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:

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. .