motion. pages is commonly run using the ion-free phase combination, but optionally L1 only, L2 only, or two wide-lane phase combinations can be used. These, in turn, can be used to create partially or completely bias fixed solutions. Details of the models used in the processing will not be discussed in detail here but are summarized in NOAA's Analysis Center Questionaire available through the IGS Central Bureau.

This program was written in FORTRAN. Predominantly ANSI standard FORTRAN 77, a few isolated routines query the operating system for time and date, user and system identification. These "system" routines are inherently non-portable but, because they are isolated, should be easily modified or disabled.

Data Files

pages uses the databases created by mergedb.

ASCII header file (REQUIRED)	The ASCII header file provides the most basic site information and serves to initialize descriptive data structures used internally in pages.
binary data file (REQUIRED)	The binary data file is the data source. In addition, the tropo correction stored in the data file can be used. This option is preserved for compatability with older programs.
binary orbit file (OPTIONAL)	Although pages can read and use the binary orbit file, it does not if a precise ephemeris is specified. Note, however, that if no precise ephemeris is available, the database can be created and editted using the broadcast orbit. A preliminary pages solution can also be made using the broadcast orbit stored in the database for manual editting and other quality control reasons. When a precise ephemeris becomes available, the final pages solution can be generated without recreating or re-editing the database.

Program Control Files

pages.inp (REQUIRED)	pages.inp controls the parameters to be estimated and describes the databases to be used.
pages.skl (REQUIRED)	pages.skl controls the models used and defines any constraints to be applied in the solution. A description of older, no longer supported options is also available.

Effectively, pages.inp contains information which will change with every solution; pages.skl contains information which will change less frequently. Some general rules for creating these files apply:

any file or database name may include the path,
the default path is always the current directory,
the maximum length of a file name plus path is 64 characters,
all characters to the right of a dollar sign, "$", are ignored,
lines starting with a dollar sign are skipped,
blanks are not significant except in names and constraint identifiers,
Control flags are not case sensitive. However, file, database, station names and constraint identifiers are case sensitive.

ephemeris (REQUIRED)	- the broadcast orbit can be used through database's binary orbit file - the SP1 format, - the SP3 format, - a binary format ephemeris, generated by the arc program, used internally for orbit generation.
antenna phase correction file (OPTIONAL)	The ant_info file corrects for differences is the electrical characteristics of the antennas. These differences have a strong observation elevation dependence and strongly alias into the tropo corrections and estimated height above ellipsoid for the site. Therefore, use of this file is strongly urged. The ant_info file name is entered through the pages.skl file. This is an ASCII file and is provided by outside source such as NOAA or the IGS.
site information file (OPTIONAL)	The site information file is designed to provide a complete description and history of a tracking site. This description will include coordinates, velocity, receiver, antenna and any changes to these data time tagged with the date the change becomes effective. A site information file is binary but can be viewed with the xsites program. The site information file names are entered through pages.skl. Currently, a maximum of five site information files can be used in one pages solution. The heirarchy used in such a case is initialization from the database header file first listed site info file second listed site info file . . . and so forth; each one superceding the ones before. This list is searched for each site so a mixture of sources is common.

Other Program Control Files

The pages.inp, pages.skl, leap seconds list, ephemeris, ant_info and site info files will be used in most pages solutions. All other files are optional in the strictest sense but may be required for a given task. These specialized files include:

break files (OPTIONAL - but very common)	Automatic or manual editing can attempt to repair cycle slips by indicating the time of the slip to pages and forcing the program to estimate a new phase ambiguity starting at that time. The break files contain this information. NOTE: a naming convention is enforced. Each break file contains instructions for one database. To strengthen this tie, these files must be named with the the database name plus the extension .brk.
integer files (REQUIRED - for bias fixed solutions)	Integer files contain the values to which phase ambiguities should be fixed.
leap seconds (OPTIONAL)	The dates of all leap seconds since January, 1980, the start of GPS time. By default, the program looks for this file in the current directory. The program will also recognize the file name leapsec.dat.
RINEX met files (OPTIONAL)	Surface met data are input through the RINEX met files. By default, a surface met model, dependent upon site latitude, height and the date is used to create the a priori tropo model and corrections. However, if available, pages can use surface met data rather than the default model. This detail modelling is essential for precipitable water vapor estimation.
leap.sec (REQUIRED - when using a binary ephemeris)	The dates of all leap seconds since January, 1980, the start of GPS time. By default, the program looks for this file in the current directory.
pole. (REQUIRED - when using a binary ephemeris)	The X and Y polar motion parameters. This file will be provided from an outside source.
ut1. (REQUIRED - when using a binary ephemeris)	The TAI - UT1 difference in time standards. This file will be provided from an outside source.

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pages.html
March 4, 1999