临近空间高度卫星光学载荷辐射定标试验与初步结果

The near-space altitude experiment for satellite radiometric calibration and the first results

卫星遥感载荷在轨辐射定标需要高稳定、高可靠、可追溯的辐射定标源支持。将辐射基准搬至空间平台,利用同步对地观测的方式将基准传递至卫星载荷,已成为未来提升在轨辐射定标精度的可行方式之一。临近空间高度上可获得与卫星相接近的观测,同时,以高空科学气球为代表的临近空间浮空器还具有长时区域驻空、可回收等平台优势,也是空间辐射基准可选择的搭载平台之一。本文介绍了将高空科学气球作为平台搭载辐射参考载荷的系统设计,以及在青海大柴旦地区开展的临近空间光学载荷辐射定标飞行试验情况。结合试验获取的临空平台位置姿态数据、观测辐射亮度数据,分析了临近空间高空科学气球平台及辐亮度计的工作稳定性,给出了在临近空间开展卫星光学载荷定标的一般性方法,并对定标不确定度进行了分析,得到气球过境均匀区和山地区辐亮度观测的不确定度分别为3.8%—4.3%和5.0%—6.8%。与MODIS、GF-6WFI同步观测数据比对结果也一定程度上证实了不确定度估算的可靠性。本次基于临近空间高空科学气球的卫星光学载荷辐射定标试验探索了高空科学气球作为空间辐射基准搭载平台的可行性,为进一步发展基于临近空间的辐射基准传递定标系统积累了经验。

On-orbit calibration and performance monitoring of satellite remote sensing payloads call for the support of the radiometric calibration source,which has high stability,reliability,and traceability.One of the most effective ways to improve the accuracy of on-orbit radiometric calibration is to move the radiometric benchmark from the laboratory to a space-borne platform to form“calibration satellites,”such as“THUTHS,”“CLARREO,”and the Chinese“LIBRA.”Then,the simultaneous nadir overpass observations obtained from the calibration satellite and other satellites can be employed to transfer the benchmark to other satellites.However,up to now,all of the abovementioned projects are at the research and development stage.At present,no operational satellites can be used to validate the benchmark transfer chain,which is one of the core functions of future calibration satellites.Given that the high-altitude scientific balloon has the advantages of being close to TOA observations,long-term regional flight,and recyclability,it can be regarded as an optional platform for space radiometric benchmarks.This study examined the composition of the demonstration system that can operate at a near-space altitude,with the high-altitude scientific balloon as a platform and a radiometer covering the spectrum range of 400—2500 nm as the main Earth observation instrument.A flight experiment was also performed by utilizing this system in Da-Qaidam in Qinghai Province.During the flight,the position and attitude data of the balloon platform and the observed radiance data were obtained and fully recorded.These data were initially used to analyze the stability of the high-altitude scientific balloon platform and the radiometer in near-space.Results revealed that during the whole flight,the radiometer was in a stable environment and worked well.Then,a general method of satellite radiometric calibration with the balloon observation in near-space was established in consideration of balloon flight tracks that are difficult to fully control.The uncertainty of the proposed method reached 3.15%—3.35%and 4.60%—4.75%in the uniform and mountain areas,respectively.A comparison with MODIS and GF-6/WFI synchronous observations was performed to confirm the reliability of the uncertainty analysis.The satellite and balloon observations showed good agreement with each other.The successful flight experiment revealed the feasibility of using high-altitude scientific balloons as a space radiometric benchmark-carrying platform.It can also serve as a reference for the further development of near-space-borne radiometric benchmark transfer calibration systems.