Abstract
Satellite remote sensing data, such as moderate resolution imaging spectroradiometers (MODIS) and advanced very high-resolution radiometers (AVHRR), are being widely used to monitor sea ice conditions and their variability in the Bohai Sea, the southernmost frozen sea in the Northern Hemisphere. Monitoring the characteristics of the Bohai Sea ice can provide crucial information for ice disaster prevention for marine transportation, oil field operation, and regional climate change studies. Although these satellite data cover the study area with fairly high spatial resolution, their typically limited cloudless images pose serious restrictions for continuous observation of short-term dynamics, such as sub-seasonal changes. In this study, high spatiotemporal resolution (500 m and eight images per day) geostationary ocean color imager (GOCI) data with a high proportion of cloud-free images were used to monitor the characteristics of the Bohai Sea ice, including area and thickness. An object-based feature extraction method and an albedo-based thickness inversion model were used for estimating sea ice area and thickness, respectively. To demonstrate the efficacy of the new dataset, a total of 68 GOCI images were selected to analyze the evolution of sea ice area and thickness during the winter of 2012–2013 with severe sea ice conditions. The extracted sea ice area was validated using Landsat Thematic Mapper (TM) data with higher spatial resolution, and the estimated sea ice thickness was found to be consistent with in situ observation results. The entire sea ice freezing–melting processes, including the key events such as the day with the maximum ice area and the first and last days of the frozen season, were better resolved by the high temporal-resolution GOCI data compared with MODIS or AVHRR data. Both characteristics were found to be closely correlated with cumulative freezing/melting degree days. Our study demonstrates the applicability of the GOCI data as an improved dataset for studying the Bohai Sea ice, particularly for purposes that require high temporal resolution data, such as sea ice disaster monitoring.
Highlights
The Bohai Sea is a semi-enclosed sea located at approximately 117◦–122◦ E, 37◦–41◦ N in North China (Figure 1)
The sea ice area extracted on 22 December 2012 was validated using the Thematic Mapper (TM) data with a much higher spatial resolution (30 m), and compared to results obtained from the moderate resolution imaging spectroradiometers (MODIS) data with a spatial resolution of 500 m
The sea ice area extracted from both geostationary ocean color imager (GOCI) and MODIS data tend to be overestimated compared to TM data—the sea ice area extracted from the TM data is 3.93 × 103 km2, whereas those extracted from the GOCI and MODIS data are 4.05 × 103 km2 and 4.12 × 103 km2, respectively
Summary
The Bohai Sea is a semi-enclosed sea located at approximately 117◦–122◦ E, 37◦–41◦ N in North China (Figure 1). It freezes every winter for about three to four months from December to the next. The Bohai Sea possesses rich fishery, oil, and gas resources, making the Bohai Rim a critical economic zone in China [1]. Varying Bohai Sea ice conditions severely influence marine navigation, offshore oil exploitation, mariculture, and coastal construction [1,6,7]. Sea ice can be desalinated using proper techniques to produce freshwater for industrial and agricultural consumption, with the Supstoaitneanbitliitayl2t0o18b, 1e0c,oxmFOeRanPEaElRteRrEnVaItEivWe freshwater resource that may help alleviate the severe fres3howf a18ter sesahwoartteargiesionntlhye3r0egPiSoUn,[w8–h1i0c]h. Tahtee cfrhoaznegnepsetruioddieos,f athnedBsoehaaiice Seraesisougercneereasltliymfartoiomn.early December to mid-March
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