Landfill & emissions

Gas moves. Concentration at a point tells you about that point at that moment under those wind conditions, and it may say very little about where the gas came from.

That makes wind data as important as the gas sensor itself. Without it you have numbers on a map and no way to work backwards to a source.

Second problem is scale mismatch. Finding a plume across a hundred hectare cell and pinpointing the crack in a cap are different resolutions of the same task. Trying to do both with one capture method means doing one of them badly.

And the regulatory context keeps moving. What was good practice for reporting three years ago may not satisfy an obligation now.

Fly the area first, at consistent height and spacing, with wind data logging alongside the gas sensor. That produces the concentration map and tells you which parts of the site are worth a closer look.

Read the map with the wind, not without it. A downwind plume points back to a source that may sit some distance upwind.

Walk the hotspots. A handheld unit at ground level, moving slowly across the area the flight identified, is what turns a plume into a location. Same sensor, same data format, so it goes into one report.

Record conditions. Wind speed and direction, temperature, barometric pressure and time. A concentration reading without them is difficult to defend and impossible to compare.

Repeat on a consistent cycle so the comparison means something.

Coarse to fine. Fly to find the area, walk to find the source.

Sensor type sets what you can claim. TDLAS is methane-specific by laser absorption and gives sub-ppm sensitivity. NDIR is broader and less specific. Know which you are quoting from.

Every reading needs conditions attached: wind speed and direction, temperature, pressure, time and altitude. Without them the number cannot be compared to another number, including your own from last quarter.

Detection and quantification are different claims. Finding a plume is straightforward. Quantifying an emission rate requires assumptions about dispersion that should be stated explicitly, not buried.

Calibrate on the schedule the manufacturer specifies and record when you did it.

A concentration map over the site, a list of located sources with coordinates, the conditions at capture, and a comparison against the previous survey.

Recipients are environment managers, compliance officers and sometimes regulators directly. The record has to be defensible under scrutiny, which means method and conditions matter as much as the readings.

What causes trouble: readings with no conditions, sources described as areas rather than points, and inconsistent method between cycles that makes trend analysis meaningless.

Flying without wind data. You get a map of where gas was, with no way to reason about where it came from, and the whole survey becomes descriptive rather than actionable.

The other one is stopping at the plume. A concentration map tells the client they have a problem and not where to send the repair crew. The walked follow-up is what makes the survey worth commissioning.

And changing method between cycles. Different height, different spacing, different sensor, and the trend line stops meaning anything at exactly the moment someone asks whether the situation is improving.