1. A method of terrain correction for a geophysical survey, the method comprising: capturing a multi- or hyperspectral image of a region to be surveyed; determining a surface geological composition of said surveyed region using said captured multi- or hyperspectral image; determining, using a data processing system, terrain correction data for said geophysical survey using said determined surface geological composition wherein said terrain correction data comprises density data defining a variation in surface density or porosity over said surveyed region and wherein said determining of terrain correction data comprises combining said density data with surface elevation data for said surveyed region; and using said terrain correction data for performing said terrain correction for said geophysical survey.