Radiometric Calibration of the ASTER Thermal Infrared TIR
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. • Conclusions/Future work
TIR Subsystem
TIR Subsystem Characteristics
TIR Baseline Performance Requirements
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.
Radiometric Database Status
C 1 of online RCC DB Band 12
Calibration error in using online RCC DB v 1. 0 x v 2. 05 v 2. 06
In-Flight Validation of ASTER Data at the Lake Tahoe CA/NV Automated Validation Site
2000 -09 -20 -D
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.
Bulk temperature measurements
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 E 4) • Secondary standard PRT.
Laboratory Calibration of Radiometer
Cross Comparison of Radiometers at Miami
Cross Comparison of Radiometers at Miami
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
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.
Sensitivity Analysis for Correction of Radiometric Temperature to Skin Temperature
Skin Effect Water surface After Minnett et al. 2000
Variations in the bulk-, skin-, airtemperatures and wind speed on June 7, 2001 at L. Tahoe
Consequence of Calibration Drift on Products • AST 08 – Surface temperature • AST 05 – Surface emissivity
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.
- Slides: 34