2.9.3 Common Auxiliary Data Sets
The common auxiliary files used in ASAR
processing, that have not already been discussed
in previous sections, are provided in this section.
2.9.3.1 FOS Orbit State Vectors The instrument ground processing
software uses the CFI orbit propagator software
module and an orbit state vector as input to
calculate the satellite position all along
the orbit. The following describes the product
structure of the "Flight Operations
Segment" (FOS) instrument's
predicted and restituted orbit state vector
files. These are used during ground processing
and are updated once per day. FOS
Predicted: (AUX_FPO_AX) One MDSR
per orbit, file contains MPH, SPH and MDS and
covers 6 days . FOS Restituted:
(AUX_FRO_AX) One MDSR per minute, file
contains MPH, SPH and MDS and covers 1 day, with
approximately a 60 minute overlap.
Format
The MPH and SPH of these files will follow
the standard MPH, SPH structure of all
ENVISAT auxiliary data. The SPH contains a
single DSD of type M pointing to the
MDS. The file will consist of a single MDS
containing several MDSRs. Each MDSR is of
the format shown below.
NOTE THAT ORBIT STATE VECTOR MDSRs DO NOT
FOLLOW STANDARD ENVISAT-PDS FORMAT. The MDSR
is in ASCII format and, although common to
all ENVISAT instruments, is given here
for convenient reference.
|
Table 2.70 Format of MDSR for orbit State vectors
|
| N |
MDSR Contents |
Units
|
Byte Length
|
DataType
|
Dim.
|
| 1 |
UTC of Orbit State Vector |
UTC
|
27
|
uc
|
27
|
| 2 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 3 |
Delta UT1 = UT1-UTC |
s
|
8
|
Ado06
|
1
|
| 4 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 5 |
Absolute Orbit number |
-
|
6
|
As
|
1
|
| 6 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 7 |
X position in Earth fixed
reference frame |
m
|
12
|
Ado73
|
1
|
| 8 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 9 |
Y position in Earth fixed
reference frame |
m
|
12
|
Ado73
|
1
|
| 10 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 11 |
Z position in Earth fixed
reference frame |
m
|
12
|
Ado73
|
1
|
| 12 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 13 |
X velocity relative to Earth
fixed reference frame |
m/s
|
12
|
Ado46
|
1
|
| 14 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 15 |
Y velocity relative to Earth
fixed reference frame |
m/s
|
12
|
Ado46
|
1
|
| 16 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 17 |
Z velocity relative to Earth
fixed reference frame |
m/s
|
12
|
Ado46
|
1
|
| 18 |
ASCII blank space character |
-
|
1
|
uc
|
1
|
| 19 |
Quality Flags (TBD by ESA) |
-
|
6
|
uc
|
6
|
| 20 |
ASCII newline character |
terminator
|
1
|
uc
|
1
|
|
TOTAL
|
|
129
|
|
|
2.9.3.2 DORIS Preliminary Orbit State Vectors
The preliminary orbit reconstruction is the
first orbit estimate produced from the
"Doppler Orbitography and
Radiopositioning Integrated by
Satellite" (DORIS) instrument Doppler
shift data. It is produced off-line
systematically for all DORIS data received,
and is intended as an orbit estimate of
higher quality than that of the Navigator
product. The file is used during ground
processing and is updated once per day.
The format is identical to that described
above for the FOS State vectors.
Each file covers 26 hours, with 1 MDSR per
minute. Therefore, there are 1560 MDSRs in
the MDS.
2.9.3.3 DORIS Precise Orbit State Vectors
The precise orbit reconstruction is the most
accurate orbit estimate produced from the
DORIS data. It is produced off-line
systematically for all DORIS data received,
and is intended as an orbit estimate of the
highest quality achievable using DORIS. The
file is used during ground processing
and is updated once per day.
The format is identical to that described
above for the FOS State vectors.
Each file covers 26 hours, with 1 MDSR per
minute. Therefore, there are 1560 MDSRs in
the MDS.
2.9.3.4 DORIS Navigator Level 0
The DORIS Navigator Level 0 product is a file
containing time ordered AISPs which are
output from the on-board DORIS Navigator
software. This product provides the
first estimate of satellite positioning
available from the DORIS sensor,
the accuracy of which is described in the
table below. No further processing is
applied to the Level 0 Navigator Product.
The NRT version of the product is
available within 3 hours of data
acquisition. The OFL (fully consolidated)
version is available
2 weeks after acquisition.
As with all Level 0 products, it has an MPH
and an SPH followed by an MDS containing the
annotated instrument source packets. These
formats are given in Data Formats.(Chapter 6. )
2.9.3.5 UTC/SBT Time Conversion File
The instrument ground processing software
uses the CFI time conversion software module
and this file to convert from satellite
binary time to UTC time. It is used
during ground processing, annotated into MPH
and is updated once per orbit.
Format:
The MPH and SPH of these files will follow
the standard MPH, SPH structure of all
ENVISAT auxiliary data. The SPH contains a
single DSD of type G pointing to the
GADS. The format of the GADS is shown below:
|
Table 2.71 Format of GADS for SBT/UTC Time Conversion File
|
| N |
Description |
Units |
Byte Length |
Data Type |
Dim. |
| 1 |
Reference UTC time
corresponding to SBT time below
(currently defined to be
given at the time of the
ascending node state vector)
|
UTC |
27 |
uc |
27 |
| 2 |
ASCII blank space character |
- |
1 |
uc |
1 |
| 3 |
Reference Satellite Binary
Time (SBT)
|
- |
11 |
Al |
1 |
| 4 |
ASCII blank space character |
- |
1 |
uc |
1 |
| 5 |
SBT clock step in picoseconds
|
ps |
11 |
Al |
1 |
| 6 |
ASCII newline character
|
- |
1 |
uc |
1 |
TOTAL
|
|
52
|
|
|
2.9.3.6 ECMWF Data Files
The "European Centre for Medium-range
Weather Forecasting" (ECMWF) data files
contain Meteo information. They are ingested
into the PDS ground segment on a regular
basis and are used by various instrument
processors during the generation of products.
There are two kinds of ECMWF data: Forecast
data (AUX_ECF_AX) and
Analysis data (AUX_ECA_AX).
Forecast data is used in NRT processing,
while Analysis data is used during OFL
product generation. Both Forecast data and
Analysis data files have the same
format. The data from is used in Level 1B
processing and L2 processing. The ECMWF
files enter the PDS every 6 hours. There are
4 Analysis files and 4 Forecast files,
each valid for a 12 hour time period.
ECMWF files enter the PDS every 6 hours.
There are 4 Analysis files and 4 Forecast
files, each valid for a 12 hour time period.
Format:
The high level breakdown of the file is shown below:
|
Table 2.72 Schematic Structure of ECMWF Files
|
MPH
|
SPH - standard Auxiliary
Data SPH with 1 DSD
|
| DSD for the ECMWF GADS |
ECMWF GADS
|
ECMWF data files entering the PDS are encoded
in PB-IO format. Upon entry to the PDS, the
file is modified to fit the standard ENVISAT
PDS file format. This is done by completing
the following steps:
- Place the PB-IO file (without modifying
its structure) into a GADS (the ECMWF GADS);
- Add an Auxiliary Data SPH (with one DSD
for the GADS);
- Add an MPH (fields not relevant set to
zero or filled with ASCII blank space characters);
- Assign a PDS filename as per the
auxiliary data naming convention
described earlier in this volume.
ECMWF GADS
The GADS contains information encoded in
PB-IO format. No additions or modifications
are made from the original format.
|
EO Data Access
