7 Increasing the detection of small targets masked by stronger echoes

It is often difficult to detect small targets that are masked by the echoes from nearby larger objects. A typical example is the detection of fish close to the bottom.

Context

Increasing the detection of smaller targets masked by stronger echoes are generally achieved by reducing the pulse duration. This will increase the resolution, but it will also reduce the maximum detection range because you transmit less amounts of acoustic energy into the water. Your EK80 system will also be more sensitive to noise.

For LFM transmissions, a dedicated receive filter setting is available. When set to High Resolution, the system applies short-time bandpass filters and the lowest possible decimation. We regard the receive filter as "experimental" and invite you to review the results.

Procedure

Open the Operation menu.

Select Normal Operation.

For LMF transmissions, set Filter Type to High Resolution for the relevant channel.

This setting will generally result in a shorter impulse response and higher output sample rate. These resulting echo data can be used to address range sidelobe issues from the bandpass filters while examining targets near boundaries. Note that the filter is wider in frequency, and may result in a reduced signal-to-noise ration.

Note

We recommend that you calibrate the EK80 system with the Filter Type setting that you will use during the survey.

Set Pulse Duration to as small value as possible.

Remember that in the EK80 system, the pulse duration and the bandwidth are mutually dependant.

For CW (Continuous Wave) transmissions:

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Long pulses provides longer detection range. They make the EK80 system less sensitive for noise, but offer lower range resolution.

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Short pulses provides shorter detection range. They make the EK80 system more sensitive for noise, but offer higher range resolution.

For FM (Frequency Modulated) transmissions:

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Long pulses provide longer detection range, and the range resolution is independent of the pulse duration..

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Short pulses provide shorter detection range, and they make the EK80 system more sensitive for noise.

Select OK to save the selected settings and close the dialog box.