Impact of the near-field effects on radiative transfer simulations of the bidirectional reflectance factor and albedo of a densely packed snow layer. (January 2020)

• Record Type: Journal Article
• Authors: Pohl, Christine; Rozanov, Vladimir V.; Wendisch, Manfred; Spreen, Gunnar; Heygster, Georg
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 241(2020)
• Publication Date: 2020-01
• Subjects: Near-field effects -- Far-field approximation -- Dense particulate snow layer -- Radiative transfer; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2019.106704
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: The far-field assumption is evaluated for a dense particulate snow layer. The impact of near-field effects on simulated snow BRF and albedo is estimated. Droxtals satisfactorily describe the reflection properties of a natural snow layer. The near-field effects in snow are negligibly small. The simulation of snow BRF and albedo under the far-field assumption is justified. Abstract: Phenomenological radiative transfer models commonly assume that particles in media reside in each other's far zone and, thus, are defined by their single-scattering properties. This so called far-field assumption becomes questionable for dense particulate snow layers since the location of the snow grains inside is close and in each other's near zone. Electromagnetic interactions among the particles can occur, which potentially change their single-scattering properties. In this paper, the near-field effects in radiative transfer simulations of the snow surface bidirectional reflectance factor (BRF) and the albedo of a snow layer in the wavelength range of 300 - 2500 nm are investigated using the phenomenological radiative transfer model SCIATRAN. The snow layer is composed of densely packed snow grains of droxtal shape with a maximum dimension of 60 µm. The snow grain shape assumption is justified by the good agreement of the simulated top of atmosphere BRF with satellite measurements over a pure snow surface in Greenland. To evaluate the error of the far-field assumption, the single-scattering properties of the dense particulate snow layer has been modified according to the dense-medium light-scattering theory. By applying the far-field approximation, the BRF is overestimated by less than 0.039 % at forward-scattering angles and underestimated by less than 0.006 % at backscattering angles, respectively. The albedo of the dense particulate snow layer is overestimated by less than 0.012 %. In the considered case, the near-field effects on the snow surface BRF and the albedo of radiative transfer simulations appear negligibly small. Consequently, the simulation of snow surface BRF and albedo in the wavelength range of 300 - 2500 nm by phenomenological radiative transfer models under the far-field assumption is well justified.