Bathymetry is the measurement of the depths of oceans, seas, or other large bodies of water, typically using narrow swath acoustic system.
Side scan sonar is, similar in principal to radar, for finding the distance and direction of objects in water by transmitting sound waves and detecting reflections from them. A computer keeps track of the information and makes pictures of the bottom of an ocean, lake, or river.
Seismic reflection involves the measurement of the two-way travel time of seismic waves transmitted from surface and reflected back at the interfaces between geological layers where there is acoustic impedance (the combination of seismic velocity and density) contrast. The strength of the contrast in the acoustic impedance of the two layers determines the amplitude of the reflected signal. The reflected signal is detected on surface using an array of high frequency geophones.
The seismic refraction technique is used to delineate subsurface features such as top of bedrock, buried valleys and subsurface stratigraphy with critically refracted seismic wave (generated at the surface) along the subsurface and then re-radiated back to surface. This method is based on the assumptions that include increasing velocity with depth, layered stratigraphy, and relatively low angle slope changes on the refracting boundary.
This technique is used to study variations in the magnetic field of the Earth, including local distortions or anomalies of the field caused by ferrous objects or minerals. In general, the magnitude of the magnetometer response is proportional to the mass of the ferrous object.
The electrical resistivity technique maps differences in the electrical properties of geologic materials. These differences can result from variations in lithology, water content, pore-water chemistry, and the presence of buried debris. The method involves transmitting an electric current into the ground between two electrodes and measuring the voltage between two other electrodes. The direct measurement is an apparent resistivity of the area beneath the electrodes that includes deeper layers as the electrode spacing is increased. Recent advances in technology permit rapid collection of multiple soundings, using 56 electrodes for each spread. The data are modeled to create a 2-D geo-electric cross-section that is useful for mapping both vertical and horizontal variations of the subsurface strata.
Underwater video provides visual observation of objects on sea/ocean, river and lake bed.
This technique will provide samples from marine, lake and river bottom for soil property study or contaminant analysis.
This method will provide in situ measurement of marine sediment with the STING Mk.II. This unique free-fall penetrometer provides a powerful and cost-effective alternative to the methods commonly used for determining the dynamic load bearing strength of the seabed.
