Estimating transpiration rates in a Danish agricultural area using Landsat thermal mapper data

One important step towards an integrated understanding of water balance components on plant productivity is the detection and evaluation of the plant water uptake (i.e. the transpiration rate). In this study, the transpiration 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 radiation absorbed by the vegetation, and H-v is the sensible heat flux between 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 vegetation (f(Rn)) is related to the NDVI, and the vegetation temperature is determined on the basis of the relationship between NDVI and surface temperature (T-s). The methodology is validated using field data. For successful application to remote sensing data, correct assessment of the empirical relationship between NDVI and f(Rn) is required. (C) 2000 Elsevier Science Ltd. All rights reserved.