RAL IMS retrieval of SO2 and sulphates (January to April 2022)

RAL IMS retrieval of SO2 and sulphates

Description of the product

The RAL (Rutherford Appleton Laboratory) Infrared/Microwave Sounder (IMS) retrieval core scheme (Siddans, 2019) uses an optimal estimation spectral fitting procedure to retrieve atmospheric and surface parameters jointly from co-located measurements by IASI (Infrared Atmospheric Sounding Interferometer), AMSU (Advanced Microwave Sounding Unit) and MHS(Microwave Humidity Sounder) on MetOp-B spacecraft, using RTTOV 12 (Radiative Transfer for TOVS)(Saunders et al., 2017) as the forward radiative transfer model. The use of RTTOV 12 enables the quantitative retrieval of volcanic-specific aerosols (sulphate aerosol) and trace gases (SO2). The present dataset includes IMS SO2 and sulphate aerosols retrievals from its near-real time implementation. The IMS scheme   retrieves the SO2 in the sensitive region around 1100-1200 cm−1, in ppbv assuming a uniform vertical mixing ratio. It retrieves sulphate-specific AOD (Aerosol Optical Depth) at 1170 cm−1 (i.e. the peak of the mid-infrared extinction cross section (Sellitto and Legras, 2016)), assuming a Gaussian extinction coefficient profile shape peaking at 20 km altitude, with 2 km full-width half-maximum. The bulk of the spectroscopic information on SO2 and sulphate aerosols, in the IMS scheme, thus comes from the IASI Fourier transform spectrometer (Clerbaux et al., 2009).

We refer to the two retrieved products as IMS SO2 and IMS SA OD.

References

Clerbaux, C., Boynard, A., Clarisse, L., George, M., Hadji-Lazaro, J., Herbin, H., Hurtmans, D., Pommier, M., Razavi, A., Turquety, S., Wespes, C., and Coheur, P.-F.: Monitoring of atmospheric composition using the thermal infrared IASI/MetOp sounder, Atmospheric Chemistry and Physics, 9, 6041–6054, https://doi.org/10.5194/acp-9-6041-2009, 2009.

Saunders, R., Hocking, J., Rundle, D., Rayer, P., Hayemann, S., Matricardi, A., Lupu, C., Brunel, P., and Vidot, J.: RTTOV-12 SCIENCE AND VALIDATION REPORT; Version : 1.0, Doc ID : NWPSAF-MO-TV-41, https://nwp-saf.eumetsat.int/site/download/documentation/rtm/docs_rttov12/rttov12_svr.pdf, 2017.

Sellitto, P. and Legras, B.: Sensitivity of thermal infrared nadir instruments to the chemical and microphysical properties of UTLS secondary sulfate aerosols, Atmospheric Measurement Techniques, 9, 115–132, https://doi.org/10.5194/amt-9-115-2016, 2016.

Siddans, R.: Water Vapour Climate Change Initiative (WV-CCI) - Phase One, Deliverable 2.2; Version 1.0, https://climate.esa.int/documents/1337/Water_Vapour_CCI_D2.2_ATBD_Part2-IMS_L2_product_v1.0.pdf, 2019.

Description of the data

The archive IMS-2022.tgz contains level 3 daily gridded files for the two retrieved products IMS SO2 and IMS SA OD in the period 13 January to 30 April 2022. A few days are missing between 9 March and 13 March. The first 8 letters of the name of each file contain the date. There are 4 files per day as the two products are in separate files and there is a file collecting day-time orbits and another one for night-time orbits every day.

For the 28 April 2022, the four files are

20220428_ims_metopb_tir_qnrt_aot0_day_global_g0.5_qc0.nc         SA OD day-time orbits

20220428_ims_metopb_tir_qnrt_aot0_night_global_g0.5_qc0.nc       SA OD night-time orbits

20220428_ims_metopb_tir_qnrt_so2_day_global_g0.5_qc0.nc          SO2 day-time orbits

20220428_ims_metopb_tir_qnrt_so2_night_global_g0.5_qc0.nc        SO2 night-time orbits

The names for other dates can be derived by changing the first 8 letters.

The format is netdcf4 that is readable with many programming languages and graphics packages.

The data are on a [-90,90] x [-180,180] lat x lon grid with resolution 0.25°, that is a 720 x 1440 array of centered values.

For both SO2 and SA OD, the values are in the ‘data’ variable. The variable ‘qa_value’ is a quality control value used to screen values for plotting; 0 means do not plot; -1 means mask is not defined so the mask is not used (data will be plotted).

SO2 units are ppbv (assuming a uniform mixing ratio vertical profile ). SA OD is an optical depth with no unit.

Reading software

A python package to read and process the data is available at https://github.com/bernard-legras/ASTuS/tree/master/IMS and in the IMS-reader.tgz archive

RAL IMS 二氧化硫与硫酸盐反演数据集

## 产品说明
卢瑟福阿普尔顿实验室（Rutherford Appleton Laboratory, RAL）的红外/微波探测仪（Infrared/Microwave Sounder, IMS）反演核心方案（Siddans, 2019）采用最优估计光谱拟合算法，联合利用MetOp-B卫星上搭载的红外大气探测干涉仪（Infrared Atmospheric Sounding Interferometer, IASI）、先进微波探测单元（Advanced Microwave Sounding Unit, AMSU）与微波湿度探测仪（Microwave Humidity Sounder, MHS）的同步观测数据开展大气与地表参数反演，正向辐射传输模型采用TOVS辐射传输模型（Radiative Transfer for TOVS, RTTOV）12版本（Saunders等, 2017）。
借助RTTOV 12模型，可定量反演火山专属气溶胶（硫酸盐气溶胶）与痕量气体（二氧化硫，SO₂）。本数据集包含IMS近实时运行方案下获取的SO₂与硫酸盐气溶胶反演结果。
IMS方案在1100~1200 cm⁻¹的敏感波段反演SO₂，以十亿分之一体积混合比（ppbv）为单位，假设垂直混合比均匀分布；在1170 cm⁻¹（即中红外消光截面峰值波段，Sellitto和Legras, 2016）反演硫酸盐专属气溶胶光学厚度（Aerosol Optical Depth, AOD），假设消光系数廓线为高斯型，峰值位于20 km高度，半高全宽为2 km。IMS方案中，SO₂与硫酸盐气溶胶的大部分光谱信息均来自IASI傅里叶变换光谱仪（Clerbaux等, 2009）。
本数据集的两种反演产品分别命名为IMS SO₂与IMS SA OD。

## 参考文献
1. Clerbaux C, Boynard A, Clarisse L, et al. Monitoring of atmospheric composition using the thermal infrared IASI/MetOp sounder[J]. Atmospheric Chemistry and Physics, 2009, 9: 6041-6054. https://doi.org/10.5194/acp-9-6041-2009.
2. Saunders R, Hocking J, Rundle D, et al. RTTOV-12 SCIENCE AND VALIDATION REPORT; Version 1.0, Doc ID: NWPSAF-MO-TV-41[EB/OL]. 2017. https://nwp-saf.eumetsat.int/site/download/documentation/rtm/docs_rttov12/rttov12_svr.pdf.
3. Sellitto P, Legras B. Sensitivity of thermal infrared nadir instruments to the chemical and microphysical properties of UTLS secondary sulfate aerosols[J]. Atmospheric Measurement Techniques, 2016, 9: 115-132. https://doi.org/10.5194/amt-9-115-2016.
4. Siddans R. Water Vapour Climate Change Initiative (WV-CCI) - Phase One, Deliverable 2.2; Version 1.0[EB/OL]. 2019. https://climate.esa.int/documents/1337/Water_Vapour_CCI_D2.2_ATBD_Part2-IMS_L2_product_v1.0.pdf.

## 数据说明
归档文件IMS-2022.tgz包含2022年1月13日至4月30日期间两种反演产品IMS SO₂与IMS SA OD的三级逐日网格化文件，3月9日至3月13日期间存在少量数据缺失。每个文件名的前8位字符为对应日期。每日共生成4个文件：两种产品分别单独存储，且每日各有一个昼间轨道文件与一个夜间轨道文件。
以2022年4月28日为例，4个文件分别为：
1. `20220428_ims_metopb_tir_qnrt_aot0_day_global_g0.5_qc0.nc`：SA OD昼间轨道文件
2. `20220428_ims_metopb_tir_qnrt_aot0_night_global_g0.5_qc0.nc`：SA OD夜间轨道文件
3. `20220428_ims_metopb_tir_qnrt_so2_day_global_g0.5_qc0.nc`：SO₂昼间轨道文件
4. `20220428_ims_metopb_tir_qnrt_so2_night_global_g0.5_qc0.nc`：SO₂夜间轨道文件
其余日期的文件名可通过修改前8位日期字符得到。
数据格式为netCDF4格式，可被多数编程语言与图形处理软件读取。
数据采用纬度范围[-90,90]、经度范围[-180,180]的网格，分辨率为0.25°，即包含720×1440个中心格点值。
对于SO₂与SA OD两种产品，数据均存储在`data`变量中。变量`qa_value`为质量控制值，用于筛选绘图所需数据：0表示不绘制该点；-1表示未定义掩膜，因此不使用掩膜（直接绘制数据）。
SO₂的单位为ppbv（假设垂直混合比均匀分布）；SA OD为光学厚度，无单位。

## 数据读取软件
可从https://github.com/bernard-legras/ASTuS/tree/master/IMS 或IMS-reader.tgz归档文件中获取用于读取与处理本数据集的Python工具包。