Validation of AVHRR and MODIS ice surface temperature products using in situ radiometers

Ship-borne and airborne infrared radiometric measurements during the ARISE cruise of September-October 2003 permitted in situ validation studies of two satellite-based ice surface skin temperature algorithms: the AVHRR Polar Pathfinder Ice Surface Temperature and the MODIS Sea Ice Surface Temperature. Observations of sea ice from the Aurora Australis ship's rail using a KT-19.82 radiometer were conducted between 25 September and 21 October during clear-sky overflights by AVHRR (41 passes) and MODIS (17 passes) on their respective satellite platforms. Data from both sensors show highly linear fits to 1 min integrated radiometer spot measurements, spanning the range 245-270 K with a +/- 1.4 degrees C, 1 sigma, (AVHRR) and +/- 1.0 degrees C (MODIS) variation relative to a I : 1 relationship. There was no significant offset. Helicopter observations made with a KT-19.85 radiometer on three dates (8, 19 and 20 October) provided more data (236 gridcell sites total), but over a more limited sea-ice skin temperature range (252-268 K), with higher variation ( +/- 1.7 degrees C, 1 sigma) due to mixed-pixel issues. Comparison of MODIS and AVHRR algorithms directly, with both images acquired during a helicopter flight, indicates very high correlation and near-unity slope for the two satellite-based algorithms. Ship air-temperature data during the validation indicated moderate to strong inversions over sea ice under clear skies. These formed and decayed rapidly (tens of minutes) as clouds moved out of and into the zenith area.