The relative merits and limitations of thermal radiometric measurements in estuarine studies

Observations from rias of Galicia and Asturias (northern Spain), have demonstrated that a hand-held thermal radiometer (sensitive to thermal infrared radiation in the 8-14 mu m wavelength range, fitted with a telephoto lens providing a restricted field of view at the water surface and enabling temperature estimation to +/- 0.2 degrees C) is valuable in both the exploration and surveillance of estuaries. Such an instrument enables rapid measurement of the temporal and spatial variations of water surface temperature. Near synoptic surface temperature data yield information on the modes of intermixing of marine and land derived waters, permitting the identification of tidal advection, upwelling and sinking water masses and the temporary isolation of water parcels due to estuarine morphology, bathymetry or the development of frontal :systems. The method is restricted to the measurement of surface water temperatures. It is a complement to in situ measurements, helping to optimise the location of, for example, current metering stations. It is inexpensive and rapid to use. Hundreds of measurements per tide can be made over wide areas but the positional accuracy of these is visually based. Elevated vantage points, providing unimpeded vision, are essential, so not all estuaries lend themselves to such study.