title: Comment on paper entitled, "An inversion of Freedman's 'image pulse' model in air". Acoust. Soc. Am. 119(2), 965-975 (2006).
abstract: Echolocation (i.e., perceiving objects using acoustic echoes) is well-known in underwater detection and to a lesser extent in robot guidance and machine perception. The paper by Tsakiris and McKerrow is concerned with machine perception in air using Freedman's asymptotic model, which was originally developed to predict the backscattering multiple-echo effect observed in sonar detection. This effect was subsequently shown to be due to the elastic response of underwater targets. Freedman's model can be used in air because the acoustic target is assumed to be rigid. Also, the model's prediction of multiple echoes can be used to obtain information about the shape of the target. This is the so-called inversion of the Freedman model by Tsakiris and McKerrow. In their paper, various simple bodies are tested in air using ultrasound and it is shown that the model provides relatively poor information about body shape. Several explanations are given. However, one explanation is not considered, namely that the model itself is not satisfactory. First, there is poor agreement with exact backscattering theory. Second, deriving information about target shape from the multiple echoes predicted by the model is a highly questionable procedure. Both these aspects are examined here.
authors.affiliation: Sonometrics Inc., 8306 Huntington Road, Huntington Woods, Michigan 48070, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Hickling
authors.forename: Guillermo C
authors.initials: GC
authors.lastname: Gaunaurd
mesh_terms: D000162:Acoustics; D000388:Air; D000818:Animals; D002685:Chiroptera; D004455:Echolocation / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D019576:Porpoises; D013017:Sound Localization / Q000502:physiology*; D014465:Ultrasonics