Scattering Mechanisms for the “Ear” Feature of Lop Nur Lake Basin

Abstract

Lop Nur is a famous dry lake in the arid region of China. It was an important section of the ancient "Silk Road", famous in history as the prosperous communication channel between Eastern and Western cultures. At present, there is no surface water in Lop Nur Lake basin, and on SAR (Synthetic Aperture Radar) images, it looks like an "Ear". The objective of this paper is to interpret the Lop Nur phenomenon from the perspective of scattering mechanisms. Based on field investigation and analysis of sample properties, a two-layer scattering structure is proposed with detailed explanations of scattering mechanisms. In view of the rough surface, the MIEM (Modified Integral Equation Model) was introduced to represent air-surface scattering in Lop Nur. Then, a two-layer scattering model was developed which can describe surface scattering contribution. Using polarimetric decomposition, validations were carried out, and the RMSE (root mean square error) values for the HH and VV polarizations were found to be 1.67 dB and 1.06 dB, respectively. Furthermore, according to model parametric analysis, surface roughness was identified as an apparent reason for the "Ear" feature. In addition, the polarimetric decomposition result also showed that the volume scattering part had rich texture information and could portray the "Ear" feature exactly compared with the other two parts. It is maintained that subsurface properties, mainly generating volume scattering, can determine the surface roughness under the certain climate conditions, according to geomorphological dynamics, which can help to develop an inversion technology for Lop Nur.

Salt Content Distribution and Paleoclimatic Significance of the Lop Nur “Ear” Feature: Results from Analysis of EO-1 Hyperion Imagery

“…Lop Nur, as the "drought pole" of the world, has attracted a great deal of attention from researchers studying environmental evolution and investigating the background of the natural environment in northwestern China [2][3][4]. The drying process in Lop Nur is related to environmental evolution because it may indicate variations in precipitation and evaporation in response to climate conditions.…”

Marine Coastline Polygonal Ridges and Surface Roughness Development on a Salt-Crusted Playa: Recognition by Structure-from-Motion Photogrammetry

“…RMS height and correlation length are two parameters which are widely applied in traditional measurements of surface roughness [14]. However, because just one line on a surface is measured and used to extrapolate characteristics of a whole area in these methods, they are regarded as useful but insufficient.…”

“…As a result, the additional algorithm proposed by Hobson [15] is used to quantify the roughness of a surface, as follows: roughness = surface area floor area . (14) In this expression, surface area refers to the proportion of the surface encompassed by a DEM, while floor area is the horizontally occupied area of the same surface. The unit of surface area and floor area should be the same (e.g., both in m 2 or in cm 2) ; therefore, the roughness is a ratio without unit.…”

“…where m and n are the number of rows and columns in the DEM, and 1 cm 2 is the area of a grid cell. Thus, by applying the results from Equations (17) and (18) to Equation (14), site roughness can be estimated. It is worth noting that the same unit of length should be used for both surface and floor area, and the same frame size, 100 × 2400 pixels in this research, should be adopted for DEMs in parameter calculation.…”

Detecting the Depth of a Subsurface Brine Layer in Lop Nur Lake Basin Using Polarimetric L-Band SAR

“…However, Lop Nur has completely dried up during the 20th century, leaving earshaped concentric strips (interchanging bright-grey appearance) visible in remote sensing images ( Figure 1) [4][5][6]. Many assumptions have been made about its formation, but they remain to be proven by scientific evidence, and therefore its formation has remained a mystery [7]. It has been called the "Drought Pole" and the "Sea of Death" because of its extremely dry conditions and poor accessibility [6].…”