Aerial photography, multispectral scanning and radar sensing are important tools in environmental studies. For global and continental monitoring and change detection the NOAA-AVHRR is at present the most suitable sensor. Thanks to the repeat cycle of 1 day, the NOAA-AVHRR will give a cloud free image of any geographic area during any period of time. Analysis of time series of such data enable study of spatial changes and dynamics of vegetation and land use. Therefore, the NOAA-AVHRR sensor data are highly suitable for global monitoring of land cover. New AVHRR applications are being researched. The low spatial resolution AVHRR data van be supplemented with higher resolution MSS data or radar imagery when and where available. Remote sensing of surface temperatures and correlation with meteorological measurements to estimate evapotranspiration has proved to be very accurate for agricultural crops on a large scale.
