[IGSMAIL-246] RINEX under AS
W.
W.
Fri Apr 23 14:26:00 PDT 1993
IGS Electronic Mail 23-APR-1993 14:26:00 Message Number 246
***********************************************************************
>From: W. Gurtner
Subj: RINEX under AS
----------------------
RINEX under AS
______________
Werner Gurtner
Astronomical Institute
University of Berne
The current versions (1 and 2) of the Receiver Independent Exchange
Format RINEX knows the following 7 basic observation types:
C1: C/A code pseudorange on L1
P1: P code pseudorange on L2
P2: P code pseudorange on L2
L1: phase observation on L1
L2: phase observation on L2
(D1: Doppler observation on L1)
(D2: Doppler observation on L2)
We have never distinguished between L1 phases recovered using C/A code
only or using the P-code. In the presence of both only one (the
better one) has been included in the RINEX files.
Half-wavelength phase observations (squaring receivers) have been
flagged
- by the wavelength factor (set to 2) for all satellites in the
header of Version 1 files
- using either a general or a satellite-dependent wavelength factor
in Version 2
- using bit number one (LSB being bit 0) in the loss-of-lock
indicator (LLI) to mark observations with a wavelength different
from the one given by the wavelength factor (Version 2). This is
used for instruments that may frequently switch from p-code
tracking to squaring and vice versa due to tracking reasons
With the introduction of receivers that do not merely switch to C/A
code tracking and sqaring under anti-spoofing (AS) conditions but use
cross-correlation or other techniques instead, the question came up
how RINEX will handle these new observation techniques or, strictly
speaking, these new observation types.
The discussions in the user community (especially within the
International GPS Geodynamics Service (IGS) group) showed two
different approaches:
- use the actual observations to synthesize the corresponding basic
RINEX observation types and flag them to be "special"
- define enough new observation types to cover all the different
ways the new receivers are or will be handling the AS condition
Apart from the fact that some observation types might not be available
at all or that phase observations are collected in half wavelength
under AS, the most conspicuous result is an increased noise of the
AS-affected observables. As a consequence some processing software
might have to know what observables fall into this category.
In order to not have to go through the process of actually creating a
new RINEX version (3), a process becoming more and more difficult, the
data exchange working group of IGS came to the conclusion to
propose the following moderate change of RINEX version 2:
Observables under AS having been synthesized using
cross-correlation or other techniques and therefore suffering
from an increased noise level are flagged with bit 2 of the
loss-of-lock indicator!
(To set bit 2 of the LLI its current value is increased by adding 4.)
This will most certainly affect the
L2 observations (cross-correlation, P/W tracking)
P2 observations (cross-correlation, i.e. P2=C1+(Y2-Y1)
P1 and P2 obs (P/W tracking)
Rogue / Trimble SSE types of instruments track C/A code on L1 under
AS: Their AS code observation on L1 in the RINEX file is "C1", the
same one as from any C/A tracker under non-AS condition.
True Y-code trackers would create unaffected P1,P2,L1,L2 observables
that do not have to be flagged.
Squared L2 observables of course have to be flagged with wavelength
factor 2 as described above.
When AS is switched on the LLI flag will go from (usually) zero to 4
(or most certainly for one epoch to 5, as the receiver will loose
lock). Observations of receivers that go to squaring mode will either
be additionally be flagged with bit 1 of the LLI or a new header line
(WAVELENGTH FACT L1/2) might be inserted according to the RINEX
version 2 rules.
Software that does not care about the subtleties of AS-affected
observations can ignore bit 2 of the LLI and just has to worry about
possible different wavelength factors.
I also got the proposal to introduce a floating point version number to
be able to flag this small change with a version such as 2.1. Most of
the people I contacted did not find it necessary, however, and nobody
voted for a version 3.
Please find below an example of a RINEX file containing satellites under
AS (prn 2,27,24,26,19,16) as well as non-AS satellites (prn 3,18).
I hope to help decrease or even eliminate with this step uncertainties
in the handling of AS-affected data by the different RINEX converters
and by the large variety of post-processing software.
May I ask everybody who is providing RINEX converters to follow this
proposal to help prevent the development of many different RINEX
"dialects". Do not hesitate to contact me if you have any questions.
Maybe it is a good idea to include a COMMENT line stating that bit # 2
of LLI flags AS data.
Berne, April 23, 1993 Werner Gurtner
PS: A complete RINEX version 2 format description is available as ASCII file
(RINEX2.TXT) on our anonymous ftp account (Internet 130.92.4.10)
in the directory [ASTRONOMY.RINEX].
****************************** EXAMPLE **********************************
2 OBSERVATION DATA G (GPS) RINEX VERSION / TYPE
TRRINEXO V1.8.1 L+T 21-APR-93 00:38 PGM / RUN BY / DATE
Zimmerwald LT88 COMMENT
BIT 2 OF LLI (+4) FLAGS DATA COLLECTED UNDER "AS" CONDITION COMMENT
ZIMM MARKER NAME
LOGST/COMPAQ L+T OBSERVER / AGENCY
2691 TRIMBLE 4000SSE 5.60 REC # / TYPE / VERS
17498 TRIMBLE 4000SSE ANT # / TYPE
4331354.9039 567542.1797 4633078.2930 APPROX POSITION XYZ
.0000 .0000 .0000 ANTENNA: DELTA H/E/N
1 1 WAVELENGTH FACT L1/2
5 P1 L1 L2 P2 C1 # / TYPES OF OBSERV
1 INTERVAL
1993 4 20 6 14 .000000 TIME OF FIRST OBS
END OF HEADER
93 4 20 6 14 .0000000 0 7 2 27 3 24 18 26 19
-3606452.220 5 -2658497.69346 24290247.9384 24290242.383
-17427926.331 8 -13467468.00549 20337177.6454 20337176.836
24609815.414 1492000.824 2 2024814.857 6 24609819.145
4907925.958 5 3983864.90846 23660590.2034 23660586.875
23624383.094 11049247.283 5 8651874.527 6 23624385.047
-986672.123 3 -567492.38945 24759926.0744 24759926.203
-6169648.462 6 -4701382.96849 21418332.6724 21418331.031
93 4 20 6 14 30.0000000 0 8 2 27 3 24 18 26 19 16
-3679377.118 5 -2715322.21546 24276368.9304 24276363.586
-17416465.956 8 -13458537.83849 20339358.3524 20339357.508
24622192.492 1557030.139 3 2075487.050 6 24622194.531
5028029.695 5 4077452.15346 23683446.9884 23683443.461
23646913.781 11167645.148 5 8744132.522 6 23646915.785
-1046564.357 3 -614161.67545 24748527.3754 24748527.445
-6080119.925 6 -4631620.48549 21435369.8714 21435367.984
-9083036.05917 -6998390.56559 21002894.8014 21002893.266
93 4 20 6 15 .0000000 0 8 2 27 3 24 18 26 19 16
-3752199.504 5 -2772066.79546 24262513.3834 24262507.102
-17404473.055 8 -13449192.72049 20341640.3754 20341639.742
24634693.094 1622726.990 2 2126679.334 6 24634696.039
5148356.362 5 4171213.11046 23706343.6644 23706339.984
23669457.367 11286114.710 5 8836446.376 6 23669459.344
-1106381.016 4 -660772.02245 24737147.7424 24737145.891
-5990242.516 7 -4561586.17849 21452473.0664 21452471.180
-9096979.011 7 -7009255.21749 21000242.1174 21000240.078
************************** END OF EXAMPLE *********************************
****************************************************************************
Werner Gurtner, Astronomical Institute, University of Berne, Sidlerstrasse 5
CH-3012 Bern, Switzerland, Tel: ++41-31-658591 / 658599, Fax: ++41-31-653869
E-Mail: GURTNER at AIUB.UNIBE.CH GURTNER at 130.92.4.10 20579::49203::GURTNER
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