基于深对流云的夜间微光传感器定标技术

NPP(National Polar-orbiting Parternership)卫星于2011年10月28日发射升空,其上搭载的VIIRS(Visible Infrared Imaging Radiometer Suite)传感器包含DNB(Day Night Band)波段,该波段采用三增益设置,可在白天、晨昏甚至夜间实现地球观测.其中,在夜间月光条件下,主要采用高增益,定标实现较为困难.以此为目的,首次提出了基于深对流云的夜间微光传感器替代定标方法.将月亮辐射模型引入到SCIATRAN中,实现了全天候的辐射传输计算,并利用该改进的辐射传输模式,通过确定深对流云光学属性、地表特性及大气廓线等的参考值,对接收大气层顶反射辐射进行敏感性试验,分析得到主要影响因子为云光学厚度COT(Cloud Optical Thickness)与有效粒子半径Re(Effective Radius),且利用固定参考值得到最大模拟误差小于5%.为了检验该替代方法的可行性,通过改进的辐射传输模式,对2012年08月~2013年01月共6个月夜间DNB数据所确定的深对流云替代目标像素进行辐射传输模拟,结果表明基于深对流云的替代定标方法效果较好,基于日变化的辐射不确定度在±10%之内,可实现对DNB夜间高增益阶段的直接辐射定标.

Calibration of low-level light sensor using deep convective clouds

The National Polar-orbiting Partnership (NPP) satellite was successfully launched in 28 October 2011. The day night band (DNB) is mounted on the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the NPP to greatly improve upon the night time imaging capabilities. In order to cover this wide dynamic radiation range, the three gain stages are employed to view the earth at daytime, twilight and even nighttime. Especially, the radiance measured at night is relatively low, so the radiance calibration is too difficult to realize. In order to realize radiance calibration at night, the vicarious calibration method of Low-level light detection at night using the deep convection clouds is presented. The lunar irradiance model is introduced to enhance the SCIATRAN to realize the radiance transfer simulation at all time. Then, the reference values of the surface albedo, atmospheric profiles and optical properties of deep convection cloudsDCCs are inputted to the enhanced model to study the sensitivity of the TOA radiance. The simulation results show that the main factors are the Cloud Optical Thickness (COT) and Effective Radius(Re) and the maximum reflectance errors are no more than 5%. In order to examine the feasibility of the calibration method, the 6 months NPP data range from August 2012 to January 2013 is used. The simulated albedos are calculated using the enhanced radiative transfer model and compared to the observed albedos. The result shows that the radiance uncertainties on a daily basis are in the range of ±10%, which means that the calibration method using Deep convection clouds is very well to calibrate the DNB high gain stage directly.