sensitivity to sea surface temperature differences of the order of 0.01°C. He also pointed 

 out that he was interested principally in recording point-to-point temperature differences 

 rather than absolute sea surface temperature. Temperature differences can be measured 

 with far greater accuracy than absolute temperatures. 



Robert C. Barnes: Infrafed Radiation Thermometer - an Evaluation. 



Monthly surveys of sea surface temperatures over the Atlantic Shelf between Cape 

 Henlopen, Del., and Cape Hatteras, N. C, have been made by the Virginia Institute of 

 Marine Science since June 1963. Survey flights have also been made in Virginia waters of 

 the Chesapeake Bay and its tributaries. The IRT readings have been checked against 

 immersion thermometer readings from fixed stations and from ships. The largest sources 

 of error came from variations in frequency of the available AC power supply. Battery 

 power supplied through an inverter appeared to give better results overall. Oil slicks were 

 not observed to affect the readings. 



John L. Frank; Accuracy of Airborne Infrared Thermometry 



The Barnes Engineering Company, which Mr. Frank represents, produces a 

 relatively inexpensive portable infrared thermometer, now in its third production model. 

 The IRT receives radiation from three sources: reflection from the sky, emission from 

 the atmosphere, and radiation from the ocean. The last is the only one of interest and is 

 selected for by the instnament by use of its optical system which accepts energy only in 

 the 8 to 13 micron spectral band. The major interfering factor will be water vapor in the 

 path between ocean surface and radiometer, but these effects can be corrected for if the air 

 temperature and water vapor content are known, providing absolute accuracy of microsur- 

 face sea temperature to ±1.0°F. In any event we are measuring only the temperature of the 

 top 0.1 mm. of water. This microsurface is, of course, usually at somewhat different 

 temperature than the immediate subsurface water, as is well known by now. Perhaps the 

 greatest problem in airborne use of the IT-1 or -2 has been variation in line frequency be- 

 yond the maximum 1/2 c.p.s. Changes have been made in the IT-2 which improve it over 

 the IT-1 particularly in elimination of "swish" problems — the importance of closing the 

 detector cavity for airborne operations was realized so that the late models of the IT-2 

 have completely sealed cavities. Still it is necessary to protect the sensing head from 

 excessive vibration, direct slipstream turbulence, and excessive cooling in cold weather. 

 In-flight calibration checks are suggested in the begiiming stages of the instrumental setup 

 to insure overall accuracy of the unit. 



In discussion it was brought out that the optical system used on the Barnes IRT is a 

 compromise necessitated by cost in order to keep the price of the iiistrument down to a 

 reasonable fig-ure. It was suggested to Mr. Frank that the Optical Coating Laboratory in 

 California produces a lens which could provide more specific selection within the desirable 

 8 to 13 micron band than the Indium Antimonide/Kodak IRtran-2 combination used at pre- 

 sent. Mr. Frank agreed that he would look into the matter and as always work in the 

 direction of improving the instrument's potential without substantial increase in price. 



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