  Supervised learning based methods for monocular depth estimation usually
require large amounts of extensively annotated training data. In the case of
aerial imagery, this ground truth is particularly difficult to acquire.
Therefore, in this paper, we present a method for self-supervised learning for
monocular depth estimation from aerial imagery that does not require annotated
training data. For this, we only use an image sequence from a single moving
camera and learn to simultaneously estimate depth and pose information. By
sharing the weights between pose and depth estimation, we achieve a relatively
small model, which favors real-time application. We evaluate our approach on
three diverse datasets and compare the results to conventional methods that
estimate depth maps based on multi-view geometry. We achieve an accuracy
{\delta}1.25 of up to 93.5 %. In addition, we have paid particular attention to
the generalization of a trained model to unknown data and the self-improving
capabilities of our approach. We conclude that, even though the results of
monocular depth estimation are inferior to those achieved by conventional
methods, they are well suited to provide a good initialization for methods that
rely on image matching or to provide estimates in regions where image matching
fails, e.g. occluded or texture-less regions.
