Effects of Range and Frequency on DIDSON Measurement Accuracy

The DIDSON Sonar is a multi-beam acoustic camera that produces near video quality images in two frequencies (low-1.1MHz and high- 1.8MHz). DIDSON is particularly useful in murky or rough waters because targets within the field-of-view are imaged through sound waves rather than traditional video imagery. Although studies have been conducted as to the accuracy and precision of estimating length with the DIDSON, none in which range and frequency were analyzed simultaneously have been conducted. Our artificial target was manually operated in a controlled pool environment and lengths were measured by the Fish-Marking tool in the DIDSON software. We had four test groups: low frequency at 5 m, high frequency at 5 m, low frequency at 10 m and high frequency at 10 m. The statistical analysis revealed that target range had a significant effect on DIDSON derived measurements while frequency did not. DIDSON-derived length measurements were significantly smaller than the actual target length at both ranges tested.