FY-3B/MWRI和Aqua/AMSR-E海冰密集度比较及印证

本文对2011-07-01—2011-09-30风云三号B星(FY-3B)搭载的微波成像仪MWRI(Microwave Radiometer Imager)和Aqua卫星搭载的微波扫描辐射计AMSR-E(Advanced Microwave Scanning Radiometer for Earth Observing System)观测数据获取的海冰密集度产品进行比较及印证。首先,逐日比较FY-3B/MWRI和Aqua/AMSR-E区域平均海冰密集度;其次,逐月比较FY-3B/MWRI和Aqua/AMSR-E月平均海冰密集度;最后,使用Aqua卫星搭载的中等分辨率成像光谱辐射计MODIS数据进行印证。MWRI和AMSR-E比较结果为(1)MWRI与AMSR-E逐日区域平均海冰密集度变化趋势一致,MWRI海冰密集度均高于AMSR-E,7—9月MWRI与AMSR-E逐日平均偏差月平均值分别为8.55%、7.67%、2.58%,逐日标准差月平均值分别为12.16%、12.08%、10.43%,二者差异逐月减小。(2)MWRI与AMSR-E月平均海冰密集度差呈现逐月递减趋势,7—9月MWRI与AMSR-E逐月平均偏差分别为7.37%、6.53%、1.51%,逐月标准差分别为4.61%、4.36%、3.64%,MWRI与AMSR-E差异逐月减小的原因是二者在密集度较低的边缘区域差异较大,而夏季随着边缘区域海冰的融化,二者差异逐渐减小。MWRI和AMSRE海冰密集度与MODIS印证结果为:(1)密集度小于95%情况下,MWRI与AMSR-E海冰密集度均比MODIS偏高,AMSR-E更接近MODIS,MWRI高估,误差较大。(2)密集度大于等于95%情况下,MWRI与AMSR-E海冰密集度均比MODIS偏低,AMSR-E偏低更多,MWRI结果更好。

Comparison and validation of sea ice concentration from FY-3B/MWRI and Aqua/AMSR-E observations

Sea ice concentration, which refers to the percentage of sea ice in an area, is one of the important parameters describing the characteristics of sea ice. Remote sensing monitoring of Arctic sea ice is crucial for understanding the role of the Arctic in the global climate system and in global warming. Therefore, comparing and evaluating the products of sea ice data retrieved from different satellite observations are necessary. In addition, assessing the accuracy of sea ice distribution from satellite observations is significant in studies on climate change and global warming because the extrapolation of global surface energy flows is very sensitive to the estimation of Arctic sea ice cover. To evaluate sea ice concentration from the Microwave Radiometer Imager (MWRI) onboard the FY-3B satellite, we compare the data products with the sea ice concentration from the advanced microwave scanning radiometer for earth observing system (AMSR-E) onboard the Aqua satellite. High-resolution moderate resolution imaging spectroradiometer (MODIS) data are used to validate MWRI and AMSR-E sea ice concentration. The comparison of MWRI and AMSR-E incudes daily and monthly data. MODIS L1B band 2 channel reflectance is chosen to validate the sea ice concentration of MWRI and AMSR-E. The processing procedure of MODIS mainly consists of solar zenith correction, radiometric calibration, removing bow-tie phenomenon, and map projection. The map projection is the polar stereographic projection, which is the same as the MWRI and AMSR-E products. To avoid the misjudgment of ice and water because of the cloud influence, we choose cloudfree MODIS channel 2 sub-region for ice and water recognition. Different thresholds according to the histogram of the reflectance are used to segment the ice and water pixels. The MODIS sea ice concentration in each MWRI and AMSR-E grid is calculated. The comparison results of MWRI and AMSR-E are as follows. First, MWRI and AMSR-E daily mean sea ice concentrations show a consistent change from July to September, and MWRI sea ice concentration is higher than AMSR-E each day. The monthly mean values of daily biases for July, August, and September are 8.55%, 7.67%, and 2.58%, and the monthly mean of daily standard deviations are 12.16%, 12.08%, and 10.43%, respectively. Second, from July to September, the monthly sea ice concentration difference between MWRI and AMSR-E (MWRI minus AMSR-E) shows a decreasing trend. The monthly biases for July, August, and September are 7.37%, 6.53%, and 1.51%, and the monthly standard deviations are 4.61%, 4.36%, and 3.64%, respectively. The validation results of MWRI and AMSR-E sea ice concentration with MODIS are as follows. First, in the region of MODIS sea ice concentration less than 95%, the sea ice concentration difference between MWRI and MODIS (MWRI minus MODIS) is 9.78%±16.90%, and the difference between AMSR-E and MODIS (AMSR-E minus MODIS) is 0.90%±13.09%. MWRI and AMSR-E tend to overestimate sea ice concentration compared with MODIS, the result of AMSR-E is closer to MODIS, and MWRI has a larger error. Second, when MODIS sea ice concentration is greater than or equal to 95%, the sea ice concentration difference between MWRI and MODIS is -5.45%±7.05%, and the difference between AMSR-E and MODIS is -7.97%±6.46%. MWRI and AMSR-E tend to underestimate sea ice concentration compared with MODIS, and the result of MWRI is slightly better.