Abstract
Deep convective clouds (DCC) are the brightest and most Lambertian Earth targets behaving as solar diffusers. They are above most of the Earth’s atmosphere and are nearly spectrally flat for wavelengths less than 1 µm. This makes them excellent visible inter-calibration targets when comparing simultaneous radiances between two sensors in the same line of sight otherwise known as ray-matching. When DCC pixel-level sensor visible channel reflectances are analyzed monthly over a large tropical domain as a large statistical ensemble, the reflectances are nearly temporally constant. This makes them excellent targets to monitor the visible sensor stability. Beginning with CERES on the TRMM satellite, the DCC calibration method has monitored the stability of MODIS and VIIRS as well as many GEO sensors. The DCC calibration method has even monitored the stability of AVHRR sensor on the degrading NOAA satellites as long as the DCC are observed with a SZA less than 70°.
The next logical step is to characterize DCC as an invariant target, since they are very stable in time. Similar to desert, polar and lunar invariant targets, the DCC invariant target can be characterized by a well-calibrated reference sensor. The DCC invariant target and can then transfer the reference calibration to another sensor. This suggests that any sensor, which has an IR window channel needed for DCC identification, can be absolutely calibrated to a reference sensor without requiring coincident line of site measurements. This claim needs to be validated.
This is validated by, characterizing DCC as an invariant target using Aqua-MODIS band 1 as the reference calibration instrument. Several geostationary visible imagers are calibrated using DCC invariant target calibration and then compared to the coincident ray-matched calibration using both all-sky ocean and DCC targets. Similarly, Aqua-MODIS and NPP-VIIRS are inter-calibrated using both ray-matched and the DCC invariant target calibration methods. These validation results will be presented at the conference.
Characterizing Deep Convective Clouds as an Invariant Calibration Target
Deep convective clouds (DCC) are the brightest and most Lambertian Earth targets behaving as solar diffusers. They are above most of the Earth’s atmosphere and are nearly spectrally flat for wavelengths less than 1 µm. This makes them excellent visible inter-calibration targets when comparing simultaneous radiances between two sensors in the same line of sight otherwise known as ray-matching. When DCC pixel-level sensor visible channel reflectances are analyzed monthly over a large tropical domain as a large statistical ensemble, the reflectances are nearly temporally constant. This makes them excellent targets to monitor the visible sensor stability. Beginning with CERES on the TRMM satellite, the DCC calibration method has monitored the stability of MODIS and VIIRS as well as many GEO sensors. The DCC calibration method has even monitored the stability of AVHRR sensor on the degrading NOAA satellites as long as the DCC are observed with a SZA less than 70°.
The next logical step is to characterize DCC as an invariant target, since they are very stable in time. Similar to desert, polar and lunar invariant targets, the DCC invariant target can be characterized by a well-calibrated reference sensor. The DCC invariant target and can then transfer the reference calibration to another sensor. This suggests that any sensor, which has an IR window channel needed for DCC identification, can be absolutely calibrated to a reference sensor without requiring coincident line of site measurements. This claim needs to be validated.
This is validated by, characterizing DCC as an invariant target using Aqua-MODIS band 1 as the reference calibration instrument. Several geostationary visible imagers are calibrated using DCC invariant target calibration and then compared to the coincident ray-matched calibration using both all-sky ocean and DCC targets. Similarly, Aqua-MODIS and NPP-VIIRS are inter-calibrated using both ray-matched and the DCC invariant target calibration methods. These validation results will be presented at the conference.