Methane emission verification for offset projects
Shortwave-infrared sensors can now independently verify large methane point sources for carbon offset projects, but detection thresholds of roughly 100–500 kg/hr mean small project-scale leaks still fall below the noise floor. Understanding which sensor fits which source size is the first decision any MRV buyer must make.
Sensors
- Sentinel-5P TROPOMI: Hyperspectral UV-SWIR sensor covering the 2.3 µm methane band. Nadir pixel footprint of 5.5 × 7 km (refined from original 7 × 7 km after 2019 update). Daily global coverage. Suited to regional-scale column-averaged methane (XCH4) anomalies and large industrial super-emitters above roughly 25–50 kt/yr at area-source scale; individual point-source detection threshold is roughly 500 kg/hr under good atmospheric conditions.
- GHGSat-D/C/Stream constellation: Commercial Fabry-Pérot interferometer satellites operating in the 1.65 µm methane absorption band. Pixel resolution approximately 25 m, scene footprint roughly 12 × 12 km. Targeted tasking only, not continuous survey. Published point-source detection limit approximately 100 kg/hr for the C-series; precision improves with multiple overpasses. Provides site-specific emission rate estimates suitable for project-level MRV.
- MethaneSAT: Environmental Defence Fund mission launched March 2024. Wide-swath (200 km) SWIR spectrometer at approximately 100–400 m effective resolution for area-source flux mapping. Designed explicitly for oil-and-gas basin and landfill surveys. Targets area-source sensitivity below 1 kg/hr per km², bridging the gap between TROPOMI's coarse footprint and GHGSat's narrow scene.
- EMIT (ISS hyperspectral): NASA imaging spectrometer on the International Space Station. 285-band VSWIR coverage, 60 m pixel resolution, 80 km swath. Originally a dust-mineralogy mission; methane plume detection was demonstrated post-launch, with published detections of point sources above approximately 100–200 kg/hr. Non-deterministic revisit (ISS orbit precession) limits its use for routine monitoring but makes it valuable for opportunistic plume confirmation.
- Landsat 8/9 TIRS (thermal proxy): Not a direct methane sensor. Thermal infrared bands can detect surface temperature anomalies at landfill gas flares and compressor stations as a proxy indicator of combustion activity, at 100 m resolution and 16-day revisit. Useful for flagging whether capture equipment is operating, not for quantifying methane flux directly.
What the physics actually allows
Methane absorbs shortwave infrared radiation strongly at two windows: around 1.65 µm and 2.3 µm. A satellite spectrometer looking down through the atmosphere sees sunlight that has passed twice through the air column. Where methane concentration is elevated, specific absorption lines deepen. The ratio of absorbed to unabsorbed radiance, processed against a modelled atmospheric background, yields a column-averaged dry-air mole fraction (XCH4) in parts per billion. Integrated across a known wind field, that concentration anomaly converts to a mass flux estimate.
The conversion is not clean. Wind speed and direction at the effective plume height must come from reanalysis products (ERA5 is standard) or in-situ measurements, and wind uncertainty alone contributes 20–40% error to any single-pass flux estimate. Aerosol loading, surface albedo heterogeneity and water vapour all add noise. Retrievals fail over water, dense cloud and bright snow. These are not engineering problems awaiting a fix; they are consequences of measuring a trace gas through a turbulent, optically complex atmosphere.
The detection threshold problem for project-scale MRV
TROPOMI's 5.5 × 7 km pixel footprint means it integrates signal over a large area. A single landfill emitting 200 kg/hr spreads its methane across that footprint and may not produce a statistically significant XCH4 anomaly above background variability. Published analyses place TROPOMI's practical point-source detection threshold at roughly 500 kg/hr under favourable conditions, rising to several tonnes per hour in high-background or cloudy regions. That is a large landfill or a significant coal-mine ventilation shaft, not a small agricultural digester.
GHGSat's commercial constellation pushes the threshold down to approximately 100 kg/hr at site level, which covers medium-sized landfills and active coal-mine drainage systems. EMIT has demonstrated detections in a similar range opportunistically. But none of these sensors can currently verify that a 10 kg/hr leak from a malfunctioning digester seal is absent. Buyers building MRV frameworks around small-project methane capture need to be honest with registries about this floor. Satellite data can confirm large emissions and large reductions; it cannot yet certify the absence of minor leakage.
Matching sensor to project type
Landfill gas capture projects are the strongest fit for current satellite MRV. Large municipal landfills in the 50–500 ha size range can emit at rates well above GHGSat's detection floor when capture systems fail. A time series of targeted GHGSat passes, combined with TROPOMI background monitoring, can identify whether a site is behaving consistently with its reported capture efficiency. Anomalous plumes on days when capture is claimed to be operating are a meaningful audit signal.
Coal-mine methane projects present a different geometry. Ventilation shaft emissions are concentrated point sources, often above 500 kg/hr for active longwall mines, making them detectable by TROPOMI on high-emission days. The challenge is baseline: pre-project emission rates must be estimated from production records and ventilation measurements, not from historical satellite data, because the archive depth for high-resolution commercial sensors only extends a few years. MethaneSAT's wider swath makes it more useful for basin-level coal-region surveys than for single-shaft attribution.
Agricultural digesters, unless aggregated into large clusters, are generally below current detection thresholds. Satellite data is most useful here as a negative check: persistent plumes over a digester site that claims zero fugitive emissions are a red flag. Absence of a detectable plume is not confirmation of compliance.
Turning overpass data into a verifiable emission estimate
The standard published method for point-source quantification from satellite imagery is the integrated mass enhancement (IME) approach, in which the total column enhancement across a detected plume is multiplied by an effective wind speed to yield a source rate. A cross-sectional flux method, integrating the column enhancement perpendicular to the wind vector at successive downwind transects, provides an independent check. Both methods are documented in peer-reviewed literature using AVIRIS-NG, EMIT and GHGSat data.
Uncertainty quantification matters more for carbon markets than for most remote-sensing applications, because credits are denominated in tonnes. A responsible MRV package should report not just a central estimate but a 90% confidence interval derived from wind uncertainty, retrieval noise and atmospheric modelling error. For a single GHGSat overpass of a landfill, that interval is typically plus or minus 30–50% of the central estimate. Multiple independent overpasses on different days reduce the interval substantially, which is why revisit frequency is a commercial differentiator, not just a convenience.
Satellize structures satellite-derived methane estimates as time-stamped evidence packages compatible with Verra and Gold Standard audit workflows, drawing on TROPOMI open data and commercial tasking arranged under client licence.
Archive depth, additionality and the baseline problem
TROPOMI data runs from October 2017 to present, giving a meaningful multi-year archive for regional methane background characterisation. That is genuinely useful for demonstrating that a region's background XCH4 has not drifted in ways that would confound project-level attribution. GHGSat's commercial archive is shorter and site-specific: historical tasking was not systematic, so pre-project baselines for most sites do not exist in the commercial record.
This matters for additionality claims. A project claiming to have reduced emissions from a landfill by 60% needs a credible pre-project emission rate. Satellite data can rarely supply that independently; it must be combined with engineering models, gas-flow meter records and ground-based measurement campaigns. The honest framing is that satellites provide independent corroboration of reported reductions, not a standalone replacement for ground measurement. Registries that accept satellite-only MRV for small projects should be treated with scepticism by buyers on both sides of the credit transaction.
What a satellite evidence package can and cannot claim
A well-constructed satellite MRV package for a methane offset project can legitimately assert: that no large fugitive emission above the sensor's detection threshold was observed on the overpass dates; that detected plumes on specific dates are consistent or inconsistent with reported capture rates; and that the regional methane background during the project period is characterised with known uncertainty. These are useful, auditable claims.
It cannot assert that emissions were zero, that small leaks were absent, or that the project performed as modelled on days without cloud-free overpasses. Cloud cover remains the most mundane and most consequential limitation: TROPOMI's global daily coverage sounds comprehensive until you note that tropical and temperate landfills are frequently obscured for days or weeks at a time, and that a project operator wishing to conceal a malfunction need only wait for cloud. Combining satellite passes with continuous ground-based sensors is the only way to close that gap, and no satellite programme currently eliminates the need for some in-situ measurement at project scale.
Typical figures
| TROPOMI pixel footprint | 5.5 × 7 km (post-2019); daily global coverage |
| GHGSat spatial resolution | ~25 m pixel; ~12 × 12 km scene; targeted tasking |
| EMIT spatial resolution | 60 m pixel; 80 km swath; non-deterministic ISS revisit |
| MethaneSAT swath | ~200 km; effective area-source resolution 100–400 m; launched March 2024 |
| Point-source detection threshold | ~500 kg/hr (TROPOMI); ~100 kg/hr (GHGSat C-series, EMIT); small digesters typically below threshold |
| Key spectral bands | 1.65 µm and 2.3 µm SWIR methane absorption windows |
| Single-pass flux uncertainty | ±30–50% (wind and retrieval combined); reduces with multiple overpasses |
| TROPOMI archive depth | October 2017 to present (open access via Copernicus Data Space) |
| Cloud limitation | Retrievals fail under cloud optical depth >0.5; persistent cloud can gap coverage for days to weeks |
| Delivery formats | NetCDF (TROPOMI L2); GeoTIFF plume maps; CSV flux time series; PDF audit evidence packages |
Analytics Satellize can run
| Site-level emission rate estimate | Integrated mass enhancement (IME) and cross-sectional flux methods applied to column XCH4 retrievals, with ERA5 wind fields | PDF report with central estimate, 90% confidence interval and overpass metadata; suitable for registry submission |
| Anomalous plume alert | Automated threshold detection on TROPOMI daily L2 product over registered project coordinates; confirmed by GHGSat tasking on trigger | Email alert with plume map, estimated emission rate and date-stamped evidence image within 48 hours of overpass |
| Regional methane background characterisation | Multi-year TROPOMI XCH4 time-series analysis using published bias-correction and quality-flag filtering | GIS layer and statistical summary of background XCH4 distribution for project region; used in baseline documentation |
| Capture-system consistency check | Comparison of observed plume frequency and magnitude against project-reported capture efficiency using Bayesian inference on multi-overpass dataset | Quarterly consistency report flagging statistically anomalous periods for auditor review |
| Multi-sensor corroboration package | Co-registration of TROPOMI regional signal with GHGSat or EMIT site-level detections; cross-validated flux estimates | Integrated evidence dossier combining open and commercial data, formatted for Verra or Gold Standard MRV appendix |
| Thermal proxy activity indicator | Landsat 8/9 TIRS time series over flare and compressor locations; anomaly detection against seasonal baseline | Monthly GIS layer of thermal anomaly flags indicating probable combustion activity at capture infrastructure |
Who does the work
We can get this done for you. Satellize runs its own analyst desk and a strong science team. You do not buy a data feed and work out what it means; our people source the imagery, run the analysis described on this page, and hand you the answer with its confidence limits stated. Discuss this requirement.