CLARA-A2.1: CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data - Edition 2.1

The CLARA-A2.1 record provides cloud properties, surface albedo and surface radiation parameters derived from the AVHRR sensor onboard polar orbiting NOAA and METOP satellites. It includes and temporally extends the second version of the record (Karlsson et al., 2016; CLARA-A2 DOI:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002) now providing data from 1982/01 to 2019/06, i.e., for 37.5 years. Original visible radiances were inter-calibrated and homogenised, using MODIS data as a reference, before applying the various parameter retrievals. The inter-calibration was based on an original method introduced by Heidinger et al. (2010) which was updated (MODIS Collection 6) and extended. CLARA-A2.1 features a range of cloud products: cloud mask, cloud top temperature/pressure/height, cloud thermodynamic phase, and (for liquid and ice clouds separately) cloud optical thickness, particle effective radius and cloud water path. Cloud products are available as monthly and daily averages and also as daily resampled global products (Level 2b) for individual satellites. Cloud parameter results are also presented as multi-parameter distributions (i.e., joint frequency histograms of cloud optical thickness, cloud top pressure and cloud phase) for daytime conditions. Surface albedo is presented as monthly and pentad (5 day) averages of the broadband black-sky albedo and is derived using all available data during the studied period. Surface radiation products are provided as monthly averages for the downwelling shortwave (including also daily averages) and the down- and upwelling longwave components. The monthly and daily averages are available on a 0.25°x0.25° global grid. Surface albedo and cloud products are also provided in two equal area grids with a resolution of 25 km x 25 km covering the polar regions. Daily resampled cloud products (level 2b) are provided in a global grid with a resolution of 0.05°x0.05°. For the latter, also a probabilistic cloud mask is added as an experimental product. A summary of the CLARA-A2.1 characteristics and a comprehensive evaluation of the data are available through a comprehensive set of documentations documents including user guides and, algorithm descriptions.CLARA-A2.1数据集记录了源自极轨NOAA与METOP卫星搭载的AVHRR（高级甚高分辨率辐射计）传感器反演得到的云属性、地表反照率与地表辐射参数。该数据集包含并时间延展了该数据集的第二版（Karlsson等，2016；CLARA-A2 DOI:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002），数据时间范围现已覆盖1982年1月至2019年6月，共计37.5年。原始可见光辐射数据以MODIS（中分辨率成像光谱仪）数据为参考进行了交叉定标与均一化处理，随后再开展各类参数反演。交叉定标基于Heidinger等（2010）提出的原始方法，并针对该方法进行了更新（适配MODIS Collection 6）与拓展。CLARA-A2.1包含一系列云产品：云掩码、云顶温度/气压/高度、云热力学相态，以及（分别针对液态云与冰云的）云光学厚度、粒子有效半径与云水路径。云产品支持以月均、日均数据形式提供，同时也为单颗卫星提供每日重采样的全球级产品（Level 2b）。针对日间工况，云参数结果还以多参数分布形式呈现（即云光学厚度、云顶气压与云相态的联合频率直方图）。地表反照率以宽带晴空反照率的月均与候均（5日平均）形式提供，其反演基于研究时段内所有可用数据。地表辐射产品以月均数据形式提供下行短波辐射（同时包含日均数据）以及下行与上行长波辐射分量。月均与日均数据采用0.25°×0.25°的全球网格存储。地表反照率与云产品还提供了两种等面积网格产品，分辨率为25 km×25 km，覆盖极地区域。每日重采样的云产品（Level 2b）采用0.05°×0.05°的全球网格存储，该类产品还额外新增了概率云掩码作为实验性产品。CLARA-A2.1的特性概要与数据的全面评估可通过一系列完整文档获取，其中包括用户指南与算法说明文档。

搜集汇总

背景与挑战

背景概述

CLARA-A2.1是由CM SAF发布的卫星遥感数据集，基于AVHRR传感器数据，提供1982年至2019年间的全球云属性、地表反照率和地表辐射参数。该数据集采用MODIS交叉校准方法确保数据一致性，包含云掩膜、云顶温度、云光学厚度等多种产品，并以月平均、日平均等多种时间分辨率和0.25°网格空间分辨率提供。