New permittivity measurements of seawater

Abstract

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

Passive Microwave Remote Sensing of Rain from Satellite Sensors

“…Other studies based on radiometric airborne observations of the ocean-roughened surface (Guillou et al, 1996) have extended and validated existing sea emissivity models at higher frequencies 89 and 157 GHz. Likewise, laboratory experiments with an aqueous NaCl solution and synthetic seawater modeling (Ellison et al, 1998) have demonstrated that the assessment of sea surface emissivity for the interpretation of radar and radiometer data necessarily requires accurate permittivity measurements (better than 5%) of natural seawater in the frequency range 40-100 GHz. In the last fifteen years with the increasing number of satellite platforms hosting increasingly higher spatial resolution new generation microwave sensors, the use of orbital instrument data became more widespread.…”

An Updated Geophysical Model for AMSR-E and SSMIS Brightness Temperature Simulations over Oceans

“…The most frequently used in the past model [44] is becoming increasingly inaccurate with the frequency increase [11,45]. A number of experimental studies of the last two decades [46][47][48][49] resulted in appearance of new updated models. Quite recently, a new permittivity model appeared [10] following the permittivity formulation of [47].…”

“…A number of experimental studies of the last two decades [46][47][48][49] resulted in appearance of new updated models. Quite recently, a new permittivity model appeared [10] following the permittivity formulation of [47]. Its coefficients were determined by fitting the new permittivity measurement data, mostly important for L-band BT simulation (for MIRAS on SMOS and Aquarius on SAC-D instruments).…”

The Role of Advanced Microwave Scanning Radiometer 2 Channels within an Optimal Estimation Scheme for Sea Surface Temperature

“…There are several models for the emissivity and permittivity of seawater [33][34][35][36][37][38][39]. FASTEM-6 uses a method that starts from a formulation for the permittivity based on Ellison et al [33].…”

“…FASTEM-6 uses a method that starts from a formulation for the permittivity based on Ellison et al [33]. This describes the complex permittivity with a double Debye model:…”