兰州市大气水汽含量及其时空特征分析

Inversion of Atmospheric Water Vapor Content in Lanzhou Based on MODIS Data

针对MODIS近红外法反演大气水汽值精度不高的问题,在采用遗传算法优化求解的适合兰州地区的三通道加权比值法基础上,提出了一种利用探空资料的MODIS水汽实时校正模型。以2019年6—9月的Terra/MODIS L1B数据为数据源,采用遗传算法对适合兰州地区的二通道比值法和三通道比值法加权系数优化求解,分析精度较高的三通道加权比值法反演的水汽值与探空水汽资料的相关性,利用线性回归方法建立MODIS水汽实时校正模型,通过与探空水汽资料对比验证MODIS水汽实时校正模型精度与可靠性;利用该MODIS水汽实时校正模型反演了兰州地区大气水汽含量,分析了该区域水汽含量的时空特征。研究结果表明:对于兰州地区而言,三通道比值法稍优于二通道比值法;探空水汽资料与MODIS加权水汽呈现很好的正相关;MODIS水汽实时校正模型的精度较高;该地区5—9月水汽空间分布整体呈现西北低,中部以及西南边市区内较高的特点,全市平均水汽含量呈现增长趋势。

Aiming at the problem of low accuracy of MODIS NIR inversion of atmospheric water vapor,a real-time MODIS water vapor correction model based on sounding data is proposed,which is based on the three-channel weighted ratio algorithm suitable for Lanzhou area optimized by genetic algorithm.This paper uses Terra/MODIS L1B data from June to September 2019 and uses the genetic algorithm to optimize the weighting coefficients of the two channel ratio method and three channel ratio method suitable for Lanzhou area.Based on the correlation between the water vapor value retrieved by the three-channel weighted ratio method with high analysis accuracy and sounding water vapor data,it uses a linear regression method to establish a MODIS water vapor real-time correction model,and the accuracy and reliability of the MODIS water vapor real-time correction model are verified by comparison with the sounding water vapor data.It then uses the MODIS water vapor real-time correction model to invert the atmospheric water vapor content in Lanzhou area,and the spatial and temporal characteristics of the water vapor content in this area are analyzed.The research results show that for Lanzhou city,the three-channel method is slightly better than that of the two-channel method;the sounding data and the MODIS weighted water vapor show a good positive correlation;the MODIS water vapor real-time correction model has a higher accuracy;the spatial distribution of water vapor in the region from May to September is generally low in the northwest and high in the central and southwestern urban areas,and the average water vapor content in the city shows an increasing trend.