【作者】 桂胜；

【导师】 李霖； 梁顺林；

【作者基本信息】 武汉大学 ， 地图学与地理信息系统， 2010， 博士

【摘要】 地表净辐射作为环境预测中的一个非常重要的参数,控制着蒸散、光合作用、地表和大气温度,在地气系统的相互作用中起着关键作用。高精度的地表净辐射数据对整个人类生态环境的研究具有极其重要的意义,也为使用地理信息系统作出生态环境相关的决策提供支持。毫无疑问,地表辐射观测站点可以提供最准确的地表净辐射通量的测量值,但是由于站点分布始终有限且维护费用昂贵,从而不能满足气候研究、天气预报和其他相关领域的研究需要,所以关于地表净辐射估算方法的研究仍具有巨大的现实意义,特别是卫星遥感手段的出现,其能够提供具有良好时间连续性和空间均一性的地球辐射收支资料的特点,使卫星遥感成为目前研究地表辐射收支的一个重要而有效的手段。目前使用卫星数据估算地表净辐射及其分量的成熟数据集产品普遍存在低分辨率和低精度的缺陷,而使用中高分辨率卫星数据的估算方法又普偏依赖地面观测资料,且大部分算法只适用于晴天条件,使用卫星数据估算阴天条件下的地表净辐射通量是目前存在的一个难题,在这种情况下,本文从现有的地表净辐射卫星数据集产品和算法出发,对已有的地表净辐射卫星数据集产品和算法进行了广泛综合的质量评价和误差分析,并以此为基础,进行了利用MODIS数据估算地表净辐射的相关研究,主要内容如下：1.使用全球分布的36个站点对三种主要的使用卫星数据估算的地表辐射数据集产品(GEWEX-SRB, ISCCP-FD和CERES-FSW)的短波分量(下行短波辐射和上行短波辐射)进行质量评价和误差分析。结果说明,上述产品的在某些地区存在系统性的偏差,其精度并不能完全满足相关研究机构的要求。2.使用全球分布的15个站点对三种主要的使用卫星数据估算的地表辐射数据集产品(GEWEX-SRB, ISCCP-FD和CERES-FSW)的长波分量(下行长波辐射和上行长波辐射)进行质量评价和误差分析。结果说明,上述产品的精度基本可以满足相关研究机构的要求,在部分地区发现的较大误差可以部分由高程差异和输入数据误差来解释。3.对三个利用MODIS数据估算地表净辐射分量的算法进行质量评价,包括估算全天气下行短波辐射的查找表方法、晴天下行长波辐射混合方法和晴天上行长波辐射混合方法。对短波算法,选取了全球分布的26个站点进行验证,对长波算法,选取了全球分布的15个站点进行验证。结果说明,这三种利用MODIS数据估算地表净辐射分量的算法均具有较高精度,已达到相关研究机构的精度要求,而且与GEWEX-SRB, ISCCP-FD和CERES-FSW验证结果的统计数据相比,MODIS算法在很多统计指标上都占有优势,与地表实测数据具有更高的吻合程度。4.提出了一种利用MODIS数据估算全天气条件下瞬时地表净辐射通量的算法框架。目前已有很多利用MODIS数据估算地表净辐射及各分量的算法,各有其优势和劣势,通过分析比较,在合理利用现有的理论和算法基础上,本文结合自身的具体研究情况和需求,提出了一种完全独立于地表观测数据,仅利用MODIS数据估算全天气条件下瞬时地表净辐射通量的算法框架,该框架分为两部分,晴天算法部分和阴天算法部分,完全摆脱了对地表观测数据的依赖,为本文接下来的具体算法的研究奠定了基础。5.系统总结了本文提出的利用MODIS数据估算全天气条件下瞬时地表净辐射通量算法框架所涉及到的所有算法,除此以外,针对目前缺乏阴天净辐射算法的情况,提出了一种在阴天条件下估算地表净辐射的算法,并将结果与已有的三种数据集产品进行了对比。结果显示,使用本文提出的框架和具体算法估算的结果,不仅在估算精度上高于其他的三种数据集(GEWEX-SRB, ISCCP-FD和CERES-FSW),而且拥有更高的空间分辨率。6.提出了全天气条件下估算日间总地表净辐射的具体算法并进行验证。本文将可调节正弦插值法引入日间总地表净辐射的研究中,并使用MODIS数据进行验证分析。结果说明,虽然在部分站点有着轻微的高估,但使用上述方法估算的日间总地表净辐射值与使用地表实测数据集成计算的日间总地表净辐射值具有较高的吻合程度。更多还原

【Abstract】 Net radiation at the Earth’s surface drives the process of evaporation, photosynthesis, and heating of soil and air. Net radiation and the overall surface energy budget are important for the development of the planetary boundary-layer. Its quantification over heterogenous land surfaces is crucial to study land-atmosphere interactions. Quantifying net radiation with high accuracy is significant for the whole physical environment and decision-making based on GIS. Undoubtedly, worldwide ground based measurements can provide the most accurate observations of net radiation, but given that direct measurements are expensive and limited, it is desirable to obtain global measurements of surface radiation fluxes using data provided by satellites.At present, the major satellite-estimate datasets of surface net radiation or its components are generally with low spatial resolution and low accuracy. While most of the methodologies to estimate surface net radiation using moderate/high spatial resolution satellite data are relying on meteorology data and only suitable for clear-sky conditions. Application of existing methodologies to estimate net radiation for cloudy-sky conditions from remote sensing sensors remains a significant challenge. Therefore, in this dissertation, we comprehensively evaluate the major satellite-estimate net radiation datasets and algorithms using ground measurements, present a framework to estimate instantaneous and daytime total net radiation under all sky conditions using MODIS data. Below are the major work conducted in this dissertation:Firstly, three satellite-estimated surface shortwave radiation data sets:1) GEWEX-SRB; 2) ISCCP-FD; and 3) CERES-FSW from 2000-2002, were evaluated using ground measurements at 36 sites around the world. Though the statistical errors are quite variable for the individual sites, systematic biases and tendencies may be identified. Results show that significant biases for some sites exceed the acceptable values of research community.Secondly, three satellite-estimated surface longwave radiation data sets:1) GEWEX-SRB; 2) ISCCP-FD; and 3) CERES-FSW of 2003, were evaluated using ground measurements at 15 sites around the world. Results show that, in general, the accuracy of these three datasets can meet the accuracy requirement of research community, and some uncertainties found in this evaluation can be explained by the elevation differences and input data accuracy.Thirdly, three algorithms of estimating surface radiation using MODIS data:1) Look-up table method of all-sky downwelling shortwave radiation; 2) Hybrid method of clear-sky downwelling longwave radiation; 3) Hybrid method of clear-sky upwelling longwave radiation, were evaluated using ground measurements. Results show that, these three methods have high accuracy and can meet the accuracy requirement of research community. Comparing with GEWEX-SRB, ISCCP-FD and CERES-FSW, these three MODIS algorithms outperform at most statistical indexes and agree better with the ground measurements.Fourthly, this dissertation presents a framework to estimate instantaneous net radiation under all sky conditions using only MODIS data. This framework consists of two parts:clear-sky algorithm and cloudy-sky algorithm, which establish a steady foundation for future research.Fifthly, this dissertation presents specific methods to estimate instantaneous net radiation using MODIS data, especially developed a new method to estimate instantaneous net radiation under cloudy-sky condition. Through validation, we found using the framework and specific algorithms proposed here can obtain better net radiation results than GEWEX-SRB, ISCCP-FD and CERES-FSW, besides, MODIS has higher spatial resolution.At last, this dissertation presents a method to estimate daytime total net radiation under all sky conditions using MODIS data. We applied’adjusted sinusoid interpolation’to the estimation of daytime total net radiation and validated using MODIS. Results show that, daytime total net radiation estimated by using this method agree well with the ground-measurements.更多还原