Comparing high-resolution topographic survey methods for assessing geomorphic changes of point bars

Abstract

Detailed topographic landform analyses are the foundation of many geomorphologic investigations. Terrestrial laser scanning (TLS) is the favored survey method for studies that require high-resolution surface models; however, practical considerations, such as the high cost of instrumentation and intensive field work required to implement this approach, present possible limitations for its use in budget-limited or large-area studies. In contrast, a promising alternative approach for collecting high-resolution geospatial data collection using close-range digital photogrammetry (CRDP) provides rapid results for large study areas with a low cost-of-entry. However, the lack of published data obtained regarding CRDP methods and results makes it difficult to know if the resolution and accuracy of resultant survey data is comparable to TLS. In this study, we compare the practical issues, data collection, data processing, and results obtained from a time-series of annual TLS and CRDP surveys, performed in tandem over three years, to monitor the spatial patterns of erosion and deposition along a point bar in White Clay Creek, Newark, Delaware. Evaluation of the differences between CRDP and TLS surface models reveals that the two methods produce dissimilar digital elevation models, largely due to how each method detects bare earth and vegetation differently. As such, the volumetric change measurements of erosion and deposition along our study point bar differ significantly between the two methods. Our results suggest that in rough, obstructed, and dynamic terrains, CRDP may not be suitable high-resolution topographic survey method. However, a holistic view of survey design considerations (i.e. desired spatial resolution, the need for high resolution multispectral orthoimages, total project budget, and field time) may require the consideration of CRDP as a heuristic survey method for many applications.