DIGHEM
Fig. 183 A DIGHEM system in operation. Source: Strongbow Exploration Inc.
DIGHEM is a frequency-domain multi-coil system operated by CGG. The system has evolved over years, but here we describe the basic specification of the system based on DIGHEMV system.
Coils
Frequency (Hz) |
900 |
1k |
5.5k |
7k |
56k |
|---|---|---|---|---|---|
Configuration |
HCP |
VCA |
VCA |
HCP |
HCP |
Separation (m) |
7.86 |
7.86 |
7.86 |
7.86 |
6.3 |
The system consists of five pairs of coils operating at five discrete frequencies and in horizontal coplanar (HCP) or vertical coaxial (VCA) configurations as listed above. The actual operating frequencies can be slightly different from the nominal frequencies in the table. The measured data is the secondary magnetic field (Hs) normalized by the primary field (Hp) in part per million (ppm).
Flight
DIGHEM has a nominal terrain clearance of 45 m and a nominal aircraft speed of 55 km/h. A typical sampling rate is 10 per second, equivalent to 1 sample every 3 m at a speed of 110 km/h. The aircraft is also equiped with the following ancillary instruments:
Magnetometer
Radar altimeter
Video camera,
Analog and digital recorders
GPS navigation system