; LDGPS ;--------------------------------------------------------------- ;! load GPS data from an ASCII file ;# Task Calibration VLA ;----------------------------------------------------------------------- ;; Copyright (C) 1996, 1999 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- ;--------------------------------------------------------------- LDGPS LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC LDGPS Task to load GPS TEC data from ASCII files INNAME Input UV file name (name) INCLASS Input UV file name (class) INSEQ 0.0 9999.0 Input UV file name (seq. #) INDISK 0.0 9.0 Input UV file disk unit # INFILE GPS transfer file. OUTVERS Output GP table version ---------------------------------------------------------------- LDGPS Task: Loads GPS delay data from a CONAN-ASCII file into a GP table for use by ionospheric calibration tasks. Adverbs INNAME.....Input UV file name (name). Standard defaults. INCLASS....Input UV file name (class). Standard defaults. INSEQ......Input UV file name (seq. #). 0 => highest. INDISK.....Disk drive # of input UV file. 0 => any. INFILE.....Name of file containing GPS data. OUTVERS....Version number of GP table. 0 => highest + 1 ---------------------------------------------------------------- LDGPS: Task to load GPS TEC data from ASCII files Documentor: Chris Flatters Related Programs: APGPS LDGPS loads total electron content (TEC) data from a GPS ASCII data file, corrects it for receiver and satellite delay offsets and stores it in a GP table for use by programs that calculate corrections for ionospheric delay and Faraday rotation. 1. INPUT FILE FORMAT The input file contains raw data from one or more dual-frequency GPS receivers together with information about satellite and receiver biases. This file shall contain lines of ASCII text. The end of each line shall be marked by an new-line character (hexadecimal code 0A). No line shall contain more than 200 characters (not counting the new-line character marking the end of the line). The input file shall be divided into sections. Each section shall end with the terminal character '/' (hexadecimal code 2F). Each section shall either be a structured record or a data block. A structured record shall contain one or more keyword clauses seperated by spaces and tab characters. A keyword clause shall consist of a keyword specification, optionally followed by an equals sign followed by a scalar or vector value. The equals sign may be separated from the keyword specification or value by one or more spaces or tab characters. A keyword specification shall consist of a keyword name, optionally followed by an array index in parentheses. Upper-case and lower-case letters are regarded as equivalent in the keyword name. An array index shall be a positive integer. A scalar value shall either be an integer, a floating point number (which may contain an exponent beginning with 'e', 'E', 'd', or 'D'), a time, a character string delimited by either single quotes or double quotes (but not a mixture of the two) or a simple floating-point expression in parentheses. A time shall consist of one or more digits (representing hours), followed by a colon and either a floating-number (representing minutes) or an integer (representing minutes) followed by another colon and a floating point number representing seconds. An vector value shall be a sequence of scalar values separated by commas and optional spaces or tabs. A structured record may span more than one line but a line-break shall not occur within a keyword clause unless it follows immediately after a comma separating two scalar values in a vector value. A data block shall consist of zero or more scalar values separated by spaces or tab characters. The input file may contain comments. A comment shall begin with an explamation mark ('!') and extend to the end of the line. Comments are used to provide explanatory information to human readers and may occur anywhere in the file except within a keyword clause. The file shall contain satellite bias records and receiver data blocks. A receiver data block consists of a data header record that is immediately followed by a data block containing raw GPS delay measurements. The first record in the file shall be a satellite bias record. 1.1 SATELLITE BIAS RECORD A satellite bias record specifies the transmitter offsets (the difference in the electrical delays in the signal paths for L1 and L2) for each satellite in the GPS constellation. It is identified by the presence of the keyword 'GPS'. The following keywords may occur in a satellite bias record. +---------+----------+-------+--------------------------------+ | Keyword | Required | Value | Description | +---------+----------+-------+--------------------------------+ | GPS | yes | none | Identifies the current record | | | | | as a satellite bias record. | | | | | | | BIAS | yes | float | Specifies the satellite biases | | | | array | as an array of floating point | | | | | numbers with the array indices | | | | | corresponding to satellite | | | | | PRNs. | | | | | | | TECU | no | none | Indicates that bias values are | | | | | given in TEC units. | | | | | | | NANOSEC | no | none | Indicates that bias values are | | | | | given in nanoseconds. | +---------+----------+-------+--------------------------------+ One TEC units corresponds to a column density of 10^16 electrons per square meter and is equivalent to a differential delay of 2.854 nanoseconds between L1 and L2. The TECU and NANOSEC keywords shall not both appear in the same record. If neither keyword is present in the record then the biases shall be assumed to be given in nanoseconds. 1.2 RECEIVER DATA BLOCK The following keywords may occur in a data header record. +----------+----------+--------+------------------------------+ | Keyword | Required | Value | Description | +----------+----------+--------+------------------------------+ | GPSDATA | yes | none | Identifies the record as a | | | | | data header record. | | | | | | | RECEIVER | yes | string | Specifies the name of the | | | | | receiver (no more than 8 | | | | | characters). | | | | | | | BIAS | yes | float | Specifies the receiver bias. | | | | | | | TECU | no | none | Indicates that bias value is | | | | | given in TEC units. | | | | | | | NANOSEC | no | none | Indicates that bias value is | | | | | given in nanoseconds. | | | | | | | X | yes | float | x-coordinate of receiver in | | | | | meters | | | | | | | Y | yes | float | y-coordinate of receiver in | | | | | meters | | | | | | | X | yes | float | z-coordinate of receiver in | | | | | meters | +----------+----------+--------+------------------------------+ The x, y, and z coordinates shall be given in the WGS-84 geocentric coordinate system. The TECU and NANOSEC keywords shall not both appear in the same record. If both are omitted the bias shall be assumed to be given in nanoseconds. The data header shall be followed by a data block containing no more than 36000 measurements. Each measurement shall consist of the following fields. +-------+-------+---------------------------------------------+ | Field | Type | Description | +-------+-------+---------------------------------------------+ | 1 | int | Year number | | | | | | 2 | int | Day of year (1 to 366) | | | | | | 3 | time | Time of the observation (UTC) | | | | | | 4 | int | Satellite PRN | | | | | | 5 | float | Azimuth of satellite in degrees (increasing | | | | north through east) | | | | | | 6 | float | Elevation of satellite in degrees | | | | | | 7 | float | TEC from phase measurements (TEC-phase) in | | | | TEC units | | | | | | 8 | float | TEC from delay measurements (TEC-tau) in | | | | TEC units | +-------+-------+---------------------------------------------+ The TEC measurements shall not be corrected for receiver or satellite biases. That is, given a TEC measurement t, the true TEC along the line of sight to the satellite should be t' = t - (s + r) where r is the receiver bias from the data header and s is the satellite bias from the nearest preceding satellite bias record. 1.3 EXAMPLE INPUT FILE GPS BIAS = -6.104, -2.786, -8.370, -11.275, -7.682, -9.106, -3.263, -8.059, -10.282, -3.163, -3.620, -3.620, -22.921, -4.628, -4.235, -1.263, -2.862, -9.521, -3.306, -4.719, -4.719, -7.248, -5.219, -1.190, -14.175, -12.648, -8.076, -11.628, -13.995, -14.613, -11.363, -3.620 TECU / ! ! Biases from JPL global model, September 22 1998 ! GPSDATA RECEIVER = 'PIE TOWN' BIAS = +2.961 NANOSEC X = 1640916.7642 Y = -5014781.1987 Z = 3575447.1372 / ! ! Year Day Time PRN Az El TEC-phi TEC-tau 1998 277 01:45:10.2 2 40.20 53.23 3.9281 4.2359 1998 277 01:45.10.2 15 157.63 43.09 7.2385 6.1423 ! ! ... ! / ! End of file 1.4 LIMITATIONS Although the file may contain data from several receivers, LDGPS can only handle data from a single receiver. 2. GP TABLE FORMAT This extension table for a uv data set contains corrected measurements of TEC-tau from GPS satellites. 2.1 HEADER KEYWORDS The header keywords provide information about the GPS receiver. Keyword Type Description ------- ---- ----------- RECVR A The name of the receiver RLONG R The East longitude of the receiver (degrees) RLAT R The latitude of the receiver (deg) RHEIGHT R The height of the receiver above mean sea level (m) 2.2 RECORDS Each record contains a single measurement of the TEC along the line of sight to a satellite. Title Units Code Description ----- ----- ---- ----------- TIME days 1D Time of measurement PRN 1I Satellite PRN AZ deg 1E Satellite azimuth ELEV deg 1E Satellite elevation TECTAU m^-2 1E TEC from delay TECPHS m^-2 1E TEC from phase Times are given relative to the reference time for the UV data (0h UTC or IAT on the reference date).