静止卫星闪电探测中云影响研究

Study of the cloud effect on lightning detection by geostationary satellite

相对已经在轨运行的极轨卫星,搭载在静止卫星上的闪电成像仪能够提供全天候、无间断的闪电探测,是目前全球卫星闪电探测的方向.本文分析云不同特性对云顶闪电信号的影响,以及云高对静止卫星闪电定位的订正分析,将对静止卫星闪电成像仪的研发及其业务化运行提供技术支撑.研究中,通过建立云中闪电传输模型,模拟云中闪电传输.由于云粒子散射,云的体积、光学厚度和形状,以及闪电在云中发生的深度,都影响云中或云间闪电信号传输到云顶的能量衰减和持续时间,其持续时间可能超过已知静止卫星闪电成像仪假设的2ms成像积分时间间隔,这样不能保证所有的闪电信号在一帧图像内探测到.但是,云粒子散射对云顶闪电的水平位置影响不大,闪电成像仪定位的云顶闪电可代表云中或云间的闪电位置.同时,在传统静止卫星图像定位模型的基础上,建立了闪电定位的云高订正模型.根据该模型,当云顶高度为10km,云高所引起的闪电定位最大误差达到经向0.5379°、纬向0.2273°,超过已知静止卫星闪电成像仪假设的地面探测单元大小,有必要进行订正.

By comparison to polar orbital satellite,lightning detection by geostationary satellite can be all-weather and no gap.In order to develop the technique,it is necessary to study the cloud effect on lightning imaging and lightning location.In the study,lightning signal transfer within the cloud is simulated using a Monte Carlo method,and the energy reduction and duration delay at the top of cloud are analyzed with different volume,optical thickness,and shape of cloud,even the lightning depth within the cloud.Duration delay of lightning to the top of cloud may be more than 2ms,which is larger than the imaging time of sensor,so that some lightning signal can not be detected by current lightning imager.However,the location of lightning at the top of cloud is not changed significantly by the cloud scattering.Thus,the lightning within or below the cloud can be located by the imager.Meanwhile,a model is present to modify the lightning location based on the traditional image location method to geostationary satellite.When the height of cloud is above 10 km,the deviations of lightning location are up to longitudinal 0.5379° and latitudinal 0.2273°,which are greater than the pixel resolution of lightning imager,so it is necessary to modify the lightning location.