Thermal-Infrared Scale Verifications at 10 um Using the NIST EOS TXR
Joseph P. Rice, S C. Bender, W H. Atkins
One element of a multi-year calibration program between NIST and the NASA EOS Project Science Office has been the development and deployment of a portable transfer radiometer for making verifications of the thermal-infrared scales being used for flight-instrument pre-launch calibration. This instrument, the Thermal-infrared Transfer Radiometer (TXR), has been built and the first deployment test was completed sucessfully, as has been reported previously . The 5-micrometer channel, based on a photovoltaic InSb detector, so far has demonstrated a pre-deployment uncorrected repeatability of better than 30 mK to 60 mK, which is sufficient to enable intercomparisons at useful uncertainty levels for the EOS program. However, the 10-micrometer channel, based on a photovoltaic MCT detector, shows uncorrected repeatability levels of about 0.5 K, the response changes being induced by cryocycling. This paper describes the technique that has been developed for correcting for these changes. A portable blackbody check-source trvels with the TXR that is used to verify the repeatability during the deployment trip. The check-source, in combination with the stability of the 5-micrometer channel, is used restore a high accuracy scale to the 10-micrometer channel that would otherwise be possible. This application is analogous to the use of an on-orbit calibration source to check for and correct for launch-induced or degradation-induced flight instrument detector response changes.