青藏高原纳木错站地表反照率观测与MODIS资料的对比分析

Comparison of Surface Albedo Measurement with MODIS Product at Namco Station of Tibetan Plateau

利用中国科学院纳木错多圈层相互作用综合观测研究站内太阳光度计观测的大气气溶胶光学厚度和整层气柱水汽总量,作为大气辐射传输模式的输入参数,模拟计算了2007年5月—2008年8月无雪期晴空条件下,正午时段该站的太阳总辐射和散射辐射,得到两者的比例S。基于MODIS发布的MCD43B3产品中的短波段黑空和白空反照率以及比例S,计算得到实际大气条件下地表反照率的卫星反演值,进而与地面观测值进行对比分析。结果显示,两者没有显著差别,可以满足气候模式对地表反照率绝对偏差为0.02的精度要求,且均方根偏差约为0.0156,最大偏差为0.046。雨季纳木错站的土壤含水量增加,使得该站晴空时观测的5 min平均地表反照率呈线性下降。

Aerosol optical depth and water vapor column which are observed in Namco station for Multisphere Observation and Research,Chinese Academy of Sciences by sunphotometer are utilized as input parameters of radiative transfer model.Diffuse and global irradiances around local solar noon under clear sky in snow-free condition from May 2007 to August 2008 are calculated and their ratio S is then derived.The black-sky and white-sky shortwave band albedos from MODIS surface albedo product MCD43B3 with resolution of 1 km are employed to calculate the true albedos under actual atmospheric condition.A comparison with ground measurements is performed.Results show that there is no distinctive bias between the satellite retrieved and ground measured albedos and they meet an absolute accuracy requirement of 0.02.The root-mean-square error is 0.0156 and a maximum error is about 0.046.The soil moisture increases at Namco station during the rainy season and causes the ground measured 5-min mean albedo under clear sky to linearly decrease.