Space-borne radar observation of near-surface wind effect on anomalously highly-directional backscattering of radio waves from Aeolian processes of sand and dust transporting in desert regions

Abstract

Aeolian process of sand and dust transporting is known to form the near-ground surface structures over vast territories and fill the atmosphere up with suspended aerosols-like dust particles which are spread then by winds over long distances. The presence of atmospheric dust in the planet's environment is one of the factors affecting the temperature and climatic conditions of vast regions of the Earth. A number of publications (Ivanov et al., 2015; Ivanov et al., 2016; Ivanov et al., 2016; Ivanov et al., 2018) analyze the revealed effect of anomalously highly(narrow) directed backscattering of radio waves which manifests itself in radar remote sensing (in range of local irradiation angles θ ≈ 31°÷32°) in areas covered with deep sand. At the same time, there is no specific data available from published studies investigating the impact of the near-surface wind on anomalously highly-directional backscattering of radio waves based on the results of radar remote sensing researches of Aeolian sand and dust transport processes in desert regions that, in turn, could have been used later to determine the parameters of such transport process. This article presents the results of analysis of the data obtained from long-term studies of desert regions of El-Djuf, Akshar and Trarza in Mauritania by means of space-borne SAR Envisat-1. The purpose of the analysis was actually to identify the specifics of the effect that the near-surface wind has on the anomalously highly-directional backscattering of radio waves which is identified by radar based researches of Aeolian processes of sand and dust transport in desert regions, so can be used for remote determination of such transportation parameters.

Modeling of radar scattering by aeolian desert landforms

“…This leads to a limitation of the particle bounce amplitude and actually creates a layer of negatively charged particles and dust at a height of 2-3 cm (Kok et al, 2008;Namikas, 2003;Greeley et al, 1996;Ivanov et al, 2015b), which repeats the shape of the in homogeneity growing on the surface. The normalized radar cross-section of this layer, according to Envisat-1 SAR data, is very close to the values obtained by measuring the angular scattering pattern of radio waves of the same range by an ionized particle flux in fluorescent lamps (Bychkov et al, 2020a;Bychkov et al, 2020b;Tajudin, 2014). Since ionization processes are observed only in liquids and gases, for an electrified sand-dust layer with similar scattering characteristics, we will further use the term "electrified" layer.…”

“…As primary data in this paper, we used the generalized results of processing and analysis of satellite radar images of the Amatlich erg near the village of Akzhuzht in Mauritania (Ivanov et al, 2015a;Ivanov et al, 2015b;Ivanov et al, 2016;Ivanov, 2018;Bychkov et al, 2020a;Bychkov et al, 2020b). As a result, the following regularities were determined in the observation and in the parameters of ANDBR: a) ANDBR is confidently observed on the erg surface in the autumn-winter period, when the northeast wind blows regularly at a speed of 2-8 m/s (Fig.…”

“…At the same time, simulation of scattering from aeolian structures in the Sahara Desert, using Ku-and S-band scatterometer data (ESCAT, NSCAT, QSCAT, TRMM-PR) (Stephen et al, 2005) and direct measurements of the normalized radar cross-section (NRCS) σ o (Williams et al, 2004), showed values σ o lower by 6-10 dB compared to the data of RCS surveys in the same regions, performed using the Envisat-1 SAR, SLRAR Cosmos-1500 and Sich-1 (Ivanov et al, 2015a;Ivanov et al, 2015b;Ivanov et al, 2016;Ivanov, 2018;Bychkov et al, 2020a;Bychkov et al, 2020b). Such a discrepancy indicates insufficient knowledge of the nature of the radio waves scattering by the structures created by the wind on the desert surface.…”

“…To date, a wide range of experimental and theoretical works has been carried out to study the nature of the formation of such structures and the transport of dustsand mixture into the atmosphere under the influence of wind (Kok et al, 2012;Kok et al, 2008;Stow, 1969;Namikas, 2003;Greeley et al, 1996;Schmidt et al, 1998;Malinovskaya, 2019). Methods for remote satellite monitoring of these phenomena have also been developed (Herrmann et al, 1999;Middleton et al, 2001;Ivanov et al, 2015a;Ivanov et al, 2015b;Ivanov et al, 2016;Ivanov, 2018;Bychkov et al, 2020a;Bychkov et al, 2020b;McHone et al, 1996;Stephen et al, 2005).…”

“…These RI were obtained by using the Cosmos-1500 sidelooking real-aperture (SLRAR) X-band satellite radar. The studies were continued using the Sich-1 X-band SLRAR and the Envisat-1 S-band synthetic aperture radar images (Ivanov et al, 2015a;Ivanov et al, 2015b;Ivanov et al, 2016;Ivanov, 2018;Bychkov et al, 2020a;Bychkov et al, 2020b). In 1994, multi-frequency and multi-polarization studies of the Sahara regions were carried out using the C/X-SIR-C/X-SAR space radar laboratory on board the Shuttle Endeavor (McHone et al, 1996).…”