Simulated multispectral temperature and atmospheric composition retrievals for the JPL GEO-IR Sounder

Atmos. Meas. Tech., 15, 1251–1267, 2022 https://doi.org/10.5194/amt-15-1251-2022 © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License. Simulated multispectral temperature and atmospheric composition retrievals for the JPL GEO-IR Sounder Vijay Natraj1 , Ming Luo1 , Jean-Francois Blavier1 , Vivienne H. Payne1 , Derek J. Posselt1 , Stanley P. Sander1 , Zhao-Cheng Zeng2,3 , Jessica L. Neu1 , Denis Tremblay4 , Longtao Wu1 , Jacola A. Roman1 , Yen-Hung Wu1 , and Leonard I. Dorsky1 1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA 90095, USA 3 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA 4 Global & Science Technology, Inc., Greenbelt, MD 20770, USA 2 Joint Correspondence: Vijay Natraj () Received: 20 September 2021 – Discussion started: 5 October 2021 Revised: 27 January 2022 – Accepted: 28 January 2022 – Published: 10 March 2022 Abstract. Satellite measurements enable quantification of atmospheric temperature, humidity, wind fields, and trace gas vertical profiles. The majority of current instruments operate on polar orbiting satellites and either in the thermal and mid-wave or in the shortwave infrared spectral regions. We present a new multispectral instrument concept for improved measurements from geostationary orbit (GEO) with sensitivity to the boundary layer. The JPL GEO-IR Sounder, which is an imaging Fourier transform spectrometer, uses a wide spectral range (1–15.4 µm) encompassing both reflected solar and thermal emission bands to improve sensitivity to the lower troposphere and boundary layer. We perform retrieval simulations for both clean and polluted scenarios that also encompass different temperature and humidity profiles. The results illustrate the benefits of combining shortwave and thermal infrared measurements. In particular, the former adds information in the boundary layer, while the latter helps to separate near-surface and mid-tropospheric variability. The performance of the JPL GEO-IR Sounder is similar to or better than currently operational instruments. The proposed concept is expected to improve weather forecasting as well as severe storm tracking and forecasting and also benefit local and global air quality and climate research. 1 Introduction The Program of Record (PoR) of current and planned satellite observations, as described in the 2017 US Earth Science Decadal Survey (National Academies of Sciences, Engineering, and Medicine, 2018), includes a range of spectrally resolved radiance measurements in the thermal and shortwave infrared (TIR and SWIR) wavelength regions that provide key information on atmospheric temperature (TATM), water vapor (H2 O), and a range of trace gases (see Table 1 for a definition of spectral range designations). The TIR region can be further subdivided into mid-wave, longwave, and very longwave infrared (MIR, LWIR, and VLWIR) regions. Profiling of key gases including CO, CH4 , and CO2 with sensitivity to planetary boundary layer (PBL) abundances was identified as a gap in current capability in the 2017 Decadal Survey, as was the promise of multispectral approaches for addressing this gap. In fact, combining radiances from the (thermalemission-dominated) TIR and (solar-reflection-dominated) SWIR spectral regions has been shown to increase the vertical information content for these gases, providing improved information on near-surface variations relative to retrievals from the thermal alone (e.g., Christi and Stephens, 2004; Worden et al., 2010, 2015; Kuai et al., 2013; Fu et al., 2016; Zhang et al., 2018; Schneider et al., 2021). Such retrievals have the potential to extend the utility of satellite products for air quality forecasting, greenhouse gas monitoring, and carbon cycle research. In addition, combining TIR and SWIR infrared radiances also offers opportunities for increasing the Published by Copernicus Publications on behalf of the European Geosciences Union. 1252 V. Natraj et al.: Simulated multispectral retrievals Table 1. Spectral ranges and their designations used in this study. Spectral range (µm) Spectral range (cm−1 ) VLWIR > 10 < 1000 LWIR 5–10 1000–2000 MWIR 3–5 2000–3333 SWIR 1–3 3333–10 000 TIR >3 < 3333 Designation vertical information of H2 O retrievals in the PBL, another topic highlighted by the Decadal Survey and by the NASA Decadal Survey PBL Incubation Study Team (Teixeira et al., 2021). Under clear-sky conditions, the SWIR provides sensitivity to H2 O (e.g., Noël et al., 2005; Trent et al., 2018; Nelson et al., 2016), CO (e.g., Buchwitz et al., 2004; Deeter et al., 2009; Landgraf et al., 2016; Borsdorff et al., 2017, 2018), CH4 (e.g., Buchwitz et al., 2005; Frankenberg et al., 2006; Yokota et al., 2009; Hu et al., 2018; Parker et al., 2020) and CO2 (e.g., Buchwitz et al., 2005; Yokota et al., 2009; O’Dell et al., 2018) throughout the full atmospheric column, providing complementary information to the TIR radiances that are strongly sensitive to the details of the profile of TATM, H2 O, and trace gases but have variable sensitivity to the PBL, depending on surface and atmospheric conditions. Table 2 shows a list of current and planned missions making spectrally resolved, spaceborne TIR and SWIR measurements. In low Earth orbit (LEO), the MOPITT instrument on the Terra platform has been providing a record of TIR + SWIR CO for over 2 decades (Buchholz et al., 2021). GOSAT provides spectrally resolved TIR and SWIR radiances on the same platform, with coverage of SWIR CO2 and CH4 bands, as well as H2 O absorption (Trent et al., 2018), but not SWIR CO. The TROPOMI instrument on the Sentinel-5P satellite flies in formation with the CrIS instrument on the Suomi-NPP satellite, providing nearly coincident observations of TIR and SWIR as well as presenting opportunities for multispectral retrievals of CO and CH4 . Measurements from geostationary (GEO) orbit can provide contiguous horizontal (∼ 4 km) and temporal (full sounding disk coverage in 1–2 h) resolution not possible from LEO (e.g., Schmit et al., 2009). The IRS instrument onboard the Meteosat Third Generation Sounder platform will track the four-dimensional structure of TATM and H2 O (Holmlund et al., 2021). The GIIRS instrument on the Fengyun-4 meteorological satellite has similar capabilities (Yang et al., 2017). Adkins et al. (2021) describe in comprehensive detail the value of a hyperspectral IR sounder in GEO orbit. Based on this report, an advanced high-resolution IR sounder has been recommended for the Geostationary Extended Observations (GeoXO) mission Atmos. Meas. Tech., 15, 1251–1267, 2022 (https://www.nesdis.noaa.gov/next-generation-satellites/ geostationary-extended-observations-geoxo, last access: 25 February 2022). However, none of the current or planned instru (...truncated)