首页 >  2020, Vol. 24, Issue (8) : 1032-1044

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10.11834/jrs.20208436

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2018-11-07

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FY-3B/MWRI与GCOM-W1/AMSR-2亮温数据在北极地区的交叉定标
唐晓彤1,陈海花1,管磊1,2,李乐乐1
1.中国海洋大学 信息科学与工程学院海洋技术系, 青岛 266100;2.青岛海洋科学与技术国家实验室 区域海洋动力学与数值模拟功能实验室, 青岛 266071
摘要:

为了使搭载在风云三号B星上的微波成像仪MWRI(Microwave Radiation Imager)与搭载在GCOM-W1(Global Change Observation Mission 1st-Water)卫星上的AMSR-2(Advanced Microwave Scanning Radiometer 2)的数据可以衔接使用,并为以后FY-3B/MWRI北极地区遥感参数反演研究提供基础,以GCOM-W1/AMSR-2数据为对比数据,北极海洋区域为研究区域,对两传感器对应的10个通道的升、降轨亮温数据进行交叉定标。首先,对MWRI和AMSR-2各通道逐月在研究区域进行偏差分析;其次,对MWRI和AMSR-2各通道逐月在海冰区域和开阔水域进行偏差分析;最后,对MWRI和AMSR-2各通道逐月在研究区域进行交叉定标,并对定标结果进行评价。研究结果表明:(1)MWRI各通道亮温数据小于AMSR-2,且相同频率下,垂直极化各通道逐月平均偏差的绝对值大于水平极化各通道,升、降轨数据在各通道的差异较小,逐月平均偏差的差值小于1 K;(2)在海冰区域,升、降轨各通道逐月平均偏差相差小于1 K,在开阔水域则介于0—1.5 K;(3)通过进行线性回归分析,MWRI和AMSR-2各通道相关系数大于0.99,具有强相关性,并得到升、降轨各通道各月份交叉定标的斜率和截距;(4)定标后MWRI的亮温值与AMSR-2的亮温值一致性较好,说明交叉定标的效果较好。

Intercalibration of FY-3B/MWRI and GCOM-W1/AMSR-2 brightness temperature over the Arctic
Abstract:

Microwave radiometers have been widely applied in polar region research because of their all-weather and all-time capabilities. Microwave Radiation Imager (MWRI) on FY-3B is the microwave radiometer of China’s own research and development and has aroused widespread concern. Long time series of earth observation data records play an important role in the research of earth environment changes and trends. The Arctic region is used as the study area and the data of Advanced Microwave Scanning Radiometer-2 (AMSR-2) on Global Change Observation Mission 1st-Water (GCOM-W1) are considered the standard data in providing the intercalibration result and the basis of retrieving remote sensing parameters in Arctic region in the future. Ascending and descending brightness temperatures at 10 channels in 2015 from FY-3B/MWRI are calibrated against those from GCOM-W1/AMSR-2.Before brightness temperature data analysis and intercalibration, the data are processed in five steps. The first step is reading data, in which the DN value of remote sensing is transferred to brightness temperature value in the research region. The second step is data quality control. If the standard deviation of values in a grid and eight surrounding grids is more than 3 K, then the values in the nine grids should be eliminated. The value that is more than 300 K or less than 10 K should also be eliminated. In the third step, stereographic projection is used to project the brightness temperature value, time, longitude, and latitude into 896×608 grids. In the fourth step, data at the land-sea boundary and Marginal Ice Zone (MIZ) should be eliminated because of the mixed pixel. First, the grid data of 7×7 around the land data are marked as land, and the data marked as land are removed. Then, the ratio of V187 to V365 from AMSR-2 is used to calculate the MIZ. The ratio, which is equal to 0.92, is viewed as the threshold to divide the sea ice and the open water. Thereafter, the 3×3 grid is set as a template. If the template includes the grids that represent sea ice and open water, then the nine grids are eliminated. The fifth and last step is to set the time window as 30 min and the space window as 12.5 km ×12.5 km and convert 2D matched data to 1D data for intercalibration.The intercalibration results of MWRI and AMSR-2 are as follows. First, the brightness temperature data of each channel of MWRI are smaller than those of AMSR-2, and the absolute values of monthly bias of vertical polarization channels are greater than those of horizontal polarization channels at the same frequency. The difference in monthly bias between ascending and descending orbits is small in each channel, which is less than 1 K. Second, the difference in the monthly bias in each channel between the ascending and descending orbits in the sea ice area is less than 1 K, while that in the open water is between 0 and 1.5 K. Third, linear regression analysis shows that most of the correlation coefficients of MWRI and AMSR-2 in each channel are above 0.99, which indicates a good correlation. The slope and intercept of the intercalibration of each channel in the ascending and descending orbits are obtained. Fourth, the brightness temperature of MWRI after calibration is consistent with that of AMSR-2. This consistency indicates that the intercalibration is effective.

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