A Study of the Quality of Sea Water Temperatures Reported in Logs of Ships' Weather Observations

Abstract

The differences between sea water temperature reported in the Log of Ship's Weather Observations and specially observed sea surface temperature were studied for 6826 pairs of observations taken in the Pacific Ocean from 3 Military Sea Transport Service ships and 9 U.S. Navy Radar Picket ships during 92 different trips. For each trip the mean difference (trip bias), using the surface temperature observations for the reference, and the standard deviation of the differences were computed. These results were combined to give similar measures for each ship (ship bias and standard deviation) and estimates of these measures for a large number of ships (fleet). Reported sea water (injection) temperature observations vary considerably in quality. The fleet bias, or mean difference, of injection temperature observations as compared to surface temperature observations is estimated to be 1.2±0.6F and the standard deviation of differences to he 1.6F. Among the 12 ships, the ship bias, or mean of all differences derived from observations of a given ship, ranged from ?0.5F to 3.0F, which is probably due to variations of the thermometer accuracy and of the thermometer installations between ships. The standard deviation about these means was 1.3F, which is a measure of the variability of present data records, provided that the bias for each ship could be determined and a correction applied. The variability of differences in the observations from a single ship is attributed to the system of taking and reporting sea water temperature observations from an injection thermometer. To improve the reliability of reported sea water temperature observations, a change to an electrical resistance or thermistor thermometer, specially designed and installed to measure the sea water temperature and having a remote indicator on the ship's bridge, is recommended. If this change were made, it is estimated from trip data that the standard deviation of differences would be reduced to less than 1.0F.