Developing a CNN for automated detection of Carolina bays from publicly
available LiDAR data
Abstract
For over a century, the enigmatic Carolina bays have captivated
geologists and spurred contentious debate on their origin. These
circular to ovate and shallow (median diameter of 222 m, median depth of
2.17 m, median area of 26,249 sq. m) depressions span the Atlantic
Coastal Plain (ACP) from northern Florida to southern New Jersey, with
total counts ranging between 10,000 and 500,000. Using 1 meter gridded,
1.7 km by 1.7 km LiDAR digital elevation models (DEMs) of Delaware as
training images, a convolutional neural network (CNN) was trained to
detect Carolina bays. With such a large population size and with such
uncertainty around the actual population size, mapping the Carolina bays
is a problem that requires an automated detection scheme. Manual
detection of bays from LiDAR across the entire Atlantic Coastal Plain
would be extremely time intensive and prone to human annotation errors.
Using Faster R-CNN within the TensorFlow Python library, a network was
trained on 978 LiDAR images for 24 hours (42,450 iterations) on an Intel
Core i7-4790K CPU at 4.00 GHz. This network automatically detects bays
from LiDAR images with a bounding box and a confidence level. These
bounding boxes can then be used to subset and then analyze regions of
the DEM for statistics on the bays’ three-dimensional shape. Extending
this algorithm to DEMs from other areas of the ACP will provide a better
understanding of the bays’ geographic distribution as well as any
differences in morphology between different geographic regions. This
method for detecting geomorphic features is a highly efficient process
that will provide better means for mapping various types of abundant
geomorphic features in the future.