Analyzing the "Ear" feature of a dried up lake based on volume scattering modelling

Lop Nur is a famous dried lake in Xinjiang of northwest China and finally lost its last drop of water in 1960s. It is well known for its “Human Ear Shape” feature in optical remote sensing images. Likewise, “Ear” feature is shown in Synthetic Aperture Radar (SAR) images, and even larger because of penetration effect [1, 2]. There are some explanations about external causes of the “Ear” feature according to the characteristics of the field conditions, however, the fundamental reason of the peculiar feature and the evolution process is still not revealed, and its formation is always a mystery. With the penetration capability, SAR is capable of detecting subsurface targets and materials [3, 4]. The objective of this paper is to analyze the volume scattering mechanism of subsurface and reveal the fundamental reason of “Ear” feature of Lop Nur on SAR images. Two field investigations were conducted in 2006 and 2008 respectively, in order to validate the image interpretation and calculation results. During the first field trip conducted from October 25 to November 8, 2006, a profile along northeast direction was chosen. Every 2 kilometers a soil sample underneath the salt crust was collected. The subsurface samples were put in aluminum specimen boxes sealed with wax to keep original state. Then complex dielectric constants, moisture, soil mechanical composition and chemical composition were measured in laboratory. In 2008, the second field investigation was conducted, in order to obtain more precise soil samples and establish relationships between soil parameters and SAR signatures. Meanwhile, ALOS PALSAR image for Lop Nur was collected, and the Cloude decomposition method was used to extract the volume scattering components, based on which the developed volume scattering model was validated. In this study, the scattering physical mechanisms are discussed based on the results of field investigation. A suitable volume scattering model is used to simulate the contribution of volume backscattering to a certain extent. Validation of the model is also conducted based on the surveying results of field investigation and the results of Cloude decomposition using ALOS PALSAR data, and the fitting effect is relatively good. According to the analysis of the parameters of the model, it is found that salinity at subsurface is the fundamental reason of “Ear” feature, which is strongly correlated with Lop Nur evolution.