Greenhouse Gases II

The Monitoring Nitrous Oxide Sources (MIN₂OS) satellite project submitted to the European Space Agency (ESA) Earth Explorer 10 (EE10) aims to monitor nitrous oxide (N₂O) sources on a global scale by inverting surface fluxes from N₂O space-borne measurements sensitive in the lowermost atmospheric layers. Through this approach, the MIN₂OS project will provide high-resolution (10´10 km) emission inventories of N₂O that contribute to quantify the Earth’s radiative forcing at global scale and on a daily to monthly basis depending on the applications (agricultural sector, stakeholders, policy makers, academic research oriented). Our novel approach is based on the development of 1) a space-borne instrument operating in the Thermal InfraRed (TIR) domain inherited from a more sensitive version of the Infrared Atmospheric Sounding Interferometer (IASI) and the Infrared Atmospheric Sounding Interferometer-New Generation (IASI-NG) instruments, providing N₂O mixing ratio in the lowermost atmosphere (800-900 hPa) and 2) an inversion source model to estimate, from atmospheric satellite observations, N₂O surface fluxes.

            Nitrous oxide is a greenhouse gas (GHG) that has an overall radiative forcing 10 times weaker than thus of carbon dioxide (CO₂). The emissions of N₂O mainly come from natural sources (55-61%) and the remaining from anthropogenic activities (agricultural and industrial sectors). The N₂O emissions and sources are highly uncertain both over land and ocean. Specific difficulties need to be overcome in monitoring the N₂O sources at global scale and high resolution: sensitivity of the measurements in the lowermost troposphere, sparse surface measurements, large modelling and source inversion uncertainties, high temporal and spatial variability of the N₂O surface fluxes.

            To fulfil the MIN₂OS objectives, a new TIR instrument will be developed, centred on the N₂O band at 1240-1320 cm^-1, with a resolution of 0.125 cm^-1, a Full Width at Half Maximum of 0.25 cm^-1 and a swath of 300 km. It will be on-board a platform at ~830 km altitude crossing the Equator in descending node at 09:30 local time (LT) in synergy with the two following operational platforms in 2028: 1) in time and space coincidence with Metop-SG 2A that will contain IASI-NG to use surface properties and vertical profiles of atmospheric constituents and temperature to optimally constrain the retrieval of N₂O vertical profiles and 2) with Sentinel 2 to use surface information at the field scale (land occupation and use) with no need for synchronization. The expected lifetime of the MIN₂OS project to be launched in 2028 is 4-5 years. The spectral noise could be decreased by a factor 3 to 5 compared to thus of the IASI-NG and the Greenhouse gases Observing SATellite-2 (GOSAT-2) missions. With MIN₂OS, N₂O can be obtained from 3 separate atmospheric layers: around 800-900 hPa (specific to MIN₂OS), around 500 hPa (like IASI-NG and GOSAT-2) and around 300 hPa (like IASI, IASI-NG and GOSAT-2). The N₂O total error is expected to be ~1% (3-4 ppbv) along the vertical.

The Tropospheric Monitoring Instrument (TROPOMI) was launched on 13^th of October on ESA’s Sentinel-5 Precursor satellite. For almost one year the instrument performs measurements of the ultraviolet, visible, near-infrared and shortwave infrared spectral band from space in nadir observation geometry. SRON Netherlands Institute of Space Research developed and supports the SICOR retrieval algorithm for the operational processing of the TROPOMI CO total column product. Already during the early phase of the mission, comparisons of the CO product with ECMWF-IFS model simulations and collocated TCCON and NDACC ground-based measurements demonstrated a data quality well within the mission requirements (accuracy <15%, precession < 10%), which led to a data release for public usage in July 2018. In this contribution, we summaries the findings of the first year of TROPOMI CO measurements and give a perspective for future research. We demonstrate the capability of TROPOMI to detect CO enhancements by recent fire events and to track anthropogenic CO pollution on the global scales. Based on selected cases, the emissions of pollution hot spots like cities and industrial areas are quantified and interpreted by means of dedicated simulations of the CO atmospheric transport using the regional Weather Research and Forecasting Model (WRF). Finally, we report on the long-term perspective to further improve the quality of the TROPOMI CO dataset. 

Greenhouse gas (GHG) measurements are of increasing importance to understand the evolving carbon cycle in the Anthropocene and for policy makers aiming to limit manmade climate change. Based on the research in the development of the Earth Explorer 8 CarbonSat Phase A/B1 activities and in preparation for a  forthcoming CO₂ monitoring mission within the European COPERNICUS program, an end-to-end (E2E) mission performance simulation system for GHG total column products has been successfully developed, implemented, tested and used. This mission E2E simulator is able to reproduce all significant processes, design and steps that impact the mission performance as well as output simulated data products in the aim to become a coherent test bed for L1PP and L2PP and to support the verification of space segment performance and associated sensitivity analysis. 

The GHG total column performance simulator (GHG-TCPS) comprises geometry, scene, orbit, instrument, Level 1b processing and up to Level 2 simulation modules, all embedded in an OpenSF framework infrastructure. The GHG-TCPS aims at deepening the understanding of the expected performance of a GHG observation mission focusing on CO₂ and CH₄ based on detailed observation system simulations (OSS). It includes the simulation of realistic large-scale full swath 2D scenes, which requires sophisticated instrument and retrieval simulation modules to be implemented in a consistent way.

The GHG-TCPS system has been used to run a series of simulations to estimate the performance of a GHG imaging spectrometer system to measure CO₂ and CH₄ total column content for extended areas, city scale and point scale plumes.

In this study we describe briefly the GHG end-to-end performance simulation system and present results from simulations using realistic atmospheric scenarios. These  include examples of the application for  flux inversion for selected source regions. These results enable the performance of the future CO₂ observing system to be assessed realistically up to Level 4 data products.

The Orbiting Carbon Observatory 3 (OCO-3) will continue global CO₂ and solar-induced chlorophyll fluorescence (SIF) using the flight spare instrument from OCO-2. The instrument has been through ground testing and thermal vacuum, and will be packaged for installation on the International Space Station (ISS), currently scheduled for launch in February 2019. This talk will focus on the science objectives, science data products, early operations plan, and a few highlights from the instrument performance tests.

The low-inclination ISS orbit lets OCO-3 sample the tropics and sub-tropics across the full range of daylight hours with dense observations at northern and southern mid-latitudes (+/- 52º). The combination of these dense CO₂ and SIF measurements provides continuity of data for global flux estimates as well as a unique opportunity to address key deficiencies in our understanding of the global carbon cycle. The instrument utilizes an agile, 2-axis pointing mechanism (PMA), providing the capability to look towards the bright reflection from the ocean and validation targets. In addition to the nadir-, glint-, and target-mode geometries familiar from OCO-2, OCO-3 includes a new observation mode dedicated to mapping out larger spatial-scale emitters like cities. This Snapshot Area Map (SAM) mode will be used to map areas of up to 100x100 km² on the Earth surface with the standard OCO-3 ground footprints of 2x3 km², providing unprecedented high spatial resolution coverage of large-scale CO₂ emitters worldwide. Measurements over urban centers could aid in making estimates of fossil fuel CO₂ emissions. Similarly, the snapshot mapping mode can be used to sample regions of interest for the terrestrial carbon cycle. In addition, there is potential to utilize data from the currently operating ISS instruments ECOSTRESS (ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station) and GEDI (Global Ecosystem Dynamics Investigation), which measure other key variables of the control of carbon uptake by plants, to complement OCO-3 data in science analysis.

Detailed simulations of planned operations and data quality have been completed and will be reported along with the final instrument characterization from thermal vacuum testing. The specific nature of the ISS orbit track produces spatial and temporal coverage that is something of a paradigm shift compared to low-earth-orbiting satellites like OCO-2, which provide observations at fixed overpass times and repeat cycles. OCO-3 observations will necessitate re-evaluation and adaptation of the current approaches of how satellite data are being used in model evaluation and science studies.

The European Commission is currently considering expansion of the space component of the Copernicus programme with a constellation of CO₂ imaging spectrometers to support the global monitoring of CO₂ emissions. The CO₂ instruments would allow for the observation of CO₂ plumes from individual point sources such as large cities and power plants and the quantification of their emissions. However, since the CO₂ signals of plumes can be weak and obscured by biospheric signals, measurements of auxiliary trace gases such as CO and NO₂ were proposed to help detect the plume and separate anthropogenic from biospheric signals.

We present results from the SMARTCARB study which assessed the potential synergies of CO and NO₂ measurements for detecting and quantifying CO₂ point sources. For the study, we simulated highly realistic CO₂, CO and NO₂ fields (1×1 km² resolution) with the COSMO-GHG model for the year 2015. The model domain covered the city of Berlin and several power plants. The simulations were used to generate synthetic XCO₂, CO and NO₂ satellite observations (2×2 km² pixel size with 250-km swath) for constellations of up to six satellites. The CO₂ plumes of Berlin and the power station Jänschwalde were detected using either CO₂, CO or NO₂ observations, and their CO₂ emissions were quantified by different methods.

Although a constellation of six satellites was sufficient to cover Berlin on a daily basis, only about 60 out of 365 plumes per year could be observed due to frequent cloud cover. The CO₂ instrument could detect only 6-14 plumes of these 60 plumes with high (σ_VEG50 = 1.0 ppm) and low noise (σ_VEG50 = 0.5 ppm), respectively, because the CO₂ signals were often too weak. A CO instrument performed worse than the CO₂ instrument, while the number of detectable plumes could be significantly increased to 39 plumes with an NO₂ instrument, assuming instrument specifications similar to Sentinel-5P. The NO₂ instrument also greatly helped to quantify the background XCO₂ levels required to quantify the local enhancement within the plumes. The CO₂ instrument alone could only detect a small fraction of the real plume, so that the background, estimated from the values surrounding the plume, contained significant amounts of XCO₂ emitted from Berlin. Consequently, the XCO₂ background was overestimated and Berlin's emissions were correspondingly underestimated by about 15-25%. The NO₂ instrument detected a much larger portion of the plume and therefore enabled an almost unbiased estimation of the background and the emissions of the city (<10%). The uncertainties of estimated emissions for single overpasses were about 5-10 Mt yr^-1 (30%-60%) and, for a constellation of six satellites, the RMSDs of the annual mean estimate were 4-7 Mt yr^-1 for the CO₂ instrument and about 2 Mt yr^-1 when also using the NO₂ instrument.

In conclusion, an NO₂ instrument on the same platform as a CO₂ instrument significantly improves the capability of estimating CO₂ emissions from cities and power plants by increasing the number of detectable plumes and by reducing the bias and scatter of the estimated emissions.

Carbon dioxide (CO₂) is the most important anthropogenic greenhouse gas and monitoring its emissions from space has become an important objective of (potential) future satellite missions such as the planned European anthropogenic CO₂ monitoring mission or NASA’s GeoCarb mission.

CO₂ is long lived and well mixed in the atmosphere. Globally, its natural gross fluxes are much larger than anthropogenic emissions. This makes it challenging to detect and analyze plumes of individual point sources in satellite measurements of the CO₂ column-average dry-air mole fraction (XCO₂).

In populated and industrialized areas, the largest part of tropospheric NO₂ originates from the co-emission with CO₂ during the combustion of fossil fuels, e.g., by power plants, traffic, and domestic heating. NO₂ has a short lifetime in the order of hours, so that its vertical column densities often exceed background levels by orders of magnitude near sources. This makes it a suitable tracer of recently emitted anthropogenic CO₂, i.e. close to the source before the CO₂ plumes blend into background concentrations.

In this presentation we use NO₂ measurements made by the S5P satellite to help to locate the anthropogenic CO₂ plumes in co-located XCO₂ measurements of the OCO-2 satellite, close to sources. Due to OCO-2’s narrow swath, it usually measures only a cross section of the plume. We estimate the cross sectional CO₂ flux utilizing ECMWF ERA5 wind information and discuss the results and potential source attributions by taking into account the extended NO₂ plume structures observable in S5P’s wide swath.

Chinese carbon dioxide observation satellite (TanSat) launched in 22 Dec 2016, after on-broad test and calibration, TanSat starts to record the back-scattered sunlight spectrum from scientific earth observation and produced XCO2 data from February 2017.

First, the preliminary results of XCO2 retrieved from TanSat measurements will be presented, and inter-compared with OCO-2 results will be discussed. Validation study with TCCON measurements indicate a better than 2.2 ppm with 8 stations. The first global CO2 map represented a milestone in Chinese GHGs satellite. TanSat will release level 2 and higher level products to support carbon emission estimations and climate change studies.  

Second, we use an atmospheric inversion to estimate the magnitude and distribution of land biosphere CO2 fluxes over China, the satellite observations of GOSAT, OCO-2 are applied to verify our a posteriori fluxes.