【Title】USE OF CONTRAST RATIO TO DETECT MULTI-YEAR ICE USING AMSR-E PASSIVE MICOWAVE DATA
Zhang Shugang, Guo Fadong, Zhang Jinming, Liu Lei, Bai Xuejiao
【摘要】 研究发现，AMSR-E的垂直极化的18.7 GHz (V18.7)和36.5 GHz (V36.5)的亮温比值在一年冰覆盖区域主要是相应频段的海冰微波发射率之比, 而在多年冰覆盖区域受海冰微波发射率和海冰温度共同影响，并且海冰年龄越大亮温比值也越大。应用强度比参数可以比较好地确定冬季一年冰与多年冰之间的阈值, 其中, 在该阈值处, 强度比梯度达到最大。该阈值呈现明显的季节性变化规律, 在冬季阈值比较稳定, 而在夏季受海水的影响变化范围比较大。应用强度比方法确定的多年冰范围, 与NASA Team2 (NT2)方法相比在大西洋扇区差异非常小；而在太平洋扇区出现比较大的差异。对比发现强度比法确定的多年冰范围一般大于NT2法。
【Abstract】 This study found that the ratio of vertically polarized brightness temperature of AMSR-E passive microwave data at 18.7 and 36.5 is the ratio of sea ice microwave emissivity for first-year ice. However, for multi-year ice, this ratio is also affected by sea ice temperature. Furthermore, the ratio for older ice is larger than for younger ice. The contrast ratio is a suitable parameter with which to ascertain the threshold between first-year and multi-year ice because the maximum gradient of the contrast ratio appears at the threshold. This threshold varies seasonally; it is relatively steady during winter but changes considerably during summer because of the influence of meltwater. Little difference was found in the multi-year ice coverage of the Arctic section of the Atlantic Ocean when ascertained by the contrast ratio and NASA Team2 (NT2) algorithm; however, large differences were found in the Arctic section of the Pacific Ocean. In comparison to the NT2, the coverage of multi-year ice is commonly found to be larger when ascertained using the contrast ratio.