基于亚马逊热带雨林的微波辐射计定标基准分析

Analysis of the Calibration Standard of Microwave Madiometers for the Amazon Rainforest

亚马逊热带雨林作为稳定地物目标,适合进行星载微波辐射计的外定标。但近些年亚马逊热带雨林受人为破坏严重,植被覆盖面积减少,植被覆盖率降低,适合进行外定标的区域较往年发生了变化。文中依据亚马逊热带雨林近些年的归一化植被指数(NDVI)的变化情况,发现纬度位于3°S^2°N,经度位于74°W^69°W范围内的区域植被覆盖率高,适合进行星载微波辐射计外定标。文中以AMSR2 L1R亮温数据为基准,对比分析了该区域在2015-2017年3 a的亮温变化趋势,并以此作为该区域的定标基准。分析发现,该区域在非厄尔尼诺事件期间的亮温变化趋势呈现出特定的季节变化规律:在每年的6-7月,亮温值达到最低;在11-12月,亮温值达到最高,7-11月波动上升,12-6月波动下降。在厄尔尼诺事件发生期间会出现亮温值异常现象。

As one of the default ground object targets,the Amazon Rainforest is suitable for the external calibration of the satellite-carried microwave radiometer.In recent years,however,the Amazon Rainforest has been seriously destroyed by human activities,with the vegetation coverage area sharply reduced and the vegetation coverage decreased.The areas suitable for external calibration have been changed compared with previous years.Based on the changes of NDVI in recent years for the Amazon Rainforest,it is found that the region with a latitude of 3°S^2°N and a longitude of 74°W^69°W has a high vegetation coverage,which is suitable for the external calibration of the satellite-carried microwave radiometer.Hence we choose that region is selected as the default region.Based on the data of AMSR2 L1R brightness temperature,this paper compares and analyzes the changing trend of brightness temperature from 2015 to 2017,and uses it as the benchmark for the calibration for the default region.According to the analysis,the changing trends of the brightness temperature in non-El Nino years present a specific seasonal change rule for the default region:between June and July,the bright temperature archived the lowest;between November and December,the brightness temperature archived the highest;the fluctuation increased between July and November and decreased between December and June.During the El Nino event,there is an anomaly phenomenon of the bright temperature value.