AltiKa Radiometer performance assessment

Transcription

1 AltiKa Radiometer performance assessment R. Rodriguez Suquet & N. Steunou, J.L. Courrière DCT/SI/AR 2 nd SARAL/AltiKa Science Workshop March 15 th -17 st, AHMEDABAD 1

2 Overview Radiometer Instrument Definition Radiometer Architecture Radiometer Calibration Radiometer Performance Test Results Performance Tests at Instrument Level Compatibility Test Assembly, Integration and Test (AIT) Conclusion 2

3 Overview Radiometer Instrument Definition Radiometer Architecture Radiometer Calibration Radiometer Performance Performance Tests at Instrument Level Compatibility Test Assembly, Integration and Test (AIT) Conclusion 3

4 Radiometer Parameters Design (1/2) Basically, the AltiKa Radiometer is required to correct the contribution of wet troposphere path delay to overall altimeter range measurements. Dual frequency channel microwave Radiometer: 23.8 GHz+/- 200 MHz: Brightness temperature measurements give information related to the water vapor content. 37 GHz +/- 500 MHz: Brightness temperature measurements give information about cloud liquid water. Both measurements are required to correct the wet troposphere on altimeter measurements. Both Brightness Temperatures in addition to the altimeter estimated Backscatter coefficient σ 0 are applied to calculate the troposphere correction range. 4

5 Blanking Signal for altimeter emission protection Calibration measurements: one cold and one hot Direct Power Detection Radiometer Parameters Design (2/2) Radiometer Parameters Parameter Value Radiometer band 23.8 GHz MHz 37 GHz MHz Pointing Nadir Polarisation Linear Radiometer Working Radiometric resolution K-band : < 0.4 K (requirements) Ka-band : < 0.3 K Radiometric accuracy < 3 K Radiometer averaging 200 ms T X pulse R X echo T X pulse Antenna Parameters R X echo Pulse Duration Radiometer Working Parameter Value Antenna apertures K-band : 0.85 Ka- band : 0.6 Cold Feed efficiencies K-band : freq>99% Ka-band : freq>99% PRI = 1/PRF Nadir Antenna efficiencies K-band : freq>94% Ka-band : freq>96% 5

6 Overview Radiometer Instrument Definition Radiometer Architecture Radiometer Calibration Radiometer Performance Performance Tests at Instrument Level Compatibility Test Assembly, Integration and Test (AIT) Conclusion 6

7 Radiometer Architecture 7

8 Radiometer Architecture - Interfaces (TM/TC) with the platform - Chirp pulse generation - Echos reception and processing from the altimeter (tracking and acquisition) - Digital processing of the radiometer signals - Temperature amplification - RF detection ( direct power detection ) and filtering - Transmission of the generated video voltages to BT Switch between 2 calibration types Hot: measures the thermal emission of an internal load Cold: sky antenna to get the cold reference point Brightness Temperature retrieval 8

9 Radiometer Calibration 5 measurements cycles are produced within 1s. Radiometer calibration based on: 2 Calibration Feeds: Sky Horn and Internal Load Measurements Cycle Time: 200 ms (depending on the current PRF value and the altimeter mode) Time between calibrations: 3 seconds 9

10 Overview Radiometer Instrument Definition Radiometer Architecture Radiometer Calibration Radiometer Performance Performance Tests at Instrument Level Compatibility Test Assembly, Integration and Test (AIT) Conclusion 10

11 Radiometer Performance Tests at Instrument Level Calibration of the radiometric model developed by TAS-F Estimation of the radiometer performances in terms of: sensitivity absolute accuracy Radiometric target in front of antenna horns are used for tests in thermal vacuum Brightness Temperature Dynamic : 8 measurement points going from 110 K until 300 K 3 ambient temperatures (0 C, 20 C and 40 C) 11

12 Radiometric Absolute Accuracy (1/2) Antenna Temperature Absolute Accuracy in K band Absolute Accuracy (K) 1,0 0 0,80 0,60 0,40 0,20 0,00-0,20-0,40-0,60-0,80 40 C TV St ep (n 1) 0 C TV St ep ( n 2) 20 C TV St ep (n 3) -1, Ta (K) Total Absolute Accuracy (with reflector characteristics) Required Absolute Accuracy < 0.4 K < 3 K 12

13 Radiometric Absolute Accuracy (2/2) -0,40-0,60-0,80-1,00 1,00 1,00 0,80 0,80 0,60 0,60 0,40 0,40 0,20 0,20 0,00 0,00-0,20 Ant enna Temperat ure Absolut e Precision en bande Ka Antenna Temperature Absolute Accuracy in Ka band ,20-0,40-0,60-0,80 Ta (K) Palier 40 C (n 1) TV Palier 0 C(n 2) TV Palier 20 C(n 3) 40 C TV Step (n 1) 0 C TV Step (n 2) 20 C TV Step (n 3) -1, Ta (K) Total Absolute Accuracy (with reflector characteristics) Required Absolute Accuracy < 0.4 K < 3 K 13

14 Radiometer Resolution (1/2) Sensitivity (K) 0,3 0,25 0,2 0,15 0,1 Antenna Temperature Sensitivity in K band 40 C TV Step (n 1) 0 C TV Step (n 2) 20 C TV Step (n 3) 0, Ta (K) Input Nadir Antenna Sensitivity Total Sensitivity (with reflector characteristics) Required Sensitivity < 0.15 K < 0.17 K < 0.30 K 14

15 Radiometer Resolution (2/2) Antenna Temperature Sensitivity in Ka band Sensitivity(K) 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 40 C TV Step (n 1) 0 C TV Step (n 2) 20 C TV Step (n 3) Ta (K) Input Nadir Antenna Sensitivity Total Sensitivity (with reflector characteristics) Required Sensitivity < 0.17 K < 0.19 K < 0.40 K 15

16 Radiometer/Altimeter Compatibility Tests Dedicated tests have been performed in order to check the compatibility between altimeter and radiometer in the following context: For all altimeter operational modes Without and with antenna connected Neither an impact on radiometric bias or on radiometric sensitivity has been recorded 16

17 Assembly, Integration and Test (AIT) 17

18 Radiometric Absolute Accuracy (1/2) Antena Temperature Absolute Accuracy in K band Initial Instrument Initial Payload Previb Postvib Pre-TV TV Absolute Accuracy ( K) AIT Test Input Nadir Antenna Absolute Accuracy Total Absolute Accuracy (with reflector characteristics) Required Absolute Accuracy < 0.4 K < 0.8 K < 3 K 18

19 Radiometric Absolute Accuracy (2/2) Antena Temperature Absolute Accuracy in Ka band Initial Instrument Initial Payload Previb Postvib Pre-TV TV 0.5 Absolute Accuracy ( K) AIT Test Input Nadir Antenna Absolute Accuracy Total Absolute Accuracy (with reflector characteristics) Required Absolute Accuracy < 0.8 K < 1 K < 3 K 19

20 Radiometer Resolution (1/2) Antena Temperature Sensitivity in K band Initial Instrument Initial Payload Pre-vib Postvib Pre-TV TV Sensitivity ( K) AIT Test Input Nadir Antenna Sensitivity Total Sensitivity (with reflector characteristics) Required Sensitivity < 0.16 K < 0.17 K < 0.30 K 20

21 Radiometer Resolution (2/2) Antena Temperature Sensitivity in Ka band Initial Instrument Initial Payload Previb Postvib Pre-TV TV 0.17 Sensitivity ( K) AIT Test Input Nadir Antenna Sensitivity Total Sensitivity (with reflector characteristics) Required Sensitivity < 0.17 K < 0.19 K < 0.40 K 21

22 Summary of Performance Results Characteristics & Performances Ka - Band K- Band Results Spec Results Spec Sensitivity (including reflector contribution) Absolute Accuracy (including reflector contribution) < 0.19 K < 0.4 K < 0.17 K < 0.3 K < 1.3 K < 3 K < 1.0 K < 3 K Nadir Antenna Efficiency 99.6 % > 99 % 99.5 % > 99 % Cold Feed Efficiency 97 % > 96% 94.6 % > 94 % 22

23 Overview Radiometer Instrument Definition Radiometer Architecture Radiometer Calibration Radiometer Performance Performance Tests at Instrument Level Compatibility Test Assembly, Integration and Test (AIT) Conclusion 23

24 CONCLUSION & OUTLOOK During instrument performances tests all radiometer instrument performances have been reached. These results prove a very good instrument stability on the overall tests. After instrument calibration, the updated radiometric model have been implemented in ground processing segment to retrieve the Brightness Temperature. The AIT test results contribute successfully to the validation of the Payload Instrument Module (PIM). Further AIT tests are being performed to achieve a complete validation. 24

25 Questions or Remarks? Thanks for your attention Contact : raquel.rodriguezsuquet@cnes.fr Phone :

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27 ADDITIONAL SLIDES 27

28 Blanking Signal Protection Radiometer is in operation during the altimeter reception echos in order to avoid any possible perturbations on radiometer measurements coming from the altimeter emission. Radiometer Working Radiometer Working T X pulse R X echo T X pulse R X echo Pulse Duration PRI = 1/PRF 28

29 Radiometer Architecture (2/2) Radiometer BHR is based on a Direct Power Detection architecture for each frequency channel. Detection T A T A Pre-Detection G Gain-B Band-Noise Trec Integrator (low-pass filter) C A N Post Integration V x BHR Calibration Feeds 29