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05 / Potential field
Microgravity surveys
Every other method looks for something. Gravity looks for the absence of something — which makes it the most direct way to prove a void exists, and one of the few that works where radar and resistivity are both defeated.
What it measures
A microgravity meter measures minute variations in the Earth's gravitational field — parts per billion. A cavity in rock is a deficit of mass, and it produces a small negative anomaly at the surface directly above it.
Getting to that signal is mostly a matter of discipline in corrections. Latitude, elevation, terrain, instrument drift and the tidal pull of the sun and moon all exceed the target signal and must be removed. Elevation in particular has to be surveyed to a fraction of an inch, which is why a microgravity survey is as much a precision leveling exercise as a geophysical one.
Why it is worth the effort
Gravity is sensitive to density alone. It does not care whether the ground is conductive, saturated, made of clay or covered in reinforced concrete — conditions that variously defeat radar, EM and resistivity. On a site where those methods have returned an ambiguous answer about a suspected void, gravity frequently settles it.
It is also the natural partner to resistivity. The two measure entirely independent properties, so agreement between them is strong evidence and disagreement is a warning worth having.
What it will not tell you
The signal falls off sharply with depth and is proportional to the missing mass. A small void at depth may be genuinely undetectable, and we will give you a detectability estimate for your target size and depth before you commit rather than after. It is also slow — each station is an occupation, not a walking pass — so coverage costs real money and the survey has to be aimed at a defined area rather than sprayed across a site.
Equipment and capability
- Micro-gravity for voids and cavities
- Precision elevation control to survey grade
- Full terrain and tidal correction
- Mine working and sinkhole detection
- Karst dissolution feature mapping
- Bouguer and residual anomaly modeling
What you receive
Corrected Bouguer and residual anomaly maps, forward models showing the mass deficit consistent with each anomaly, and a stated detection threshold for the target size and depth agreed at the outset.
Ask before you commission
Tell us the target, the ground and the constraint and we will say whether this method answers it, whether it needs a second method alongside, or whether something else entirely is the better route. That conversation is free and it is usually short.