A comparative study of land surface emissivity retrieval from NOAA data

A comparative study has been carried out on the most recent algorithms for the estimation of land surface emissivity (epsilon) using Advance Very High Resolution Radiometer (AVHRR) data. Three of the algorithms are based on the Temperature-Independent Spectral Indices (TISI) concept using atmospherically corrected channels 3,4, and/or 5, namely: (1) TISIBL, (2) TS-RAM, and (3) Delta day. The fourth is a simplified method based on the estimation of epsilon using atmospherically corrected data in the visible and near-infrared channels, called Normalized Difference Vegetation Index (NDVI) Thresholds Method (NDVITHM). This method integrates a wide spectral data set of bare soil reflectivity measurements in the 0.4-14-mum band and uses different approaches in function of the NDVI value. All methods have been applied to the Iberian Peninsula using AVHRR/National Oceanic and Atmospheric Administration (NOAA-14) data during March 17th, 1997. In terms of emissivity, the results dhow that the difference between the NDVITHM method and the other methods is always positive, with a bias of less than 0.010 and a root mean square (rms) error of 0.012 when compared to the TS-RAM method. In terms of land surface temperature, the NDVITHM method shows a bias of less than -0.4 K when compared to Delta day, and a bias of -1.1 K and an rms error of 0.5 K when compared to TS-RAM. In conclusion, although the TISIBL is a precise method, it needs the AVHRR channel 3 for its application, which is not alway available, for example, as in the AVHRR archives provided in the frame of the Pathfinder AVHRR Land project (more than 18 years of data). In this case we have shown that he NDVITHM method shows promising results and can be applied to obtain land surface temperature and emissivity from NOAA data without losing accuracy. (C) Elsevier Science Inc., 2001. All Rights Reserved.