Gasdetection Helicopter
GNSS two-antenna system on a gas-detecting helicopter with semi-automatic target beam direction
More and more companies in Germany are using GNSS correction data from the ascos satellite positioning services for their navigation requirements. E.ON Ruhrgas AG commissioned a feasibility study from ALLSAT to investigate the positional accuracy of a GNSS receiver with ascos correction data in a gas-detection helicopter. The objective was to attain an accuracy of better than 1 meter.
In the interest of safe and environmentally compatible operation, natural gas transmission pipelines are regularly inspected across the world by walking surveys, by motor vehicle, or by surveillance flights with small helicopters and aircraft. In these procedures, innovative technologies provide the key for efficiency-enhancing measures. For this reason, CHARM (CH4 Airborne Remote Monitoring), a remote sensing system based on infrared laser light, was developed under the auspices of Ruhrgas AG together with the German Aerospace Center (DLR) and the Brandenburg-based company Adlares. The gas-leak detection system enables even minimal amounts of discharged gas to be discovered at an early stage during routine pipeline control flights with small helicopters by identifying its main ingredient methane (CH4).
The underlying measuring principle for this development, the so-called DIAL (Differential Absorption Lidar) procedure, is an active, optical remote sensing system based on laser light that is widely used to detect trace gases in the atmosphere. Lidar (Light Detecting And Ranging) functions through the transmission of pulsed laser light and the subsequent detection and analysis of the light scattered back to a receiver system as the beam hits particles in the atmosphere or a target object. Trace gas concentrations can be determined by synchronizing the laser wavelengths with the spectral signature and absorption properties of the gas to be measured.
The target specifications for the CHARM system are:
Remote detection of natural gas leaks during pipeline surveillance from a small helicopter
- Flight altitude: 50 - 250 m;
- Flight velocity: 20 - 42 m/s;
- Identifiable natural gas emissions: 0.01 - 10 m³/h;
- Width of pipeline section that can be examined: 18 m;
- Automatic positioning of measuring beam (semi-automatic positioning via video image and manual control insofar as precise digital pipeline coordinates are not available);
- Registration of the leakage position in a reporting system.
The field trial phase has now been successfully completed. The measurement system is currently being tested on a helicopter of the type MD500E. To this end, the complete measuring equipment has been built into an external load container. This is fixed on the lifting hook beneath the helicopter cabin and between the landing skids.
In a feasibility study of the system described above, ALLSAT showed that ascos correction data (Realtime Service, ED) are necessary to achieve a positional accuracy during flight of 0.25 rms (route mean square).
