| Antarctica is a very special area.Its land area accounts for about 10% of the total land area of the world,and 98% of its area is covered by snow and ice all year round.Under the current global warming trend,the study of the Antarctic ice sheet's mass balance,rapid changes,and its stability is particularly important for global sea level prediction and ocean temperature-salt circulation analysis.Ice-penetrating radar(IPR)is a geophysical detection method that uses radar echoes to study the characteristics of ice and snow media based on electromagnetic wave theory.Because of the low electrical conductivity of ice and the good layering and uniformity of the ice sheet,compared to other geophysical detection methods,ice detection radar has a high penetration capacity and the ability to resolve the internal layers of glaciers.At the same time,it has the characteristics of large amount of collected information and high efficiency.Therefore,ice-penetrating radar is widely used in the scientific investigation of polar ice sheet,and data processing and the study of ice cap structure and temperature become very meaningful based on ice-penetrating radar data.In this paper,based on the high-gain data of the F13R47 a survey line of the Antarctic airborne ice-penetrating radar obtained during the 32 nd Chinese Antarctic scientific research survey,the following five contents were studied: conventional processing of ice-penetrating radar data;radar forwarding;application of variational mode decomposition(Variational Mode Decomposition,abbreviated as VMD)method on airborne ice-penetrating radar data noise reduction;analysis of ice sheet structure based on high gain data of airborne ice-penetrating radar line F13R47a;calculate the average temperature inside the ice sheet using the high gain data of the airborne ice detection radar line F13R47 a.To analyze and interpret the data of airborne ice-detecting radar,preprocessing alone is not enough.It also needs to be further processed by conventional methods to suppress noise and obtain more abundant and accurate information.At present,it mainly refers to the processing method of ground penetrating radar data.In this paper,a small segment of the high-gain data of the pre-processed F13R47 a line is taken for DC removal,band-pass filtering,migration by constant velocity delete mean trace.Good results have been obtained,and the isochronous layer and bedrock surface have become clearer,providing an effective radar data profile for interpretation and analysis.Radar forward modeling is an effective method based on Maxwell's equations to study the propagation of electromagnetic waves in media.It has very important significance in the application and research of geological radar.Based on the electrical properties of the ice sheet,two simple ice sheet models are established: simple layered ice sheet conductivity model and relative permittivity model;layered ice sheet conductivity model and relative permittivity model with simple structure.Then use FDTD method to perform forward simulation to summarize the characteristics of the echo signal generated by the internal structure of a simple ice sheet.VMD is a new method of signal decomposition estimation.This paper introduces it into the noise reduction of ice-penetrating radar data.Using VMD,an adaptive and quasi-orthogonal signal decomposition method,the airborne radar data is decomposed into multiple band-limited quasi-orthogonal intrinsic mode functions(IMF).According to the noise distribution in the IMF component,the IMF mainly containing noise is removed,and the remaining IMF is reconstructed.The method is implemented to process such actual ice radar data,which effectively removes the interference noise in the data,improves the signal-to-noise ratio,and better displays the inner layer information of the ice.The results show that this method can be very well applied to the noise reduction processing of polar ice-penetrating radar data,and provides a better foundation for data interpretation and understanding of ice sheet structure.Compared with foreign countries,Chinese polar scientists started to study the Antarctic ice sheet late.Mainly based on the ice exploration radar data section to study the structure of ice sheet.After introducing the causes and characteristics of the isochronous layer inside the ice sheet,this paper describes the high-gain data profile of the airborne ice-penetrating radar line F13R47 a after conventional processing,and analyzes the ice sheet structure.The height of the ice sheet surface gradually increased from more than 700 meters to more than 3600 meters along the survey line,but the slope of the ice sheet surface gradually became slower.The continuity of the isochronous layer inside the ice sheet of the entire survey line is better,and the shape has better consistency with the bedrock surface,and there are fewer unconformity surfaces.It shows that the overall sedimentary environment of the ice sheet is relatively stable,and is less affected by the disturbance of ice flow and wind erosion.The overall elevation of the bedrock face does not change much,but there are local uplifts and valleys with large elevation changes.The flow of polar ice is related to temperature,and understanding the temperature of the ice sheet is very helpful to understand the ice flow.Because the attenuation of the electromagnetic waves emitted by the airborne ice-penetrating radar in the ice sheet is related to the temperature of the ice sheet and is more sensitive,the average temperature inside the ice sheet can be calculated from the ice-penetrating radar data.Unfortunately,no one in China has carried out research in this area.In this paper,the airborne ice-penetrating radar data obtained in China is used to estimate the average attenuation rate of electromagnetic waves in the ice sheet,and then to calculate the average temperature of the ice sheet.It can provide a new constraint for the Antarctic ice sheet temperature model,which is conducive to subsequent ice flow analysis. |
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