Glossary

  • Eotvos: This is a unit of measure, like an inch or a pound, and just as an inch is a measure of length and a pound is a measure of weight, an eotvos is a measure of how much the “pull due to gravity,” changes over distance. The eotvos unit is abbreviated by “E”.

  • Geodesy: The science of accurately measuring and understanding three of Earth’s fundamental properties – its geometric shape, its orientation in space and its gravity field.

  • Gravity Gradient: Gravity does not exert a constant “pull,” it varies over distance and the “change in pull” can be measured. The predominant change in pull is known as the gravity gradient, and measured by gradiometers as a Gravity-Gradient Signal.

  • Noise Level vs Spatial Resolution:  Generally, there is an inverse relationship between the Noise Level of a gravity-gradient system and its ability to increase its Spatial Resolution. Typically, one can lower the Noise Level (and thus detect weaker Gravity-Gradient Signals) only if one also decreases the Spatial Resolution by smoothing the data.  

  • Noise Level:  By noise one means spurious readings, collectively known as the Noise Level, that “hide” the Gravity-Gradient Signal trying to be measured — as such, it represents the smallest detectable Gravity-Gradient Signal.

  • Spatial Resolution: This term refers to the number of independent measurements taken over a given distance (on the ground).  A higher Spatial Resolution means that the distance between each measurement is smaller.   To achieve this, the measurements must be taken more frequently — higher Spatial Resolution permits smaller and more closely-spaced targets to be detected.