Radiometers a. Barnes Engineering model 14-312 



b. Barnes Engineering model IT-2 



Recorders a. Rustrak 0-1 ma D.C., 30"/hr. 



b. Varian G-14, 1" or 4"/min. 



Power supplies - ATR inverter (American Television and Radio) 



a. 12 Vdc. to 120 Vdc, 60 cy. 



b. 28 Vdc. to 120 Vac, 60 cy. 



Plus voltmeters, clocks, mounting panel for IRT console and recorder, and shock- 

 mount for detector. 



Observation on the field operation of the airborne IRT reviewed in this paper will 

 attempt to answer some of the questions regarding physical effects upon the instrument 

 readout, its accuracy m measurement of sea surface temperature, described by Weiss (1962) 

 to be within 0.5°F., and conclusions regarding its field use. 



CALIBRATION 



The measurement of "sea surface temperature" as generally defined and practiced 

 in most routine observations is a highly variable measurement, even with a mercury 

 thermometer. It is dependent upon the accuracy of the instrument, the depth of the water 

 sample, and the position of the water sample in relation to objects (hull, piling, etc.) from 

 which the sample is taken, and their relation to wind and current. 



One of the problems in conducting IRT surveys is the calibration of the instrument to 

 give an accurate and therefore reliable picture of sea surface temperatures. The IRT is an 

 electronic instrument of complex circuitry and is subject to changes in the resistance and 

 capacitance of its electronic components throughout its useful life. These changes can re- 

 sult in the gradual decrease in the original calibration accuracy. Therefore, IRT meter 

 readouts from our instruments usually vary from known temperatures. The reasons for the 

 variations are not completely understood. However, the operation of the IRT from an air- 

 craft moving at a high rate of speed 500' above the surface is placing the instrument in an 

 environment of high vibration and electronic noise that is not the sam^ condition as experi- 

 enced in the laboratory. 



An IRT calibration check requires a controllable radiation source having the approxi- 

 mate emissivity of unity. Clark and Frank (1963) state the ocean surface has essentially 

 the characteristics of a blackbody radiation source in the infrared region from 4 to 13 mi- 

 crons, its emissivity (0.98) is nearly unity. To meet the needs of field operations, and since 

 we do not have a controlled blackbody reference source, a controlled temperature water bath 

 equipped with a magnetic stirrer has been used. The IRT detector is positioned at a three 

 foot distance from the water. This allows the calibration of a recorder readout grid directly 

 from water temperature as determined by an accurate mercury thermometer. 



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