用FY-1C两个近红外太阳反射光通道的观测数据反演水汽总含量
REMOTE SENSING OF TOTAL COLUMN PERCEPTIBLE WATER VAPOR WITH TWO SUN REFLECTANCE CHANNELS OF FY-1C SATELLITE
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摘要: FY-1C极轨气象卫星扫描辐射仪第10通道的观测波长为0.90~0.965μm,位于弱水汽吸收区,邻近的第2通道观测波长为0.84~0.89μm,位于大气窗区。该文根据R.Frouin提出的算法,用FY-1C资料实现了近红外水汽吸收区和窗区两个通道联合反演水汽总含量。所用的反演关系式为
其中,水汽吸收区与窗区两个通道的反射率之比r可以从卫星测值中求出;在探空站所在的地方,沿光路的水汽总含量m为己知量,可以用统计方法求出系数A和B;在没有探空站的地方,可以根据系数A和B,用反演关系式求m。影响系数A的因素主要是大气的温、压、湿廓线和仪器的通道响应函数,影响系数B的因素是地表反射率。由于这些对反演关系式中的系数取值有影响的因素随时间和地点有变化,对不同地区和时段的探空站分别进行统计,得到不同的系数进行反演,取得了较好的效果。另外,还用质量控制手段控制了定位误差可能带来的影响。独立样本真实性检验表明,反演值和探空测值之间的偏差约为15%~20%,相关系数在90%以上。Abstract: Remote sensing of the total column perceptible water vapor with the imaging spectrometer on the FY-1C polar orbiting satellite is realized based on the algorithm suggested by R. Frouin et al. (1990). With the two sun reflectance channels (a water absorption channel and a window channel), the total column perceptible water vapor is derived. The water absorption channel is at the wavelength of 0.90 to 0.965μm, and the window channel at 0.84 to 0.89μm. The basic formula used is: In the formula, r, the ratio of observation values between the water absorption channel and the window channel, is known. At the locations around radiosonde stations, the total water vapor amount along the observation path is also known. Coefficients A and B can be derived by means of the statistic method. At other locations far from radio sonde stations, m is calculated with coefficients A and B. Factors affecting A are the atmospheric profiles of temperature, pressure and humidity and the channel response function of the imaging spectrometer. The factor affecting B is the surface reflectance. These factors are time-and location-related. Statistic calculation is performed respectively at different time periods and locations. The possible errors that otherwise may be introduced from the incorrect navigation of the images are limited by the quality control measure. Reality examination with independent radiosonde samples shows that the bias is about 15% to 20%, and the correlation coeffecient is above 90%. -
表 1 FY-1C星扫描辐射计第2、第10通道的特征
表 2 1999~2000年辐射校正场外定标的结果[9]
表 3 水汽通道与窗区两个通道的典型反照率之比r的计算结果
表 4 个别探空站分别统计所得的水汽总量反演系数A和B
表 5 2000年6~7月分区统计所得的水汽总量反演回归系数A和B
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