A Deep‐Learning Model Cascade for Automating Large‐Scale Shoreline Mapping From Satellite Imagery

This study describes a machine learning model cascade for automating large‐scale shoreline mapping from time‐series of coastal satellite imagery. Our model cascade consists of independent supervised deep learning models for image suitability, image segmentation, and image segmentation suitability. The segmentation model determines shoreline locations, while the other models in this cascade filter imagery not suitable for segmentation or segmentations not suitable for shoreline detection. The SegFormer‐based segmentation model is trained with almost 2,300 labeled satellite images from a large variety of globally distributed coastal environments. The image segmentation model operates on imagery that has been deemed suitable by an image classification model that classifies whole satellite images as either suitable or unsuitable for segmentation. Another supervised whole image classification model is used to determine the suitability of each segmentation output. Finally, a spatial kernel density filters removes outlier shoreline points, with further timeseries analysis techniques to remove any remaining outliers. This study demonstrates the effectiveness of this system at two sites that are challenging to map: one at a sandy spit near Moses Point Fishing Village, Alaska, USA, and one at the mouth of the Elwha River, Washington, USA. This study demonstrates that these automated techniques produce shorelines with similar or better accuracies when compared to semi‐automated techniques. Ensembling model outputs better constrains the error and uncertainty of shoreline positions. Together, the set of models presented in this paper constitute an operational workflow for the generation and quality control of large‐scale records of satellite‐derived shoreline change.