一种基于地表能量平衡的遥感干旱监测新方法及其在甘肃河东地区干旱监测中的应用初探

A new method for drought monitoring based on land surface energy balance and its preliminary application to the Hedong region of Gansu province

目前遥感干旱监测方法的精度普遍不高,探求新的遥感干旱监测方法有助于干旱监测预警技术的提升与发展.波文比是感热通量与潜热通量之比,能综合反映地表水热特征,可尝试将其引入到遥感干旱监测领域加以利用.应用甘肃河东地区的EOS-MODIS卫星资料和同步地面气象资料,基于地表能量平衡原理构建了波文比干旱监测模型,对比分析了波文比（β）指数、温度植被指数（TVX）与土壤水分的相关性,并以典型晴空影像（2014年10月5日）为例初步建立了β的干旱分级标准,对研究区进行了旱情评估.结果表明：β与土壤相对湿度呈现出高度负相关,相比于当下广泛应用的TVX,β与0-20cm平均土壤相对湿度具有更好的相关性,监测精度得到了显著提高.用β干旱分级标准评估的研究区干湿状况与前期降水空间分布吻合得相当好,评估表明2014年10月5日研究区基本为适宜（无旱）,与2014年9月的降水距平百分率特征一致.基于地表能量平衡的波文比（β）指数在干旱监测中效果突出,具有很好的应用前景.

Current drought monitoring methods based on remote sensing technique generally are not of high precision.Seeking a new remote sensing drought monitoring technique is of great help to improve and develop the technique of drought monitoring and alert.The Bowen ratio,the ratio of sensible heat flux against latent heat flux,reflecting surface hydro-thermal characteristics,canbe introduced to drought monitoring field.Using EOS-MODIS satellite data and synchronized meteorological data,the Bowen ratio drought monitoring model was established based on surface energy balance.Then,the correlation between soil moisture against Bowen ratio index（β）and temperature-vegetation index（TVX） was analyzed.Finally,taking the clear-sky imagery（October 5,2014）as an example,a drought level classification standard based onβwas established and droughts in the study region were evaluated.Results show thatβis highly negatively related to soil relative humidity,which has a better correlation than that between TVX and soil relative humidity in the depth range of 0-20cm.The precision of drought monitoring is significantly improved.The distribution of dry-wet condition based on theβdrought classification standard is well consistent with the distribution of antecedent precipitation over the study region.Evaluation results show that generally no drought took place over the study region on October 5,2014,which is consistent with precipitation anomaly percentage for the period of September,2014.Our study suggests that the surface energy balance based Bowen ratio index can achieve excellent results when applied to drought monitoring and has a good application prospect.