Estimating transpiration rates in a Danish agricultural area using Landsatthermal mapper data

One important step towards an integrated understanding of water balance com ponents on plant productivity is the detection and evaluation of the plant water uptake (i.e. the transpiration rate). In this study, the transpiratio n rates from agricultural fields (LEv) are calculated using Landsat thermal mapper data through applying an energy balance approach to the vegetation component of the land surface: LEv = R-n(v)-H-v, where R-n(v) is the net ra diation absorbed by the vegetation, and H-v is the sensible heat flux betwe en the leaves and the air. The method requires field data of incoming solar radiation, air temperature and windspeed. The surface albedo is evaluated using the satellite data. The fraction of net radiation absorbed by the veg etation (f(Rn)) is related to the NDVI, and the vegetation temperature is d etermined on the basis of the relationship between NDVI and surface tempera ture (T-s). The methodology is validated using field data. For successful a pplication to remote sensing data, correct assessment of the empirical rela tionship between NDVI and f(Rn) is required. (C) 2000 Elsevier Science Ltd. All rights reserved.