Point source vs. diffuse methane emissions: how to tell them apart
If you've spent any time reconciling an aerial survey report against a facility's own LDAR logs, you've run into this problem: the report flags "elevated methane" in a general area, but it doesn't tell you whether that's one bad valve or a dozen small leaks spread across the pad. Those are different problems with different fixes, and telling them apart starts with understanding the two basic categories of methane emission source.
What makes a source "point" vs "diffuse"
A point source is methane coming from one discrete piece of equipment, concentrated enough that it reads as a distinct plume. A compressor seal that's started leaking, a thief hatch left open on a tank battery, a pipeline blowdown valve that didn't fully reseat, a wellhead flange that lost its gasket. These produce a plume with a visible point of origin and a concentration gradient that falls off as the gas disperses downwind. You can trace it back to a specific piece of hardware on a specific pad.
Diffuse emissions don't behave that way. They're spread across an area rather than concentrated at a point: fugitive losses from dozens of small connections across a gathering system, low-level venting from a tank farm with no single dominant leak, methane seeping from a landfill cap or a wastewater lagoon, background flux from wetlands or cropland sitting in the same scene as your asset. The enhancement is lower, the footprint is wider, and there's no single spot you can circle and call "the source."
A basin-level advisory often reports several small point sources as one diffuse signal, simply because its resolution can't separate them. Three leaking connections on three different wellheads each need their own repair order. A basin-wide process review triggered by the combined signal won't send a crew to any of them.
Why the distinction drives what happens next
A point source usually means a repair order: isolate the component, send a crew, close the ticket. A diffuse source usually means a process review: is the facility's overall design leaking more than it should, is a lagoon or impoundment under-controlled, is there a category of fugitive emissions nobody's been counting.
If you're trying to attribute emissions to a specific operator's balance sheet, or decide whether a reported reduction is real, the distinction is the whole ballgame. A single super-emitter event at one pad can swing a site's annual number more than months of steady diffuse background. Treat the two the same way in your MRV workflow and you'll either chase ghosts, sending a crew to a pad with no fixable point source, or miss the flange nobody's checked in a year.
How you tell them apart on imagery
The tell is in the SWIR absorption signature itself. Imaging spectrometry resolves methane's spectral fingerprint well enough to see plume morphology, not just "methane present in this pixel." A point source shows a tight, high-concentration core with a clean dispersion gradient trailing off with the wind. A diffuse source shows a flatter, lower-magnitude enhancement smeared across a wider footprint, no sharp core to anchor on.
Persistence helps too. A point source from a stuck valve often shows up again the next overpass, same spot, same rough magnitude, until someone fixes it. Diffuse background tends to vary with wind, temperature, and whatever's happening at the lagoon or landfill that day, without resolving into a repeatable origin point.
The catch is resolution. A regional advisory built on coarser instruments can tell you a basin has elevated methane. It usually can't tell you whether that's one tank battery with a stuck valve or three wellpads with a shared diffuse problem, and it almost never tells you which specific site boundary the plume sits inside. That's the gap a per-site plume map is built to close: resolve the plume shape, match it to the SWIR signature of a point source, and attribute it back to the facility boundary it belongs to, daily where tasking allows.
If your current workflow stops at "elevated methane in this basin," it's worth seeing what the plume looks like at the site itself.