The performance of the multispectral thermal imager (MTI) surface temperature retrieval algorithm at three sites

This work describes the surface temperature retrieval algorithm for the U.S. Department of Energy Multispectral Thermal Imager (MTI) satellite and its performance at three test sites. The MTI is a 15-band multispectral research and technology development satellite that provides high spatial resolution imagery of the earth's surface from a polar orbit. It has a capability for pixel-by-pixel retrieval of total atmospheric water vapor during the day. The surface temperature retrieval process uses atmospheric profiles of temperature and water vapor from numerical weather prediction data assimilation products available for the globe. The profiles of water vapor are scaled using the retrieved pixel-by-pixel water vapor during the day to improve atmospheric compensation within the image. The algorithm requires specification of a maximum emissivity or the acceptance of a default: here the maximum band emissivity is known and specified. The results of the algorithm are evaluated at three sites with a high degree of surface uniformity and known spectral emissivity: Lake Tahoe, NV/CA, Ivanpah Playa, NV/CA, and the Mauna Loa caldera, HI. At the first two sites, coincident measurements of surface temperature and emissivity are available. At Mauna Loa, surface emissivity measurements are available, but surface temperature measurements are not. Therefore, at Mauna Loa, the surface emissivity estimates derived from the surface temperature retrieval are compared with emissivity measurements. The results show that the surface temperature retrievals had a root mean square (RMS) difference with surface measurements of 0.6 K during the day and 1.0 K at night. This indicates, albeit weakly, that the use of pixel-by-pixel water vapor retrieved by the satellite improves the overall surface temperature retrievals. At Ivanpah Playa, all the data are daytime, and the surface temperature retrievals have an RMS difference with the in situ measurements of 0.8 K. The Mauna Loa emissivities derived from the surface temperature retrieval agreed excellently with in situ emissivity measurements. The approach taken to perform surface temperature retrieval, used operationally within the MTI research and development program, is seen to be simple and effective.