A modified model for specular sea surface emissivity at microwave frequencies

Abstract

Modifications to the [14] model for specular ocean emissivity have recently been suggested by [7] in order to improve the performance at high microwave frequencies. The work presented here tests both the original and modified models using a set of satellite and ground-based observations that is designed to eliminate as much as possible the dependence of the test on parameters other than the surface emission itself. Clear sky, low humidity, and low wind conditions were used exclusively to reduce the dependence of the test on atmospheric and wind-roughened sea models. Radiosonde observations (RaObs) coincident with TOPEX satellite overpasses were used to reduce errors due to inexact knowledge of the atmosphere. Our tests confirm the superior performance of the Ellison model at higher frequencies. In an effort to remove the residual bias between the models and the observations, we also suggest a parameterized modification to both models that "best fits" the models to the data. In this case, the modified Ellison model maintains its superior performance at high frequencies, suggesting that it has an inherently more accurate frequency dependence. The root mean-squared (RMS) error in the modified Ellison emissivity model, over the range of 18-40 GHz, is found to be 0.0037, which translates into a model error of approximately 1 K in terms of brightness temperatures.

The Fast EPILE Combined With FBM for Electromagnetic Scattering From Dielectric Targets Above and Below the Dielectric Rough Surface

“…The wind speed is 5 m/s. The temperature of the sea water is 20 • C, the salinity is 36 • / •• , hence, according to the Debye's theory [40], the relative dielectric permittivity of dielectric rough sea surface is (70. 34, 40.63).…”

Retrieval of atmospheric and ocean surface parameters from ADEOS‐II Advanced Microwave Scanning Radiometer (AMSR) data: Comparison of errors of global and regional algorithms

“…The values of the sea surface emissivity κ V (ν, t s ) as a function of the sea surface temperature t s were found with the Fresnel equations for θ = 55° using the corrected dependencies of the seawater dielectric permittivity ε(ν, t s ) at salinity s = 35‰, as given by [ Cruz‐Pol and Ruf , 2000].…”

“…Usage of [Ellison et al, 1998] approximations changes (6.9) and (10.7) only slightly and do not influence the t s and W retrieval errors. However, at the shorter wavelengths the differences are increased and thus the data of Ellison et al [1998] andRuf [2000] were used to calculate emissivity at 18.7, 23.8 and 36.5 GHz. Increments of emissivity associated with the wind action were estimated on the basis of data [Wentz, 1992;Rosenkranz, 1992;Sasaki et al, 1987].…”

“…Emissivity of the calm sea surface was computed from the Fresnel formulas with “old” [ Klein and Swift , 1977; Stogryn , 1971] and “new” [ Ellison et al ., 1998; Cruz‐Pol and Ruf , 2000] approximations for dielectric permittivity of saline water. Usage of [ Ellison et al ., 1998] approximations changes κ(6.9) and κ(10.7) only slightly and do not influence the t s and W retrieval errors.…”

“…However, at the shorter wavelengths the differences are increased and thus the data of Ellison et al . [1998] and Cruz‐Pol and Ruf [2000] were used to calculate emissivity at 18.7, 23.8 and 36.5 GHz. Increments of emissivity associated with the wind action were estimated on the basis of data [ Wentz , 1992; Rosenkranz , 1992; Sasaki et al ., 1987].…”