Hydroacoustics and ground truth

A major incentive for the use of hydroacoustics is the deficiencies of the alternate techniques that are available for such ground truth data. However, such data are often required for biological information including species composition. In addition, since hydroacoustic techniques are not universally accepted, ground truth information is sometimes needed to establish confidence in the results. The author has been involved in over 2,000 hydroacoustic surveys of various species in a variety of locations. Many different approaches were used to obtain ground truth data. Examination of these results provides some interesting insights into the characteristics of both the hydroacoustic and the ground truth techniques and suggests some principles for ground truth efforts in conjunction with hydroacoustic surveys. A major conclusion is that the appropriate role of ground truth efforts is not verification, but is to aid interpretation of the hydroacoustic data. (Author abstract)