主被动微波遥感在农区土壤水分监测中的应用初探

Soil moisture monitoring in agricultural lands via active-passive microwave remote sensing

土壤水分是农作物生长和旱情监测的重要参数。微波遥感具有全天时、全天候、高穿透性和对水分敏感的特点,主被动微波遥感的结合能够发挥各自优势,实现区域尺度土壤水分的连续监测,与单纯使用被动微波遥感相比,能够提高空间分辨率。本研究基于TRMM卫星搭载的微波成像仪TMI和降雨雷达PR的特点,利用粗糙地表的微波辐射传输模型AIEM模型、参数化模型Qp模型和植被覆盖地表的辐射传输模型ω-τ模型,建立了基于被动微波遥感的土壤水分反演模型,并利用简单散射模型(SSM)和几何光学模型(GOM),将被动微波与主动微波相联系,建立了主被动微波遥感相结合的土壤水分变化反演算法,对2008年1-4月期间30°-38°N、110°-120°E范围内农田覆盖区的土壤水分变化进行了反演。并选取江苏省连云港南部农区中心经纬度为34.45°N、119.25°E的降雨雷达0.05°×0.05°的网格,对该网格2008年1月2日-4月30日土壤水分逐日变化量的反演值和相应网格的降水逐日变化量进行了对比,两者具有很好的响应关系。

Soil moisture is a critical element for monitoring crop growth and drought in agricultural lands.Microwave remote sens-ing is a reliable mode of retrieving soil moisture in real time and under all weather and physiographic conditions.Retrieving soil moisture via combined active and passive microwave remote sensing has the advantage of high spatial resolution and real-time mea-surement at regional scale.Although it has practical significance for agricultural lands,this technique has largely been previously applied in retrieving soil moisture under natural vegetation.Here,the technique was used to retrieve soil moisture in agricultural lands.The TRMM Microwave Imager（TMI） emissivities at different soil moisture and surface roughness conditions were simulated using the Advanced Integral Equation Model（AIEM）.After emissivity sensitivity analysis of soil moisture and roughness,a soil moisture inversion model for bare surfaces via passive microwave remote sensing was established based on the parameterized mi-crowave radiation model（Qp model）.The inversion algorithm for vegetated surface was established using the microwave radiation transfer model（ω-τ model）.Then a soil moisture variation inversion algorithm that combines active and passive microwave remote sensing（using TRMM Microwave Imager and Precipitation Radar data） was developed based on the Simple Scattering Model（SSM） and Geometry Optical Model（GOM）.The daily soil moisture variations in agricultural lands between 30o-38oN and 110o-120oE was estimated for January through April of 2008.The retrieved daily soil moisture variations were compared with interpolated daily pre-cipitation variations at the grid which is located at 34.45oN and 119.25oE in the croplands of Lianyungang,Jiangsu Province.The study showed that microwave remote sensing was practicable in monitoring and managing soil moisture in agricultural lands.