Effect of salinity on the dielectric properties of water

The complex permittivity ∈=∈′− j∈′′ of distilled water and NaCl solutions of concentrations varying from 5000 to 35000 ppm have been measured in the frequency range from 200 MHz to 1.4 GHz using a Vector Network Analyzer (VNA). The complex permittivity of saline water collected from Kanyakumari sea bank has also been measured in this frequency range. It has been observed that the dielectric constant of water decreases slowly with increase in frequency from 200 MHz to 1.4 GHz for given salinity of water. At given frequency, the dielectric constant decreases slowly with increase in salinity from 5000 to 35000 ppm. The dielectric loss of distilled water increases with increase in frequency from 200 MHz to 1.4 GHz, but for saline water it decreases with increase in frequency, over this frequency range. The decrease in dielectric loss with increase in frequency is more for higher salinity in water. The variation of complex permittivity of water with salinity and frequency is calculated using the Stogryn equations [IEEE Trans. On Microwave Theory and Techniques, August 1971, pp. 733-736] as well as with the Klein and Swift [IEEE Transactions on Antennas and Propagation, Vol. AP25, No.1, January 1977, pp. 104-111] equations, and the results are found to be in good agreement with corresponding experimental values. The variation of emissivity with variation of salinity calculated at fixed frequencies of 0.5, 0.9 and 1.4 GHz have also been presented in the paper, which is very much useful for remote sensing applications of oceans.