Effects of Reflection Properties of Natural Surfaces in Aerial Reconnaissance

Abstract

Measurements of the reflecting and polarizing properties of various soils, sands, and vegetation in the visible-and near-ir spectral regions show that dark surfaces polarize the reflected radiation strongly while highly reflecting surfaces have relatively weak polarizing properties. In general, the reflectance of mineral surfaces increases, and the degree of polarization of the reflected radiation decreases, with increasing wavelength and increasing angle of incidence. There is little or no indication of specular reflection from the surfaces for which measurements were made. Introduction of the reflection data into the equation of radiative transfer for clear and slightly turbid models of the earth's atmosphere shows that the upward radiation that would be incident on a high-altitude aircraft or satellite would be dominated by surface-reflected radiation for the red and near-ir regions over highly reflecting surfaces such as deserts, whereas atmospheric scattering is most important for short wavelengths and dark surfaces. Because of polarization effects, atmospheric transmission of optical contrasts is better in one orthogonal intensity component than the other, the difference being sufficient to merit polarizing optics in reconnaissance instrumentation under certain conditions.

Changes in reflectance anisotropy of wheat crop during different phenophases

“…This results in gap effect, while back shadow effect occurs as in forward view angles the sensor captures reflectance from shadowed leaf surfaces. The distinct bowl shapes in BRDF produced from minimum reflectance near nadir and maximum reflectance (hot spot) in backscatter direction have been reported for dense erectopile canopies by other researchers (Coulson, 1966, Jensen and Schill, 2000, Ni et al, 1999. At flowering, when crop canopy achieves more uniformity in height and appearance of heads, BRDF difference diminishes with small angular changes in view zenith (Fig.…”

Inferring the roughness of desert rocky surfaces from their bidirectional reflectance data

“…Desert gypsum and quartz sands display a high reflectance and maximum forward scattering in the optical domain (Coulson, 1966). The forward scattering, as well as the backward scattering characteristics of a dune sand surface and an alkali flat bare soil have been observed by Deering et al (I 990).…”

Resposta espectral de solos em razão do ângulo de visada, da umidade e da rugosidade superficial

“…A relação FRB seco/FRB úmido mostrou-se dependente do comprimento de onda, notadamente no solo Epitaph. (Coulson, 1966).…”

“…Tanto em dados de laboratório (Coulson et al, 1965;Coulson, 1966) quanto nos dados coletados sob condição de campo (Coulson & Reynolds, 1971;Eaton & Dirmhirn, 1979;Kimes, 1983;Kimes & Sellers, 1985;Kimes et al, 1985), a maioria dos solos apresenta um comportamento anisotrópico que é assimétrico em relação à linha do Nadir. O conhecimento desse comportamento (também conhecido como fator de refletância bidirecional ou FRB) é indispensável para a extração de informações sobre os solos de uma dada região a partir de imagens de satélite, principalmente dos sensores que apresentam grande visão angular (e.g.…”

“…Na maioria dos solos, o FRB aumenta quando o ângulo de visada aumenta em relação ao Nadir na direção do retroespalhamento. As areias, entretanto, podem apresentar um comportamento anisotrópico em que o FRB aumenta na direção do espalhamento da energia refletida (Coulson, 1966). O pronunciado pico de refletância na direção do retroespalhamento tem sido atribuído à redução do efeito da sombra em superfícies com elevado grau de rugosidade (Eaton & Dirmhirn, 1979).…”