Deriving High Spatial-Resolution Coastal Topography From Sub-meter Satellite Stereo Imagery

Abstract

High spatial resolution coastal Digital Elevation Models (DEMs) are crucial to assess coastal vulnerability and hazards such as beach erosion, sedimentation, or inundation due to storm surges and sea level rise. This paper explores the possibility to use high spatial-resolution Pleiades (pixel size = 0.7 m) stereoscopic satellite imagery to retrieve a DEM on sandy coastline. A 40-km coastal stretch in the Southwest of France was selected as a pilot-site to compare topographic measurements obtained from Pleiades satellite imagery, Real Time Kinematic GPS (RTK-GPS) and airborne Light Detection and Ranging System (LiDAR). The derived 2-m Pleiades DEM shows an overall good agreement with concurrent methods (RTK-GPS and LiDAR; correlation coefficient of 0.9), with a vertical Root Mean Squared Error (RMS error) that ranges from 0.35 to 0.48 m, after absolute coregistration to the LiDAR dataset. The largest errors (RMS error > 0.5 m) occurred in the steep dune faces, particularly at shadowed areas. This work shows that DEMs derived from sub-meter satellite imagery capture local morphological features (e.g., berm or dune shape) on a sandy beach, over a large spatial domain.Among topographic survey methods of suitable quality, those based on Global Navigation Satellite Systems (GPS), such as Real Time Kinematic GPS (RTK-GPS), have been used extensively to map and monitor coastal morphology [2]. Beach topographic surveys using RTK-GPS method can be performed either by walking and carrying a GPS receiver, or driving a mobile unit (e.g., quad bike). In both cases, the vertical precision is approximately 0.05 to 0.1 m, depending on the terrain relief [2]. This method typically requires an intense human effort, which normally is optimized by reducing the number of measurements to a limited number of cross-shore sections of the beach. Nevertheless, this limited spatial coverage results in an incomplete representation of topographic spatial patterns and evolving features, especially in the case of complex topographies such as steep and unconsolidated slopes. In such cases, interpolation methods are typically required, introducing additional uncertainty into the DEM [3].Remote sensing techniques, such as airborne LiDAR (Light Detection and Ranging) and Unmanned Aerial Vehicle (UAV), emerge in this context as a solution to overcome the limited spatial coverage of the RTK-GPS method [4][5][6][7][8][9]. The use of airborne LiDAR to measure geomorphological changes in coastal areas is relatively new. This instrumentation acquires millions of x, y, z points per hour, with a horizontal spacing of typically 1 to 3 m. This high spatial resolution, together with the capacity to survey over large areas (from 10 1 to 10 5 m), allows overcoming traditional survey limitations found with RTK-GPS [2]. The vertical accuracy of LiDAR ranges from 0.05 m to 0.15 m [5], which is in the same order as RTK-GPS and appropriate for studying beach morphology. Nonetheless, LiDAR-based DEMs are costly [5,6], which limits the frequent (e.g., monthly or-post-...

Monitoring Beach Topography and Nearshore Bathymetry Using Spaceborne Remote Sensing: A Review

“…In [17], beach and dune topography was retrieved using Pleiades-1A stereoscopic imagery. An evaluation of the precision and accuracy of the derived 2-meter Pleiades DEM was performed by [17] through comparison between the satellite derived topography and traditional survey methods, such as airborne light detection and ranging (LiDAR) and RTK-GPS surveys. The pilot site selected for this comparison was a 40 km stretch of coastline in southwest France (Figure 1).…”

“…sensors. By analyzing satellite stereo-pairs [16], beach topography can be produced and large coastal stretches can be surveyed using satellite acquired stereo images [17]. Intertidal areas situated between the upper and lower limits of spring tides also benefit from the wide range of available satellite data.…”

Corridor Mapping of Sandy Coastal Foredunes with UAS Photogrammetry and Mobile Laser Scanning

“…On the other hand, coastal scientists ask for ever more frequent observations of sand and shoreline displacements to better understand the underlying physics and to improve the accuracy of prediction tools. Demand will likely increase with rising sea level and changing storm patterns [2,3], which has fostered the development and application of new surveying methods [4][5][6], and the so-called Blue Economy [7] is a chance to contribute to this effort.…”

Sub-Pixel Waterline Extraction: Characterising Accuracy and Sensitivity to Indices and Spectra

“…Although data cube platforms have driven a paradigm shift in the maximum spatio-temporal scale of analyses that are possible using remote sensing, the ability to accurately monitor environmental change at fine spatial scales remains critical for many potential coastal and inland water applications based on accurately modelling the position of the waterline. These include monitoring coastal erosion along narrow, steep coastlines [13], modelling dynamic intertidal topography and geomorphic change [14,15], and assessing small changes in water levels within narrow or steep sided inland rivers and waterbodies [16,17]. Most remote sensing studies to date have mapped the boundary between land and water in the landscape using binary classifiers based on either machine learning [11,12,18], or thresholding either a single satellite band [19][20][21] or remote sensing water index such as the normalised difference water index or NDWI [7,[22][23][24][25][26][27].…”