title: Estimating fish orientation from broadband, limited-angle, multiview, acoustic reflections.
abstract: This article demonstrates that multiview, broadband (635-935 kHz), nearly monostatic, acoustic reflections recorded from lateral views of juvenile fish can be used to infer animal orientation. Calibrated acoustic data were recorded from live fish in a laboratory, while orientation was measured simultaneously via optical images. Using eight animals, two-dimensional data sets of target strength as a function of frequency and orientation were obtained. Fish length, lateral thickness, and dorsoventral thickness ranged from 24 to 48 mm, 3 to 7 mm and 10 to 20 mm, respectively. Preliminary estimates of orientation were computed from the direction of the gradient of the local autocorrelation function in the target strength image. These local estimates were then median-filtered over the full system bandwidth (but still limited-angle) to improve accuracy. Angular estimates were then corrected for systematic bias via a simple, one-dimensional model that approximated the animals' reflection by that of a bar target. Taken over all orientations, the average absolute error in orientation estimation is 5.6° to 17°, dependent on the data set. Results indicate, for most sets of views, reasonable estimates of lateral orientation can be obtained from broadband, multiview data over a set of limited angular reflections.
authors.affiliation: Marine Physical Laboratory, Scripps Institution of Oceanography, La Jolla, California 92093-0238, USA. jules@mpl.ucsd.edu
authors.forename: Jules S
authors.initials: JS
authors.lastname: Jaffe
authors.forename: Paul L D
authors.initials: PL
authors.lastname: Roberts
mesh_terms: D000162:Acoustics; D000465:Algorithms; D000818:Animals; D002138:Calibration; D003198:Computer Simulation; D004784:Environmental Monitoring / Q000379:methods* / Q000592:standards; D005399:Fishes / Q000033:anatomy & histology / Q000502:physiology*; D011156:Population Density; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013550:Swimming