A method and system for processing geophysical survey data is provided. Gravity gradiometry data is processed by approximating density values of terrain signals to remove contributions of the terrain from the gravity gradiometry data. Initially, a predicted gravity gradient data set for a geographical area is calculated using terrain data with unit density. Next, a mathematical transformation is applied to recorded gravity gradiometer data of the geographical area and the predicted gravity gradiometry data. The transformation divides the data into component sub-functions so that each component function can be processed separately. The component sub-functions are processed to estimate densities of the geographical area. Then, using all the estimated densities, gravity gradients due to all of the terrain can be calculated, and subtracted from the recorded gravity gradient signals to reveal gravity gradients due to subsurface masses, for example.