[IGSMAIL-3281]: RINEX Modifications for LEO Satellites (Vers. 2.20)
Werner Gurtner
werner.gurtner at aiub.unibe.ch
Thu Apr 12 00:47:10 PDT 2001
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IGS Electronic Mail 12 Apr 00:48:08 PDT 2001 Message Number 3281
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Author: W. Gurtner
The following message contains fixed-formatted tables and examples of up to 80
characters. In case the message cannot be easily read please get it as a text
file from
ftp://ftp.unibe.ch/aiub/rinex/rnx_leo.txt.
RINEX Version 2.20
Modifications to Accommodate Low Earth Orbiter Data
***************************************************
Werner Gurtner <gurtner at aiub.unibe.ch>
Lou Estey <lou at unavco.ucar.edu>
April 12, 2001
Summary
-------
In order to accommodate GPS data from LEO satellites some moderate
modifications of the RINEX Version 2.10 format are proposed:
- New header records for
- marker / vehicle characterization
- antenna position and orientation
- increased precision of the phase observations
- Two new observation types
- LA for L1 phase derived from C/A code tracking
- SA for SNR of L1 phase derived from C/A code tracking
- CH for the receiver channel numbers
- File naming recommendations
- format for hourly files
- format for 15-minute files
The modifications have been accepted for LEO data used in the IGS LEO
Pilot Project by the IGS LEO Working Group.
The modifications are only necessary for RINEX files containing LEO
data. Some of the modifications could be a valuable extension for
ground-based GPS data, too.
We are looking for comments about the implementation of the
modifications for ground-based data.
1. Introduction
---------------
The current RINEX Observation File definition does not fully
accommodate data from low earth orbiters equipped with GPS or
GPS/GLONASS receivers.
The following deficiencies have been defined:
1) The RINEX file should show the nature of the antenna marker /
receiver carrier, i.e. if the receiver/antenna are mounted on a
satellite or another non-typical "marker"
2) Antenna position w/r to the center of mass should be stored
3) Antenna boresight in body-fixed coordinate system has to be known
4) Attitude data: It is proposed to put satellite attitude data into
a separate file
5) Precision (resolution) of the data fields. As the format is fixed
(i.e., F14.3), the resolution of 0.001 cycles = 0.2 mm might not
fulfill all future requirements.
6) Some receivers track satellites on more than one antenna or assign
more than one channel to the same satellite (on the same or on
different antennas). The RINEX obs format does not allow for more
than one antenna at the same time. Data on more than one channel to
the same satellite can be stored, however, the channel information
gets lost.
7) It was noted that for some applications both possible phase
observations on the first frequency, L1(CA) as well as L1(P1), should
be stored in the RINEX files.
2. Proposed Modifications
-------------------------
In order to indicate the nature of the marker (spaceborne receiver) a
new MARKER TYPE header record has been defined:
+--------------------+------------------------------------------+------------+
|MARKER TYPE | Type of the marker. | A20,40X |
| | | |
| | Currently defined are: | |
| | | |
| | GEODETIC : Earth-fixed, high- | |
| | precision monumentation | |
| | NON_GEODETIC : Earth-fixed, low- | |
| | precision monumentation | |
| | SPACEBORNE : Orbiting space vehicle | |
| | AIRBORNE : Aircraft, balloon, etc. | |
| | WATER_CRAFT : Mobile water craft | |
| | GROUND_CRAFT : Mobile terrestrial vehicle| |
| | FIXED_BUOY : "Fixed" on water surface | |
| | FLOATING_BUOY: Floating on water surface | |
| | FLOATING_ICE : Floating ice sheet, etc. | |
| | BALLISTIC : Rockets, shells, etc | |
| | ANIMAL : Animal carrying a receiver| |
| | HUMAN : Human being | |
| | | |
| | Record required except for GEODETIC | |
| | and NON_GEODETIC marker types. | |
| | | |
+--------------------+------------------------------------------+------------+
Attributes other than GEODETIC and NON_GEODETIC will tell the user
program that the data were collected by a moving receiver. The
inclusion of a "start moving antenna" record (event flag 2) into the
data body of the RINEX file is therefore not necessary. Event flags 2
and 3 are still necessary to flag alternating kinematic and static
phases of a moving receiver, however.
The following new optional header fields have additionally been
defined:
+--------------------+------------------------------------------+------------+
*|ANTENNA: DELTA X/Y/Z| Antenna position in body fixed coordinate| 3F14.4 |
| | system (meters) | |
+--------------------+------------------------------------------+------------+
*|ANTENNA: B.SIGHT XYZ| Boresight of antenna: | 3F14.4 |
| | Direction of the antenna axis towards the| |
| | GPS satellites. Corresponds to the | |
| | vertical axis on earth-bound antenna. | |
| | Unit vector in body-fixed coord.system. | |
+--------------------+----------------------------------------+------------+
*|OBS SCALE FACTOR | - Factor to divide stored observations | I6, |*
| | with before use. | |
| | - Number of observation types involved | I6, |
| | - List of observation types | 8(4X,A2) |
| | | |
| | Repeat record if different factors are | |
| | applied to different observation types | |
+--------------------+------------------------------------------+------------+
The OBS SCALE FACTOR record allows e.g., to store phase data with
0.0001 cycles resolution if the data was multiplied by SCALE FACTOR 10
before being stored into RINEX file.
As the antenna position data could be given in a body-fixed coordinate
system with the origin not coinciding with the satellite's center of
mass we have to define an additional header line with the current
center of mass coordinates:
+--------------------+------------------------------------------+------------+
*|CENTER OF MASS: XYZ | Current center of mass of vehicle in | 3F14.4 |*
| | body-fixed coordinate system (meters) | |
| | (same system as used for attitide) | |
+--------------------+------------------------------------------+------------+
In order to distinguish between L1(CA) and L1(P1) we define LA and SA
as new observation types:
+--------------------+------------------------------------------+------------+
|# / TYPES OF OBSERV | - Number of different observation types | I6, |
| | stored in the file | |
| | - Observation types | 9(4X,A2) |
| | | |
| | If more than 9 observation types: | |
| | Use continuation line(s) |6X,9(4X,A2) |
| | | |
| | The following observation types are | |
| | defined in RINEX Version 2.20: | |
| | | |
| | L1, L2: Phase measurements on L1 and L2, | |
| | L1 being derived from P (Y) code | |
| | LA : Phase measurements on L1 derived | |
| | from C/A code tracking. | |
| | Use L1 if origin is not known. | |
| | C1 : Pseudorange using C/A-Code on L1 | |
| | P1, P2: Pseudorange using P-Code on L1,L2| |
| | D1, D2: Doppler frequency on L1 and L2 | |
| | T1, T2: Transit Integrated Doppler on | |
| | 150 (T1) and 400 MHz (T2) | |
| | S1, S2: Raw signal strengths or SNR | |
| | values as given by the receiver | |
| | for the L1,L2 phase observations | |
| | SA : Raw signal strength or SNR for LA| |
| | CH : Receiver channel number | |
+--------------------+------------------------------------------+------------+
A future C/A code-derived phase observation on the second frequency
could be called LB, with the associated signal strength or SNR value
called SB.
As there are new header records and a new observation type defined, we
will have to increase the RINEX version number from 2.10 to 2.20.
Signal strength data can be stored into the RINEX file using the S1
(or SA) and S2 observation types (the format F14.3 is good enough to
handle all requirements regarding the maxumum range and precision).
Receiver channel numbers can be stored as special "observations" CH.
Lowest channel number allowed is 1 (re-number channels beforehand, if
necessary). In case of a receiver using multiple channels for one
satellite the channels could be packed with two digits each
right-justified into the same data field, order corresponding to the
order of the observables concerned. Format according to
(<5-nc>(2X),<nc>I2.2,'.000'), nc being the number of channels.
Restriction: Not more than 5 channels and channel numbers <100.
Examples: 0910.000 for channels 9 and 10
010203.000 for channels 1, 2, and 3
---- F14.3 ---
We propose to convert the "open-loop data" into standard phases and
signal strengths before reformating the data into RINEX files for data
exchange.
This proposal does not handle data collected by one receiver and
multiple antennas. In this case the data have to be stored in
separate RINEX files (one per antenna).
3. Filename recommendations
---------------------------
We propose to use the standard file naming scheme for LEO POD tracking
data by defining a 4-character code for each LEO receiver or
receiver/antenna combination. The RINEX data should be distributed in
daily files. Faster data exchange could use hourly files, if
necessary.
ssssdddh.yyo
| | | |
| | | +------ two-digit year
| | +-------- character for the staring hour in the day
| | (a=00, b=01, ... x=23, 0=one-day file)
| +----------- day of the year
+--------------- 4-character ID for the LEO receiver/antenna
For the 15-minutes high-rate ground station tracking data we recommend
the following extended filenames:
ssssdddhmm.yyo
| | || |
| | || +----- two-digit year
| | |+-------- starting minutes within the hour (00, 15, 30, 45)
| | +--------- character for the starting hour in the day
| | (a=00, b=01, ... x=23)
| +------------ day of the year
+---------------- 4-character ID for the LEO receiver/antenna
4. Consequences for Ground Based Data Files
-------------------------------------------
Basically no changes are mandatory for ground-based GPS/GLONASS
observation data files. However, the MARKER TYPE header record could
be a valuable addition to the current version 2.10 to better
characterize the marker/vehicle on which the receiver has been
mounted.
Depending on the feedback especially from receiver manufacturers the
LA and CH observation types could either be recommended to be used by
ground-based receivers, too or to be restricted to space-borne
receivers, only.
RINEX reader programs should be prepared to at least skip
uninterpreted header records, modify LA into L1 or skip LA, and apply
the OBS SCALE factor if present.
5. Implementation Plan
----------------------
The proposed modifications have been accepted by the International GPS
Service LEO Working Group in February/March 2001 to be used within the
IGS LEO Pilot Project for space-borne GPS data.
We are now requesting comments from the wider GPS/GLONASS community to
what extent the proposed modifications, especially the MARKER TYPE,
OBS SCALE FACTOR header records and the LA and CH observables, should
be used by non-space applications. We also like to get comments about
the proposed MARKER TYPE classes.
Depending on the results of the poll the modifications will be
restricted to MARKER TYPE = SPACEBORNE or opened to all classes.
6. Example
----------
----|---1|0---|---2|0---|---3|0---|---4|0---|---5|0---|---6|0---|---7|0---|---8|
2.20 OBSERVATION DATA GPS RINEX VERSION / TYPE
TESTRINEX TEST 07-AUG-00 00:44:01 PGM / RUN BY / DATE
DATE EXAMPLE OF A LEO FILE COMMENT
CHAMP MARKER NAME
00039B MARKER NUMBER
SPACEBORNE MARKER TYPE
GFZ OBSERVER / AGENCY
Main Blackjack 2.0.9 REC # / TYPE / VERS
POD_Antenna unknown ANT # / TYPE
-1.4880 0.0000 -0.3928 ANTENNA: DELTA X/Y/Z
0.0000 0.0000 -1.0000 ANTENNA: B.SIGHT XYZ
10.000 INTERVAL
1 1 0 WAVELENGTH FACT L1/2
9 LA L2 C1 P1 P2 L1 SA S1 S2# / TYPES OF OBSERV
1 3 LA L1 L2 OBS SCALE FACTOR
2000 8 7 0 0 0.0000000 TIME OF FIRST OBS
END OF HEADER
00 8 7 0 0 0.0000000 0 7 4 25 7 19 16 11 1
-5369354.141 -4183922.404 21470111.462 21470111.757 21470114.496
-5369354.140 530.000 167.000 148.000
-8742813.507 -6812576.531 22348706.474 22348706.684 22348709.446
-8742813.505 370.000 93.000 75.000
4733764.783 3688647.110 23786696.400 23786695.320 23786700.309
4733764.786 199.000 25.000 32.000
14033524.436 10935414.320 25844592.349 25844601.444 25844634.056
14033524.414 80.000 4.000 11.000
-3120775.023 -2431769.610 19832389.792 19832389.336 19832392.787
-3120775.022 839.000 448.000 394.000
9556410.416 7446601.916 25710269.924 25710274.075 25710260.983
9556410.413 75.000 6.000 9.000
1348505.455 1050780.864 20687372.600 20687372.514 20687375.419
1348505.456 699.000 295.000 254.000
00 8 7 0 0 10.0000000 0 6 4 25 7 19 16 1
-5478891.715 -4269276.375 21449267.180 21449267.588 21449270.210
-5478891.713 531.000 169.000 151.000
-8920710.764 -6951197.790 22314853.801 22314854.143 22314856.548
-8920710.762 374.000 94.000 77.000
4965160.004 3868954.973 23830729.282 23830729.763 23830733.822
4965160.003 199.000 26.000 30.000
14382375.072 11207149.974 25910977.098 25910973.565 25910995.669
14382375.062 80.000 5.000 10.000
-3028365.514 -2359762.233 19849974.840 19849974.231 19849977.901
-3028365.512 834.000 444.000 384.000
1555567.947 1212128.236 20726775.295 20726775.003 20726778.132
1555567.949 691.000 284.000 241.000
00 8 7 0 0 20.0000000 0 6 4 25 7 19 1 16
-5582917.443 -4350335.385 21429471.814 21429472.290 21429474.716
-5582917.474 530.000 167.000 153.000
-9096209.152 -7087949.770 22281457.702 22281457.735 22281460.023
-9096209.152 377.000 99.000 77.000
5199718.403 4051727.634 23875364.448 23875364.327 23875368.479
5199718.399 195.000 24.000 31.000
14730992.695 11478728.367 25977317.415 25977316.632 25977320.259
14730992.715 79.000 5.000 9.000
1766473.629 1376470.294 20766909.285 20766909.047 20766912.143
1766473.629 683.000 282.000 236.000
-2930120.571 -2283207.759 19868670.277 19868669.701 19868673.215
-2930120.571 827.000 438.000 367.000
----|---1|0---|---2|0---|---3|0---|---4|0---|---5|0---|---6|0---|---7|0---|---8|
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