Space in the service of prediction hydrological data

The studies of the hydrology of land surfaces by remote sensing from satellite altitudes are more immediately useful than those from surface or low altitude platforms. The scale is increased in hydrological studies, so the physical factors which are involved become less complex. Fortunately, largescale, low resolution data have considerable scientific and economic value especially for planning the development of the water resources of the world. The Earth Resources Technology Satellite proved particularly useful as a test-bed for experiments with fairly direct hydrological applications. The ERTS Water Resources Working Group was in general agreement that the satellite´s MSS observations provided much more useful and readily-applicable hydrological information than had been expected prior to its launch. We will summarize some of the ERTS findings and Landsat inspired suggestions for the future. Weather satellites (Essa, Nimbus and Noaa) have provided interesting data with a hydrological content in thermal infrared wavebands and the microwave region using passive sensor systems. For example, drainage networks have been traced from high resolution infrared data in atmospheric window wavebands under cloud-free conditions at night, when water and the damp soils flanking water courses maintain a higher radiation temperature than the drier interfluves. Quantitative estimates can be placed upon the differences, but by and large the resolution has been too low for-the results to be of much practical use except, perhaps in a few particularly inaccessible regions. The new Nimbus Microwave Spectrometer (NEMS) gives more hope for the future. Reflectance patterns may be mapped by such means for soil moisture, snow cover, and ice type studies. The hydrological cycle is comprised of three types of components namely storages, transports, and exchange processes. By far the greatest reservoir of water is the oceanic girdle of the globe, although significant amounts of water are retained temporarily within the rocks of the Earth´s crust, in ice caps and snow fields on the surface of the Earth, in soils, in fresh water reservoirs like lakes and inland seas, and in the atmosphere. Water is transported by circulations in the atmosphere and oceans, and by movements over and near t- he surfaces of land areas chiefly under the influence of gravity. It is left to the exchange processes to effect transformations of water from one physical state (solid, liquid or gas) into another. Microwave systems offer the most immediate description for obtaining data on rainfall intensity as well as distribution. This research will give how the water in the environment can be described with RS and GIS techniques.