Abstract
When the Haiyang-2B (HY-2B) was launched into space to form a star network with the Haiyang-2A (HY-2A), it provided new data sources for the sea ice research of the Earth’s polar regions. The ability of altimeter echoes to distinguish sea ice and sea water is usable in operational ice charting. In this research study, the level 1B (L1B) data of HY-2A/B altimeter from November 2018 was used to analyze the altimeter waveforms from the polar regions. The Suboptimal Maximum Likelihood Estimation (SMLE) and Offset Center of Gravity (OCOG) tracking packages could maintain the waveform characteristics of diffused and quasi-specular surfaces by comparison. Also, they could be utilized to distinguish sea ice from seawater in the polar regions. It was determined that the types of echoes obtained from the seawater were diffuse. Also, some “ocean-like” waveform data had existed for the old ice formations in the Arctic regions during the study period. The types of echoes obtained from Arctic sea ice were found to be mainly quasi-specular. In the present study, three methods (Threshold segmentation, K-nearest-neighbor (KNN), and Lib-Support Vector machine (LIBSVM)) with four waveform parameters (Automatic Gain Control (AGC) and Pulse Peaking (PP) values of the Ku and C Bands) were adopted to distinguish between the sea ice and seawater areas. The accuracy rate of the separation results for the LIBSVM except band Ku from HY-2B ALT was found to be less than 40% in Antarctic. Meanwhile, the other two methods were observed to have maintained the waveforms correctly at accuracy rates of approximately 80% in Antarctic and the Arctic. In addition, the observed distinguishing errors were located in the regions of the old ice of the Arctic region. In addition, due to the summer melting processes, the large number of ice floes and the snow cover had made it difficult to distinguish the seawater and sea ice in the Antarctic regions.
Highlights
Sea ice plays a key role in sea-air interaction processes, as well as shortwave radiation transference between the Earth’s atmosphere and its marine regions
In the edges of sea ice (Figure 12F,G), the Pulse peaking (PP) values from some nilas were less than 3 whose waveform similar to seawater
The biggest differences between the radar altimeters used by Zygmuntowska and Drinkwater were that the footprints on the ground were much smaller than the ground footprint of the HY-2A/B ALT
Summary
Sea ice plays a key role in sea-air interaction processes, as well as shortwave radiation transference between the Earth’s atmosphere and its marine regions. Sea ice reflects 80% to 90% of the shortwave radiation from the sun and prevents the long-wave radiation transfer from marine regions to the atmosphere [1]. HHee ffoouunndd tthhaatt tthhee vvaalluueess ooff tthhee AAuuttoommaattiicc GGaaiinn CCoonnttrrooll ((AAGGCC)) oonn tthhee ssuurrffaacceess ooff tthhee iiccee ffoorrmmaattiioonnss wweerree llaarrggeerr tthhaann tthheesseeaaiiccee. AAtt tthhee ssaammee ttiimmee,, hhee ddeefifinneedd aann iinnddeexx wwhhiicchh ccoommbbiinneedd AAGGCC aanndd AAvveerraaggee AAttttiittuuddee//SSppeeccuullaarr GGaattee ((AAAASSGG)) wwhhiicchh pprreesseenntteedd ddiiffffeerreenntt vvaalluueess oonn ddiiffffeerreennttssuurrffaacceess. Since the previous related studies had mainly used the band Ku, with only a few studies adopting the HY-2 ALT data to distinguish between sea ice and seawater, this study used the two different bands to complete the experimental processes. This study was able to successfully distinguish the sea ice and seawater based on the above-mentioned research results
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