A statistical sea surface specular BRDF (bidirectional reflectance distribution function) model is developed that includes mutual shadowing by waves, wave facet hiding, and projection weighting. The integral form of the model is reduced to an analytical form by making minor and justifiable approximations. The new form of the BRDF thus allows one to compute sea reflected radiance more than 100 times faster than the traditional numerical solutions. The repercussions of the approximations used in the model are discussed. Using the analytical form of the BRDF, an analytical approximation is also obtained for the reflected sun radiance that is always good to within 1% of the numerical solution for sun elevations of more than 10 degrees above the horizon. The model is validated against measured sea radiances found in the literature and is shown to be in very good agreement.
The Rough Evaporation Duct experiment aimed to see if the effects of ocean waves account for errors in modeling the ranges at which radar and infrared can detect low-flying targets.
When radars first came into operation during the late 1930s, they were not expected to detect targets much beyond the geometrical horizon. These early radars, operating at a wavelength of 13 m, generally met expectations. As new radars were rapidly developed, operating at shorter and shorter wavelengths for better target detection, observations of anomalous propagation effects became more frequent. When 10-cm radars were installed along the south coast of England during World War II, they were often able to see the coast of France, even though the coast was well beyond the geometric horizon (Booker 1948). These anomalous propagation effects also became more pronounced as the operating area became more tropical. For example, a 1.5-mwavelength radar operating in Bombay, India, re-
[1] Sea surface slope variances are obtained by inverting narrowband (444, 501, 677, and 864 nm) Sun glint radiance measurements using a detailed analytical specular sea surface bidirectional reflectance distribution function (BRDF) that includes mutual wave shadowing and hiding. The resulting data set spans a wide range of environmental conditions including wind speeds from 0.5 to 13.5 m s À1 and many different viewing and source geometries. Analysis against wind speed and atmospheric stability produces trends similar to those found in previous studies, as well as finer tendencies that were formerly difficult to detect. Furthermore, the detailed nature of the BRDF model used in the analysis permits an investigation of the correlation of the statistics with viewing geometry, revealing a strong relationship between sensor elevation and measured slope variance, especially at grazing angles.Citation: Ross, V., and D. Dion (2007), Sea surface slope statistics derived from Sun glint radiance measurements and their apparent dependence on sensor elevation,
Results of over 300far JR and mid JR transmission measurements taken during several EOPACE (BO Propagation Assessment in Coastal Environments) intensive operational periods (lOP's) over the low-level 15 km transmission path across San Diego bay are presented. A thorough comparison with calculations obtained using simultaneously measured bulk meteorological parameters with the IR Boundary Layer Model (IRBLEM), illustrate the effects thatrefractance, aerosol extinction and molecular extinction can have on the transmission. Discrepancies between the transmission measurements and the model's predictions are identified and investigated by varying various model parameters, and looking at available measured aerosol size distributions and refraction measurements over the path. Comparison with the measured transmissions are reasonably good and show that the total transmission depends critically on all three effects, with the molecular transmittance depending upon the water vapour density and the characteristics of the JR source and detector, the aerosol transmittance upon the visibility (aerosol concentration), and the refractive effects on the stability of the marine boundary layer or the virtual potential air-sea temperature difference.
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