Abstract. We have measured the permittivity of representative samples of natural seawater, synthetic seawater, and aqueous NaC1 solutions over the frequency range 3-20 GHz, in 0.1-GHz steps and over the temperature range -2ø-30øC in 1 ø steps. Additional measurements have been made at spot frequencies (23.8, 36.5, and 89 GHz) and at selected temperatures between -2 ø and 30øC. The data from these measurements have allowed us to deduce an interpolation function for e(v, t, S) in the ranges 2 <-v <-20 GHz, -2 ø <-t <-30øC, and 20%0 <-S <-40%0 with a precision of 1%. If the frequency range is extended up to 40 GHz, the precision of the interpolation function is about 3%. The data have also allowed us to compare the permittivities of natural seawater, synthetic seawater, and aqueous NaC1 solution with the same salinities. Natural and synthetic seawater have the same permittivities within a 1% experimental error estimate. An aqueous NaC1 solution has a significantly different permittivity (up to about 6% difference, depending upon the frequency and temperature). IntroductionFor microwave remote sensing applications over the ocean using radars and radiometers, a precise knowledge of the emissivity and reflectivity properties of the sea surface is required. The dielectric permittivity of seawater e(v, t, S) for a frequency v, temperature t, and salinity S is a vital parameter in all models describing the interaction of a wind-roughened sea surface with microwave radiation.The main objectives of the research program were to (1) deduce an interpolation function for e(v, t, S) with a precision good enough to satisfy the technical improvements in radiometric sensitivities for use in radiative transfer models in the frequency range 1-100 GHz and (2) The goal of such models is to provide the permittivity and conductivity of seawater at any frequency as a function of the "salinity" and temperature. Such a model has to be based upon experimental data. We have found only three authors who report permittivity

Abstract. As part of a measuring program dedicated to the analysis of the dielectric properties of seawater in the frequency range 3-89 GHz, a new dielectric permittivity model based on the standard Debye theory has been developed for remote sensing applications over the ocean below 40 GHz, together with polynomial interpolations at the millimeter frequencies 85.5 and 89 GHz. The aim of this paper is to test the relevance of these new dielectric measurements through statistical comparisons of radiative transfer predictions with satellite and airborne radiometric data between 18 and 89 GHz. A radiometric sensitivity analysis to the permittivity measurement errors is proposed, which yields a sea surface brightness temperature accuracy of at least 0.5 K below 20 GHz, 1 K at 24 GHz, and 1.5 K at 37 and 89 GHz. At frequencies less than 40 GHz, superiority of the revised Debye model is pointed out over the most commonly used model of Klein and Swift [1977]. At millimeter frequencies the new permittivity expressions deviate significantly from the standard Debye predictions, especially at low temperature, suggesting the influence of a second "high-frequency" Debye relaxation. Our comparisons with radiometric data at 89 GHz and in the channel 85.5V of the special sensor microwave imager tend to support this hypothesis. The results emphasize the importance of an adequate modeling of the complex permittivity of seawater as input to the surface emissivity models, at any frequency of the microwave spectrum, and augur interesting outputs in both in-flight calibration and interpretation of satellite data.

Measurements of the electrical conductivity and the complex permittivity near a percolation threshold in the ternary microemulsion system composed of water, iso-octane, and AOT are reported. It is shown that the electrical conductivity, which implies charge transfer process, is well described by a dynamic percolation model. The frequency dependence of the dielectric constant and the behavior of the relaxation frequency are also found to be in close agreement with the scaling power laws of the dynamic percolation model.

We describe a free air transmission method for the determination of the permittivity of lossy liquids in the frequency range 26-110 GHz and the temperature range −5 to 70 • C. For pure water the method gives permittivity values with a dispersion of less than 3% about the true value. We give new permittivity data for an aqueous NaCl solution and for synthetic sea water in the temperature range −2 to 30 • C. The permittivity data obtained with this technique have been incorporated in a number of numerical weather prediction models and have resulted in more accurate ocean surface emissivity functions for use with microwave and millimetre wave imaging and sounding instruments.

No abstract