140
T.W. Cranford
all the species thus far examined (Cranford 1992a). Across the odontocete
suborder, the central low-density lipid core of the melon normally exits the
anterior surface of the forehead. The central pathway to the forehead
surface from each sound generation complex ranges from slightly curved
to spiraling or completely folded, sometimes with discontinuities.
A greater understanding of melon function could be attained by comparing the topography of sound velocity in the lipids with beam shape and
direction in the same species. Making these same comparisons across
species would probably also be enlightening of melon structure and function. Unfortunately, most of what we know about experimentally demonstrated underwater biosonar beam patterns is from a small handful of
delphinoid species and individuals. It would be interesting to know how
melon morphology and topography interact with the generator signal to
form the beam pattern. This is perhaps a valuable and promising application of computer simulation tools.
5.5 Nasal and Rostral Musculature
The nasal and rostral muscle complexes are key to the sound generation
and beam formation processes. They probably have their greatest effect by
adjusting tension or fine-tuning the shapes or positions of various structures. Active accommodation of melon geometry by the rostral muscles
may effect changes in beam shape and direction or acoustic focal length,
although little evidence exists in support of these ideas (Amundin 1991a).
Short signals and complex logistical problems make this a difficult set of
questions to address. It is clear from several previous studies, that the gular
musculature provides the bulk of the power needed to pressurize the sound
generation process (Lawrence and Schevill 1965; Norris et al. 1971; Green
et al. 1980; Ridgway et al. 1980; Cranford et al. 1997).
5.6 Interference Patterns
Finally, interference patterns are probably important in understanding the
formation of the sonar beam, especially if these animals have the capacity
to actively "steer," move, or scan the beam (Amundin 1991a). This idea
deserves future investigative efforts. Interference generally comes in two
varieties, constructive and destructive. Complex combinations result whenever one or more sound sources interact with a complicated environment.
The complexity of the interference patterns are affected by the sizes, shapes,
and material composition of the structures in the head, and by the size,
shape, number, position, strength, and phase relationships of the active or
passive sources of sound. At this point very little is known about the details
of near-field acoustic structure, stability, and the interference patterns
inherent to odontocete forehead morphology. Most of what is known about
the structure of odontocete biosonar sounds in the far field has been published by Au and his colleagues (see references in Au 1993). Complex
T.W. Cranford
all the species thus far examined (Cranford 1992a). Across the odontocete
suborder, the central low-density lipid core of the melon normally exits the
anterior surface of the forehead. The central pathway to the forehead
surface from each sound generation complex ranges from slightly curved
to spiraling or completely folded, sometimes with discontinuities.
A greater understanding of melon function could be attained by comparing the topography of sound velocity in the lipids with beam shape and
direction in the same species. Making these same comparisons across
species would probably also be enlightening of melon structure and function. Unfortunately, most of what we know about experimentally demonstrated underwater biosonar beam patterns is from a small handful of
delphinoid species and individuals. It would be interesting to know how
melon morphology and topography interact with the generator signal to
form the beam pattern. This is perhaps a valuable and promising application of computer simulation tools.
5.5 Nasal and Rostral Musculature
The nasal and rostral muscle complexes are key to the sound generation
and beam formation processes. They probably have their greatest effect by
adjusting tension or fine-tuning the shapes or positions of various structures. Active accommodation of melon geometry by the rostral muscles
may effect changes in beam shape and direction or acoustic focal length,
although little evidence exists in support of these ideas (Amundin 1991a).
Short signals and complex logistical problems make this a difficult set of
questions to address. It is clear from several previous studies, that the gular
musculature provides the bulk of the power needed to pressurize the sound
generation process (Lawrence and Schevill 1965; Norris et al. 1971; Green
et al. 1980; Ridgway et al. 1980; Cranford et al. 1997).
5.6 Interference Patterns
Finally, interference patterns are probably important in understanding the
formation of the sonar beam, especially if these animals have the capacity
to actively "steer," move, or scan the beam (Amundin 1991a). This idea
deserves future investigative efforts. Interference generally comes in two
varieties, constructive and destructive. Complex combinations result whenever one or more sound sources interact with a complicated environment.
The complexity of the interference patterns are affected by the sizes, shapes,
and material composition of the structures in the head, and by the size,
shape, number, position, strength, and phase relationships of the active or
passive sources of sound. At this point very little is known about the details
of near-field acoustic structure, stability, and the interference patterns
inherent to odontocete forehead morphology. Most of what is known about
the structure of odontocete biosonar sounds in the far field has been published by Au and his colleagues (see references in Au 1993). Complex