Direct Determination of the Electromagnetic Reflection Properties of Smooth Brackish Water to the Continuous Spectrum from 108 to 4 × 109 Hertz

Abstract

The problem undertaken was to devise a remote sensing technique to measure the salinity of brackish water emerging from submarine springs and floating on coastal sea water. In the range of interest, 20° to 25° C, 0,3 ppt to 30 ppt dissolved solids, the dominant physical factor explaining the change of reflectance with salinity changes is the ionic conductivity due to the lateral flow of ions induced by the imposed electromagnetic field. The ionic conductivity of brackish water is a monotonic function of the salt content. A laboratory prototype radio reflection spectrometer was designed and assembled from commercially available swept-frequency UHF-microwave test equipment, a single horn antenna, and a handmade coaxial sample cell. Reflectance spectra from 2.5 X 109 to 4.0 × 109 Hertz of fresh and sea water were obtained with a free-wave (horn antenna and pool) system. Reflectance spec tra of brackish and sea water from 108 to 2.0 × 109 Hertz were obtained with a coax ial waveguide system. The measured spectral signatures appear to agree with the computed reflectance of aqueous sodium chloride solutions. The theoretical and experimental results indicate that free-wave radio reflectance spectrometry from 108 to 109 Hz may be feasible for use in remote sensing of large salinity anomalies on relatively smooth water bodies.