| Summary: | 학위논문 (박사)-- 서울대학교 대학원 : 지구환경과학부, 2014. 2. 김덕진. This thesis presents an overview of the interactions between microwaves and physical properties of sea ice and snow, such as the dielectric constant and surface roughness, in order to successfully measure sea ice thickness from polarimetric radar systems. Using a ground-based scatterometer system and various microwave scattering models, polarimetric backscattered signatures from sea ice and snow were investigated as evidence of the evolution of the physical properties during the freezing and melting seasons. Based on these results, the optimum method for measuring the thickness of sea ice covered with snow using polarimetric SAR data was explored via numerical simulations and experimental measurements. Experiments conducted using the ground-based scatterometer system as well as the in-situ measurements showed that most of the polarimetric signatures (C-band) with relatively high incidence angles (i.e., about 40°) can be backscattered from the interface between snow cover on sea ice and the surface of the sea ice over the freezing season. Microwaves can penetrate the snow cover during this season owing to the lower dielectric properties of the snow cover (about 1.25). Conversely, the signatures were predominantly backscattered from the surface of the snow cover during the melting season due to high dielectric properties induced by surface melting water. For the freezing season, the in-situ measurements and numerical simulations showed that the number of polarimetric signatures backscattered within the sea ice volume can increase with sea ice growth due to evolutions of the dielectric properties induced by the desalination process, and the surface roughness of sea ice can increase with sea ice growth due to superimposed and ridging processes. Based on these observations, the relationship between the depolarization effects of polarimetric signatures (C- and X-band) and sea ice thickness was investigated using various numerical simulations and a case study. A strong correlation was found between the in-situ sea ice thickness and the SAR-derived depolarization factors (i.e., the co-polarized correlation and cross-polarized ratio). These results clearly demonstrate a one-to-one relationship between the thickness and the depolarization factors, which further suggests that the depolarization factors could be effective parameters in measuring the thickness of snow-covered sea ice with space-borne polarimetric SAR data Table of Contents Chapter 1. Introduction 1 1.1. Overview 1 1.2. Remote sensing of ice and snow 3 1.3. Motivation and Objectives of this thesis 11 Chapter 2. Polarimetric microwave remote sensing systems 13 2.1. Ground Based POLarimetric SCATterometer (GB-POLSCAT) 13 A. Set-up of GB-POLSCAT 14 B. System calibration of GB-POLSCAT 16 B.1. Basic concept of the system calibration 16 B.2. Conventional system calibration 18 C. New system calibration of GB-POLSCAT 21 C.1. Background 21 C.2. New technique to extract radar distortions 21 C.3. Validation using field experiments and numerical simulation 21 2.2. Space-borne SAR systems 30 A. RADARSAT-2 and TerraSAR-X 30 B. Radiometric calibration of the SAR systems 33 B.1. Background 33 B.2. Backscattering coefficient computation of TerraSAR-X and RADARSAT-2 33 Chapter 3. Polarimetric signatures characterized by scattering features from sea ice and snow 42 3.1. Background 42 3.2. Polarimetric scattering features of snow 49 A. Dielectric properties of snow 49 B. The scattering features from snow 55 3.3. Polarimetric scattering features of sea ice 63 A. Dielectric properties of sea ice 63 B. Surface roughness of sea ice 70 C. The scattering features from sea ice 74 3.4. Depolarization effects based on the polarimetric scattering features of sea ice 76 A. Numerical experiments of the depolarization effects due to surface scattering from rough surface 78 B. Numerical experiments of the depolarization effects due to volume scattering within sea ice layer 83 C. Field experiments of the depolarization effects due to volume scattering within ice layer 92 Chapter 4. Measurement of sea ice thickness using space-borne SAR data in the Arctic Ocean 102 4.1. In-situ measurements and SAR data acquisition 102 4.2. Depolarization-to-sea ice thickness relationship using space-borne SAR data 108 Chapter 5. Conclusion 111 5.1. Summary 111 5.2. Discussion 113 Appendix 115 Reference 127 Doctor
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