Adjacency effects on imaging by surface reflection and atmospheric scattering: cross radiance to zenith

Abstract

An analytical solution is discussed for the nadir radiance as measured from a satellite, based on a simplified single-scattering approximation in which the scattered radiation is not subject to extinction. In the solution, terms can be identified as due to a reflection from the vicinity of the object pixel, and, respectively, (1) upward scattering to zenith above the object pixel, and (2) downward scattering from the entire atmosphere to the object pixel. The first term is referred to as the cross radiance, the second as the cross irradiance. The cross radiance is proportional to the forward scattering optical thickness, as defined, and the cross irradiance to the backscattering optical thickness. The cross radiance usually constitutes the predominant effect. The effect, even at low atmospheric turbidity, can be large enough to constitute a significant fraction of the radiance registered at the satellite, thus hampering determination of spectral signature of the object pixel or identification of pixels with inherently the same spectral signature. Explicit expressions and computer solutions for the cross radiance from annular or from rectangular reflecting areas are presented. The effect depends on the height distribution and on the sharpness of the forward peak of the scattering particles.

Assessment of Atmospheric Correction Methods for Sentinel-2 MSI Images Applied to Amazon Floodplain Lakes

“…These multiple scattering regimes of photons from adjacent areas modify the spectral signal of the target pixel. The magnitude of these effects depends on the: (i) atmospheric turbidity, at a particular aerosol scattering phase function; (ii) spectral contrast of the surface reflectance; and (iii) sensor characteristics [61][62][63]. The influence of atmospheric scattering on adjacency effects increases as a result of the high optical thickness [64,65].…”

Vegetation, topography and daily weather influenced burn severity in central Idaho and western Montana forests

“…We established the minimum distance of 127.5 m as it is the rounded minimum distance required such that no two points were sampled from adjacent Landsat pixels. Moreover, setting this minimum sampling distance precluded the confounding factor of spectral mixing between pixels that are adjacent to one another, known as the adjacency effect (Otterman andFraser 1979, Jianwen et al 2006). Random points that fell within areas of MTBS's ''Non-processed Area Masks'' were removed from analysis; these areas are generally associated with Landsat 7 scan-line corrector error lines, v www.esajournals.org cloud cover, cloud shadow, and other data gaps.…”

Role of adjacency effect in the remote sensing of aerosol

“…Nonhomogeneity of surface gives rise to horizontal fluxes of radiation in the atmosphere, directed from the brighter surface areas to the darker areas. As a result, after several instances of scattering in the atmosphere, some of the photons reflected from the bright surface may be detected over the dark pixels (adjacency effect) [Otterman and Fraser, 1979]. In satellite images these 3-D radiation effects appear as blurring of the fine spatial structure of the surface and reduction of the image contrasts [Mekler and Kaufman, 1980;Pearce, 1977].…”