It also appeared that to each site and each date corresponds a different atmospheric correction
equation (Figure 3), depending on atmospheric conditions. It is evident that the wide difference between these
equations (up to 25°C for DN = 190) does not allow using a single equation for all conditions, even on the same
site. The presented method thus appears of great interest for operational uses of Landsat TM thermal IR data.
Figure 3 : Intercomparison of the different atmospheric correction equations derived for each study site
where correction equation could be derived and validated using both warm and cold targets..
4 - CONCLUSION
This study aiming at designing a new atmospheric correction method of Landsat TM thermal
infrared data has shown that:
• surface temperatures of warm (bare soil, rangeland) and cold (irrigated fields, wet forest) sites
can be successfully derived from surface energy balance equation on various study sites, using
usual meteorological measurements;
• this surface temperature estimation can be improved by at least one ground-measurement of
the warm target surface temperature ;
• when applied to a simple equation of radiative transfer (Wukelic et al., 1989), these warm and
cold targets temperatures can be used to derive a local atmospheric correction equation for the
day of Landsat TM overpass ; ground measurements of mid-temperature targets have shown
the validity of such a derived equation.
This method can be applied easily to a Landsat TM thermal IR image, even if it was acquired
in the past, under the condition that meteorological data are available and sites where LE=LEp and LE=0 can
be identified. It can therefore considerably increase the interest of using Landsat TM thermal IR data for local
mapping of surface energy balance of various land surfaces, as it is only based on easily available
meteorological and TM data. 5
5 - ACKNOWLEDGEMENTS
The authors would like to acknowledge the many people who were involved in the ground
measurement acquisitions on the various sites : people of ORMVAG and IAV Hassan II, Morocco, for the
Gharb measurement campaign of 1987, of USDA-ARS Water Conservation Lab., Phoenix Az., for the MAC
campaigns of 1985-1986, and of USDA-ARS Tombstone Laboratory and Univ. of Arizona, Dept, of Hydrology
and Water Resources and Dept of Soil and Water Science, for the Walnut Gulch '92 campaign. This study was
conducted in the framework of the NASA EOS program (NASA Ref. Num. NAG-W2425, NSF grant BSC8920851),
BSC8920851), of the CEMAGREF Natural Hazards program, and of the EOSAT Grant Program (EOS AT Grant
