CALIBRATION OF LOW GAIN RADIANCE AT VIIRS EMISSIVE BAND (M13) and VIIRS IMAGE ABOUT MOON TEMPERATURE

摘要

Early assessment of the VIIRS thermal emissive bands (TEBs) show that all VIIRS TEBs except M13 are stable and exceed the specifications. M13 is a dual gain band, and is used for determining the surface temperature at low radiance (high gain) and fire detection at high radiance (low gain). At a low gain stage, the onboard blackbody temperature at an operational temperature of 292 Kelvin is far below the lowest temperature at the low gain, which prevents from any attempt to radiometric calibration. This study found that the VIIRS calibration data during the blackbody temperature warm up and cool down (WUCD) may be useful to check the gain stability and to estimate noise equivalent deviation of temperatures (NEdT). During the VIIRS blackbody temperature warm up and cool down, the blackbody temperature was cooled down to 267 K and warmed up to 315 K. The contrast at the low gain for M13 band between blackbody and space views may be useful, although the highest blackbody temperature is still below the low boundary for the low gain. Moon surface temperature can be as hot as 400 Kelvin, high enough for M13 band radiometric calibration at a low gain. The advantages using the observation data of Moon are that it is very stable and there is no gaseous absorption. However, Moon surface emissivity for infrared spectrum needs to be known. This study found that Moon may be used to check measurement range of the VIIRS M13 band at a low gain. We have developed a calibration algorithm to determine the moon temperature and generated the first VIIRS image about moon temperature. There are some other sources such gas flares that may also be used to estimate the radiometric accuracy at low gain.