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ENVISAT Calibration Review MWR Cal/Val

ENVISAT Calibration Review MWR Cal/Val. Illustrative picture for this presentation. Pierre Féménias ESA-ESRIN. ENVISAT Calibration Review MWR Cal/Val. Introduction MWR Cal/Val Objectives and Approach Cal/Val Team and Organization MWR Sensor presentation

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ENVISAT Calibration Review MWR Cal/Val

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  1. ENVISAT Calibration Review MWR Cal/Val Illustrative picture for this presentation Pierre Féménias ESA-ESRIN

  2. ENVISAT Calibration Review MWR Cal/Val • Introduction • MWR Cal/Val Objectives and Approach • Cal/Val Team and Organization • MWR Sensor presentation • MWR Instrument performance • MWR level 1b Eng. Verification • Summary • MWR Cal/Val activities and results • Conclusion Illustrative picture for this presentation

  3. MWR Cal/Val Objectives and Approach • The objectives of the MWR Cal/Val are • to calibrate and validate the following parameters: • Brightness Temperatures at 24 & 36 GHz • Water vapour content • Liquid water content • Water vapour path length correction With respect to the MWR instrument and algorithms performances • Ensure continuity with ERS MWRs (Cross-Calibration with ERS-2 MWR)

  4. MWR Cal/Val Objectives and Approach • In Flight Verification • Control of the functioning of the MWR sensor • Control of the radiometric counts, gains, hot and cold loads, radiometric resolution, residual error, etc • Control of the antenna pointing angles (using measurements over coasts or islands) • Direct comparison with ERS-2 measurements over the Antarctic plateau : ENVISAT/MWR frequencies are exactly the same than ERS-2/MWR ones => possibility to compare brightness temperatures over this area with weak spatial and temporal variability

  5. MWR Cal/Val Objectives and Approach • Calibration - In flight Validation • Control and correction of the calibration by comparison with simulated fields, using the UCL radiative transfer model and ECMWF global meteorological fields • filtering of cloudy pixels and meshes • statistical parameters of measurements in each mesh • analyses of the comparison for different situations (wet or dry atmosphere, low or strong wind speed) • Comparison with other in-flight radiometers: for the same set of ECMWF fields, comparison between simulations and measurements from ERS-2 MWR and/or TMR, JMR, SSMI, TMI, AMSR sensors.

  6. MWR Cal/Val Objectives and Approach • Validation and Long Term Survey • Validation with in-situ measurements • ECMWF radiosounding measurements for water vapor content and wet tropospheric correction • Long Term Survey • Survey of the internal parameters • Analyses of brightness temperatures measured over specific areas with very dry atmosphere and stable annual cycle (Sahara for hot brightness temperatures and Antarctic plateau for cold ones • Analyze of raw data in case of anomaly detection

  7. ENVISAT PDS MWR level 0 IPF RA-2/MWR Lev1 & 2 MWR Cal/Val Team and Organization ERS-2 MWR, ECMWF, TMR, JMR, GPS, etc data F-PAC RA-2/MWR Level2 CETP Laurence Eymard Michel Dedieu CLS Estelle Obligis, ESL ESA/ ESRIN Pierre Féménias - ESRIN Annalisa Martini -Serco Juan Guijarro - ESTEC ALS Michele l’Abbate Univ. Aquila Piero Ciotti

  8. MWR Sensor Description • The MWR Instrument is a dual channel radiometer, operating at 23.8 GHz and 36.5 GHz, based on the Dicke radiometer principle. • The nadir pointing antenna receives radiation in two microwave frequency bands, in linear (vertical) polarisation. • A 2 point calibration scheme is adopted, with Hot and Cold reference calibration points: • The deep Cold Space measurement is accomplished via the Sky-horn feed. • The on-board calibration reference load, kept by the thermal control at the instrument physical temperature, provides a Hot Reference signal. The Envisat MWR is a re-design of the ERS MWRs, benefiting of new improvements: structure subsystem, active thermal control, antenna design for performance improvement, RF Front End design, etc.

  9. MWR Sensor Description • MWR Model

  10. Reflector Main Horns Sky_Horn Thermal Radiator & Electrical I/F MWR Instrument PFM overview during vibration tests MWR Sensor Description

  11. MWR Sensor Description Sky_Horn Main Horns MWR Instrument PFM during optical alignment

  12. MWR Sensor Characteristics

  13. SODAP activities and MWR Switch-on • MWR SODAP (Switch-On and Data Acquisition Phase) Activities governed by the DORIS/MWR package SODAP Plan. • SODAP MWR In-Orbit Operations - ICU Switch-On 13-Mar-02 - Transition to Heater 15-Mar-02 - Measurement Mode 15-Mar-02 End of MWR SODAP completed on March 15, 2002 (anticipated by 2 days) MWR was switched ON for the first time in flight at 074.16.17.27 (15th March) => first MWR Science data

  14. SODAP activities and MWR Switch-on • Envisat MWR Radiometric Counts ( From March 15 to March 29, 2002 )

  15. SODAP activities and MWR Switch-on Envisat MWR Gain trend from the first Measurement Data Set. Already very close to the MWR on-ground characterization from the first day !

  16. SODAP activities and MWR Switch-on MWR First Orbit Abs. Orbit 210 (March 15/02) First Envisat MWR 24 & 36 GHz Brightness Temperatures Envisat

  17. MWR Instrument Performance • MWR unavailability and on-board anomalies • Few on-board anomalies occurred since the switch-on of the MWR sensor (< 10) • Most of them due to an ICU software counter problem • Therefore affecting more the data availability that the sensor performances itself • Only slowing down the warming-up of the MWR sensor. • ICU shared with the DORIS instrument. • A corrective patch for the ICU anomaly is currently planned to be uploaded in September.

  18. MWR Instrument Performance • MWR functional assessment of thermal behavior and radiometric performance goes through the analysis of the following parameters: • Radiometric Counts • Gain • Residual Temperature • Radiometric sensitivity • MWR on-board Temperature Distribution

  19. MWR Instrument Performance • Radiometric Counts

  20. MWR Instrument Performance • Radiometric Counts • Hot Counts mean values are 558 and 661 (CH1, CH2) Compared with T/V calibration it appears as the instrument is still in cold conditions, e.g. at • 0°C (CEU ref. temp) 549 CH1 and 671 CH2 • +20°C (CEU ref. temp) 531 CH1 and 650 CH2 • Cold counts mean values are 3290 and 3585 (CH1, CH2) Of course we have no reference data for Sky Horn counts (targets on ground were at 80 K), but looking to the gain and relevant values they look nominal • Offset Counts values are nominally around (almost constant) 520 for CH1 and 642 (CH2). The T/V measured offset are: • 0°C (CEU ref. temp) 522 CH1 and 643 CH2 • +20°C (CEU ref. temp) 519 CH1 and 641 CH2.

  21. MWR Instrument Performance • MWR Gain

  22. MWR Instrument Performance • MWR Gain • The radiometric gain values, derived from Level 0 data, can be considered acceptable, as they are very close to predictions and to on ground measurements executed during MWR T/V calibration. • The reported gain values, 9.5 counts/K (CH1) and 10.4 counts/K (CH2), are very close to those measured during MWR on ground characterization.

  23. MWR Instrument Performance • MWR Gain For example in table 4.2-8 attached hereafter (extracted from doc.PO-RP-ALS-MR-0025 Iss 2.0), the following gain values were derived from ground measurements

  24. MWR Instrument Performance • Residual Temperature (Te)

  25. MWR Instrument Performance • Residual Temperature (Te) • Temperature offset entering in the computation of the Ta • Absolute values of the Envisat MWR Te values are ~0.8 K for Channel 1 and ~1.5K for channel 2 • From on ground test, the Residual Temperature is expected to be around 0.5 K for Channel 24 (CH1) and a bit higher, 0.5-0.7 K for channel 36 (CH2), i.e. close to the ERS ones • Varying Te from 0.5 K to 1-2 K produces only marginal changes (few cents) on Ta • Further analysis shall be done anyway (ALS)

  26. MWR Instrument Performance • Radiometric Sensitivity (Resolution) • The Radiometric Resolution is calculated as the standard deviation of the Brightness Temperature for both channels. • Of particular significance, when the condition TA = TREF is met DT < 0.4 K As during Ground Test

  27. MWR Instrument Performance • Radiometric Sensitivity (Resolution) and Stability • Only preliminary result as different changes in the MWR characterization parameters have been performed these last months. • Radiometric Resolution estimation shall be pursued over predefined and low variability geographical targets. • Radiometric Stability analysis shall also be performed over low variability geographical targets.

  28. MWR Instrument Performance • MWR Temperature Distribution • Review has been done by comparing the in-flight 32 thermistor temperatures profiles with respect to the predicted temperatures • All Temperatures are within the min and max limits and their behavior is consistent with thermal analysis predictions from ground tests

  29. MWR Instrument Performance • MWR Temperature Distribution • The Tcc (LC 21 Sky Horn) shows a visible round-orbit variation. This is also visible in the temperature of main horns (LC 10 and LC 14) and reflector (LC 22). • Feed Horns temperature have also some fluctuation effects due to RF Front End thermal control, superimposed to the round-orbit variation. • Tref , Th, Tcal, Thc, and in general all the RF Front End passive components temperatures, show some rapid fluctuations with amplitudes ranging between 2 to 5 degrees peak-peak. This is consistent with the instrument nominal operation, due to the on-aboard active thermal control.

  30. MWR Instrument Performance Physical Temp. of the Reflector (LC22) over 6 orbits

  31. MWR Instrument Performance Physical Temp. of the Reflector (LC22) over 5 Orbits x 5 months

  32. MWR Instrument Performance • MWR Temperature Distribution • The active thermal control is operating through a set of Heaters and Thermostats. The thermostats set points are as follows : Switch-on Temperature 16.7  1.7°C, Switch-off Temperature 21.7  1.7°C. • These temperatures set-points are consistent with the variations observed in measured temperatures of the RF Front End (e.g. the Dicke Loads). • After a longer stabilization period the active thermal control may be no more active, as the mean temperature of the RF Front end plate may raise above the 16.7 °C set point of the thermostats

  33. MWR Instrument Performance • MWR Temperature Distribution • The behavior of temperature measured by thermistors T1, T2, T2bis,T3, T4, T4bis (from CEU temp board) are exactly as expected, i.e. flat. These are ultra high stability resistors simulating the resistance of a PT100 thermistor at the temperature of about –23°C, 0°C, +26°C and +52°C. Used for test and calibration of the overall temperature measurement system implemented on board. • T1 and T3 are two thermistors on the temperature board of CEU, and they report the temperature of one section of the CEU. They behavior is nominal, as no significant fluctuations are expected within active units of CEU and RF Front End.

  34. MWR Level 1B Eng. Verification • MWR Level 1B algorithms • Different upgrades of the MWR Lev 1 B processing chain algorithms have been identified & developed before the Envisat Launch • Inclusion of the Main Reflector Temperature in the computation of the induced noise temperature accounted in the estimated Ta • Definition of 2 Tsh fields (Sky Horn Target Temperature)

  35. MWR Level 1B Eng. Verification • New algorithm have also been developed (needed w.r.t. to the Envisat Side Lobe contribution) • MWR Side Lobe contribution correction as a function of the geographical location and season (validation is on-going) • Proposal for algorithm upgrades (validation is on-going) • Simplification of the Resistance to Temperature conversion ( to K algorithm) • Reduced number of MWR characterization table, 1 instead of 4, including a polynomial approximation of the gain vs. temperature.

  36. MWR Level 1B Eng. Verification • The receiver Physical Temperature (Trec) corresponds to the mean value of the IF module, local oscillator and to the mixer for both channels. • Min & Max Trec for channel 1 21.67 & 22.49 Deg • Min & Max Trec for channel 2 20.43 & 21.60 Deg • Trec is computed to determine the characterization data set table to be used (5 in total) • Currently the one at 20 Deg is used !

  37. MWR Level 1B Eng. Verification • Algorithm verification has been based on the analysis of the output of the different algorithm steps: • MWR level 0 extraction and decoding • Gain processing and Antenna Temperature retrieval • Brightness Temperature Evaluation • Antenna axis registration • Level 1B Data formatting All discrepancies/bugs found between the IPF and the Reference processing chain has been explained and fixed. No other fix is currently planned.

  38. MWR Level 1B Eng. Verification • ADF parameters monitoring and optimization Validation of the MWR Lev1B SPH Quality Information (flags and percentages) • MWR_*_ERROR & MWR_*_QUALITY SPH fields are related to ADF thresholds • Refinement of the ADF threshold parameters shall be done on the basis of the MWR thermal analysis • Final release of the ADF files at the End of the Com. Phase. IPF MWR Level 1 B setting – Configuration parameters • Gain moving window size set to 6 as for ERS-2 • Moving window size: 6 6 gain values smoothed (To be noted that the on-board calibration period is fixed to 38.4 sec) • Side_lobe_table: 1 ERS-2 SL algorithm

  39. Summary • Envisat MWR thermal behavior and radiometric performance are nominal • MWR Lev 1 B data products are validated • Validated Lev 1 B algorithm proposed upgrades shall be implemented in the ESA IPF processing chain after the Commissioning Phase • Updated MWR ADF Files shall be implemented at the end of the Envisat MWR Commissioning Phase

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