Assessing the Utility of Open-Access Bathymetric Data for Shipwreck Detection in the United States

heritage Article Assessing the Utility of Open-Access Bathymetric Data for Shipwreck Detection in the United States Dylan S. Davis 1, * , Danielle C. Buffa 1,† 1 2 * † and Amy C. Wrobleski 2,† Department of Anthropology, The Pennsylvania State University, University Park, PA 16802, USA; Ecology Intercollege Graduate Program, The Pennsylvania State University, University Park, PA 16802, USA; Correspondence: These authors contributed equally to this work. Received: 1 April 2020; Accepted: 22 May 2020; Published: 24 May 2020



 Abstract: Investigation of submerged cultural heritage is an important area of archeological focus. However, the expense of acquiring the necessary data to conduct studies of underwater landscapes is often prohibitive to many researchers. Within the United States, highly resolved bathymetric data are openly available from governmental agencies, and yet little to no marine archaeological exploration has occurred using this information. Here, we investigate the archaeological utility of freely available bathymetric datasets from the National Oceanic and Atmospheric Administration (NOAA) in the United States. These datasets have not previously been utilized for archaeological publications, and include swath bathymetric and topographic LiDAR data, which are widely used by marine archaeologists. We present three case studies from Long Island, New York, coastal Massachusetts (on the Eastern coast of North America), and New Orleans (on the Gulf Coast of North America) to demonstrate the potential of this open-access information for locating shipwreck sites. Results indicate that shipwrecks at varying levels of preservation can be identified at depths up to 160 m, and that even in extremely turbid waters, bathymetric LiDAR can detect some wreckage. Following this assessment, we develop an automated shipwreck detection procedure using an inverse depression analysis. Our results are promising for automated detection methods in marine archaeology research. We argue that archaeologists in the United States should take advantage of these freely available data, as it is possible that these bathymetric data can be used for detection and conservation of cultural and environmental resources even without large funding acquisitions. Keywords: bathymetric lidar; multibeam echosounders; shipwrecks; remote sensing; automated object detection; United States 1. Introduction Much of human history is dominated by coastal living arrangements and connections to maritime environments [1–4]. While there is an abundant underwater cultural record [5], the vast majority of this heritage is at risk and unprotected [6–13]. Studies around the world have demonstrated that an abundance of archaeological deposits lie submerged beneath present day sea levels [1,14–17] including shipwrecks [10–12,18,19]. In North America alone, the Eastern coastline contains a rich maritime history [20,21]. The application of remote sensing technology has capabilities to detect objects submerged at shallow and deeper depths near the coast, even in extremely turbid and high-energy waters. The archaeological utility of high-resolution bathymetric sensors has been well established [10–12,22–26]. For example, Warren et al. [27] use high-resolution swath bathymetry Heritage 2020, 3, 364–383; doi:10.3390/heritage3020022 www.mdpi.com/journal/heritage Heritage 2020, 3 365 data to locate an aircraft carrier sunk by the Germans in WWII. Plets et al. [11] use multibeam bathymetry data to survey a large section of seafloor on Ireland’s northern coast. They demonstrate how shipwrecks can be identified but note that resolution of the data limited detection of smaller, less well-preserved wrecks. In the United States, researchers have used bathymetric data to locate the USS Independence, a WWII aircraft carrier used to test the effectiveness of atomic weapons [24]. Other research has demonstrated the utility of multibeam sonar for detecting shallow wrecks from the American Civil War (1861–1865) and WWII [28]. Additionally, researchers in the United States documented shipwrecks using photogrammetry for inclusion in the National Register of Historical Places (NRHP) [29]. In many European countries (e.g., Ireland, Norway, the U.K., etc.), open-access bathymetry data have been highly impactful to the marine archaeological community [25,30,31]. Unlike many nations in Europe, however, the use of open-access bathymetric data has been slower to make its way into archaeology in the United States (e.g., [32]). Detecting archaeological features from image data is often accomplished using depth/elevation profiles [11,22,33–38]. Bathymetric data produce depth measurements for seafloors, which can help to characterize seabed morphology [39]. One limitation of the use of bathymetric datasets is their cost. To acquire large-scale bathymetric data by ship can range in the tens-of-thousands of dollars for some commercial contracts [40,41]. While smaller datasets (i.e., single-beam scans of targeted areas) are more affordable, some data require commercial operations. Furthermore, data acquisition in shallow waters is often more expensive and time consuming than deeper environments [41]. The availability of open-access data from the United States government makes conducting important underwater research possible for a greater number of scholars. Despite the availability of these data in the United States, little to no archaeological case studies have been published using such information. While governmental agencies have produced reports detailing the capabilities of bathymetric data for recording submerged archaeological sites, the data generated are not always made publicly available. Here, we assess freely available bathymetric datasets from the United States Geologic Service (USGS) and the National Oceanic and Atmospheric Administration (NOAA) for archaeological prospection. These data are available for most of the eastern and western seaboards of the contiguous United States, Alaska and Hawaii, and several U.S. territories. Because of the abundance of shipwrecks and maritime history along the eastern coastline of the U.S. (see the Atlantic OCS Shipwreck Database [32]; also see [20]), we specifically target areas with high densities of known shipwrecks to investigate the capabilities of these datasets. This will also provide an assessment of the abilities of the aerial components of these data (i.e., LiDAR) in extremely turbid environments that are prone to damaging tropical storms and dynamic seabed motion. In what follows, we briefly review bathymetric remote sensing technology and its applications in archaeological research. While archaeologists have conducted similar studies elsewhere (e.g., [11,19,26]), the specific datasets used here have not been evaluated for archaeological purposes. As such, we begin by evaluating its utility for detecting shipwreck sites using three case studies from Long Isla (...truncated)