We Invent to Prevent.
We Invent to Prevent.
+39 030 353-14-23
Via Lorenzo Bernini 12, 25010 San Zeno Naviglio BS

Detecting Small Gas Leaks: Helicopter Pipeline Inspections with ALMA

ALMA is the most sensitive unit on the market and below you can find a proof of this sentence. In the past few years, we have been conducting helicopter surveys of gas pipelines in Europe using our ALMA instruments. We have surveyed more than 100,000 km of underground gas pipelines in various countries.
 
 
 

Introduction

This article describes helicopter-based pipeline inspections using the Pergam ALMA G4 remote laser methane detector. It presents examples from flights conducted in France on June 12 and 20, 2025, during which several minor leaks were recorded.

June 12 flight (two methane detections):
  • Above a large manure pile, detected during two helicopter passes.
  • Over a field with a herd of cattle.
June 20 flight (four methane detections):
  • Above surface facilities along an underground pipeline.
  • Above cattle in a field.
Note: Cattle-related methane detections are included because gas companies report total methane emissions from agricultural sources to Greenpeace.
As for the suitability of a remote methane detector for inspecting normal, high-quality gas pipelines from an aircraft, the simplest test is to detect methane over a field where cows are grazing. If the device detects methane from every cow in the field, it is suitable for this type of work. Our ALMA family detectors has repeatedly detected methane under these conditions while flying over gas pipelines. ALMA, while inspecting gas pipelines in Europe, picks up methane from individual cows at 7–15 ppm·m from 40+ m altitude.

Cow methane emissions

A single dairy cow emits roughly 300–450 g of methane per day
The figures below show:
  • The data processing software interface (right).
  • A window with a previously acquired satellite image of the inspection area.
These satellite images display the projected helicopter flight path, locations of detected gas leaks, and measured methane concentrations in ppm×m.

The data processing interface shows details of a gas leak detection over a short flight segment. It includes five time plots:
  • Methane concentration (ppm×m)
  • Normalized methane concentration
  • Signal intensity in the analytical channel (from reflected laser beam)
  • Solar illumination of the inspection area
  • Helicopter altitude above ground level
In the top two plots, red points mark measurements at 0.2-second intervals, and blue points at 0.04-second intervals. The vertical dashed line across all plots indicates the moment the gas leak was detected.
Normalized methane concentration is the ratio of the measured methane concentration (in ppm×m) to the measurement noise (in ppm×m). Measurement noise depends on the analytical channel signal intensity at the time of measurement, which in turn is influenced by flight altitude and ground reflectivity at the given laser power. For example, a normalized concentration peak of 3 indicates a leak with a signal three times greater than the current measurement noise.
On the right side of the screen, the "Leak Line" plot illustrates:
  • Red line: signal in the detector's reference channel (with gas cell).
  • Blue line: signal in the analytical channel (laser beam reflected from ground).
The methane absorption line appears in the reference channel. The analytical channel signal reveals how closely it correlates with the shape of this absorption line.

The data processing software also provides information on numerous other helicopter flight parameters (e.g., airspeed) and instrument settings, although these are not shown in the main window. It includes a procedure to estimate gas flow rate in liters per minute for each detected leak.
The ALMA G4 is equipped with an HD video camera. However, video footage from these European pipeline inspections is currently unavailable and therefore not included in this document. Geographical coordinates of the pipeline and the leak locations are omitted, as this information is confidential to the gas company.

What Is ppm×m?

Path-integrated concentration: how ALMA measures gas along the full laser beam path from helicopter to ground

Concept

ppm×m is the integrated gas concentration along the laser beam. It equals the average concentration (ppm) multiplied by the path length (m) through the gas cloud.

Live Reading
0ppm×m

Helicopter A path-integrated concentration

Why It Matters

Unlike point ppm, ppm×m enables remote detection from aircraft without direct air sampling — stable across altitudes and terrain.

Laser Beam Gas Cloud (CH₄) Pipeline

Results

Fig. 1
Fig. 1. Gas leak detection at a pipeline facility, as seen in the satellite image. The concentration plot displays two closely spaced peaks, with amplitudes of 45 ppm×m and 19 ppm×m. The “Leak Line” plot shows the analytical signal during the larger peak, closely matching the methane absorption line in the reference channel. The normalized concentration plot indicates that the larger peak exceeds instrument measurement noise by roughly 15 times. The lower plot shows the helicopter altitude at detection was about 37 m, with a low speed of 14 km/h over the facility. The estimated gas flow rate for this leak is 0.9 L/min.
Fig. 2(a)
Fig. 2(a). Methane detection over a field. The satellite image shows flattened grass at the detection site; cattle were visible there in video footage. The concentration plot shows a 9 ppm×m peak. The "Leak Line" plot shows the analytical signal shape during detection, which reasonably matches the methane absorption line in the reference channel. The normalized concentration is twice the measurement noise. Helicopter altitude: 46 m; speed over field: 75 km/h. Estimated gas flow rate: 0.1 L/min.
Fig. 2(b). ALMA G4 video image.

Fig. 2(b)
Fig. 3. Gas leak detection at a small pipeline facility, as seen in the satellite image. The concentration plot reveals two closely spaced peaks of 13 ppm×m and 17 ppm×m. The "Leak Line" plot shows the analytical signal during the larger peak, which reasonably matches the methane absorption line in the reference channel. The normalized concentration is 3.6 times the measurement noise. Helicopter altitude: 46 m; speed over the facility: 34 km/h. Estimated gas flow rate: 0.25 L/min.
Fig. 3
Fig. 4(a)
Fig. 4(a). Methane detection over a field near farm buildings. Cattle walking at the detection site were visible in video footage. The concentration plot shows a 10 ppm×m peak. The "Leak Line" plot shows the analytical signal during this "leak," reasonably matching the methane absorption line in the reference channel. The normalized concentration is 2.7 times the measurement noise. Helicopter altitude: 41 m; speed over the field: 65 km/h. Estimated gas flow rate: 0.1 L/min.
Fig. 4(b). ALMA G4 video image.

Fig. 4(b)
Fig. 5(a)
Fig. 5(b)
Fig. 5. Detection of a gas "leak" above a large manure pile, recorded twice during repeated flights. The concentration plots in fig. 5(a) and 5(b) show peaks of 19 ppm×m and 13 ppm×m. In both detections, the analytical signal closely matches the methane absorption line in the reference channel. The normalized concentration is 5.5 times the measurement noise at the larger peak and 3.3 times at the smaller peak. Helicopter altitude during the two detections was 41 m and 45 m, with speeds of 56 km/h and 149 km/h. Estimated gas flow rates are 0.8 L/min and 0.4 L/min.
Fig. 5(b) also presents a satellite map with all detections of elevated methane concentration.
Fig. 5(c). ALMA G4 video image captured during one of the two flights over the detection site.

Fig. 5(c)
Fig. 6(a)
Fig. 6. Methane detection above a herd of cattle. The concentration plot in Fig. 6(a) shows two peaks of 26 ppm×m and 23 ppm×m. In both detections, the analytical signal closely matches the methane absorption line in the reference channel. The normalized concentration reaches 5.8 times the instrument measurement noise at the larger peak and 5.1 times at the smaller peak. The helicopter altitude was approximately 42 m, and the speed was about 40 km/h. The estimated gas flow rate is 0.3 L/min for each detection. Fig. 6(b) presents a satellite map showing all detections of elevated methane concentration. Fig. 6(c) shows an ALMA video image captured during the helicopter pass over the herd.
The ALMA G4 remote laser methane detector offers exceptional sensitivity and detects extremely low methane emissions during aerial inspections. The system can even register methane released by individual grazing cattle during helicopter flights. Typical measured concentrations range from 7 to 15 ppm×m, with methane plumes from individual animals usually less than 2 meters, demonstrating the instrument’s ability to identify very small and localized gas sources.

Conclusion

  • ALMA G4 reliably detects small methane emissions during helicopter pipeline inspections.
  • It identified low-intensity sources associated with pipeline facilities as well as agricultural activities such as livestock and manure storage.
  • The analytical and reference channel signals show consistent correlation across different flight altitudes and speeds.
  • ALMA G4 provides sufficient sensitivity for emission rate estimation during aerial inspections.
Learn more about ALMA laser methane detectors