An Analysis Of Ice Profiles Obtained By Submarine Sonar In The Beaufort Sea

Abstract

ABSTRACT. A profile of the ice cover in the southern Beaufort Sea was obtained by the submarine U.S.S. Gurnard in April 1976, using a narrow-beam upward-looking sonar. The I 400 km profile consisted of three legs, of which the long south-north and east-west legs intersected near the Caribou camp of the AIDJEX experiment. A statistical analysis was carried out over contiguous 50 km sections to yield probability-density functions of the drafts of ice and of level ice, the distributions of keel spacings and drafts, and the frequencies and widths of leads. Two distinct types of ice cover were found in the profile. The first, nearest the coast in the south and west of the experimental area, consisted of heavily ridged ice with mean drafts of up to 5. I m. The rest of the track (I 200 km) consisted of a homogeneous ice cover with a mean draft of 3.7 m. The percentage of thin ice varied greatly from section to section, with a range of 0.4 to 12.3% for ice of 0-1 m draft. Level ice, defined as ice with a local gradient of less than I in 40, made up 56% of the homogeneous cover, with a preferred draft of2.7 to 2.9 m. Keel spacings obeyed a negative exponential distribution, with a deficit at small spacings due to a keel shadowing effect and a surfeit at very large spacings due to the contribution of polynyas. The draft distribution of keels was a negative exponential of form P (h) dh = B exp ( -bh) dh, with Band b as parameters. This differs from the distribution of Hibler and others (1972), probably because the narrow beam records a complex structure for every keel. The homogeneous cover had a lower keel frequency and mean draft than the ice nearest the coast. Maximum keel draft was 31.12 m. The average separation of leads was 2 12 m, with almost all leads being less than 50 m in width. REsuME. AnalYse de projils de glace obtenus par sonar sous-marin dans la mer de Beaufort. Un profil de la couverture de glace du sud de la mer de Beaufort a ete obtenu par le sous-marin U.S.S. Gurnard en avril 1976 en utilisant un sonar dirige vers le haut a faisceau etroit. Les I 400 km de profil se composent de trois branches dont les longues branches sud-nord et est-ouest se coupent pres du camp Caribou de I'experience AIDJEX. On a pratique une analyse statistique sur des sections contigues de 50 km pour obtenir les fonctions de densite de probabilite des tirants d'eau de glace et des glaces a fond plat, les distributions des espacements entre cretes de pression sous-glace et des tirants d'eau, et les frequences et la largeur des chenaux. On a trouve deux types distincts de couverture de glace dans le profil. La premiere, la plus proche de la cote dans le sud et dans I'est de la zone exploree consistait en une glace fortement plissee avec des tirants moyens d'eau de plus de 5,1 m. Le reste de I'itineraire (I 200 km ), consistait en une couverture de glace homogene avec des tirants moyens de 3,7 m d'epaisseur. Le pourcentage de glace mince variait beaucoup d'une section a I'autre avec une proportion allant de 0,4 a 12,3 % pour la glace...

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