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Instrument Gain Setting for Dynamic Range Analysis in Spaceborne Applications

This document details the Instrument Gain Setting and FBAQ Encoding for in-orbit measurements, receiver gain adjustments, and verification processes. It covers ADC sampling, compression techniques, reconstruction methods, and calibration pulse considerations. Receiver Gain Adjustment is crucial for reliable measurements and normalization. The analysis includes histograms of FBAQ Block IDs and conclusions on gain adjustments in different modes and beams.

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Instrument Gain Setting for Dynamic Range Analysis in Spaceborne Applications

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  1. ASAR Instrument Gain Setting • FBAQ encoding – the block ID for analysis of the dynamic range • In-orbit measurements • Receiver gain (down-converter level) adjustments • Verification M. Zink ESA-ESTEC

  2. FBAQ Encoding (1) • I/Q channels are sampled by 8-bit ADC • For 8/4bit compression data divided into blocks of 63 I/Q samples • Sum of unsigned I/Q samples divided by scale factor representative for input stdev • Selection of quantizer – block ID, thresholds, reconstruction levels • Data block coded as block ID (8-bit), 63*2*4-bit codes for I and Q

  3. Block ID - # quantizer FBAQ Encoding (2) • 8/4-bit compression using 256 quantizers (block IDs) • For block IDs higher than 100 saturation starts • Reconstruction via look-up tables • ADC characteristics included in loop-up tables • Similar properties for 8/2-bit compression (WV mode)

  4. Signal Dynamic of Early Products • Signal saturation in all beams • Cal pulses heavily saturated – not usable • Very low signal dynamic in high incidence angle beams • Low dynamic in SS4 & SS5

  5. Upper Constraint on Receiver Gain • Calibration pulse levels fixed – no separate adjustment • Down-converter levels of –13dB result in maximum cal pulse levels between 100 and 110 (signed 8-bit ADC output)

  6. Receiver Gain Adjustment • Reliable calibration pulse measurements required for instrument gain monitoring and radiometric normalization • Down-converter levels in all modes & all beams set to –13dB • WV from –3dB • IM/AP from –15/-14/-16/-15/-16/-16/-19dB • WS&GM already at –13dB – no update applied

  7. Gain Adjustment Verification in WV Mode before after

  8. Gain Adjustment Verification in IM Mode before after

  9. Instrument gain setting analysis based in FBAQ Block ID histograms Launch settings too high for WV (saturation), too low for other modes (especially high incidence angle beams in IM/AP) Upper constraint -> avoid calibration pulse saturation Receiver gains adjusted in IM/AP – now consistent in all modes/beams Gain increase/decrease in IM/WV verified Conclusions

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