Gl. Jin et al., ACOUSTIC SCATTERING LOSSES IN THE GREENLAND SEA MARGINAL ICE-ZONE DURING THE 1988-89 TOMOGRAPHY EXPERIMENT, The Journal of the Acoustical Society of America, 96(5), 1994, pp. 3045-3053
Using arrival amplitude data from the 1988-89 Greenland Sea tomography
experiment, the effects of ice scattering at 250 Hz in the marginal i
ce zone (MIZ) are estimated. The resolution of the arrivals is examine
d first, showing that arrivals are resolved as rays from about 8 degre
es to 13 degrees launch angle and a normal modes for low angles, below
about 4 degrees launch angle. The under-ice reflection losses of reso
lved rays and modes are then considered using two methods. First, the
ratio of arrival amplitudes during ice-free and ice-covered periods is
estimated. Second, the ratio of members of a ray group with different
reflection numbers is used, showing similar (but not identical) resul
ts to the first method. For higher grazing angle reflections, fast fie
ld calculations using the program SAFARI are observed to model the dat
a reasonably, using a combination of measured and historical ice param
eter values. For the low angle arrivals, the amplitudes of the arrival
s are observed to depend strongly upon both the details of the surface
mixed layer and the ice cover itself. Using reasonable mixed layer es
timates from both data and model inputs, it is observed that part of t
he amplitude reduction seen in the data is indeed due to ice, though t
he exact amount is sensitive to the details of the mixed layer.