INTERCALIBRATION OF 2 AIRBORNE THERMAL INFRARED RADIOMETERS - TIMS AND PRT5 - APPLICATION TO LAND-SURFACE TEMPERATURE RETRIEVAL

An earlier analysis of the data acquired by TIMS (Thermal Infrared Mul tispectral Scanner) operating from the NASA C-130 during HAPEX (Hydrol ogic Atmospheric Pilot Experiment) MOBILHY experiment, showed that the brightness temperatures for all six channels were too high, and that the magnitude of the error was more or less a function of the aircraft altitude. This problem is certainly due to the ambient air stream whi ch could cool the two blackbodies used as reference targets. To correc t the TIMS data, the PRT5 (Precision Thermometer) non-scanning radiome ter is used. The PRT5/TIMS comparison is based upon a relationship bet ween a combination of the TIMS surface brightness temperatures, T(i), and the PRT5 surface brightness temperature, T. TIMS and PRT5 correspo nding transects are superposed by maximizing the linear correlation be tween the two sets of temperatures. The correlations are always greate r than 0.92. T(c) and T(h) the cold and hot actual blackbody temperatu res, can be deduced from the slope and the origin of the preceding fit . Final precision on TIMS temperature is about 1-degrees-C. The valida tion, made with the ground KT17 radiothermometer, gives satisfactory r esults. A simple empirical correction is deduced from the 22 mid altit ude corrected transects. It gives the same precision on the temperatur e retrieval when it is applied on high altitude TIMS measurements for which the PRT5 is not available. As expected, the correction is larger for high altitude flights-until 10-degrees-C and more-than for mid al titude flights-from 2 to 5-degrees-C.