Some gravity reductions that can be used include normal gravity, latitude, free-air, complete Bouguer, and isostatic. The choice of the Earth gravity model depends on the specific application. Gravity anomalies represent the differences between the measured gravity acceleration and the gravity acceleration computed or predicted by an Earth gravity model. The corrected gravity acceleration serves as input for gravity reductions. The first step is to apply gravity corrections, which include those for drift, tides, Eötvös (centrifugal acceleration), and loop ties. The data processing workflow (raw measurement -> corrections -> reductions -> anomalies) will convert the raw measured gravity acceleration into interpretable gravity anomalies. Before practical usage, various corrections and reductions are required to separate the gravity signal from noise and external contributions.
The gravity acceleration on the Earth's topographic surface is measured using gravimeters. Edit: please find the details about the model and the visualisation in the comments.
