S. Vagle et Dm. Farmer, A COMPARISON OF 4 METHODS FOR BUBBLE-SIZE AND VOID FRACTION MEASUREMENTS, IEEE journal of oceanic engineering, 23(3), 1998, pp. 211-222
We compare the performance of four different bubble-sensing techniques
in a range of environments from the surf zone to the open ocean: a re
mote sensing method using high-frequency backscatter, two in situ meth
ods using an acoustical resonator and a pulse propagation sensor, and
a bulk method using electrical conductivity. Comparisons between the t
echniques show general consistency within the appropriate operational
bubble density ranges, although spatial variability in bubble clouds i
ntroduces substantial variance. Each technique has its strengths and l
imitations. Our acoustical resonator is suitable for bubble concentrat
ions with air fractions greater than approximately 10(-9) and the puls
e propagation sonar for air fractions from 10(-6); the upper limit for
both is constrained by attenuation and the validity of the Foldy scat
tering approximation. Both sensors can be implemented to encompass a w
ide frequency range with high resolution, corresponding to resonant bu
bble radii of 10 similar to 1200 mu m. Far air fractions higher than s
imilar to 5x10(-4), bulk measurement using electrical conductivity pro
vides a measure of air fraction. Sufficient overlap in operational air
-fraction range exists between in situ acoustical techniques and condu
ctivity measurement to permit comparison and demonstrate consistency i
n the measurement, Single- and multifrequency backscatter sonars may b
e used for low air fractions (<1x10(-5)) and provide a continuous vert
ical profile from a deployment beneath the active surface zone, but ar
e subject to masking by dense bubble clouds and are unable to resolve
high air fractions close to the surface. This study suggests that the
best approach is to use a combination of sensors to probe the bubble f
ield.