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Radiometric Calibration of the ASTER Thermal Infrared (TIR) Subsystem

Radiometric Calibration of the ASTER Thermal Infrared (TIR) Subsystem. Simon J. Hook NASA/JPL. Outline. ASTER TIR subsystem. On-board calibration (OBC) of TIR subsystem. In-flight validation of TIR subsystem. Consequence of instrument drift on higher level data products.

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Radiometric Calibration of the ASTER Thermal Infrared (TIR) Subsystem

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  1. Radiometric Calibration of the ASTER Thermal Infrared (TIR) Subsystem Simon J. Hook NASA/JPL

  2. Outline • ASTER TIR subsystem. • On-board calibration (OBC) of TIR subsystem. • In-flight validation of TIR subsystem. • Consequence of instrument drift on higher level data products. • Conclusions/Future work

  3. TIR Subsystem

  4. TIR Subsystem Characteristics

  5. TIR Baseline Performance Requirements

  6. On Board Calibration of TIR • Short term calibration performed for every strip with blackbody set to nominal value. • Long term calibration performed by periodically looking at blackbody a 4 temperatures between 270 K and 340 K. Temperatures are: 270 K, 300 K, 320 K and 340 K. To date ~ 50 long term calibrations have been performed.

  7. Radiometric Database Status

  8. C1 of online RCC DB Band 12

  9. v1.0x v2.05 v2.06 Calibration error in using online RCC DB

  10. In-Flight Validation of ASTER Data at the Lake Tahoe CA/NV Automated Validation Site

  11. 2000-09-20-D

  12. Measurements • Offshore • bulk temperature, skin temperature, air temperature, wind speed, wind direction, relative humidity, net radiation. • Onshore • air temperature, wind speed, wind direction, relative humidity, short and longwave radiation (up and down), sky imager, aerosols, total column water.

  13. Bulk temperature measurements

  14. Laboratory Calibration: Radiometer • NIST designed cone in a 44 liter temperature controlled bath. Stability at 25 C: +/- 0.0007 C (7008-IR) • Thermistor standard probe with an accuracy specification of 0.0015 ° C over 0-60 ° C and stability/yr of 0.005 ° C. (Model 5643-R) • Readout system with an accuracy of 0.0025 ° C at 25 ° C and resolution of 0.0001 ° (Chub E4) • Secondary standard PRT.

  15. Laboratory Calibration of Radiometer

  16. Cross Comparison of Radiometers at Miami

  17. Cross Comparison of Radiometers at Miami

  18. Means and standard deviations of the estimated skin SST differences between pairs of radiometers for the entire cruise period, and for each half of the cruise

  19. Data Reduction: Methodology For Radiance at Sensor Validation • Extract the bulk temperatures. • Extract the radiometric temperature. • Correct the radiometric temperature to skin kinetic temperature. • Propagate the skin temperature to the satellite using a radiative transfer model and interpolated atmospheric profile. • Convolve the propagated at-sensor radiance to the instrument response function to obtain the Vicarious Radiance (VR). • Extract the image radiance derived using the On Board calibrator (OBC). • Compare and contrast the OBC and VR Radiance values.

  20. Sensitivity Analysis for Correction of Radiometric Temperature to Skin Temperature

  21. Skin Effect Water surface After Minnett et al. 2000

  22. Variations in the bulk-, skin-, air-temperatures and wind speed on June 7, 2001 at L. Tahoe

  23. Consequence of Calibration Drift on Products • AST08 – Surface temperature • AST05 – Surface emissivity

  24. Summary/Future • Calibration of the TIR subsystem is changing with time. • Rate of change is currently increasing. • Radiometric coefficients are not updated with sufficient frequency, introducing artifacts into data. • Artifacts exceed calibration requirement. • Consequence of calibration drift depends on product. • ASTER team currently working on a procedure to correct the drift.

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