Paleoclimate Evolution Of Lop Nur Salt-crust Based On Hyperspectral Analysis

In 1972,the image of Landsat-1 satellite in the United States showed that the Lop Nur region had a peculiar "Great Ear" texture feature,and its cause has been widely concerned by scholars.Various sedimentary minerals are formed during the withdrawal process of Lop Nur Lake,they are the carriers of paleoclimate information.The unique salt-crust geomorphology records the process of lake water growth and decline.The study of sedimentary minerals and salt-crusts is of great significance in explaining the origin of “Great Ear” and revealing the environmental changes in arid areas.Based on the hyperspectral data of UAVRSS and used the spectral unmixing technology,combined with the results of field investigation and laboratory parameter measurement,this paper have established the spectral inversion model of sedimentary minerals in salt-crust,in order to study the sedimentary mineral composition and distribution of bright-dark textures,the essential cause of the “Great Ear” feature has been discussed qualitatively and quantitatively.At the same time,the micro-topography,chemical composition and image characteristics of the bright-dark textures of the salt-crust were integrated analyzed by using the orthophoto images and the salt-crust reflectance value.The apparent and essential causes of the texture formation have been carried out.Finally,the climate and environment significance are discussed.The findings of this paper will promote the application and development of UVA hyperspectral remote sensing technology in the arid environment.In addition,it will deepen the understanding of the evolution of arid climate in the Lop Nur regionThe main conclusions of the paper are as follows:(1)It is the first time to using the UAV hyperspectral remote sensing technology to gain the spectral data of the bright-dark textures.Based on the hyperspectral decomposition technology,the paper focuses on the linear unmixing model—SUnSAL.The results of the spectrum inversion model shows that the original residual(res-p)accuracy of the SUnSAL model is less than 0.008,which can better invert the sediment composition characteristics and abundance distribution in Lop Nur Basin,at the same time,analyze the complex surface sediment reflection mechanism at sub-pixel level.(2)The relative spectral abundance of clay minerals,carbonate minerals and cold-warm minerals in typical texture areas fluctuates in the horizontal range.The fluctuation of spectral abundance of chlorite is negatively correlated with the illite/montmorillonite commingled layers.This negative correlation also exists in cold-warm phase minerals.Image texture is essentially related to its sediment composition,which provides objective and direct evidence for the comprehensive study of paleoclimate and environment.(3)It is found that the micro-topography of salt-crust with bright and dark texture is in different development stages.The reflectance of salt-crust is compared and analyzed.The results show that the spectral reflectance and the composition structure of sediment are different according to the salt-crust types.The apparent cause of texture formation is the differences of micro-morphology of salt-crust,and the essential reason is the differences of composition and relative content of sediments.Through the multi-dimensional indicators,it is concluded that "Great Ear" are formed in the alternation of warm-dry,cold-wet seasonal climate or in the climatic change events over the years.