Resources

March 29, 2023

Tips for surveying over soft & muddy bottoms

Knowledge & Training

Many surveys are in areas that are less than ideal for acoustics.  These types of areas have seafloors that are soft and comprised mostly of mud as opposed to sand or gravel.

The multibeam transmitter emits an acoustic pulse that reflects mostly off of the bottom and back to the multibeam receiver.  In areas of sand or gravel much more of the acoustic energy is reflected back to the receivers.  In areas of mud or soft bottom a large portion of the acoustic energy is absorbed by the soft seafloor so much less energy is returned to the receivers.  The soft bottom will also cause more refraction and scatter the acoustic return, which will reflect off of the water surface and bounce back to the sea floor before being reflected to the receivers; this causes a second return and can even cause a tertiary return.

The Acoustic Imagery should always be turned on (Display settings) as this will give the surveyor a good indication of the reflectivity of the sea floor (brighter colors). The stronger the return the more energy will be seen.  The Acoustic Image will also make it easier to see if a second return is causing an issue, in which case the use of the gates will eliminate the second return interference. Another tool is the Saturation Monitor, which shows the actual receiver intensity level.

To overcome bottom absorption, in soft areas, a little basic acoustic theory helps.  The acoustic pulse is always at a certain frequency.  Frequency is the number of cycles per second; the more the cycles per second the more damage is done when the cycles are interrupted.  400kHz has twice as many cycles per second as 200kHz so more attenuation is seen at 400kHz even when the power level is the same for both frequencies.

Lower frequencies provide a better swath when surveying soft bottoms; there is less bottom absorption and less signal attenuation.

It is important to keep in mind the relationship between Power and Pulse width.  Power is the amplitude of the transmitted pulse, whereas pulse width is the length of time the pulse is being transmitted.  In soft bottom areas, increasing the amplitude does not do much good, whereas increasing the length of time the pulse goes into the water does by getting more total power to the outer beams.

Therefore, in soft areas, increase the Pulse Width first before increasing Power.

In the Saturation Monitor, the increased Pulse Width will show stronger outer beam energy, which translates to better swath coverage.


coverage   Resolution   Survey   

March 19, 2023

MultiSpectral versus Multifrequency Backscatter: A Generational Advancement

Multibeam Backscatter is a tool used in seafloor characterization, and R2Sonic‘s recent MultiSpectral Backscatter advancement dramatically improves this process.  MultiSpectral Backscatter comprises two or more frequencies collected in one-pass using an advanced sonar capable of multifrequency transmissions, either interleaved or simultaneous. MultiSpectral Backscatter should not be confused with MultiFrequency Backscatter Older sonars can collect Multifrequency Backscatter…


Installation   Survey   

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March 16, 2023

Focus on what matters to you when reviewing a spec sheet

Multibeam echosounders are defined by technical features that are specific to acoustic devices. Some of the technical terms may not initially be intuitive even to surveyors. The objective of this document is to define each technical term to help you understand the importance and implication of each of those concepts in the…


Survey   

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March 29, 2023

1024 beams vs 1024 soundings, are they the same?

The difference lies in the data collection method: interpolated vs independent Three years ago, R2Sonic was the first MBES manufacturer to launch the “then new” technical mode Ultra High Density (UHD) which consists in collecting 1024 independent soundings, an improvement from the traditional 256 soundings. This 400% increase in number…


coverage   surroundings   uhd   

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