Optical Geodesy and the Measurement of Ground Deformation by Image Correlation

Optical geodesy is a relatively new technique which allows deformation of the Earth’s surface to be retrieved from the correlation of remotely sensed optical satellite or aerial images. In this chapter, we summarize the main aspects of optical geodesy, with a particular focus on using correlation methods for measuring ground deformations due to earthquakes. We discuss the various datasets which can be used, and common problems associated with using them for geodetic purposes. We touch upon bundle adjustment, which allows the fusion of many small images to produce seamless mosaics, which can then be used for correlation. Correlation methods are also discussed, with a focus on the two main approaches: zero mean normalized cross correlation in the spatial domain, and phase correlation in the frequency domain. We discuss various methods of denoising used to minimize outliers, or unwanted artifacts and signals in the correlation maps. We finish with a brief discussion of future directions in optical geodesy, such as generating 3D displacement fields from stereo imagery, processing optical time-series, and potential methodological improvements to correlator performance.