What is an ocean
survey all about? Did your ship steam up and down, sideways or around
in circles?Michelson surveyed areas of interest by steaming in a north/south and east/west grid pattern pinging along with its single beam sonar and guided by the Loran C radio navaid. This is called a trackline survey.
The NAVDAC computer looked at Loran once a minute and after 35 seconds of deep thought began to print out the computed latitude, longitude and UTMs (universal transverse mercator) map coordinates as well some other data. This took another 25 seconds, then it was time for another look at Loran. Meanwhile the ocean below was probed by the sonar. Depth plus date and time were recorded on a precision depth recorder (PDR).
In the survey control center the duty oceanographer plotted position information on a chart and issued course corrections to the mate in the pilot house. Due to winds, currents and who knows what else a 000º (north) heading sometimes required course changes of a few degrees east (001º, 002º, 003º) or west (359º, 358º, 357º) to stay on track. There was kind of an art to all this. Too much or too little correction could mean having to run the line again. The delay built into the system by the painfully slow computer didn't help.
Generally, tracks 1000 yards apart were run inside of ten nautical mile squares, with additional tracks between those already surveyed as required to increase granularity. It took the better part of two days, sometimes longer, to complete one survey area, then we steamed off to the next selected site, sonar still pinging away.
This trackline grid survey was the norm while I was aboard Michelson. Multibeam sonar came into use in late 1964 which likely changed the survey methodology.
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Typical
Survey Pattern |