Subject: [IGSMAIL-3281]: RINEX Modifications for LEO Satellites (Vers. 2.20)
From: Werner Gurtner <[email-masked]>
To: [email-masked], igsmail <[email-masked]>, [email-masked], eurefmail at aiub <[email-masked]>
Date: Thu, 12 Apr 2001 07:47:10 +0000

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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 <[email-masked]>
                   Lou Estey   <[email-masked]>

                           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
----------

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     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

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