Laboratory Tests 



Isolation of surface noise from instrument noise in the flight record has been a 

 problem. The model 14-320 ART is not designed to military specifications and responds 

 unfavorably to shock and air turbulence. The noise can be reduced to a tolerable level 

 (approximately 0.5°C). It is assumed that this noise or record trace fluctuation is com- 

 posed of both spatial surface temperature variations and instrument-induced noise. 



Turbulence tests have been performed at various speeds and altitudes. When the 

 sensing unit is flush-mounted over the opening and exposed to the air stream, the tempera- 

 ture trace is completely obscured by noise. This noise due to turbulence has been attributed 

 to instantaneous obstruction in the operation of infrared beam chopping mechanism. This 

 effect has been partially eliminated by raising the sensing unit and pressurizing the aircraft 

 in order to force air out of the opening. 



Acoustics, vibration, and shock have been suggested as other possible sources of in- 

 terference. Two ART'S were subjected to high intensity sound ranging from 3 to 50 cycles 

 per second. One unit demonstrated output fluctuation of the order of 0.2°C at 20 cps and 0.1°( 

 at 10 cps. The infrared chopper speed is 20 cps; the sound may create resonance at this 

 frequency and at its harmonics . 



Tests were performed using a vibration test machine at frequencies and amplitudes 

 matching those of the aircraft. The unit was vibrated from to 60 cps at 0.012- and 0.025- 

 inch double amplitude vertical displacement. (Aircraft vibration is maximum at 30 cps and 

 0.0076-inch amplitude.) Fluctuations of the order of 0.15°C appeared in the trace at 20 and 

 60 cps. 



Shock tests were performed by allowing the sensing unit to drop 0.15 to 0.25 inches 

 onto a wooden surface— as much as 1.0°C of noise resulted. The ART is shock-mounted in 

 the aircraft; it is unlikely that the instrument would be subjected to these force equivalents 

 during flight. 



By far, the most serious physical influence on the instrument is air turbulence. 



EXPERIMENTAL FLIGHT TESTS 



Initially, aerial surveys were made to determine how well ART field measurements 

 over an ocean area compared with the ASWEPS sea surface temperature chart, a subjective 

 analysis of sea surface temperature observations collected by naval and commercial ships. 

 Aerial surveys were also made to test ART reliability by observing the agreement of ART 

 measurements repeated over a given area. More flight tests were made to compare ART 

 readings with bucket thermometer, towed thermistor, and injection temperatures taken 

 simultaneously from ships. On one occasion, measurements were also compared with 

 bucket thermometer temperatures taken at ARGUS ISLAND, an oceanographic tower off 



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