Joining multi-epoch archival aerial images in a single SfM block allows 3-D change detection with almost exclusively image information

Archival aerial imagery is a worldwide resource for documenting past 3-D change at very high-resolution. However, external information is normally required so that accurate 3-D models can be computed from archival aerial imagery. In this research, we propose and test a new method which joins multi-epoch images in a single block in the first steps of the structure from motion (SfM) processing. It allows for computing coherent multi temporal digital elevation models (DEMs) using just image information. This method is based on the invariance properties of the feature detection procedures that are at the root of the SfM algorithms. On a test site covering 170 km(2), we applied SfM algorithms to a single image block consisting of all images captured at four different epochs and spanning a forty year period. We compared this approach to the more classical methods which imply a separation of epochs in different processing blocks. We tested different densities of ground control points derived simply and cheaply from a recent orthophoto and DEM, different ways of image preprocessing and different autocalibration procedures. By determining which choice most affected the final result through this extensive testing procedure, we evaluated the potential of the proposed method for detecting 3-D change. Our study showed that the proposed method resolves the problem of registration between epochs, so allowing the production of informative DEMs of difference using almost exclusively image information and limited photogrammetric expertise and human intervention. As the proposed method can be automatically applied using just image information, our results pave the way to more systematic processing of archival aerial imagery with very large spatio-temporal windows, which should greatly help document of past 3-D change.