2.9.2 Auxiliary Data Sets for Level 1B Processing
The auxiliary files used by PF-ASAR
to create the ASAR products are described in
this section. A depiction of the antenna
beam characterisation measurements that supply
the data for the files discussed here, is given
in figure2.67 below:
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Figure 2.67 Antenna beam characterisation measurements |
External Characterisation Data (ASA_XCH_AX)
The ASAR instrument has an External
Characterisation Mode which is operated
overflying a receiver set up for H or V
polarisation located in the ground. During
the mode, the ASAR transmits a sequence of
pulses from each antenna row in turn. These
pulses are received and digitised on the
ground and the data recorded for off-line
analysis. Simultaneously during the mode the
calibration loop in the instrument is used
to couple transmit pulses which are then sampled
within a calibration widow in order to provide
comparative values. The External
characterisation Data file is provided as the
output of the external characterisation analysis
and is used for internal calibration
processing correction. It is updated nominally
every 6 months.
The MPH and SPH of these files will follow the
standard MPH, SPH structure of all ENVISAT-1
auxiliary data. There is one DSD in the SPH,
known as the ASA_XCH_AX_GADS. The formats for
all of these records are given in the Data
Formats(Chapter 6. ) section.
External Calibration Data (ASA_XCA_AX)
The external calibration scaling factor is
determined by ESA using three calibrated
transponders, and the in-flight elevation
pattern estimates are obtained using natural
targets with known properties such as the
rainforest. The file is used during image
calibration and is updated nominally every 6 months
The MPH and SPH of these files will follow the
standard MPH, SPH structure of all ENVISAT-1
auxiliary data. There is one DSD in the SPH,
known as the ASA_XCA_AX_GADS. The formats for
all of these records are given in the Data
Formats(Chapter 6. ) section.
Processor Configuration File (ASA_CON_AX)
This file contains static processing parameters
used by the PF-ASAR which includes the threshold
values used for setting PCD flags. This file
is available in the inventory so a user may
check what the processing configuration and
threshold values were for the product of
interest. The file is updated infrequently, only
if static processing parameters change or PCD
thresholds are updated.
The MPH and SPH of these files will follow the
standard MPH, SPH structure of all ENVISAT-1
auxiliary data. There is one DSD in the SPH,
which is a GADS called ASA_CON_AX_GADS. Details
of the formats for all of these records are
given in the Data Formats(Chapter 6. ) section.
Instrument Characterisation
File (ASA_INS_AX)
This file contains key parameters which
characterise the instrument. This includes look
up tables and other parameters needed in the
ground processing. It contains a subset of the
data found in the Instrument Characterisation
database. The file is updated infrequently,
only if instrument operating parameters change.
The MPH and SPH of these files will follow the
standard MPH, SPH structure of all ENVISAT-1
auxiliary data. There is one DSD in the SPH
called the ASA_INS_AX_GADS. Details of the
formats for all of these records are given in
the Data
Formats(Chapter 6. ) section.
Orbit State Vectors
Vectors may be from the "Flight Operations
Segment" (FOS) or from the "Doppler
Orbitography and Radiopositioning Integrated
by Satellite" (DORIS) instrument. FOS and
DORIS vectors are described in "Common Auxiliary Data Sets" 2.9.3. .
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