Accounting for surface reflectance spectral features in TROPOMI methane retrievals
Accounting for surface reflectance spectral features in TROPOMI methane retrievals
复制标题
考虑 TROPOMI 甲烷反演中的表面反射光谱特征
DOI：
10.5194/amt-16-1597-2023
复制
发表时间：
2023
影响因子：
3.8
通讯作者：
J. Landgraf
中科院分区：
文献类型：
--
作者：
A. Lorente;T. Borsdorff;Mari C. Martinez;J. Landgraf
抽象的。使用哥白尼 Sentinel-5 Precursor (S5-P) 卫星上的对流层监测仪器 (TROPOMI) 进行甲烷 (CH4) 卫星遥感是监测和量化全球排放的关键。总体而言，S5-P 甲烷数据的质量令人满意，这一点通过总碳柱观测网络 (TCCON) 地面测量的产品验证得到证明。然而，对 TROPOMI 干空气柱混合比 (XCH4) 数据的分析表明，存在一些高达 20-40ppb 的虚假甲烷异常，这些异常可能会被误解为由于强排放源而导致的增强。这些伪影是由特定材料（例如碳酸盐岩）下垫表面的光谱特征引起的，这些特征在检索算法的正演模型中没有得到很好的体现。在这项研究中，我们表明观察到的异常是由于表面模型造成的，该模型通过波长的二阶多项式描述了朗伯反照率的光谱依赖性。通过分析包含不同类型表面的实验室光谱的 ECOSTRESS 库，我们发现二次函数可能不是短波红外 (SWIR) 范围内表面反射光谱依赖性的最佳表示。三阶多项式的使用已经改善了甲烷数据，使得异常在多个地点（例如西伯利亚、澳大利亚和阿尔及利亚）消失，而不会影响其他地方的数据质量，并且拟合质量显着提高。我们还发现，低反照率场景中检索到的甲烷的已知偏差略有改善，但仍然需要应用后验校正，从而留下了关于反照率偏差的根本原因的问题。在全球范围内应用调整后的表面模型后，我们使用 TCCON 和温室气体观测卫星 (GOSAT) 数据进行常规验证。 GOSAT 比较并没有显着改善，而 TCCON 验证结果显示，某些站点有 2-4ppb 的小幅改善，比人工 XCH4 增强小 10 倍。这反映出 TCCON 站并不接近任何已校正的人工制品，暗示 S5-P XCH4 数据产品当前验证方法的局限性。
Abstract. Satellite remote sensing of methane (CH4) using the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Copernicus Sentinel-5 Precursor (S5-P) satellite is key to monitor and quantify emissions globally. Overall, the S5-P methane data are of satisfying quality, demonstrated by the product validation with ground-based measurements from the Total Carbon Column Observing Network (TCCON). However, analysis of TROPOMI dry-air column mixing ratio (XCH4) data has pointed to a few false methane anomalies up to 20–40 ppb that can potentially be misinterpreted as enhancements due to strong emission sources. These artefacts are caused by spectral features of the underlying surfaces of specific materials (e.g. carbonate rocks), which are not well represented in the forward model of the retrieval algorithm. In this study we show that the observed anomalies are due to the surface model which describes the spectral dependence of the Lambertian albedo by a second-order polynomial in wavelength. By analysing the ECOSTRESS library that contains laboratory spectra for different types of surfaces, we find that a quadratic function might not be the most optimal representation of the surface reflectance spectral dependencies in the short-wave infrared (SWIR) range. Already the use of a third-order polynomial improves the methane data such that the anomalies disappear at several locations (e.g. Siberia, Australia and Algeria) without affecting the data quality elsewhere, and the quality of the fit significantly improves. We also found that the known bias in retrieved methane for low-albedo scenes slightly improves, but still, a posterior correction needs to be applied, leaving open the question about the root cause of the albedo bias. After applying the adjusted surface model globally, we perform the routine validation with TCCON and Greenhouse gases Observing SATellite (GOSAT) data. GOSAT comparison does not significantly improve, while TCCON validation results show a small improvement in some stations of 2–4 ppb, up to a factor of 10 smaller than the artificial XCH4 enhancements. This reflects that TCCON stations are not close to any of the corrected artefacts, hinting at a limitation of the current validation approach of the S5-P XCH4 data product.
根据卫星数据推断 2010 年至 2016 年间热带非洲甲烷排放量增加
DOI：
10.5194/acp-2019-477
发表时间：
2019
期刊：
--
影响因子：
--
作者：
Lunt M
通讯作者：
Lunt M
影响因子：
13.5
作者：
Buchwitz, M.;Reuter, M.;Wunch, D.
通讯作者：
Wunch, D.
影响因子：
4.4
作者：
Guerlet, S.;Butz, A.;Aben, I.
通讯作者：
Aben, I.