AIPS HELP file for LDGPS in 31DEC24
As of Thu Apr 25 0:15:38 2024
LDGPS: Task to load GPS TEC data from ASCII files
INPUTS
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
HELP SECTION
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
EXPLAIN SECTION
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 2560 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).