2D Marine seismic exploration investigates and maps the structure and character of subsurface geological formations underlying a body of water. In the 2D method, a single seismic cable or streamer is towed behind the seismic vessel, together with a single source. The reflections from the subsurface are assumed to lie directly below the sail line that the seismic vessel traverses – hence the name 2D. The processing of the data is, by nature of the method, less sophisticated than that employed for 3D surveys. 2D lines are typically acquired several kilometres apart, on a broad grid of lines, over a large area. The method is generally used today in frontier exploration areas before drilling is undertaken, to produce a general understanding of the regional geological structure. For high resolution survey, the hydrophone space in streamer is reduced, and also the length of streamer itself and space between survey lines, and so get the shallow result in subsurface sequence.
Source, such as air gun generate aqoustic wave which propagates through water, seabed, and sub-seabed Streamer receives and records every reflected aqoustic signal
Sonar measurements carried out by firing the acoustic wave. When the release of a pulse wave and the return echo is the time taken for the wave propagates down and back again. By way of knowing that time and the speed of sound in water medium can determine the distance of the depth.
Sonar projector requires continuously producing acoustic pulses with appropriate precision, control, and repetition with the same character. The projector used is made of piezo-electric ceramic material, a material that can change if imposed voltage. Echosounders use some fatherly voltage causes the piezo-electric projector oscillates, emitting a wave of press with a certain frequency characteristics into the water.
Multibeam echosounder (MBES) is based on combination of singlebeam echosounder. The purpose of this multibeam is to get depth value in several places at one time. The depth is measured and then combined to obtain three-dimensional view.
Multibeam echo sounders, like other sonar systems, transmit sound energy and analyze the return signal (echo) that has bounced off the seafloor or other objects. Multibeam sonars emit sound waves from directly beneath a ship's hull to produce fan-shaped coverage of the seafloor. These systems measure and record the time for the acoustic signal to travel from the transmitter (transducer) to the seafloor (or object) and back to the receiver. Multibeam sonars produce a “swath” of soundings (i.e., depths) to ensure full coverage of an area. The coverage area on the seafloor is dependent on the depth of the water, typically two to four times the water depth.
Many MBES systems are capable of recording acoustic backscatter data. Multibeam backscatter is intensity data that can be processed to create low resolution imagery. Backscatter is co-registered with the bathymetry data and is often used to assist with bathymetric data interpretation and post-processing.
Density or data density is determined by the amount of data obtained perpendicular to the direction and path surveys can also be regarded as lateral resolution. Distribution of unidirectional data path depends on the temporal resolution, based on the period of the ping and speed boats. Distribution data perpendicular trajectory depends on the spatial resolution, based on the number of beam, the sector angle (angle sweep, fan-width), beam width, and beam spacing
It was only in the early 1960's that Dr. Harold Edgerton (an electrical engineering professor at the Massachusetts Institute of Technology) started to adapt his techniques on high-speed flash photography to acoustics, having concluded that photography was not best suited to the murky conditions underwater By sending 'flashes' of acoustic energy into the water and recording the echoes, Edgerton (who later worked with famous French underwater explorer Jacques Cousteau), developed a towed side-looking sonar that could create a continuous image of the seafloor.
By transmitting a narrow fan-shaped acoustic pulse (ping) perpendicular to its direction of travel, the side-scan sonar sends acoustic pulses outwards. The seabed and other objects reflect some of the sound energy back in the direction of the sonar (known as backscatter), and the travel time of the returned pulse is recorded together with its intensity. As sounds travels at a known velocity (of approximately 1500 metres per second) through water, we can directly relate the time we received an echo, to the range of the target that reflected it.
This scan-line of information is sent to a topside computer for interpretation and display, and by stitching together data from successive pulses, a long continuous image of the seafloor is created, as the sonar is towed from the survey vessel.
The sub-bottom profiler is a geophysical echo-sounding system. The acoustic signal can penetrate the sea-floor due to the low frequencies reached by the echosounder in conjunction with transducers. Depending on the characteristics of the sea-floor, various layers can be made visible in the first few meters.
Sub-bottom profiling systems identify and measure various sediment layers that exist below the sediment/water interface. These acoustic systems use a technique that is similar to simple echosounders. A sound source emits a signal vertically downwards into the water and a receiver monitors the return signal that has been reflected off the seafloor. Some of the acoustic signal will penetrate the seabed and be reflected when it encounters a boundary between two layers that have different acoustical properties (acoustic impedance). The system uses this reflected energy to provide information on sediment layers beneath the sediment-water interface.
Acoustic impedance is related to the density of the material and the rate at which sound travels through the material. When there is a change in acoustic impedance, such as the water-sediment interface, part of the transmitted sound is reflected. However, some of the sound energy penetrates through the boundary and into the sediments. This energy is reflected when it encounters boundaries between deeper sediment layers having different acoustic impedance. The system uses the energy reflected by these layers to create a profile of the sub-bottom sediments. Several sonar parameters (output power, signal frequency, and pulse length) affect the instrument performance.
High-resolution sub-bottom systems have been used to detect and measure the thickness of dredged material deposits, detect hard substrate that has been covered by sedimentation, identify buried objects (such as cables and pipelines), and define the basement (or bedrock) layer for potential confined aquatic disposal sites for dredged material
The origin of the Earth’s magnetic field is not fully understood, but it is generally accepted that it is caused by electric current generated by movement of the Earth’s conductive, liquid iron-nickel core – a phenomenon known as the dynamo effect. As a result of this effect, the Earth resembles a large rotating permanent magnet. The magnitude of the Earth’s magnetic field varies from approximately 20,000nT at the southern Brasilian coast to over 65,000nT in northern Canada and Antarctica. The inclination (the angle between the Earth’s field and the horizontal) varies from 90o at the magnetic poles to 0o at approximately the equator.
Every metal object has magnetism. The signal is used to identify object location and or its dimension. Magnetic anomaly which is identified by sensor are from native earth, form regional anomaly (basin, etc.), and from local anomaly (object itself).
Total Field Earth Magnetic