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ASAR Instrument Gain Monitoring

Internal calibration scheme Instrument gain stability. ASAR Instrument Gain Monitoring. Christopher Buck ENVISAT Project. P3. P2. Tx Aux. P1A. P1. P1. P1. Cal BFN. Cal. Rx Aux. Internal Calibration. T/R Module (1 of 32x10). ASAR is equipped with an automatic temperature

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ASAR Instrument Gain Monitoring

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  1. Internal calibration scheme Instrument gain stability ASAR Instrument Gain Monitoring Christopher Buck ENVISAT Project

  2. P3 P2 Tx Aux P1A P1 P1 P1 Cal BFN Cal Rx Aux Internal Calibration T/R Module (1 of 32x10) • ASAR is equipped with • an automatic temperature • compensation scheme to • compensate for phase/gain • drifts at T/R module level • Direct monitoring of any • residual gain drifts for • later correction • Continuous measurements • even during data acquisition • Use of special calibration signals (cal pulses) and additional hardware (cal network) Radiating Row Signal BFN Tx Main Rx Main

  3. Early phase, many system parameters being changed Later phase, chirp power much more stable, basically follows temperature. Occasional “outliers” Chirp Power, Image Mode, IS2, VV

  4. Calibration Pulse Stability P1 P2 Single row (#18, IS2, VV) Stability < 0.2dB P3 P1a

  5. Internal Calibration – Image Mode, IS2, VV (1) About 30 products, ~5 chirp ADS per product overlaid P1 P1a White asterisks are the computed geometric mean used for nominal values

  6. Internal Calibration – Image Mode, IS2, VV (2) P2 P3

  7. Occasional spurious results Internal Calibration – Wide Swath Mode, SS5, HH (1) P1 P1a

  8. Internal Calibration – Wide Swath Mode, SS5, HH (2) P2 P3

  9. Occasional spurious results Fall outside threshold limits and are replaced by the nominal values in the processor Internal Calibration – Wide Swath Mode, SS5, HH (3)

  10. Elevation Gain Factor WSM, SS2, VV IM, IS3, VV Elevation gain computation for the same beam in different modes is constant

  11. Stability of all calibration pulses (transmit and receive) typically better than 0.2dB for all modes, all beams => ASAR instrument is very stable Calibration pulses are used for normalization of the processor Occasional “outliers” => replaced by computed nominal values in processor Conclusions

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