- Email: [email protected]
Acoustic interactions
355 ACOUSTIC INTERACTION A complete understanding of the observed acoustic phenomena in the MIZ requires
simul-
taneous definitions of the ice, ocean, atmosphere, and to some extent, the biological environment. Areas of particular importance identified were: Acoustic propagation in MIZ. Because of extreme spatial variability in the thermal structure of the water column in the MIZ, future transmission experiments in this region should incorporate multiple frequencies and multiple sources, spacings and receivers, along with a definition of the ice conditions and sound speed profiles along the datas.
Tomography of the
signal paths might provide a technique to analyze this complex propagation field.
Transmission
studies across the various MIZ fronts should attempt to determine the losses associated with scattering through these turbulent inhomogeneous boundaries. Underice r e f l e c t i v i t y .
Most measurements have been made in the shallow SSIZ regions where
unusual refraction patterns, bottom reflections, topography, and partially open water confuse the situation.
Diatoms in the underice surface make this a mushy vice discrete boundary,
changing the degree of r e f l e c t i v i t y and modifying the underice roughness character. Ambient noise.
We have data on ambient noise at the SSIZ generated by wave/ice inter-
action, but no biological
source measurements have been identified.
population is especially large at the SSIZ.
The noise-making mammal
We need temporal and spatial
animal types, numbers, and spectral characteristics.
distributions of
We have many hypotheses concerning the
generation of noise associated with ice fracture, but l i t t l e
proof of these hypotheses.
Noise
characteristics associated with the various ice zones need to be identified, e.g., the noise generated by the MIZ, the shear zone, pressure ridge zones, etc.
Acoustic emission character-
istics of ice fracture need to be made so that we can predict when ice failure is about to occur - can we determine this from changes in ice elastic moduli? noise from melting icebergs can mask real targets. level changes from unidentified noise sources.
I t was also noted that the
Many records show directional and energy
We briefly discussed man-made noise, noting
increased activity in MIZ associated with oil d r i l l i n g and production.
Studies need to be made
of the effect of man-made noise on the biota prior to inquiries from environmental groups. Studies need to be conducted on vibration of fixed d r i l l i n g rigs induced by the moving ice. Observations indicate destructive vibration vice ice destruction leads to metal failure. Biological scattering from scattering layers.
Organisms and acoustical characteristics are
known to some degree for the Central Arctic, but the only SSIZ values existing are from the Chukchi Sea in summer. Future programs are planned, but none are in the SSIZ.
In contrast to
more temperate waters, the Deep Scattering Layer (DSL) consists of smaller organisms and therefore the acoustic impact is much more serious at weapons frequencies. The DSL of Arctic cod are from a larger fish clustered in f a i r l y large shoals.
356 Attenuation of sound in ice.
Measurements to date come predominantly from f i e l d studies.
Can we make these measurements in the newer laboratories where ice sheets can be grown to test the f i e l d results? be determined.
Attenuation in different types of ice and at different frequencies should
simul-
taneous definitions of the ice, ocean, atmosphere, and to some extent, the biological environment. Areas of particular importance identified were: Acoustic propagation in MIZ. Because of extreme spatial variability in the thermal structure of the water column in the MIZ, future transmission experiments in this region should incorporate multiple frequencies and multiple sources, spacings and receivers, along with a definition of the ice conditions and sound speed profiles along the datas.
Tomography of the
signal paths might provide a technique to analyze this complex propagation field.
Transmission
studies across the various MIZ fronts should attempt to determine the losses associated with scattering through these turbulent inhomogeneous boundaries. Underice r e f l e c t i v i t y .
Most measurements have been made in the shallow SSIZ regions where
unusual refraction patterns, bottom reflections, topography, and partially open water confuse the situation.
Diatoms in the underice surface make this a mushy vice discrete boundary,
changing the degree of r e f l e c t i v i t y and modifying the underice roughness character. Ambient noise.
We have data on ambient noise at the SSIZ generated by wave/ice inter-
action, but no biological
source measurements have been identified.
population is especially large at the SSIZ.
The noise-making mammal
We need temporal and spatial
animal types, numbers, and spectral characteristics.
distributions of
We have many hypotheses concerning the
generation of noise associated with ice fracture, but l i t t l e
proof of these hypotheses.
Noise
characteristics associated with the various ice zones need to be identified, e.g., the noise generated by the MIZ, the shear zone, pressure ridge zones, etc.
Acoustic emission character-
istics of ice fracture need to be made so that we can predict when ice failure is about to occur - can we determine this from changes in ice elastic moduli? noise from melting icebergs can mask real targets. level changes from unidentified noise sources.
I t was also noted that the
Many records show directional and energy
We briefly discussed man-made noise, noting
increased activity in MIZ associated with oil d r i l l i n g and production.
Studies need to be made
of the effect of man-made noise on the biota prior to inquiries from environmental groups. Studies need to be conducted on vibration of fixed d r i l l i n g rigs induced by the moving ice. Observations indicate destructive vibration vice ice destruction leads to metal failure. Biological scattering from scattering layers.
Organisms and acoustical characteristics are
known to some degree for the Central Arctic, but the only SSIZ values existing are from the Chukchi Sea in summer. Future programs are planned, but none are in the SSIZ.
In contrast to
more temperate waters, the Deep Scattering Layer (DSL) consists of smaller organisms and therefore the acoustic impact is much more serious at weapons frequencies. The DSL of Arctic cod are from a larger fish clustered in f a i r l y large shoals.
356 Attenuation of sound in ice.
Measurements to date come predominantly from f i e l d studies.
Can we make these measurements in the newer laboratories where ice sheets can be grown to test the f i e l d results? be determined.
Attenuation in different types of ice and at different frequencies should