Sp-461 ers-envisat Symposium

Temperature

Profiles

MS22

External

Characterization

Preflight Data

Antenna

Model

Transponder

Measurements

Calibration

Pulses

PF-ASAR

processor

normalization

antenna pattern

gain drift

ACF

Rain Forest

Inflight Antenna

Pattern Verification

Absolute

Calibration

In-Orbit

Check-Out

Internal

Monitoring/

Calibration

Calibrated

Products

Figure 1: ASAR Calibration Steps

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determined. Furthermore the influence of different operation scenarios (e.g. image mode following Wave mode and

vice versa) on the temperature conditions will be determined.

With an active antenna in-flight antenna pattern verification is a major task and it includes measurements in special

modes, like module stepping and external characterisation, as well as acquisitions over rain forest and pre-flight

characterisation. A sophisticated antenna model will combine the various data and provide the elevation and azimuth

patterns for the processor.

Monitoring of any instrument gain drifts requires a separate calibration network, to couple out part of the transmit signal

or to inject chirp signals into the receiver chain. This data will be included into the high-rate data stream and will be

analysed by the ground processor in order to estimate the necessary gain drift corrections.

The absolute overall system gain can be most accurately determined from the image response of point targets with high

and well-known RCS. ASAR high precision transponders will be deployed in the Netherlands and will serve as the

main external calibration targets. Well-characterised distributed targets will be used for the low-resolution Global

Monitoring mode.

All the above corrections have to be applied in the processor to generate calibrated products. In the following sections

the above methods for internal calibration, antenna pattern verification and absolute calibration will be discussed in

more detail. Furthermore the expected performance and the in-flight evaluation of performance parameters will be

presented.