A comparison of lidar and echosounder measurements of fish schools in the Gulf of Mexico

• Published in: ICES journal of marine science 2003-02, Vol.60 (1), p.147-154
• Main Authors: Churnside, James H., Demer, David A., Mahmoudi, Behzad
• Format: Article
• Language: English
• Subjects: echosounder; fish; lidar; Marine; survey; volume backscatter coefficient
• ISSN: 1054-3139; 1095-9289
• DOI: 10.1006/jmsc.2002.1327

In December 2000 the US National Oceanic and Atmospheric Administration's Fish Lidar (Light Detection And Ranging) system was operated from an airplane off the west coast of Florida. Schools of fish were located and their volume-backscattering coefficients, rβ(π), measured at the lidar wavelength of 532 nm. Concurrently, a 208 kHz echosounder was deployed from a small boat to measure the acoustic volume-backscattering coefficients, sv, of the same schools. Seven schools were characterized with both the lidar and the echosounder. The correlation between these seven pairs of rβ(π) and sv measurements was 0.994. A linear regression of rβ(π) versus sv had a negative y-intercept, which supports aerial observations of some degree of avoidance reaction of fish to the passing survey boat. The slope was slightly greater than unity, in agreement with previous calculations that the acoustic backscatter of similar fish is slightly greater than the lidar backscatter. The results of this study indicate that lidar is a suitable tool for surveying rapidly the distributions and abundances of epipelagic fish stocks in the shallow waters off the west coast of Florida. Aerial lidar surveys do not have the biases of fish-avoidance reaction potentially affecting acoustic and trawl surveys.