Since a large number of electronic and physical variables are influencing the meas- 

 urement of sea surface temperatures with both the airborne IRT observation and mercury 

 surface cast, the problem of calibration for IRT surveys over large sections of ocean within 

 a relatively short period of time is accomplished using the following technique. After each 

 survey flight a readout grid is obtained in the laboratory by observing water temperatures 

 within the range of those obtained during field operations. During the flight, a surface tem- 

 perature observation is obtained from a reliable source, such as the Naval Electronics 

 Laboratory (N.E.L.) oceanographic tower of U.S.C.G. lightships using U. S. Weather Bureau 

 surface thermometers. The recorder chart is marked at the moment of passing over a point 

 where the comparative observation is being taken. 



In the laboratory the IRT recorder readout grid is adjusted to the mercury sea sur- 

 face thermometer observation, and readouts are made on an average of every 30 seconds 

 of flight. These are averaged for each two minutes of flight, plotted on the master chart 

 and isotherms drawn for each one °F. change. The accuracy of charts issued by the Tiburon 

 Marine Laboratory is estimated to be within 1.0°F. of the mercury thermometer sea surface 

 temperature observation as determined by the most reliable source available. 



COMPARISON OF AIRBORNE IRT AND SEA SURFACE OBSERVATIONS 



The laboratory limits of sensitivity (> 0.5 ''F.) and accuracy (±2°F.) for infrared de- 

 tectors of the type used in these observations have been established by the manufacturer. 

 Interest in the field use of an airborne unit for determining sea surface temperatures raises 

 the question of the limits of accuracy for temperature ranges normally observed during 

 field surveys. Comparisons of IRT meter readout temperatures taken in September 1963 

 from a U. S. Coast Guard aircraft over the N.E.L. oceanographic tower and the San Francisco 

 lightvessel were within about -0.4°F. for the N.E.L. tower and about -0.2°F. for the San 

 Francisco lightship. Four checks were made over the lightvessel within a 20 minute 

 period and each check resulted in the recorder returning to the same point. 



In the normal marine environment it is difficult to find an area having wide range of 

 temperatures over which the instrument can be tested. However, about the outfalls of steam- 

 electric generating plants using sea water as a cooling medium for steam condensers, a 

 situation exists where changes in sea surface of up to 20°F. might be observed. 



The following comparative data for an airborne IRT (model IT-2) calibrated in the 

 laboratory and for surface temperatures taken from a small boat using a standard therm- 

 ometer has been made available through the cooperation of Mr. Joseph Joy and Mr. James 

 Jones of Marine Advisers, Inc., La Jolla, California, and the engineering department of 

 Southern California Edison Company. 



Location : Offshore from Southern California Edison Huntington Beach 



generator plant; observations taken close (within 1/4 mile) to 

 the coolir^ water outlet. 



-78- 



