Upgrade of LSA-SAF Meteosat Second Generation daily surface albedo (MDAL) retrieval algorithm incorporating aerosol correction and other improvements

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Geoscientific Instrumentation Methods and Data Systems Pub Date : 2022-11-24 DOI:10.5194/gi-11-389-2022
D. Juncu, X. Ceamanos, I. Trigo, S. Gomes, Sandra C. Freitas
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Abstract

Abstract. MDAL is the operational Meteosat Second Generation (MSG)-derived daily surface albedo product that has been generated and disseminated in near real time by EUMETSAT Satellite Application Facility for Land Surface Analysis (LSA-SAF) since 2005. We propose and evaluate an update to the MDAL retrieval algorithm which introduces the accounting for aerosol effects as well as other scientific developments: pre-processing recalibration of radiances acquired by the SEVIRI instrument aboard MSG and improved coefficients for atmospheric correction as well as for albedo conversion from narrow- to broadband. We compare the performance of MDAL broadband albedos pre- and post-upgrade with respect to three types of reference data: the EPS Ten-Day Albedo product ETAL is used as the primary reference, while albedo derived from in situ flux measurements acquired by ground stations and MODIS MCD43D albedo data are used to complete the validation. For the comparison to ETAL – conducted over the whole coverage area of SEVIRI – we see a reduction in average white-sky albedo mean bias error (MBE) from −0.02 to negligible levels (<0.001) and a reduction in average mean absolute error (MAE) from 0.034 to 0.026 (−24 %). Improvements can be seen for black-sky albedo as well, albeit less pronounced (14 % reduction in MAE). Further analysis distinguishing individual seasons, regions and land covers show that performance changes have spatial and temporal dependence: for white-sky albedo we see improvements over almost all regions and seasons relative to ETAL, except for Eurasia in winter; resolved by land cover we see a similar effect with improvements for all types for all seasons except winter, where some types exhibit slightly worse results (crop-, grass- and shrublands). For black-sky albedo we similarly see improvements for all seasons when averaged over the full data set, although sub-regions exhibit clear seasonal dependence: the performance of the upgraded MDAL version is generally diminished in local winter but better in local summer. The comparison with in situ observations is less conclusive due to the well-known problem of the spatial representativeness of near-ground observations with respect to satellite pixel footprint sizes. Comparison with MODIS at the same locations shows mixed results in terms of change in performance following the proposed upgrade but proves the good quality of the MDAL products in general. Based on the evidence presented in this study, we consider the updated algorithm version to be able to deliver a valuable improvement of the operational MDAL product. This improvement is two-fold: primarily, there is the refinement of the albedo values themselves; secondarily, the increased alignment with the ETAL product is beneficial for those who wish to exploit synergies between EUMETSAT's geostationary and polar satellites to generate data sets based on the LSA-SAF albedo products from the two different missions.
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基于气溶胶校正和其他改进的LSA-SAF Meteosat第二代日地表反照率(MDAL)反演算法升级
摘要MDAL是气象卫星第二代(MSG)衍生的每日地表反照率产品,自2005年以来由EUMETSAT陆地表面分析卫星应用设施(LSA-SAF)生成和传播。我们提出并评估了对MDAL检索算法的更新,该算法引入了气溶胶效应的计算以及其他科学发展:MSG上的SEVIRI仪器获得的辐射度的预处理再校准,改进的大气校正系数以及从窄带到宽带的反照率转换系数。我们比较了MDAL宽带反照率升级前后的三种参考数据的性能:以EPS 10天反照率产品ETAL作为主要参考数据,利用地面站现场通量测量所得的反照率和MODIS MCD43D反照率数据完成验证。对于与ETAL的比较——在SEVIRI的整个覆盖区域进行——我们看到平均白天反照率平均偏差误差(MBE)从- 0.02降低到可忽略的水平(<0.001),平均平均绝对误差(MAE)从0.034降低到0.026(- 24%)。在黑天反照率上也可以看到改善,尽管不那么明显(MAE降低14%)。对不同季节、地区和土地覆盖的进一步分析表明,性能变化具有时空依赖性:除了欧亚大陆冬季外,我们看到几乎所有地区和季节的白天反照率都比ETAL有所改善;从土地覆盖的角度来看,除冬季外,所有类型在所有季节都有类似的改善效果,其中一些类型的结果略差(作物、草地和灌木地)。对于黑天反照率,在整个数据集的平均值上,我们同样看到所有季节的改善,尽管分区域表现出明显的季节依赖性:升级后的MDAL版本的性能在当地冬季普遍下降,但在当地夏季更好。由于众所周知的近地观测相对于卫星像元足迹大小的空间代表性问题,与原位观测的比较不太具有结论性。与MODIS在相同地点的比较显示,拟议升级后性能变化的结果好坏参半,但总体上证明了MDAL产品的良好质量。基于本研究中提出的证据,我们认为更新后的算法版本能够对可操作的MDAL产品进行有价值的改进。这种改进是双重的:首先是反照率值本身的改进;其次,对于那些希望利用EUMETSAT的地球静止卫星和极地卫星之间的协同作用来生成基于两个不同任务的LSA-SAF反照率产品的数据集的人来说,增加与ETAL产品的校准是有益的。
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来源期刊
Geoscientific Instrumentation Methods and Data Systems
Geoscientific Instrumentation Methods and Data Systems GEOSCIENCES, MULTIDISCIPLINARYMETEOROLOGY-METEOROLOGY & ATMOSPHERIC SCIENCES
CiteScore
3.70
自引率
0.00%
发文量
23
审稿时长
37 weeks
期刊介绍: Geoscientific Instrumentation, Methods and Data Systems (GI) is an open-access interdisciplinary electronic journal for swift publication of original articles and short communications in the area of geoscientific instruments. It covers three main areas: (i) atmospheric and geospace sciences, (ii) earth science, and (iii) ocean science. A unique feature of the journal is the emphasis on synergy between science and technology that facilitates advances in GI. These advances include but are not limited to the following: concepts, design, and description of instrumentation and data systems; retrieval techniques of scientific products from measurements; calibration and data quality assessment; uncertainty in measurements; newly developed and planned research platforms and community instrumentation capabilities; major national and international field campaigns and observational research programs; new observational strategies to address societal needs in areas such as monitoring climate change and preventing natural disasters; networking of instruments for enhancing high temporal and spatial resolution of observations. GI has an innovative two-stage publication process involving the scientific discussion forum Geoscientific Instrumentation, Methods and Data Systems Discussions (GID), which has been designed to do the following: foster scientific discussion; maximize the effectiveness and transparency of scientific quality assurance; enable rapid publication; make scientific publications freely accessible.
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