This output signal is preamplified in the optical 

 unit and is transmitted via cable to the electronic 

 processing unit where it is further amplified and 

 then read by a panel meter or a recorder. Sensitiv- 

 ity of the PRT-5 is advertised by the manufacturer 

 to be better than 0. 1°C when sampling in the 500 

 millisecond mode at 25°C ambient temperature, 

 and its accuracy is advertised to be ±.5°C. The 

 sensing unit is mounted inside the aircraft, point- 

 ing through an open hatch at an angle near normal 

 to the sea surface. 



The infrared temperature is monitored on a dial 

 meter calibrated in degrees Celsius. For perma- 

 nent record, a solid-state Varian GIOOO strip 

 chart recorder manufactured by Varian Aer- 

 ograph is used. The infrared (IR) signal is dis- 

 played at variable linear settings, e.g., the range 

 is adjusted to match the expected SST range being 

 surveyed. Standard strip chart paper having 100 

 equal divisions of 1.3 mm across its width is used. 

 A range of 20°C full scale means that each divi- 

 sion is 0.2°C (fig. 3). 



The aircraft electrical output systems supply 

 28 Vdc. A Transpac Model IT2106RS transis- 

 torized d.c. to a.c. inverter manufactured by 

 Electronic Research Associates is connected to 

 the aircraft's 28 Vdc system to deliver 115 Vac, 

 60 Hz for the ART package operation. This in- 

 verter contains a unitiue magnetic regulator-filter 

 assembly made of the ferroresonant type which 

 suppresses aircraft electrical power fluctuations. 

 This regulator prevents the 115 Vac output volt- 

 age frequency (60 Hz) from drifting. Such a drift 

 can speed up or slow down the recorder's paper 

 drive motor distorting its fixed inch/minute rate. 



The ART package contains a control panel 

 module from which the technician can remotely 

 operate and monitor all of the electronic systems. 

 An elapsed time clock is included on the control 

 panel. This clock is manually synchronized with 

 the aircraft's instrument clocks at the stait of each 

 survey to allow synchronization of the naviga- 

 tional notations between the navigator and the 

 ART operator. 



OPERATIONAL PROCEDURES 



In-flight ART Calibration 



The PRT-5 internal reference cavity tempera- 

 ture is remotely monitored by a dial meter on the 

 PRT-5 console. Further quality control of ART 

 data is accomplished through frequent in-flight 

 calibration checks. The calibration procedure 

 consists of aiming the sensor head alternately into 

 a vacuum bottle filled with warm water and a sec- 

 ond bottle filled with cold water and comparing 

 the recorder readout with that of a calibrated mer- 

 cury thermometer immersed in the bottle. If 

 necessary, the recorder is adjusted to agree with 

 the mercury thermometer. 



Since the greatest percentage of infrared radia- 

 tion energy detected by the IR thermometer is 

 emitted only, from the top 20 (Mm of the sea sur- 

 face, ART measurements may not be directly 

 comparable to "ground truth" surface tempera- 

 tures obtained by mercurial bucket thermometer 

 readings of water taken from the upper one to two 

 feet, (Saunders, 1967). To minimize atmospheric 

 attenuation, surveys are flown at altitudes of 150 

 meters or less. 



Simultaneous measurements of SST by vessels 

 and fixed offshore stations using a bucket ther- 

 mometer and aircraft using a PRT-5 at an altitude 

 of 1.50 meters, typically show a difference of 

 ±0.5°C or less. 



Navigation 



Long Range Aid to Navigation (LORAN-A), on 

 board radar, and dead reckoning are used for 

 navigation on the HU16-E "Albatross" during 

 ART surveys. Of these three methods, LORAN-A 

 is the most accurate, allowing a position determi- 

 nation of ± 1 nautical mile ( ± 1 .8 km) to be made. 

 Standard survey tracks allow "landfall naviga- 

 tion" and "back course corrections" to be applied 

 at approximately 1 hour intervals or less. Thus, 

 navigation by LORAN-A, corrected by "post 

 navigation." is the most reliable method. 



