. The Earth beneath the sea : History . Fig. 1. Photograph of oceanographic camera interior showing "in-line" construction in a cylindrical steel housing. A "data" chamber at the rear of the camera gives a photo- graphic record of j^ressure (depth), time (24-h clock), positional data, and notes. wrongly or accidentally interchanged. One examjjle of a data-chamber record is shown in Fig. 1. B. Sonar A sonar "pinger" on a camera, operated by internal batteries, has proved to be very useful for signalling information to the surface. The sonar can be used as a "g
. The Earth beneath the sea : History . Fig. 1. Photograph of oceanographic camera interior showing "in-line" construction in a cylindrical steel housing. A "data" chamber at the rear of the camera gives a photo- graphic record of j^ressure (depth), time (24-h clock), positional data, and notes. wrongly or accidentally interchanged. One examjjle of a data-chamber record is shown in Fig. 1. B. Sonar A sonar "pinger" on a camera, operated by internal batteries, has proved to be very useful for signalling information to the surface. The sonar can be used as a "go" or "no-go" device operated by a bottom switch. Also, it can be used to measure the camera-bottom surface by measuring the time interval betw^een the direct ping and the reflected ping, since the velocity of sound in sea-water is known (about 5000 ft/sec). A 5-ft sonar-bottom distance corre- sponds to a 2-msec interval, which can be conveniently measured on a cathode- ray oscillograph or a standard graphical recorder such as is commonly used as a sonar receiver on oceanographic shijjs. 3. Cables and Winches for Cameras Many of the practical problems of johotography in the sea are caused by lowering methods. Most oceanographic ships are equipped with winches which do many duties besides camera lowering, such as the lowering of Nansen
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
