= Solution
A \b[<gravity anomaly>] is measured gravity minus a specified reference gravity after the stated reductions. A <Bouguer gravity anomaly> aims to remove the predictable effects of latitude, observation elevation and surrounding topographic mass, so residual variations can be related to subsurface <geophysical density contrasts>.
Measure relative gravity with a calibrated <gravimeter> at stations across and beyond the crater, and survey station positions and elevations accurately, preferably with <GNSS> tied to a reference datum. Repeat a base station through the day to estimate instrument drift and tie the traverse to a gravity datum. Record station times, because tidal and drift corrections are time dependent.
Apply instrument scale and drift corrections, solid-Earth and relevant ocean-loading tidal corrections, latitude/reference-ellipsoid gravity subtraction, the <free-air correction>, the <Bouguer slab> correction for material between station and datum, and a <terrain correction> for departures from a flat slab. The crater’s strong relief makes the last correction important. A local regional-field/background estimate is also needed if the target is the crater’s residual anomaly. State the reduction density; it is not the inferred breccia density.<Geophysical Data Grids for the Conterminous United States by United States Geological Survey>[Gravity-anomaly discussion: latitude, free-air, simple Bouguer and terrain reductions]{ref} For a fixed land traverse there is no moving-platform <Eötvös correction> to add.
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