Geophysical survey
GeophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. involves ways of mapping what is on and below the seafloor. This was a key element of all four RECsRegional Environmental Characterisation surveys - scientific research projects to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area..
Using all types of geophysical survey data collected over time we can create maps of what the seafloor looks like
Marine geophysicists undertake a variety of geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. techniques to provide different information about the physical environment of the seafloor. They can work with and for archaeologists and geologists, as this work is essential to each of these areas’ day-to-day research.
For each survey technique the boat travels along survey lines set out across the RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area. study area. The survey cannot cover the entire area of each RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area.. It relies on collecting data for a proportionate representation of the area.
As well as new survey data, the RECsRegional Environmental Characterisation surveys - scientific research projects to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area. used previously collected data. Seazone, a marine data company, supplied the majority of this information, amalgamated from years of previous geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. undertaken for a variety of reasons by a variety of organisations and companies. They provided an overall bathymetrica bathymetric map, records the structure or topography of the seafloor map of each survey area. This map provided a foundation for the RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area., helping scientists plan where to survey in more detail.
Combining all this data, and using modelling, allows each RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area. study to produce an overall assessment of the physical environment for the whole of the study area.
Each of the four RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area. studies is unique and the geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. was adapted depending on the local environment and the research questions that are being asked. Whilst all four RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area. studies used the same key methods, they may have used them in slightly different ways.
You can find out more about the results that the scientists produced in the general RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area. webpages.
Here are the principal techniques used. Click on the links to visit sections, or scroll down to read the whole page.
- Sidescan sonaremit sound waves, which travel through the sea and reflect back up when they meet either
an obstruction or the seafloor surface. Sonar geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey techniques are used to record what they seafloor looks like.is a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. technique, which uses soundwaves to record the physical properties of the seafloor. It measures the intensity of the sound waves that are reflected back from the seafoor. This can indicate hard surfaces (reflected sound) compared to soft surfaces (where less sound is reflected). Areas of no return, where there is no reflection, are shown as shadows, which are the most useful for interpreting shipwreck features as they indicate where something rises up from the seafloor.
- Multibeamis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like. Bathymetryis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like.
- Sub-bottom Profileris a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey technique, which uses soundwaves to record a profile or section of what the seafloor looks like underneath the surface.
- Marine Magnetometryis a geophysical survey technique, which measures magnetic changes. It is useful for locating metal shipwrecks.
Sidescan sonaremit sound waves, which travel through the sea and reflect back up when they meet either
an obstruction or the seafloor surface. Sonar geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey techniques are used to record what they seafloor looks like.is a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. technique, which uses soundwaves to record the physical properties of the seafloor. It measures the intensity of the sound waves that are reflected back from the seafoor. This can indicate hard surfaces (reflected sound) compared to soft surfaces (where less sound is reflected). Areas of no return, where there is no reflection, are shown as shadows, which are the most useful for interpreting shipwreck features as they indicate where something rises up from the seafloor.
Sidescan sonaremit sound waves, which travel through the sea and reflect back up when they meet either
an obstruction or the seafloor surface. Sonar geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey techniques are used to record what they seafloor looks like.is a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. technique, which uses soundwaves to record the physical properties of the seafloor. It measures the intensity of the sound waves that are reflected back from the seafoor. This can indicate hard surfaces (reflected sound) compared to soft surfaces (where less sound is reflected). Areas of no return, where there is no reflection, are shown as shadows, which are the most useful for interpreting shipwreck features as they indicate where something rises up from the seafloor. uses a sonaremit sound waves, which travel through the sea and reflect back up when they meet either
an obstruction or the seafloor surface. Sonar geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey techniques are used to record what they seafloor looks like. device called a “tow-fish” to record images of the seafloor.
The tow-fish is towed behind the boat. It emits regular soundwaves from transducers on the side of the tow-fish, hence the name sidescan. These pulses are reflected back to the tow-fish when they encounter an obstruction in their path, for example the seafloor or a shipwreck.
The intensity of the reflection is recorded and this can illustrate characteristics of the seafloor. A colour-graded image displays the results, with changes in the shade of the colour indicating the varying intensity of the reflection. Areas of no return, where there is no reflection, are shown as shadows, which help us understand the images i.e. where something rises up from the seafloor.
The different scientists working on the RECRegional Environmental Characterisation survey - a scientific research project to assess the physical (geology), biological (ecology) and archaeological environment of a particular study area. can use these images to help them understand the physical environment of the seafloor. So, for example, geologists use this method to identify seafloor sediment types. Fine sediments such as muds and silts will often absorb the sound, so the intensity of the soundwave reflection is low and on the image the area appears darker. Harder sediments such as coarse gravels or bedrockThe first cemented (solid) layer underlying the surface the Earth. will reflect the sound back, so the intensity of the reflection is strong and so appear lighter in shade.
The quality or detail of the image depends on the frequency, which is how many soundwaves are sent per second. However, high frequency soundwaves can only travel a short distance, while low frequency can travel further but produce lower resolution images.
Sidescan produces a flat image, it does not measure the depth of the seafloor, for this scientists use other techniques.
Dornier 17 Bomber: This is the result of a detailed sidescan survey, it is rare that a sidescan image is this clear.
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Multibeamis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like. Bathymetryis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like.
Multibeamis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like. sounders collect data that allows scientists to make 3-Dimensional images of the seafloor.
Multibeamis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like. sonaremit sound waves, which travel through the sea and reflect back up when they meet either
an obstruction or the seafloor surface. Sonar geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey techniques are used to record what they seafloor looks like. is called a variety of names: swathe, swath or echosounders.
The geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. technique uses a transducer that is located underneath the boat. Similarly to the sidescan, it emits regular soundwaves from the transducer, which are reflected back when they encounter an obstruction in their path.
However instead of measuring the intensity of the returned reflection, it measures the time it takes for the pulse to travel to the obstruction and return.
By doing this scientists can calculate the depths of the seafloor. This allows scientists to produce bathymetrica bathymetric map, records the structure or topography of the seafloor images, recording the contours or terrain of the seafloor. It is not a flat image.
A computer on board the boat processes the returning signal. Each survey line that the boat navigates collects a corridor of data known as a swath.
Back in the laboratory the data is processed. This involves filtering out any interference from the images and checking other information that could affect the results, for example the daily tides. The results provide not only 2D but 3D representations of the seafloor. This information helped map what the seafloor looks like.
- World War One SS Mendi: An example of a multibeamis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like. bathymetryis a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. technique, which measures the time it takes sound waves to travel to the seafloor and return. From this it can create an image of what the seafloor looks like. image showing a shipwreck.
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Sub-bottom Profileris a geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. survey technique, which uses soundwaves to record a profile or section of what the seafloor looks like underneath the surface.
Sub-bottom profiling does not map the seafloor but rather records a section of the layers below the surface.
This technique has several names including “boomer”. The device is either mounted on the boat or towed behind. It uses sound pulses to penetrate the seafloor and make an image of the geological layers beneath it. As the sound waves travel through the ground, they are reflected back when a change in the geology occurs. These reflections are called “horizons”, which can be mapped across the study area.
A horizon can be a change in the seafloor sediment type, for example between a layer of rock and a layer of sand. It can also show where there is a major change in angle and character of deposits, for example where there is a cut of an ancient river channel, which has been infilled by mud and sands.
The results produce profiles of the seafloor that can help geologists and archaeologists understand how the seafloor formed over time and reconstruct ancient landscapes. For example, they can map buried river channels that formed a long time ago and then filled up with seafloor sediment, revealed in profile by the geophysicalUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of. surveyUsing scientific techniques to take images and map the physical properties of the seafloor, what it looks like and what it is made of..
Similarly to sidescan, the frequency of the soundwave affects the detail of the information. High frequency provides a detailed high-resolution image of the changes in the seafloor but cannot travel as deep underground as low frequency, which produces less detailed, lower resolution images.
As it takes vertical images, rather than images of the surface, marine geophysicists must carefully select where to use this technique to get the best information they can.
This is a profile of a buried river channel that ran across a REC study area when it was dry land, but has infilled with seafloor sediments.
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Marine Magnetometryis a geophysical survey technique, which measures magnetic changes. It is useful for locating metal shipwrecks.
Marine magnetometryis a geophysical survey technique, which measures magnetic changes. It is useful for locating metal shipwrecks. is different from the previous techniques. It does not use soundwaves but detects variations in the Earth’s total magnetic field.
The variations in the magnetic field are caused by the presence of ferrous (iron) material on or under the seafloor. Marine magnetic surveying has become a standard technique for mapping the location of ferrous material on the seabed. In particular it is used by archaeologists to detect ship and aircraft wrecks.
The equipment needs to be towed behind the boat at a sufficient distance to avoid any magnetic disturbance caused by the boat itself. The data collected is combined and displayed in different ways. In the line graph below, the rise in readings indicates the location of a metal wreck.
World War One SS Mendi: A graph like this is one of the ways to record magnetometry data. The rise in the graph indicates the presence of a metal shipwreck.
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The tow-fish is towed behind the boat. It emits regular soundwaves from transducers on the side of the tow-fish, hence the name sidescan. These pulses are reflected back to the tow-fish when they encounter an obstruction in their path, for example the seafloor or a shipwreck.
Multibeam sonar is called a variety of names: swathe, swath or echosounders.
This technique has several names including “boomer”. The device is either mounted on the boat or towed behind. It uses sound pulses to penetrate the seafloor and make an image of the geological layers beneath it. As the sound waves travel through the ground, they are reflected back when a change in the geology occurs. These reflections are called “horizons”, which can be mapped across the study area.
