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引用本文:

DOI:

10.11834/jrs.20210131

收稿日期:

2020-04-29

修改日期:

2021-03-29

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FY3B/MWRI北极海冰密集度ASI算法反演研究
李乐乐, 王晓雨, 陈海花, 苏洁, 管磊
中国海洋大学
摘要:

近年来,由于“北极放大”的气候效应,使得北极海冰变化受到了越来越多的关注。而作为海冰被动微波遥感的主要参数,海冰密集度能够表征海冰的主要状态,可用于指导极区走航以及进行不同尺度的海冰变化研究。通过该参数还可以计算出海冰面积、海冰范围等信息,对极区冰情预测以及气候变化研究具有重要意义。本研究探讨了如何利用FY3B/MWRI(FengYun-3B/MicroWave Radiometer Imager)较高分辨率通道数据来反演北极地区海冰密集度。基于ASI(ARTIST(Arctic Radiation and Turbulence Interaction STudy)Sea Ice)算法,本研究通过改进算法系点值的方法反演了北极地区海冰密集度,并将反演结果与MWRI海冰密集度产品进行了对比。首先利用Aqua/MODIS(Moderate Resolution Imaging Spectroradiometer)反射率数据获得的海冰密集度对二者进行了验证。结果表明,本研究选用的新系点值ASI算法在全部数据集范围内的平均偏差与MWRI海冰密集度产品相当,但标准偏差和均方根误差均较之明显降低,且在海冰密集度低于95%时精度远高于MWRI产品。然后将二者与不莱梅大学的SIC_UB(Sea Ice Concentration from University of Bremen)海冰密集度产品进行了对比,其中本研究反演海冰密集度与SIC_UB产品的平均偏差和标准偏差分别为3.3%和10.6%,低于MWRI产品与SIC_UB产品之间的5.9%和16.4%。最后,对本研究反演结果、MWRI产品、NSIDC/AMSR-E(National Snow and Ice Data Center/Advanced Microwave Scanning Radiometer-EOS)产品以及SIC_UB产品的日均海冰密集度和海冰面积、海冰范围进行了时间序列对比,结果表明本研究反演海冰密集度的数值在三种统计方式下均显著低于MWRI产品,且较之更接近NSIDC/AMSR-E和SIC_UB产品。本研究利用国产卫星亮温数据反演的北极地区海冰密集度具有较高空间分辨率和较高精度,有利于北极地区气候变化的长时间序列研究。

Retrieval of sea ice concentration in the Arctic from FY3B/MWRI observations by ASI algorithm
Abstract:

Objective The change of Arctic sea ice has attracted much attention among climate researchers recently due to the climate effect of “Arctic Amplification”. As the main parameter of passive microwave remote sensing of sea ice, sea ice concentration can characterize the sea ice conditions which can be used to guide the polar navigation and study the sea ice change in different scales. The sea ice area and sea ice extent can also be calculated by sea ice concentration, which is of great significance for the forecast of polar sea ice conditions and the study of climate change. This paper discusses how to use the high resolution channels of FY3B/MWRI (FengYun-3B/Microwave Radiometer Imager) to retrieve sea ice concentrations in the Arctic. Method Based on ASI (ARTIST (Arctic Radiation and Turbulence Interaction Study) Sea Ice) algorithm, the Arctic sea ice concentration is calculated in this study by improving the tie points of the algorithm. According to the cross calibration of brightness temperatures between the FY3B/MWRI and the Aqua/AMSR-E (Advanced Microwave Scanning Radiometer-EOS), the differences between the two brightness temperature data are between ±4K which will result in a maximum bright temperature difference of 8K. Therefore, this study firstly sets the variation range of the tie points for FY3B/MWRI centered on the original values of the ASI algorithm to 11.7±8K for sea ice and 47±8Kfor open water, separately, with a step length of 1K. After combination, 289 series of point value combinations are obtained. Then the sea ice concentrations corresponding to each set of tie points are compared with the AMSR-E L3 product, and the tie points corresponding to the smallest deviation of the two data sets are select. According to the tie points determined above, this study calculated the Arctic sea ice concentrations based on FY3B/MWRI brightness temperatures, hereinafter referred to as RSIC (retrieved sea ice concentration). Result The retrieved sea ice concentrations of this study, RSIC, are compared with the MWRI Level 2 sea ice concentration product (hereinafter referred to as MWRI). Firstly, the sea ice concentrations obtained from the Aqua/MODIS (Moderate Resolution Imaging Spectroradiometer) reflectivity data from July to September 2011 are used to verify the two data sets. The results show that for the bias of RSIC is equivalent compared to the MWRI product, but the standard deviation and root mean square error are significantly reduced. While for the areas that the sea ice concentration is lower than 95%, the accuracy of RSIC is much higher than the MWRI product. Then, the two sea ice concentration data sets are compared with the sea ice concentration product from the University of Bremen (SIC_UB). The bias and the standard deviation between RSIC and SIC_UB are 3.3% and 10.6%, respectively, which are lower than the values between the MWRI and SIC_UB products: 5.9% and 16.4%. Finally, the time series of daily averaged sea ice concentration, sea ice area and sea ice extent from RSIC, MWRI, SIC_UB and NSIDC/AMSR-E (National Snow and Ice Data Center/ Advanced Microwave Scanning Radiometer-E) sea ice concentration products are compared. The results show that the values of RSIC are significantly lower than that of the MWRI product in three statistical methods and much closer to the AMSR-E and SIC_UB products. Conclusion In this study, based on the brightness temperatures from FY3B/MWRI high frequency channels, the sea ice concentrations in the Arctic region are retrieved. Compared with the FY3B/MWRI L2 sea ice concentration product, the sea ice concentrations in this study have higher spatial resolution and better accuracy, which is conducive to the long-time series study of climate change in the Arctic.

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