We have applied a Land Surface Temperature algorithm to the whole Pathfinder AVHRR Land (PAL) database, aiming at studying the evolution of the vegetation at a global scale. The Land Surface Temperature parameter, along with NDVI, will allow retrieving vegetation changes between July 1981 and September 2001. We have also built a classification which takes into account both vegetation variations and thermal patterns, from NDVI and Air Temperature at 2 meters height data. This classification allows differentiating areas which present close vegetation changes throughout the year, but totally different climates, as for example in mountainous and semiarid regions. The main quality of this classification is that it does not need any a priori information on the encountered vegetation, and thus can evolve from year to year. Through the 20 years of data, the evolution of Land Surface Temperature shows to be strongly affected by orbital drift and satellite changes. This will require an adequate correction to allow deeper study. On the other hand, NDVI does not show this trend, but aerosol absorption from Mount Pinatubo's eruption in June 1991 seems to corrupt temporarily the data in the northern hemisphere.
In this paper, it is shown the importance of thermal measurements to characterize different surfaces carried out in boreal environment in the SIFLEX (Solar Induced and Fluorescence Experiment) campaign. The data was acquired in Sodankyla (Finland), over the boreal forest, from 23rd April to 10th June 2002. Bio-geophysical parameters such as land surface temperature and emissivity were retrieved in relationship with other parameters from fluorescence measurements made with a Passive Multiwavelength Fluorescence Detector (PMFD).
The thermal measurements of different targets (soil, vegetation, sky) under different observation angles have been carried out using a four-band field radiometer (CIMEL CE312) and two single band radiometers (EVEREST 3000.4ZLC and RAYTEK ST6). Angular measurements and transects have been also carried out concurrently to the satellites flights over the region.
WATERMED project contributes to the international efforts in analyzing efficiency in water use, in particular for the Mediterranean Basin countries. The general aim of this project is to develop a comprehensive method for the study of the water use and the resistance to the drought of the natural and irrigated vegetation in the Mediterranean Basin, by means of a combined historical remote sensing database, vegetation models and field measurements. The project has provided regional maps of critical parameters at regional scale, such as land surface temperature, emissivity, and NDVI. A multi-temporal analysis using the PATHFINDER AVHRR land data has been carried out into the frame of this project to map and monitor changes in the biophysical characteristics of land cover over the last 20 years. On the other hand, REANALYSIS data, which is a result of a joint project NCEP/NCAR, have been incorporated to provide mean monthly climate data over the study area.