By Dr. George Schwarz, NHHC Underwater Archaeology
Naval History and Heritage Command’s Underwater Archaeology Branch (UA) collaborated with NAVAIR UX-24 last week to complete an aerial magnetometer survey over a marshy section of the Patuxent River, where it is thought remains of naval vessels from the War of 1812 are buried.
Between 2009-2011 UAB, along with Maryland Historic Trust and Maryland State Highways Administration, relocated, mapped, and excavated what is believed to be the gunboat Scorpion, flagship of Commodore Joshua Barney‘s Chesapeake Flotilla. After months of staving off British naval attacks and encroachments on the nation’s capital, in August of 1814 the flotilla was ordered to be scuttled by Secretary of the Navy William Jones. Scorpion, along with 15-16 other vessels, were burned on the Upper Patuxent River. Records vary on the location of the scuttling, though it was written that Scorpion was destroyed apart from the remaining flotilla ships, which were sunk in a line north of the flagship according to surviving sources. Navy researchers believe that the scuttled vessels are buried under the sediment in the river, and may be detectable by marine magnetometer given the amount of iron ordnance, anchors, ballast, and fasteners which could still be present. Scorpion was buried under approximately 1.2 to 2.4 m (4 to 8 ft.) of sediment below the river bottom, and was found to have a strong magnetic signature, with at least one pig iron ballast bar recovered from the wreck. Ongoing research into the possible migration of the Patuxent River since 1814 suggests that the remaining flotilla vessels could also be buried underground or in marshland adjacent to the current river.
Since 2014, UA has worked with various partners, including the College of Charleston in 2014 and 2016, and SUPSALV’s Phoenix International in 2015 to survey the river in search of the flotilla, using hydrographic survey equipment to study the river bottom. Since the boats could not enter the marshland, however, the team needed to find a way to survey these wetlands for the wrecks. In April of 2019, UA and UX-24, a branch of NAVAIR which operates unmanned aerial systems (UAS), spent one day in a Patuxent River marsh to run the first of the aerial magnetometer surveys using a UAS, designated OA-8C Dragonfly, from Offshore Aviation and the Geometrics MagArrow, a lightweight magnetometer designed to be suspended from a drone. The 2019 survey was successful, but was limited to only one day to test the methodology.
In April 2021, staging out of the Jug Bay Wetlands Sanctuary, the team returned to the backchannel of the Upper Patuxent, one of the suspected locations of the sunken flotilla, and ran the aerial survey for four days. UAB and UX-24 were able to cover over 86 acres with the drone during this period. This was the perfect time of year as the vegetation was low in the marsh which allowed for team members to keep eyes on the drone as it was flying the pre-planned grid over the study area.
Some of the area that was covered included parts of the river that were surveyed in previous years in order to compare the results of aerial magnetometer with the marine magnetometer. As this is a relatively new application for marine archaeology, in addition to helping to find the buried flotilla, these studies will allow researchers to compare data sets and refine methods and expectations for future surveys.
The UAS, a multi-rotor octocopter, was programmed to survey the back channel with the 1-meter (3.3 ft) lightweight long sensor suspended 3 meters (10 ft.) below. The flight pattern followed lines spaced 5-meters (16.4 ft) apart along the grid. The UAS flew with the magnetometer suspended at an altitude of 5 meters (16.4 ft), which meant two team members with radios needed to be in the swamp monitoring the craft to avoid possible tree collisions.
The survey area was divided into three blocks which equaled a total area of 86 acres (34 hectares). The entire area was covered in under three days. This is over seven times the area that was covered when UA attempted a terrestrial magnetometer survey (where archaeologists trudged through the marsh carrying a hand-held magnetometer, often falling waist deep in watery holes) of this same area over an entire week in 2017!
Now that the data collection is complete for 2021, UA archaeologists will begin the task of processing, interpreting, and mapping the data sets to find out if there are potential wrecks in the wetlands. Should the data give us encouraging results, the team will organize a return visit to pinpoint the areas of interest and look for shipwrecks buried in the marsh.
Test Pilot Kyle Matthew had this to say of the project: “Partnering with other Navy commands broadens NAVAIRs experience base contributing to the overall quality of our pilots and testers. NAVAIR’s core mission is to help the Fleet and we are happy to be a small part in exploring, discovering and learning about our long and proud naval history.”