RIASSUNTO
In a perfect acoustic world, acoustic backscatter energy would only be received from targeted animals in experimental measurements or surveys. Backscatter from unwanted targets is considered noise. To increase backscatter from targets of interest the amount of energy in the transmit pulse can be increased but this will also increase all backscatter, and it reduces the ability to resolve individual targets. To balance the tradeoff between high signal-to-noise ratios (SNR) and single target resolution, John Ehrenberg and colleagues advocated the use of broadband signals and matched filters in scientific echosounders. Broadband signals have center frequency to bandwidth ratios less than 3. Matched filter signal processing compresses received echoes in time and increases echo amplitude, with a resulting SNR amplitude ratio gains. Increased SNR increases target resolution and maximizes accuracy of echo counting, individual backscatter measurements, and echo integration. Broadband transmit signals and matched filters have not been widely used in scientific echosounders. The first commercial scientific echosounder with a broadband transmit signal and matched filter was the HTI model 240 in 1995. Over the last four years, Kongsberg-Simrad has released the EK80 echosounder product line that includes broadband FM transmit pulse options and matched signal filter processing. This represents the latest transfer of technology developed for radar and first transitioned to fisheries acoustics by Ehrenberg. Data acquisition, comparison measurements, and data processing routines are now being developed to provide best practices to the fisheries acoustics community for mapping, counting, and classifying aquatic organisms.