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Summary of the Second OMI–TROPOMI Science Team Meeting
Introduction
The second joint Ozone Monitoring Instrument (OMI)–TROPOspheric Monitoring Instrument (TROPOMI) Science Team (ST) meeting was held June 3–6, 2024. The meeting used a hybrid format, with the in-person meeting hosted at the National Center for Atmospheric Research (NCAR) in Boulder, CO. This was the first OMI meeting to offer virtual participation since the COVID-19 travel restrictions. Combining the onsite and virtual attendees, the meeting drew 125 participants – see Photo.
OMI flies on NASA’s Earth Observing System (EOS) Aura platform, launched July 15, 2004. TROPOMI flies on the European Space Agency’s (ESA)–Copernicus Sentinel-5 Precursor platform. OMI has collected nearly 20 years of data and TROPOMI now has amassed 5 years of data.
Meeting content was organized around the following four objectives:
discussion of the final reprocessing of OMI data (called Collection 4) and of data preservation; discussion of OMI data continuity and enhancements using TROPOMI measurements; development of unique TROPOMI products [e.g., methane (CH4)], applications (e.g., tracking emissions – and using them as indicators of socioeconomic and military activities), and new focus regions (e.g., Africa); and leverage synergies between atmospheric composition (AC) and greenhouse gas (GHG) missions, which form the international constellation of low Earth orbit (LEO) and geostationary orbit (GEO) satellites. The remainder of this article summarizes the highlights from each day of the meeting.
Photo. Group photo of the in-person participants at the OMI–TROPOMI Science Team meeting. Photo credit: Shaun Bush/NCAR’s Atmospheric Chemistry Observations & Modeling DAY ONE
The topics covered on the first day of the meeting included OMI instrument performance, calibration, final Collection 4 reprocessing, and plans for data preservation.
OMI and Data Products Update
Pieternel Levelt [Royal Netherlands Meteorological Institute (KNMI)—OMI Principal Investigator (PI) and NCAR’s Atmospheric Chemistry Observations & Modeling (ACOM) Laboratory—Director] began her presentation by dedicating the meeting to the memory of Johan de Vries, whose untimely death came as a shock to the OMI and TROPOMI teams – see In Memoriam: Johan de Vries for a celebration of his accomplishments and contributions to the OMI-TROPOMI team. She then went on to give a status update on OMI, which is one of two currently operating instruments on EOS Aura [the other being the Microwave Limb Sounder (MLS)]. OMI is the longest operating and stable ultraviolet–visible (UV-VIS) spectrometer. It continues to “age gracefully” thanks to its design, contamination control measures undertaken after the launch, and stable optical bench temperature. Lessons learned during integration of OMI on the Aura spacecraft (e.g., provide additional charged couple device shielding) and operations (i.e., monitor partial Earth-view port blockages) guided the development and operations of the follow-on TROPOMI mission.
Continued monitoring of OMI performance is crucial for extending science- and trend-quality OMI records to the end of the Aura mission (currently expected in 2026). Antje Ludewig [KNMI] described the new OMI Level-1B (L1B) processor (Collection 4), which is based on TROPOMI data flow and optimized calibrations. The processor has been transferred to the U.S. OMI ST, led by Joanna Joiner [NASA’s Goddard Space Flight Center (GSFC)]. Matthew Bandel [Science Systems and Applications, Inc. (SSAI)] described NASA’s new OMI monitoring tools.
Sergey Marchenko [SSAI] discussed OMI daily spectral solar irradiance (SSI) data, which are used for monitoring solar activity and can be compared with the dedicated Total and Spectral Solar Irradiance Sensor (TSIS-1) on the International Space Station. Continuation of OMI measurements will allow comparisons with the upcoming NASA TSIS-2 mission. Antje Inness [European Centre for Medium-range Weather Forecasts (ECMWF)] described operational assimilation of OMI and TROPOMI near-real time data into the European Copernicus Atmosphere Monitoring Service (CAMS) daily analysis/forecast and re-analysis – see Figure 1.
In Memoriam: Johan de Vries
Johan de Vries
June 10, 1956 – May 8, 2024 Johan de Vries [Airbus Netherlands—Senior Specialist Remote Sensing] passed away suddenly on May 8, 2024, after a distinguished career. As a member of the Ozone Monitoring Instrument (OMI)–TROPOspheric Monitoring Instrument (TROPOMI) program, Johan conceptualized the idea of using a two-dimensional (2D) charged couple detector (CCD) for the OMI imaging spectrometer. This “push-broom” design led to high-spatial resolution spectra combined with high-spatial resolution and daily global coverage capability. His pioneering design for OMI has now been repeated on several other U.S. and international atmospheric composition measuring instruments – in both low and geostationary orbits – that are either in orbit or planned for launch soon. This achievement ensures that Johan’s legacy will live on for many years to come as these push-broom Earth observing spectrometers result in unprecedented data for environmental research and applications. The OMI and TROPOMI teams express their deepest condolences to de Vries family and colleagues over this loss.
Figure 1. An example of TROPOMI pixel nitrogen dioxide (NO2) observations over Europe on September 8, 2018 [top] and the corresponding super observations [bottom] for a model grid of 0.5 x 0.5o. Cloudy locations are colored grey. TROPOMI super observations are tested for use in the European Centre for Medium Range Weather Forecasting (ECMWF) Copernicus Atmosphere Monitoring Service (CAMS) data assimilation framework and will also be used for combined OMI–TROPOMI gridded datasets. Figure credit: reprinted from a 2024 paper posted on EGUSphere. Updates on OMI and TROPOMI Level-2 Data Products
The U.S. and Netherlands OMI STs continue to collaborate closely on reprocessing and improving OMI and TROPOMI L2 science products. During the meeting, one or more presenters reported on each product, which are described in the paragraphs that follow.
Serena Di Pede [KNMI] discussed the latest algorithm updates to the Collection 4 OMI Total Column Ozone (O3) product, which is derived using differential absorption spectroscopy (DOAS). She compared results from the new algorithm with the previous Collection 3 and with both the TROPOMI and OMI NASA O3 total column (Collection 3) algorithms. Collection 4 improved on previous versions by reducing the retrieval fit error and the along-track stripes of the product.
Juseon “Sunny” Bak and Xiong Liu [both from Smithsonian Astrophysical Observatory (SAO)] gave updates on the status of the Collection 4 O3 profile products.
Lok Lamsal [GSFC/University of Maryland, Baltimore County (UMBC)] and Henk Eskes [KNMI] compared Collection 3 and Collection 4 of the nitrogen dioxide (NO2) products.
Zolal Ayzpour [SAO] discussed the status of the OMI Collection 4 formaldehyde (HCHO) product.
Hyeong-Ahn Kwon [SAO] presented a poster that updated the Glyoxal product.
Omar Torres [GSFC] and Changwoo Ahn [GSFC/SSAI] presented regional trend analyses using the re-processed OMI Collection 4 absorbing aerosol product – see Figure 2.
Figure 2. Reprocessed OMI records (from Collection 4) of monthly average aerosol optical depth (AOD) at 388 nm derived from the OMI aerosol algorithm (OMAERUV) over Western North America (WNA): 30°N–50°N, 110°W–128°W) [top] and over Eastern China (EC): 25°N–43°N, 112°E–124°E) [bottom]. A repeatable annual cycle over WNA occurred with autumn minimum at around 0.1 and a spring maximum in the vicinity of 0.4 during the 2005–2016 period. After 2017 much larger AOD maxima in the late summer are associated with wildfire smoke occurrence. Over EC (bottom) the 2005–2014 AOD record depicts a large spring maxima (0.7 and larger) due to long-range transport of dust and secondary pollution aerosols followed by late autumn minima (around 0.3). A significant AOD decrease is observed starting in 2015 with reduced minimum and maximum values to about 0.2 and 0.5 respectively. The drastic change in AOD load over this region is associated with pollution control measures enacted over the last decade. Figure credit: Changwoo Ahn/GSFC/SSAI and Omar Torres/GSFC Updates on EOS Synergy Products
Several presenters and posters during the meeting gave updates on EOS synergy products, where OMI data are combined with data from another instrument on one of the EOS flagships. These are described below.
Brad Fisher [SSAI] presented a poster on the Joint OMI–Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products.
Wenhan Qin [GSFC/SSAI] presented a poster on the MODIS–OMI Geometry Dependent Lambertian Equivalent Surface Reflectivity (GLER) product.
Jerry Ziemke [GSFC and Morgan State University (MSU)] presented on the OMI–MLS Tropospheric Ozone product that showed post-COVID tropospheric O3 levels measured using this product, which are consistent with similar measurements obtained using other satellite O3 data – see Figure 3.
Figure 3. Anomaly maps of merged tropospheric column O3 (TCO) satellite data (Dobson Units) for spring–summer 2020–2023. In this context, an anomaly is defined as deseasonalized O3 data. The anomaly maps are derived by first calculating seasonal climatology maps for 2016–2019 (i.e., pre-COVID pandemic) and then subtracting these climatology maps from the entire data record.
Note: The sensors used in this analysis include: the Ozone Mapping and Profiler Suite (OMPS)/ Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and Cross-track Infrared Sounder (CrIS) on the Joint Polar Satellite System (JPSS) missions, which currently include the joint NASA–NOAA Suomi National Polar-orbiting Partnership (Suomi NPP), NOAA-20, and NOAA-21; the Earth Polychromatic Imaging Camera (EPIC)/MERRA-2 on the Deep Space Climate Observatory (DSCOVR); the Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS), both on EOS Aura; the Infrared Atmospheric Sounding Interferometer (IASI)/ Fast Optimal Retrievals on Layers (FORLI), IASI/SOftware for Fast Retrievals of IASI Data (SOFRID), and IASI/Global Ozone Monitoring Experiment–2 (GOME2). IASI flies on the European MetOp-A, -B, and -C missions. The OMPS/MERRA-2 and EPIC/MERRA-2 products subtract coincident MERRA-2 stratospheric column O3 from total O3 to derive tropospheric column O3. Figure credit: Jerry Ziemke/GSFC and Morgan State University (MSU) Updates on Multisatellite Climate Data Records
The OMI ST also discussed refining and analyzing multisatellite climate data records (CDRs) that have been processed with consistent algorithms. Several presenters reported on this work, who are mentioned below.
Jenny Stavrakou [Koninklijk Belgisch Instituut voor Ruimte-Aeronomie, Royal Belgian Institute for Space Aeronomy (BIRA–IASB)], reported on work focusing on the OMI and TROPOMI HCHO CDR and Huan Yu [BIRA–IASB)] reported harmonized OMI and TROPOMI cloud height datasets based on improved O2-O2 absorption retrieval algorithm.
Lok Lamsal [GSFC/UMBC, Goddard Earth Sciences Technology and Research (GESTAR) II], Henk Eskes, and Pepijn Veefkind [KNMI] reported on the OMI and TROPOMI NO2 CDRs – see Figure 4.
Si-Wan Kim [Yonsei University, South Korea] reported on OMI and TROPOMI long-term NO2 trends.
Figure 4. OMI nitrogen dioxide (NO2) time series bridging the first GOME mission (which flew on the European Remote Sensing Satellite–2 (ERS–2) from 1995–2011 with limited coverage after 2003) and measurements from the two currently operating missions – OMI (2004–present) and TROPOMI (2017–present) – offer consistent climate data records that allow for studying long-term changes. This example shows tropospheric NO2 column time series from three instruments over Phoenix, AZ. The overlap between the OMI and TROPOMI missions allows for intercomparison between the two, which is crucial to avoid continuity-gaps in multi-instrument time series. The ERS-2 (GOME) had a morning equator crossing time (10:30 AM), while Aura (OMI) and Metop (TROPOMI) have afternoon equator crossing times of 1:45 PM and 1:30 PM respectively. Figure credit: Lok Lamsal/GSFC/University of Maryland, Baltimore County (UMBC) Update on Aura’s Drifting Orbit
Bryan Duncan [GSFC—Aura Project Scientist] closed out the first day with a presentation summarizing predictions of Aura’s drifting orbit. Overall, the impact of Aura’s drift is expected to be minor, and the OMI and MLS teams will be able to maintain science quality data for most data products. He thanked the OMI/TROPOMI ST and user community for expressing their strong support for continuing Aura observations until the end of the Aura mission in mid–2026.
DAY TWO
The second day of the meeting focused on current and upcoming LEO and GEO Atmospheric Composition (AC) missions.
TROPOMI Mission and Data Product Updates
Veefkind presented an update on the TROPOMI mission, which provides continuation and enhancements for all OMI products. Tobias Borssdorf [Stichting Ruimte Onderzoek Nederland (SRON), or Netherlands Institute for Space Research] explained how TROPOMI, with its innovative shortwave infrared (SWIR) spectrometer, measures CH4 and carbon monoxide (CO). This approach continues measurements that began by the Measurements of Pollution in the Troposphere (MOPITT) instrument on Terra.
Hiren Jethva [NASA Airborne Science Program] and Torres presented new TROPOMI near-UV aerosol products, including a new aerosol layer optical centroid height product, which takes advantage of the TROPOMI extended spectral range – see Figure 5.
Figure 5. Global gridded (0.10° x 0.10°) composite map of aerosol layer optical centroid height (AH) retrieved from TROPOMI O2-B band observations from May–September 2023. Figure credit: Hiren Jethva/NASA Airborne Science Program GEMS–TEMPO–Sentinel-4 (UVN): A Geostationary Air Quality Constellation
TROPOMI global observations serve as a de facto calibration standard used to homogenize a new constellation of three missions that will provide AC observations for most of the Northern Hemisphere from GEO. Two of the three constellation members are already in orbit. Jhoon Kim [Yonsei University—PI] discussed the Geostationary Environmental Monitoring Spectrometer (GEMS), launched on February 19, 2020 aboard the Republic of Korea’s GEO-KOMPSAT-2B satellite. It is making GEO AC measurements over Asia. The GEMS team is working on validating measurements of NO2 diurnal variations using ground-based measurements from the PANDORA Global Network over Asia and aircraft measurements from the ASIA–AQ field campaign.
Liu discussed NASA’s Tropospheric Emission Monitoring of Pollution (TEMPO) spectrometer, launched on April 7, 2023, aboard a commercial INTELSAT 40E satellite. From its GEO vantage point, TEMPO can observe the Continental U.S., Southern Canada, Mexico, and the coastal waters of the Northwestern Atlantic and Northeastern Pacific oceans.
Gonzales Abad [SAO] presented the first measurements from TEMPO. He explained that TEMPO’s design is similar to GEMS, but GEMS includes an additional visible and near infrared (VNIR) spectral channel (540–740 nm) to measure tropospheric O3, O2, and water vapor (H2Ov). TEMPO can perform optimized morning scans, twilight scans, and scans with high temporal resolution (5–10 minutes) over selected regions. Abad reported that the TEMPO team released L1B spectra and the first provisional public L2 products (Version 3), including NO2, HCHO, and total column O3. Andrew Rollins [National Oceanic and Atmospheric Administration’s (NOAA) Chemical Sciences Laboratory (CSL)] reported that the TEMPO team is working on validation of provisional data using both ground-based data from PANDORA spectrometers and data collected during several different airborne campaigns completed during the summer of 2023 and compiled on the AGES+ website.
Ben Veihelmann [ESA’s European Space Research and Technology Center—PI] explained that ESA’s Copernicus Sentinel-4 mission will be the final member of the GEO AC constellation. Veefkind summarized the Sentinel-4 mission, which is expected to launch on the Meteosat Third Generation (MTG)-Sounder 1 (MTG-S1) platform in 2025. The mission is dedicated to measuring air quality and O3 over Europe and parts of the Atlantic and North Africa. Sentinel-4 will deploy the first operational UV-Vis-NIR (UVN) imaging spectrometer on a geostationary satellite. (Airbus will build UVN, with ESA providing guidance.) Sentinel-4 includes two instruments launched in sequence on MTG-S1 and MTG-S2 platforms designed to have a combined lifetime of 15 years. The mission by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) will operate Sentinel-4, and the Deutsches Zentrum für Luft- und Raumfahrt (DLR) or German Aerospace Center will be responsible for operational L2 processing.
These three GEO AC missions, along with the upcoming ESA/EUMETSAT/Copernicus LEO (morning orbit, 9:30 a.m.) Sentinel-5 (S5) mission, will complete a LEO–GEO satellite constellation that will enable monitoring of the most industrialized and polluted regions in the Northern Hemisphere into the 2030s. Sentinel-5 will not continue the OMI–TROPOMI data record in the early afternoon; however, it will be placed in the morning orbit and follow ESA’s Global Ozone Monitoring Experiment (GOME) and EUMETSAT GOME-2 missions. By contrast, GEO AC observations over the Southern Hemisphere are currently not available. Several presenters described ongoing projects for capacity building for LEO satellite air quality data uptake and emission monitoring in Africa and advocated for the new geostationary measurements.
Synergy with Other Current or Upcoming Missions
Attendees discussed the synergy between upcoming AC, GHG, and ocean color missions. Current trends in satellite AC measurements are toward increased spatial resolution and combined observations of short-lived reactive trace gases – which are important for air quality (AQ) monitoring – and long-lived GHG – which are important for climate monitoring and carbon cycle assessments. Some trace gases (e.g., O3 and CH4) are both polluters and GHG agents. Others [e.g., NO2 and sulfur dioxide (SO2 )] are aerosol [particulate matter (PM)] and O3 precursors and are used as proxies and spatial indicators for anthropogenic CO2 and CH4 emissions.
Yasjka Meijer [ESA—Copernicus Anthropogenic Carbon Dioxide Monitoring (CO2M) Mission Scientist]) reviewed the plans for CO2M, which includes high-resolution measurements [~4 km2 (~1.5 mi2)] of CO2 , CH4 , and NO2.
Jochen Landgraf [SRON] described ESA’s new Twin Anthropogenic Greenhouse Gas Observers (TANGO) mission, which has the objective to measure CO2 , CH4 , and NO2 at even higher spatial resolution [~300 m (~984 ft)] using two small CubeSat spectrometers flying in formation.
Hiroshi Tanimoto [National Institute for Environmental Studies, Japan] described the Japan Aerospace Exploration Agency’s (JAXA) Global Observing SATellite for greenhouse gases and water cycle (GOSAT-GW) mission, which includes the Total Anthropogenic and Natural Emission mapping SpectrOmeter (TANSO-3) spectrometer to simultaneously measure CO2 , CH4, and NO2 with ~1–3 km (~0.6–1.8 mi) spatial resolution in focus mode. GOSAT-GW will also fly the Advanced Microwave Scanning Radiometer 3 (AMSR3).
Joanna Joiner [GSFC—Geostationary Extended Operations (GeoXO) Project Scientist and ACX Instrument Scientist] described the plans for the next-generation U.S. geosynchronous satellite constellation, which will consist of three satellites covering the full Earth disk: GEO-East, GEO-West, and GEO-Central. (By contrast, the current Geostationary Operational Environmental Satellite (GOES) series has two satellites: GOES–East and GOES–West.) GEO-Central will carry an advanced infrared sounder (GXS) for measuring vertical profiles of many trace gases, temperature and humidity, and a new UV-VIS spectrometer (ACX), which is a follow-on to TEMPO for AQ applications. Both GXS and ACX instruments will be built by BAE Systems, which acquired Ball Aerospace and Technology, and will also build the GeoXO ocean color spectrometer (OCX).
Andrew Sayer [UMBC] described NASA’s Plankton, Aerosols, Clouds, and ocean Ecosystem (PACE), which launched on February 8, 2024. The PACE payload includes a high-spatial resolution [~1 km (~0.6 mi) at nadir] Ocean Color Instrument (OCI), which is a UV-Vis-NIR spectrometer with discrete SWIR bands presenting additional opportunities for synergistic observations with the AC constellation. Sayer presented OCI “first light” aerosol data processed using the unified retrieval algorithm developed by Lorraine Remer [UMBC].
The second day concluded with a joint crossover session with NASA’s Health and Air Quality Applied Sciences Team (HAQAST) followed by a poster session. Several OMI–TROPOMI STM participants presented on a variety of topics that illustrate how OMI and TROPOMI data are being used to support numerous health and AQ applications. Duncan, who is also a member of HAQAST team, presented “20 years of health and air quality applications enabled by OMI data.” He highlighted OMI contributions to AQ and health applications, including NO2 trend monitoring, inferring trends of co-emitted species [e.g., CO2, CO, some Volatile Organic Compounds (VOCs)], validation of new satellite missions (e.g., TEMPO, PACE), and burden of disease studies.
DAY THREE
Discussions on the third day focused on advanced retrieval algorithms, leading to new products and new applications for OMI and TROPOMI data. Several presentations described applications of TROPOMI CH4 data and synergy with small satellites.
Advanced Retrieval Algorithms and New Data Products
Ilse Aben [SRON] described TROPOMI global detection of CH4 super-emitters using an automated system based on Machine Learning (ML) techniques – see Figure 6. Berend Schuit [SRON] provided additional detail on these methods. He introduced the TROPOMI CH4 web site to the meeting participants. He explained how TROPOMI global CH4 measurements use “tip-and-cue” dedicated satellites with much higher spatial resolution instruments [e.g., GHGSat with ~25-m (~82-ft) resolution] to scan for individual sources and estimate emission rates. Most CH4 super-emitters are related to urban areas and/or landfills, followed by plumes from gas and oil industries and coal mines.
Figure 6. Methane plume map produced by SRON shows TROPOMI large CH4 emission plumes for the week of the OMI–TROPOMI meeting (June 3–6, 2024). Figure credit: Itse Aben/Stichting Ruimte Onderzoek Nederland (SRON) Alba Lorente [Environmental Defense Fund—Methane Scientist] introduced a new MethaneSAT satellite launched in March 2024, which aims to fill the gap in understanding CH4 emissions on a regional scale [200 x 200 km2 (~77 x 77 mi2)] from at least 80% of global oil and gas production, agriculture, and urban regions. Alex Bradley [University of Colorado, Boulder] described improvements to TROPOMI CH4 retrievals that were achieved by correcting seasonal effects of changing surface albedo.
Daniel Jacob [Harvard University] presented several topics, including the highest resolution [~30 m (~98 ft)] NO2 plume retrievals from Landsat-8 – see Figure 7 – and Sentinel-2 imagers. He also discussed using a ML technique trained with TROPOMI data to improve NO2 retrievals from GEMS and modeling NO2 diurnal cycle and emission estimates. He introduced the ratio of ammonia (NH3) to NO2 (NH3/NO2) as an indicator of particulate matter with diameters less than 2.5 µm (PM2.5) nitrate sensitivity regime. Jacob emphasized the challenges related to satellite NO2 retrievals (e.g., accounting for a free-tropospheric NO2 background and aerosols).
Figure 7. Landsat Optical Land Imager (OLI) image, obtained on October 17, 2021 over Saudi Arabia, shows power plant exhaust, which contains nitrogen dioxide (NO2) drifting downwind from the sources (the two green circles are the stacks). The ultra-blue channel (430–450 nm) on OLI enables quantitative detection of NO2 in plumes from large point sources at 30-m (~98-ft) resolution. This provides a unique ability for monitoring point-source emissions of oxides of nitrogen (NOx). The two stacks in the image are separated by 2 km (~1.2 mi). Figure credit: Daniel Jacob – repurposed from a 2024 publication in Proceedings of the National Academies of Sciences (PNAS) Steffen Beirle [Max Planck Institute for Chemistry, Germany] explained his work to fit TROPOMI NO2 column measurements to investigate nitric oxide (NO) to NO2 processing in power plant plumes. Debra Griffin [Environment and Climate Change Canada (ECCC)] used TROPOMI NO2 observations and ML random forest technique to estimate NO2 surface concentrations. Sara Martinez-Alonso [NCAR] investigated geographical and seasonal variations in NO2 diurnal cycle using GEMS and TEMPO data. Ziemkecombined satellite O3 data to confirm a persistent low anomaly (~5–15%) in tropospheric O3 after 2020. Jethva presented advanced OMI and TROPOMI absorbing aerosol products. Yu described improved OMI and TROPOMI cloud datasets using the O2-O2 absorption band at 477 nm. Nicholas Parazoo [Jet Propulsion Laboratory (JPL)] described TROPOMI Fraunhofer line retrievals of red solar-induced chlorophyll fluorescence (SIF) near O2-B band (663–685 nm) to improve mapping of ocean primary productivity. Liyin He [Duke University] described using satellite terrestrial SIF data to study the effect of particulate pollution on ecosystem productivity.
New Applications
Zachary Fasnacht [SSAI] used OMI and TROPOMI spectra to train a neural network to gap-fill MODIS and Visible Infrared Imaging Radiometer Suite (VIIRS) ocean color data under aerosol, sun glint, and partly cloudy conditions. This ML method can also be applied to PACE OCI spectra. Anu-Maija Sundström [Finnish Meteorological Institute (FMI)] used OMI and TROPOMI SO2 and O3 data as proxies to study new particle formation events. Lindsey Anderson [University of Colorado, Boulder] described how she used TROPOMI NO2 and CO measurements to estimate the composition of wildfire emissions and their effect on forecasted air quality. Heesung Chong [SAO] applied OMI bromine oxide (BrO) retrievals to the NOAA operational Ozone Mapping and Profiling Suite Nadir Mapper (OMPS-NM) on joint NOAA–NASA Suomi-National Polar-orbiting Partnership (Suomi NPP) satellite with the possibility to continue afternoon measurements using similar OMPS-NM instruments on the four Joint Polar Satellite System missions (JPSS-1,-2,-3,-4) into the 2030s. (JPSS-1 and -2 are now in orbit and known as NOAA-20 and -21 respectively; JPSS-4 is planned for launch in 2027, with JPSS-3 currently targeted for 2032.)
Kim demonstrated the potential for using satellite NO2 and SO2 emissions as a window into socioeconomic issues that are not apparent by other methods. For example, she showed how OMI and TROPOMI data were widely used to monitor air quality improvements in the aftermath of COVID-19 lockdowns. (Brad Fisher [SSAI] presented a poster on a similar topic.)
Cathy Clerbaux [Center National d’Études Spatiale (CNES), or French Space Agency] showed how her team used TROPOMI NO2 data to trace the signal emitted by ships and used this information to determine how the shipping lanes through the Suez Canal changed in response to unrest in the Middle East. Iolanda Ialongo [FMI] showed a similar drop of NO2 emissions over Donetsk region due to the war in Ukraine. Levelt showed how OMI and TROPOMI NO2 data are used for capacity-building projects and for air quality reporting in Africa. She also advocated for additional geostationary AQ measurements over Africa.
DAY FOUR
Discussions on the final day focused on various methods of assimilating satellite data into air quality models for emission inversions and aircraft TEMPO validation campaigns. The meeting ended with Levelt giving her unique perspective on the OMI mission, as she reflected on more than two decades being involved with the development, launch, operation, and maintenance of OMI.
Assimilating Satellite Data into Models for Emissions
Brian McDonald [CSL] described advance chemical data assimilation of satellite data for emission inversions and the GReenhouse gas And Air Pollutants Emissions System (GRA2PES). He showed examples of assimilations using TROPOMI and TEMPO NO2 observations to adjust a priori emissions. He also showed that when TEMPO data are assimilated, NOx emissions adjust faster and tend to perform better at the urban scale. Adrian Jost [Max Planck Institute for Chemistry] described the ESA-funded World Emission project to improve pollutant and GHG emission inventories using satellite data. He showed examples of TROPOMI SO2 emissions from large-point sources and compared the data with bottom-up and NASA SO2 emissions catalogue.
Ivar van der Velde [SRON] presented a method to evaluate fire emissions using new satellite imagery of burned area and TROPOMI CO. Helene Peiro [SRON] described her work to combine TROPOMI CO and burned area information to compare the impact of prescribed fires versus wildfires on air quality in the U.S. She concluded that prescribed burning reduces CO pollution. Barbara Dix [University of Colorado, Boulder, Cooperative Institute for Research in Environmental Sciences] derived NOx emissions from U.S. oil and natural gas production using TROPOMI NO2 data and flux divergence method. She estimated TROPOMI CH4 emissions from Denver–Julesburg oil and natural gas production. Dix explained that the remaining challenge is to separate oil and gas emissions from other co-located CH4 sources. Ben Gaubert [NCAR, Atmospheric Chemistry Observations and Modeling] described nonlinear and non-Gaussian ensemble assimilation of MOPITT CO using the data assimilation research testbed (DART).
Andrew (Drew) Rollings [CSL] presented first TEMPO validation results from airborne field campaigns in 2023 (AGES+ ), including NOAA CSL Atmospheric Emissions and Reactions observed from Megacities to Marine Aeras (AEROMMA) and NASA’s Synergistic TEMPO Air Quality Science (STAQS) campaigns.
A Reflection on Twenty Years of OMI Observations
Levelt gave a closing presentation in which she reflected on her first involvement with the OMI mission as a young scientist back in 1998. This led to a collaboration with the international ST to develop the instrument, which was included as part of Aura’s payload when it launched in July 2004. She reminisced about important highlights from 2 decades of OMI, e.g., the 10-year anniversary STM at KNMI in 2014 (see “Celebrating Ten Years of OMI Observations,” The Earth Observer, May–Jun 2014, 26:3, 23–30), and the OMI ST receiving the NASA/U.S. Geological Survey Pecora award in 2018 and the American Meteorological Society’s Special award in 2021.
Levelt pointed out that in this combined OMI–TROPOMI meeting the movement towards using air pollution and GHG data together became apparent. She ended by saying that the OMI instrument continues to “age gracefully” and its legacy continues with the TROPOMI and LEO–GEO atmospheric composition constellation of satellites that were discussed during the meeting.
Conclusion
Overall, the second OMI–TROPOMI STM acknowledged OMI’s pioneering role and TROPOMI’s unique enhancements in measurements of atmospheric composition:
Ozone Layer Monitoring: Over the past two decades, OMI has provided invaluable data on the concentration and distribution of O3 in the Earth’s stratosphere. This data has been crucial for understanding and monitoring the recovery of the O3 layer following international agreements, such as the Montreal Protocol. Air Quality Assessment: OMI’s high-resolution measurements of air pollutants, such as NO2, SO2, and HCHO, have significantly advanced our understanding of air quality. This information has been vital for tracking pollution sources, studying their transport and transformation, and assessing their impact on human health and the environment. Climate Research: The data collected by OMI has enhanced our knowledge of the interactions between atmospheric chemistry and climate change. These insights have been instrumental in refining climate models and improving our predictions of future climate scenarios. Global Impact: The OMI instrument has provided near-daily global coverage of atmospheric data, which has been essential for scientists and policymakers worldwide. The comprehensive and reliable data from OMI has supported countless research projects and informed decisions aimed at protecting and improving our environment. OMI remains one of the most stable UV/Vis instruments over its two decades of science and trend quality data collection. The success of the OMI and TROPOMI instruments is a testament to the collaboration, expertise, and dedication of both teams.
Nickolay Krotkov
NASA’s Goddard Space Flight Center
Nickolay.a.krotkov@nasa.gov
Pieternel Levelt
National Center for Atmospheric Research, Atmospheric Chemistry Observations & Modeling
levelt@ucar.edu
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By European Space Agency
As BepiColombo sped past Mercury during its June 2023 flyby, it encountered a variety of features in the tiny planet’s magnetic field. These measurements provide a tantalising taste of the mysteries that the mission is set to investigate when it arrives in orbit around the Solar System’s innermost planet.
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By NASA
On Sept. 30, 1994, space shuttle Endeavour took to the skies on its 7th trip into space. During the 11-day mission, the STS-68 crew of Commander Michael A. Baker, Pilot Terrence “Terry” W. Wilcutt, and Mission Specialists Steven L. Smith, Daniel W. Bursch, Peter J.K. “Jeff” Wisoff, and Payload Commander Thomas “Tom” D. Jones operated the second Space Radar Laboratory (SRL-2) as part of NASA’s Mission to Planet Earth. Flying five months after SRL-1, results from the two missions provided unprecedented insight into Earth’s global environment across contrasting seasons. The astronauts observed pre-selected sites around the world as well as a volcano that erupted during their mission using SRL-2’s U.S., German, and Italian radar instruments and handheld cameras.
Left: The STS-68 crew patch. Right: Official photo of the STS-68 crew of Thomas D. Jones, front row left, Peter J.K. “Jeff” Wisoff, Steven L. Smith, and Daniel W. Bursch; Michael A. Baker, back row left, and Terrence W. Wilcutt.
In August 1993, NASA named Jones as the SRL-2 payload commander, eight months before he flew as a mission specialist on STS-59, the SRL-1 mission. When NASA could not meet JPL’s request to fly their personnel as payload specialists on the SRL missions, the compromise solution reached had one NASA astronaut – in this case, Jones – fly on both missions. Selected as an astronaut in 1990, STS-59 marked Jones’ first flight and STS-68 his second. In October 1993, NASA named the rest of the STS-68 crew. For Baker, selected in 1985, SRL-2 marked his third trip into space, having flown on STS-43 and STS-52. Along with Jones, Wilcutt, Bursch, and Wisoff all came from the class of 1990, nicknamed The Hairballs. STS-68 marked Wilcutt’s first spaceflight, while Bursch had flown once before on STS-51 and Wisoff on STS-57. Smith has the distinction as the first from his class of 1992 – The Hogs – assigned to a spaceflight, but the Aug. 18 launch abort robbed him of the distinction of the first to actually fly, the honor going instead to Jerry M. Linenger when STS-64 ended up flying before STS-68.
Left: The Spaceborne Imaging Radar-C (SIR-C) in Endeavour’s payload bay in the Orbiter Processing Facility at NASA’s Kennedy Space Center in Florida. Middle: Endeavour on Launch Pad 39A. Right: STS-68 crew in the Astrovan on its way to Launch Pad 39A for the Terminal Countdown Demonstration Test.
The SRL payloads consisted of three major components – the Spaceborne Imaging Radar-C (SIR-C), built by NASA’s Jet Propulsion Laboratory in Pasadena, California, the X-band Synthetic Aperture Radar (X-SAR) sponsored by the German Space Agency DLR and the Italian Space Agency ASI, and the Measurement of Air Pollution from Satellites (MAPS), built by NASA’s Langley Research Center in Hampton, Virginia. Scientists from 13 countries participated in the SRL data gathering program, providing ground truth at preselected observation sites. The SIR system first flew as SIR-A on STS-2 in November 1981, although the shortened mission limited data gathering. It flew again as SIR-B on STS-41G in October 1984, and gathering much useful data.
Building on that success, NASA planned to fly an SRL mission on STS-72A, launching in March 1987 into a near-polar orbit from Vandenberg Air Force, now Space Force, Base in California, but the Challenger accident canceled those plans. With polar orbits no longer attainable, a 57-degree inclination remained the highest achievable from NASA’s Kennedy Space Center (KSC) in Florida, still allowing the radar to study more than 75% of Earth’s landmasses. As originally envisioned, SRL-2 would fly about six months after the first mission, allowing data gathering during contrasting seasons. Shuttle schedules moved the date of the second mission up to August 1994, only four months after the first. But events intervened to partially mitigate that disruption.
Left: Launch abort at Launch Pad 39A at NASA’s Kennedy Space Center in Florida. Right: A few days after the launch abort, space shuttle Discovery arrives at Launch Pad 39B, left, with space shuttle Endeavour still on Launch Pad 39A, awaiting its rollback to the Vehicle Assembly Building.
Endeavour arrived back at KSC following its previous flight, the STS-59 SRL-1 mission, in May 1994. Workers in KSC’s Orbiter Processing Facility refurbished the SRL-1 payloads for their reflight and serviced the orbiter, rolling it over to the Vehicle Assembly Building (VAB) on July 21 for mating with its External Tank and Solid Rocket Boosters (SRBs). Endeavour rolled out to Launch Pad 39A on July 27. The six-person STS-68 crew traveled to KSC to participate in the Terminal Countdown Demonstration Test on Aug. 1, essentially a dress rehearsal for the launch countdown. They returned to KSC on Aug. 15, the same day the final countdown began.
Following a smooth countdown leading to a planned 5:54 a.m. EDT launch on Aug. 18, Endeavour’s three main engines came to life 6.6 seconds before liftoff. With just 1.8 seconds until the two SRBs ignited to lift the shuttle stack off the pad, the Redundant Set Launch Sequencer (RSLS) stopped the countdown and shutdown the three main engines, two of which continued running past the T-zero mark. It marked the fifth and final launch abort of the shuttle program, and the closest one to liftoff. Bursch now had the distinction as the only person to have experienced two RSLS launch aborts, his first one occurring on STS-51 just a year earlier. Engineers traced the shutdown to higher than anticipated temperatures in a high-pressure oxygen turbopump in engine number three. The abort necessitated a rollback of Endeavour to the VAB on Aug. 24 to replace all three main engines with three engines from Atlantis on its upcoming STS-66 mission. Engineers shipped the suspect engine to NASA’s Stennis Space Center in Mississippi for extensive testing, where it worked fine and flew on STS-70 in July 1995. Meanwhile, Endeavour returned to Launch Pad 39A on Sept. 13.
Liftoff of Endeavour on the STS-68 mission.
On Sept. 30, 1994, Endeavour lifted off on time at 6:16 a.m. EDT, and eight and half minutes later delivered its crew and payloads to space. Thirty minutes later, a firing of the shuttle’s Orbiter Maneuvering System (OMS) engines placed them in a 132-mile orbit inclined 57 degrees to the equator. The astronauts opened the payload bay doors, deploying the shuttle’s radiators, and removed their bulky launch and entry suits, stowing them for the remainder of the flight.
Left: The Space Radar Laboratory-2 payload in Endeavour’s cargo bay, showing SIR-C (with the JPL logo on it), X-SAR (the long bar atop SIR-C), and MAPS (with the LaRC logo on it). Middle: The STS-68 Blue Team of Daniel W. Bursch, top, Steven L. Smith, and Thomas D. Jones in their sleep bunks. Right: Tile damage on Endeavour’s starboard Orbital Maneuvering System pod caused by a strike from a tile from Endeavour’s front window rim that came loose during the ascent.
Left: Steven L. Smith, left, and Peter J.K. “Jeff” Wisoff set up the bicycle ergometer in the shuttle’s middeck. Middle: The STS-68 Red Team of Terrence W. Wilcutt, top, Wisoff, and Michael A. Baker in their sleep bunks. Right: Wilcutt consults the flight plan for the next maneuver.
The astronauts began to convert their vehicle into a science platform, and that included breaking up into two teams to enable 24-hour-a-day operations. Baker, Wilcutt, and Wisoff made up the Red Team while Smith, Bursch, and Jones made up the Blue Team. Within five hours of liftoff, the Blue Team began their sleep period while the Red Team started their first on orbit shift by activating the SIR-C and X-SAR instruments in the payload bay and some of the middeck experiments. During inspection of the OMS pods, the astronauts noted an area of damaged tile, later attributed to an impact from a tile from the rim of Endeavour’s front window that came loose during the ascent to orbit. Engineers on the ground assessed the damage and deemed it of no concern for the shuttle’s entry.
Left: Michael A. Baker prepares to take photographs through the commander’s window. Middle: Thomas D. Jones, left, Daniel W. Bursch, and Baker hold various cameras in Endeavour’s flight deck. Right: Terrence W. Wilcutt with four cameras.
Left: Thomas D. Jones, left, and Daniel W. Bursch consult a map in an atlas developed specifically for the SRL-2 mission. Middle: Jones takes photographs through the overhead window. Right: Steven L. Smith takes photographs through the overhead window.
By sheer coincidence, the Klyuchevskaya volcano on Russia’s Kamchatka Peninsula began erupting on the day STS-68 launched. By the mission’s second day, the astronauts trained not only their cameras on the plume of ash reaching 50,000 feet high and streaming out over the Pacific Ocean but also the radar instruments. This provided unprecedented information of this amazing geologic event to scientists who could also compare these images with those collected during SRL-1 five months earlier.
Left: Eruption of Klyuchevskaya volcano on Russia’s Kamchatka Peninsula. Middle: Radar image of Klyuchevskaya volcano. Right: Comparison of radar images of Mt. Pinatubo in The Philippines taken during SRL-1 in April 1994 and SRL-2 in October 1994.
The STS-68 crew continued their Earth observations for the remainder of the 11-day flight, having received a one-day extension from Mission Control. On the mission’s eighth day, they lowered Endeavour’s orbit to 124 miles to begin a series of interferometry studies that called for extremely precise orbital maneuvering to within 30 feet of the orbits flown during SRL-1, the most precise in shuttle history to that time. These near-perfectly repeating orbits allowed the construction of three-dimensional contour images of selected sites. The astronauts repaired a failed payload high rate recorder and continued working on middeck and biomedical experiments.
Left: Steven L. Smith, left, conducts a biomedical experiment as Michael A. Baker monitors. Right: Peter J.K. “Jeff” Wisoff, left, and Smith repair a payload high rate recorder.
A selection of STS-68 crew Earth observation photographs. Left: The San Francisco Bay area. Middle left: The Niagara Falls and Buffalo area. Middle right: Riyadh, Saudi Arabia. Right: Another view of the Klyuchevskaya volcano on Russia’s Kamchatka Peninsula.
The high inclination orbit afforded the astronauts great views of the aurora australis, or southern lights.
On this mission in particular, the STS-68 astronauts spent considerable time looking out the window, their images complementing the data taken by the radar instruments. Their high inclination orbit enabled views of parts of the planet not seen during typical shuttle missions, including spectacular views of the southern lights, or aurora australis.
Two versions of the inflight STS-68 crew photo.
On flight day 11, with most of the onboard film exposed and consumables running low, the astronauts prepared for their return to Earth the following day. Baker and Wilcutt tested Endeavour’s reaction control system thrusters and aerodynamic surfaces in preparation for deorbit and descent through the atmosphere, while the rest of the crew busied themselves with shutting down experiments and stowing away unneeded equipment.
Left: Endeavour moments before touchdown at California’s Edwards Air Force Base. Middle: Michael A. Baker brings Endeavour home to close out STS-68 and a successful SRL-2 mission. Right: Baker gets a congratulatory tap on the shoulder from Terrence W. Wilcutt following wheels stop.
Left: As workers process Endeavour on the runway, Columbia atop a Shuttle Carrier Aircraft (SCA) flies overhead on its way to the Palmdale facility for refurbishment. Right: Mounted atop an SCA, Endeavour departs Edwards for the cross-country trip to NASA’s Kennedy Space Center in Florida.
On Oct. 11, the astronauts closed Endeavour’s payload bay doors, donned their launch and entry suits, and strapped themselves into their seats for entry and landing. Thick cloud cover at the KSC primary landing site forced first a two-orbit delay in their landing, then an eventual diversion to Edwards Air Force Base (AFB) in California. The crew fired Endeavour’s OMS engines to drop out of orbit. Baker piloted Endeavour to a smooth landing at Edwards, ending the 11-day 5-hour 46-minute flight. The crew had orbited the Earth 182 times. Workers at Edwards safed the vehicle and placed it atop a Shuttle Carrier Aircraft for the ferry flight back to KSC. The duo left Edwards on Oct. 19, and after stops at Biggs Army Airfield in El Paso, Texas, Dyess AFB in Abilene, Texas, and Eglin AFB in the Florida panhandle, arrived at KSC the next day. Workers there began preparing Endeavour for its next flight, STS-67, in March 1995. Meanwhile, a Gulfstream jet flew the astronauts back to Ellington Field in Houston for reunions with their families.
Diane Evans, SIR-C project scientist, summarized the scientific return from STS-68, “We’ve had a phenomenally successful mission.” The radar instrument collected 60 terabits of data, filling 67 miles of magnetic tape during the mission. In 1990s technology, that equated to a pile of floppy disks 15 miles high! In 2006, using an updated comparison, astronaut Jones equated that to a stack of CDs 65 feet high. The radar instruments completed 910 data takes of 572 targets during about 80 hours of imaging. To complement the radar data, the astronauts took nearly 14,000 photographs using 14 different cameras. To image the various targets required more than 400 maneuvers of the shuttle, requiring 22,000 keystrokes in the orbiter’s computer. The use of interferometry, requiring precision orbital tracking of the shuttle, to create three-dimensional topographic maps, marks another significant accomplishment of the mission. Scientists published more than 5,000 papers using data from the SRL missions.
Enjoy the crew narrate a video about the STS-68 mission. Read Wilcutt’s recollections of the mission in his oral history with the JSC History Office.
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By European Space Agency
Video: 00:01:25 Watch the closest flyby of a planet ever, as the ESA/JAXA BepiColombo spacecraft sped past Mercury during its latest encounter on 4 September 2024.
This flyby marked BepiColombo’s closest approach to Mercury yet, and for the first time, the spacecraft had a clear view of Mercury’s south pole.
This timelapse is made up of 128 different images captured by all three of BepiColombo’s monitoring cameras, M-CAM 1, 2 and 3. We see the planet move in and out of the fields of view of M-CAM 2 and 3, before M-CAM 1 sees the planet receding into the distance at the end of the video.
The first few images are taken in the days and weeks before the flyby. Mercury first appears in an image taken at 23:50 CEST (21:50 UTC) on 4 September, at a distance of 191 km. Closest approach was at 23:48 CEST at a distance of 165 km.
The sequence ends around 24 hours later, on 5 September 2024, when BepiColombo was about 243 000 km from Mercury.
During the flyby it was possible to identify various geological features that BepiColombo will study in more detail once in orbit around the planet. Four minutes after closest approach, a large ‘peak ring basin’ called Vivaldi came into view.
This crater was named after the famous Italian composer Antonio Vivaldi (1678–1741). The flyover of Vivaldi crater was the inspiration for using Antonio Vivaldi’s ‘Four Seasons’ as the soundtrack for this timelapse.
Peak ring basins are mysterious craters created by powerful asteroid or comet impacts, so-called because of the inner ring of peaks on an otherwise flattish floor.
A couple of minutes later, another peak ring basin came into view: newly named Stoddart. The name was recently assigned following a request from the M-CAM team, who realised that this crater would be visible in these images and decided it would be worth naming considering its potential interest for scientists in the future.
BepiColombo’s three monitoring cameras provided 1024 x 1024 pixel snapshots. Their main purpose is to monitor the spacecraft’s various booms and antennas, hence why we see parts of the spacecraft in the foreground. The photos that they capture of Mercury during the flybys are a bonus.
The 4 September gravity assist flyby was the fourth at Mercury and the seventh of nine planetary flybys overall. During its eight-year cruise to the smallest and innermost planet of the Solar System, BepiColombo makes one flyby at Earth, two at Venus and six at Mercury, to help steer itself on course for entering orbit around Mercury in 2026.
BepiColombo is an international collaboration between ESA and JAXA.
BepiColombo’s best images yet highlight fourth Mercury flyby
BepiColombo images in ESA’s Planetary Science Archive
Processing notes: The BepiColombo monitoring cameras provide black-and-white, 1024 x 1024 pixel images. These raw images have been processed to remove electronic banding in the cameras. The M-CAM 1 images have been cropped to 995 x 995 pixels
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By European Space Agency
The ESA/JAXA BepiColombo mission has successfully completed its fourth of six gravity assist flybys at Mercury, capturing images of two special impact craters as it uses the little planet’s gravity to steer itself on course to enter orbit around Mercury in November 2026.
The closest approach took place at 23:48 CEST (21:48 UTC) on 4 September 2024, with BepiColombo coming down to around 165 km above the planet’s surface. For the first time, the spacecraft had a clear view of Mercury’s south pole.
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