Subglacial Environment Analysis Based On Airborne Ice-sounding Data

The Antarctic ice sheet is the largest continental ice sheet on earth,and its mass blance and stability have an important impact on global sea level change,water circulation and atmospheric thermal cycling.The subglacial environment of the Antarctic ice sheet,as the internal feature of the ice sheet,is a key factor affecting the mass balance and stability of the ice sheet.On the one hand,the mass balance and stability of the Antarctic ice sheet have been difficult to predict due to the lack of detailed subglacial environment data and data analysis results.High-resolution icesounding radar is the main method to detect subglacial environment data.Therefore,in order to obtain subglacial environment data,the original ice-sounding data obtained by ice-sounding radar should be processed first to obtain high-resolution ice-sounding radar profile data of ice sheet.On the other hand,the relationship of age-depth of ice core is the key to using deep cores revealed the ancient climate,and the the spatial correlation of ice-sounding data associated with the relationship between age-depth of ice core in different sits.Therefore,in order to obtain continuous and accurate subglacial environment data and conduct analysis and research on it,it is necessary to improve the spatial correlation of high-resolution ice-sounding data processing results.Then,the high spatial correlation and high-resolution ice-sounding radar profile data obtained from ice-sounding data processing are used to extract and analyze the subglacial environment data.In the subglacial environment,ice flow controls the material budget of the ice sheet and is a key factor affecting the mass balance and stability of the Antarctic ice sheet.It is the product of the balance between gravity and drag,which is mainly influenced by the roughness of bed.Therefore,quantitative analysis of bed roughness is regarded as an important research direction in subglacial environmental analysis,which is of great value to the follow-up research on the mass balance and stability of the Antarctic ice sheet,and is of great significance to the study of future evolution of the Antarctic ice sheet.In this study,the propagation mode of radar signal in multiple media,the relationship between spatial correlation of ice-sounding data and length of synthetic aperture,the principle of wavelet transform and decomposition and reconstruction of subglacial terrain are analyzed.The research work focuses on the imaging processing of ice-sounding data based on spatial correlation and the quantification method of bed roughness.The main work and innovative contributions of this study are as follows:(1)To conquer the phenomena of refraction and wavelength change of icesounding radar signal when passing through the ice layer,by modifying the echo time and geometric relationship of ice-sounding radar in the case of multiple media,the fast back-projection algorithm is extended to multiple media,and an ice-sounding radar imaging algorithm based on fast back-projection is proposed,which solves the problem that the existing focused ice-sounding radar imaging algorithm based on time domain can not process the high-resolution imaging results efficiently.Furthermore,in view of the impact of the spatial correlation of imaging results on the subsequent extraction and analysis of subglacial environment,by adding the calculation of spatial correlation and the relationship formula between synthetic aperture length and spatial correlation,the spatial-correlation-based ice-sounding radar imaging algorithm using fast back-projection is proposed,which solves the problem that the imaging results of existing ice radar imaging algorithms do not consider spatial correlation.(2)On the basis of the ice-sounding data results that using the spatial-correlationbased ice-sounding imaging algorithm using fast back-projection to process icesounding data,aiming at the fixed scale moving window and the principle of multiscale roughness quantization in frequency domain roughness quantization,an adaptive two-parameter roughness quantization method is proposed by analyzing the results of frequency domain roughness quantization methods under different scales in different terrain,It solves the problems that the existing frequency domain roughness quantization methods have different roughness results under each single scale,small multi-scale roughness range and too fast local change of the results.(3)Based on the spatial-correlation-based ice-sounding radar imaging algorithm using fast back-projection and the adaptive two-parameter roughness quantization method proposed above,in view of the current lack of detailed data and analysis results of the subglacial environment under the Antarctic ice sheet,the ice-sounding data imaging processing and bed roughness quantization algorithm are applied to the Antarctic ariborne ice-sounding data,to achieve the purpose of providing detailed data support for the follow-up study of the material balance and stability of the Antarctic ice sheet.