Gary S. Brown

Bio: Gary S. Brown is an academic researcher. The author has contributed to research in topics: Surface roughness & Wind gradient. The author has an hindex of 2, co-authored 2 publications receiving 104 citations.

Estimation of surface wind speeds using satellite‐borne radar measurements at normal incidence

Abstract: The results of a study to determine the correlation of the surface scattering cross section per unit area at normal incidence σ°(0°) and 13.9 GHz with surface wind speed are presented. Comparing σ°(0°) measurements with ship reports of wind speed, it was found that an algorithm could be devised which is capable of producing wind speed estimates from σ°(0°) measurements to a precision of 2.6 m/s for winds in the range of 1–21 m/s. Correlations with buoy measurements in the range of 1–10 m/s show an rms precision of 2.1 m/s with the possibility of a slight bias in the ship report based algorithm. A study of σ°(0°)-inferred wind speeds in relation to hindcast estimates shows a distinct tendency in the hindcast results to be biased toward the low side in the absence of sufficient ship reports of wind and pressure. The results of this study indicate that a short-pulse radar altimeter can provide reasonably accurate estimates of surface wind speeds over a rather large range of wind speeds.

Sea Salt Aerosol Production: Mechanisms, Methods, Measurements, and Models - A Critical Review

Abstract: Sea salt aerosol (SSA) exerts a major influence over a broad reach of geophysics. It is important to the physics and chemistry of the marine atmosphere and to marine geochemistry and biogeochemistry generally. It affects visibility, remote sensing, atmospheric chemistry, and air quality. Sea salt aerosol particles interact with other atmospheric gaseous and aerosol constituents by acting as sinks for condensable gases and suppressing new particle formation, thus influencing the size distribution of these other aerosols and more broadly influencing the geochemical cycles of substances with which they interact. As the key aerosol constituent over much of Earth's surface at present, and all the more so in pre-industrial times, SSA is central to description of Earth's aerosol burden.

A physical radar cross-section model for a wind-driven sea with swell

Abstract: A new spectrum model for the ocean surface is proposed. We determine the two unknown parameters in this spectrum by fitting it to radar observations. We find that this spectrum combined with two-scale scattering theory can predict much of the observed dependence of the radar cross section on radar frequency, polarization, angle of incidence, and wind velocity at incidence angles in the 0\deg-70\deg range. The spectrum model is combined with a model for swell to examine the effect of swell on the radar cross section. We find that the effect of swell is significant for low radar frequencies ( L band) and near normal incidence but can be nearly eliminated by using higher frequencies ( K_{u} band) and large angles of incidence ( \approx 50\deg ).

Use of the Surface Reference Technique for Path Attenuation Estimates from the TRMM Precipitation Radar

Abstract: Estimates of rain rate from the precipitation radar (PR) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite require a means by which the radar signal attenuation can be corrected. One of the methods available is the surface reference technique in which the radar surface return in rain-free areas is used as a reference against which the path-integrated attenuation is obtained. Despite the simplicity of the basic concept, an assessment of the reliability of the technique is difficult because the statistical properties of the surface return depend not only on surface type (land/ocean) and incidence angle, but on the detailed nature of the surface scattering. In this paper, a formulation of the technique and a description of several surface reference datasets that are used in the operational algorithm are presented. Applications of the method to measurements from the PR suggest that it performs relatively well over the ocean in moderate to heavy rains. An indication of the reliability of...

Theoretical model for scattering of radar signals in K u - and C-bands from a rough sea surface with breaking waves

Abstract: A small-slope approximation (SSA) is used for numerical calculations of a radar backscattering cross section of the ocean surface for both Ku- and C-bands for various wind speeds and incident angles. Both the lowest order of the SSA and the one that includes the next-order correction to it are considered. The calculations were made by assuming the surface-height spectrum of Elfouhaily et al for fully developed seas. Empirical scattering models CMOD2-I3 and SASS-II are used for comparison. Theoretical calculations are in good overall agreement with the experimental data represented by the empirical models, with the exception of HH-polarization in the upwind direction. It was assumed that steep breaking waves are responsible for this effect, and the probability density function of large slopes was calculated based on this assumption. The logarithm of this function in the upwind direction can be approximated by a linear combination of wind speed and the appropriate slope. The resulting backscattering cross section for upwind, downwind and cross-wind directions, for winds ranging between 5 and 15 m s −1 , and for both polarizations in both wave bands corresponds to experimental results within 1–2 dB accuracy.

A geosat altimeter wind speed algorithm and a method for altimeter wind speed algorithm development

Abstract: A Geosat altimeter wind speed algorithm is derived by cross-calibrating Geosat and Seasat altimeter estimates of the normalized radar cross section σ0 and modifying an existing Seasat altimeter wind speed model function to obtain a model function appropriate for Geosat observations. It is argued that the σ0 distribution measured by an altimeter is relatively stable over a sufficiently large geographical region and a long enough time period. Systematic differences between σ0 estimates from two altimeters can therefore be identified based on comparisons of their σ0 histograms. Any such systematic differences can then be corrected using independent σ0 estimates. When this method is applied to the Geosat and Seasat altimeters, a systematic difference between the two σ0 histograms is shown to be consistent with differences between Seasat altimeter and nadir Seasat scatterometer estimates of σ0 deduced independently by a previous study. This supports the conclusions that (1) the σ0 distribution is stable, and (2) the Seasat altimeter estimates of σ0 were miscalibrated. After modifying the existing Seasat altimeter wind speed algorithm to account for this apparent σ0 error, the resulting Geosat estimates of wind speed agree with high-quality buoy observations to within an rms difference of less than 2 m/s.