The accuracy of length measurements made using imaging SONAR is inversely proportional to the beam width

Multibeam imaging SONARs have been used for a range of measurement applications, such as measurements of fish lengths. This study aimed to quantify the accuracy of imaging SONAR systems, that varied in frequency and beam geometry, to measure the length of synthetic targets positioned perpendicularly. Blueprint Oculus imaging SONAR systems, with four different (centre) frequencies (750 kHz, 1.2 MHz, 2.1 MHz, and 3 MHz), were used to measure the length of three targets of nominal lengths: 10 cm, 20 cm, and at ranges between 1 m and 15.5 m. The effect of beam geometry on measurement error was then examined using regression analysis. This study found that there was an overestimation of the actual length of the target for all measurements that was inversely proportional to the horizontal beam width. The measurement error can be reduced by normalising for beam width. However, the variation of measurements (i.e. the precision), was found to also increase with range, which was attributed to the..., Data collection
To investigate measurement accuracy, three different Blueprint Oculus imaging SONAR systems were used in this study, models: M750d, M1200d, and M3000d. Between them, they operated at four different (centre) frequencies: 750 kHz, 1.2 MHz, 2.1 MHz, and 3 MHz. These imaging SONAR systems were used to measure the length of three rectangular targets of nominal lengths: 10 cm, 20 cm, and 1 m. The targets were designed to present consistent, uniform acoustic scattering. The measurements were carried out in a (freshwater) swimming pool on 16th September 2021. The targets were created from layers of hollow polycarbonate sheets, with the edges sealed to maintain the airspaces and backed with a 1 mm thick aluminium sheet. The targets were completely wrapped in black PVC duct tape (Figure 3). The actual final length of each nominal target size was 1 m = 1005 mm, 20 cm = 195 mm, 10 cm = 105 mm, but are referred to by their nominal lengths. The height of each target was 1 m = 255 mm, ..., , # The accuracy of length measurements made using imaging SONAR is inversely proportional to the beam width

Iain M. Parnum1*, Benjamin J. Saunders 2, Melanie Stott2, Travis S Elsdon3,2, Michael J Marnane3, Euan S. Harvey2

1 Centre for Marine Science and Technology, Curtin University, Bentley, 6102, Western Australia, Australia

2 School of Molecular and Life Sciences, Curtin University, Bentley, 6102, Western Australia, Australia

3 Chevron Technical Centre, 250 St Georges Tce, Perth, 6000, Western Australia

Citation for this dataset: https://doi.org/10.5061/dryad.dfn2z358w

## **Abstract**

In this study, Blueprint Oculus imaging SONAR systems, with four different (centre) frequencies (750 kHz, 1.2 MHz, 2.1 MHz, and 3 MHz), were used to measure underwater the length of three targets: 10.5 cm, 19.5 cm, and 100.5 cm, at ranges between 1 m and 15.5 m. This was to investigate the effect of beam geometry on measurement error.

## **Description of the data and file structure**

The Bluepr...