Geophysical, Underwater & Airborne Remote Sensing

MAGNETIC GRADIOMETERS

Magnetic gradiometers, a type of magnetometer, are passive instruments that measure the gradient of the magnetic field strength at a point on the Earth’s surface. Archaeological features exhibit either permanent or induced types of magnetism. Permanent magnetization, also called remnant magnetism, is enhanced when hearths, perishable structures, and other features are burned. Induced magnetism, or magnetic susceptibility, is increased by the organic content of pits and middens in the presence of the magnetic field of the Earth. Because of its rapid collection speed and its response to a wide array of targets, magnetic gradiometry is an excellent archaeological prospection technique.

CEI’s Marine Archaeology Division has been involved in marine geophysical studies in a variety of environments since 1977. Many of these projects have involved intensive remote-sensing and cultural resource investigations of marine and riverine environments in Louisiana, Texas, Mississippi, Alabama, Arkansas, Florida, as well as in the waters of the Gulf of Mexico. These studies have included remote-sensing surveys, processing of geophysical datasets, and archaeological interpretation of remote-sensing data. In addition, we conduct hydrographic surveys, remote-sensing surveys designed to specifically identify underwater hazards, such as pipelines and well heads, and remote-sensing surveys to collect information on the natural environment, including seabed classification and identification of oyster reefs and sea grass beds.

Magnetometer

Magnetometers measure the Earth’s ambient magnetic field. Deviations from the ambient background are called anomalies, which typically are generated by the presence of ferrous objects. Each anomaly recorded by the magnetometer is measured, and the magnetic intensity, signature, and persistence of each anomaly is used to make inferences about the identity of the source object. For marine survey projects, magnetometers are used to locate metallic objects that might represent submerged cultural resources (e.g., shipwrecks or anchors), as well as hazards or impediments to planned activities (e.g., pipelines).

Side-Scan Sonar

Side-scan sonar is an instrument that, through the transmission of dual fan-shaped pulses of sound and reception of reflected sound pulses, produces an acoustic image of the bottom. The side-scan sonar data are used to map bottom conditions within the project area and identify features of interest.

Sub-Bottom Sonar

Sub-bottom profilers use low-frequency acoustic waves to collect information on subsurface features and shallow subsurface stratigraphy in the survey area. These returns are received by hydrophones in the tow fish. The data sets are computer processed and reproduced as a cross-section scaled in two-way travel time (the time taken for the pulse to travel from the source to the reflector and back to the receiver). Using estimates of the velocity of sound through the water and the seabed, this travel time can then be converted to depth in the sediment column.

Fathometer

Echo sounders are used to obtain information on bathymetry in the surveyed area. In addition, it also can be used to identify objects that extend above the seabed.

AIRBORNE REMOTE SENSING

CEI employs airborne remote-sensing data from a variety of sources, including from drone / Unmanned Aerial Systems (UAS) platforms. We operate a DJI Phantom 4 Pro V2.0 UAS and Pix4D Mapper software, which allow us to create a variety of 2D and 3D spatial products for many applications. The data can be enhanced with ground control points in order improve the spatial accuracy. CEI operates using FAA Part 107 guidelines for commercial drone / UAS operation.” 

CEI UAS LiDAR surveys produce elevation data at extremely high resolutions. LiDAR sensors can penetrate tree canopy, revealing archaeological features and many other types of targets. CEI staff can process and classify LiDAR data, creating bare-earth digital

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