Mapping land surface emissivity from NDVI: Application to European, African, and South American areas

Thermal infrared emissivity is an important parameter both for surface characterization and for atmospheric correction methods. Mapping the emissivity from satellite data is therefore a very important question to solve. The main problem is the coupling of the temperature and emissivity effects in the thermal radiances. Several methods have been developed to obtain surface emissivity from satellite data. In this way we propose a theoretical model that relates the emissivity to the NDVI (normalized difference vegetation index) of a given surface and explains the experimental behavior observed by van de Griend and Owe. We can use it to obtain the emissivity in any thermal channel, but in this work we have focused on the 10.5- to 12.5-μm region, where most thermal sensors on board satellites work at present. The model is applicable to areas with several soil and vegetation types and where the vegetation cover changes. From the theoretical model we have developed an operational methodology to obtain the effective emissivity combining satellite images and field measurements. The error of the methodology ranges from 0.5% (due to the experimental limitations of the field methods) to 2% (considering the case in which we have no information about the studied area). To check the general validity of the model, we have validated and applied it in different atmospheric environments and in areas with a different degree of roughness, i.e., from midlatitude (France, Argentina) to tropical (Sahel, Botswana) atmospheres, and from flat (La Mancha, Spain) to rough (Valencia, Spain) surfaces, and we have obtained an error of estimate of 0.6% on the emissivity.