# SWIR absorption - global screening
*methodologies*

Wide-area survey for anomalous methane or CO2 concentrations at coarse spatial resolution; good for prioritising follow-up with finer sensors.

## Specifications
- **family**: Imaging spectroscopy
- **requirements envelope**: {"kind":"spectral","spectral_range_nm":{"min":1600,"max":2050},"bands_min":50,"calibration_tier_min":"radiometric","snr_min":100,"daylight_required":true,"cloud_tolerant":false}
- **entity type**: methodology
- **last verified date**: 2026-06-04
- **verified by**: agency-doc
- **claim status**: unclaimed
- **attributes**: {"family":"Imaging spectroscopy","summary":"Wide-area survey for anomalous methane or CO2 concentrations at coarse spatial resolution; good for prioritising follow-up with finer sensors.","requirements_envelope":"{\"kind\":\"spectral\",\"spectral_range_nm\":{\"min\":1600,\"max\":2050},\"bands_min\":50,\"calibration_tier_min\":\"radiometric\",\"snr_min\":100,\"daylight_required\":true,\"cloud_tolerant\":false}"}
- **technology**: optical-spectral-sensing

## Editorial
SWIR absorption spectroscopy applies the same core retrieval physics across three operational scales: point-source plume imaging, regional-flux quantification, and global-screening surveys. All three exploit passive solar backscatter in shortwave infrared absorption windows, chiefly the 1.61-1.70 um methane band and the 2.2-2.4 um methane feature, along with CO2 windows near 1.6 and 2.0 um. Instruments compare spectral radiance inside and outside these absorption features; column-averaged dry-air mixing ratios (XCH4 or XCO2) are recovered via Beer-Lambert attenuation through the atmospheric column, using CO2-proxy, full-physics radiative-transfer, or Beer-Law column-enhancement retrieval approaches.[^acp-22-9617-2022]

The three scales differ primarily in how the photon budget is allocated between spatial resolution and signal integration time, producing a direct sensitivity-versus-coverage trade-off.[^acp-22-9617-2022]

**Point-source scale (25-60 m pixels, ~10-100 km2 scenes):** Fine spatial resolution resolves sub-kilometre plume structure, enabling attribution to individual super-emitting facilities such as oil and gas wellpads, landfills, and compressor stations. Because scene size is small, coverage is tasked rather than routine. Representative missions include GHGSat (WAF-P Fabry-Perot spectrometer; 1630-1675 nm; approximately 25 m resolution; 12x12 km scene; detection threshold approximately 100-1000 kg/h),[^ghgsat-amt-2021][^esa-ghgsat] EMIT (NASA/JPL; ISS-mounted hyperspectral 380-2500 nm; 60 m; deployed 2022), PRISMA (ASI; 30 m; 2.3 um window), EnMAP (DLR; 30 m; 2.3 um window), and Carbon Mapper (Planet/JPL; approximately 30 m; detection threshold approximately 100 kg/h).

**Regional-flux scale (100 m - 7 km pixels, basin to sub-continental coverage):** Wide-swath or frequent-revisit designs characterise area emissions across oil and gas basins and agricultural regions for use in atmospheric inverse modelling. Representative missions include TROPOMI on Sentinel-5P (SWIR band 2305-2385 nm; 7x5.5 km pixels; 2600 km swath; near-daily global coverage; XCH4 precision 0.6%)[^tropomi-pmc-2023] and MethaneSAT (EDF; 1.61-1.68 um; 100x400 m pixels; 260 km swath; launched 2024).[^methanesat-eoportal] Spatial resolution is insufficient to attribute emissions to individual facilities, so this scale relies on inverse modelling to recover lower emission values via aggregation.

**Global-screening scale (10-30 km footprints, routine global coverage):** Coarse footprints enable systematic multi-year records of column-averaged greenhouse gas concentrations, supporting long-term trend detection and identification of regional anomaly hotspots for follow-up by finer instruments. Coverage is cloud-dependent and sparsely sampled. Representative missions include GOSAT (JAXA/MOE/NIES; TANSO-FTS; 10.5 km circular footprint; 3-day global repeat; 1.6 and 2.0 um windows; operating since 2009),[^essd-12-3383-2020] SCIAMACHY on Envisat (ESA; first satellite global CH4 measurements; 30x60 km pixels; 2002-2012), and OCO-2/OCO-3 (NASA; 1.61 and 2.06 um CO2 windows; global XCO2 screening).

## Sources
- [acp-22-9617-2022] | Quantifying methane emissions from the global scale down to point sources using satellite observations of atmospheric methane, Saunois et al. 2022, ACP | https://acp.copernicus.org/articles/22/9617/2022/ | tier=peer-reviewed | accessed=2026-06-04 | published=2022-07-21
- [ghgsat-amt-2021] | The GHGSat-D imaging spectrometer, Jervis et al. 2021, AMT | https://amt.copernicus.org/articles/14/2127/2021/ | tier=peer-reviewed | accessed=2026-06-04 | published=2021-03-24
- [essd-12-3383-2020] | A decade of GOSAT Proxy satellite CH4 observations, Parker et al. 2020, ESSD | https://essd.copernicus.org/articles/12/3383/2020/ | tier=peer-reviewed | accessed=2026-06-04 | published=2020-12-14
- [tropomi-pmc-2023] | Global observational coverage of onshore oil and gas methane sources with TROPOMI, Pandey et al. 2023, Scientific Reports | https://pmc.ncbi.nlm.nih.gov/articles/PMC10555993/ | tier=peer-reviewed | accessed=2026-06-04 | published=2023-10-02
- [esa-ghgsat] | GHGSat Mission Overview, ESA Earth Online | https://earth.esa.int/eogateway/missions/ghgsat/description | tier=agency-doc | accessed=2026-06-04
- [methanesat-eoportal] | MethaneSAT mission profile, eoPortal | https://www.eoportal.org/satellite-missions/methane-sat | tier=community | accessed=2026-06-04

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Source: https://eo-atlas.org/methodologies/swir-absorption-global-screening
Maintainer: SpectraWorks B.V. (CC-BY 4.0)