Appendix D 



Use of Air-deployed Expendable Bathythermographs 



during the 1988 IIP Season 



Lt M. A. Alfultis, USCG 



Introduction 



The International Ice Patrol's (IIP) 

 primary mission is to determine 

 the southern, southeastern, and 

 southwestern limits of all known 

 ice in the vicinity of the Grand 

 Banks of Newfoundland. This 

 service is provided to transatlantic 

 shipping by the U.S. Coast Guard, 

 as required by international treaty 

 and U.S. law, in response to the 

 tragic sinking of the RMS TI- 

 TANIC. The IIP uses U.S. Coast 

 Guard HC-130 and HU-25 aircraft 

 operating out of Newfoundland 

 every other week to provide 

 iceberg reconnaissance. 



In addition to the aerial iceberg 

 reconnaissance, IIP uses a 

 computer model to predict iceberg 

 drift and deterioration in support of 

 its primary mission. Ocean 

 temperatures are an important 

 parameter to the iceberg deterio- 

 ration computer program, and are 

 an indication of water mass 

 boundaries from which flow can be 

 inferred. However, there is only a 

 limited amount of temperature 

 data collected in MP's operating 

 area. IIP sought a system to 

 gather ocean temperature data 

 from Coast Guard aircraft which 

 would require no extensive 

 airframe modifications, was 

 portable, inexpensive, and easy to 

 operate. 



The use of Air-deployed expend- 

 able BathyThermograph (AXBT) 

 probes to collect ocean tempera- 

 ture data from aircraft is well 

 established in the U.S. Navy. The 

 U.S. Navy equips dedicated 

 aircraft (P-3's and LAMPS Heli- 

 copters) for AXBT operations. 

 The U.S. Coast Guard aircraft, 

 however, have several missions to 

 support which makes this ap- 

 proach unsuitable. Since the 

 Coast Guard aircraft are multi- 

 mission, the AXBT system must 

 be portable, so that any available 

 aircraft could be used. The AXBT 

 system would have to be inexpen- 

 sive to procure, operate, and 

 maintain. Because of these 

 factors, IIP tested and procured an 

 AXBT system using commercially 

 available components. This paper 

 summarizes the results of MP's 

 evaluation and operational use of 

 this AXBT system. 



Description of AXBT System 



The AXBT system consists of the 

 AN/SSQ-36 AXBT, which is 

 deployed from the aircraft, and the 

 receiving/recording equipment and 

 Sippican MK-9 Data Acquisition 

 System on the aircraft. The AN/ 

 SSQ-36 AXBT has been used for 

 many years by the U. S. Navy for 

 collecting subsurface temperature 

 data from both fixed wing aircraft 

 and helicopters. It consists of a 



standard sonobuoy size cannister 

 (12 cm in diameter, 91 cm long), a 

 parachute, a 1-watt VHP transmit- 

 ter, a monopole antenna, signal 

 conditioning electronics, a seawa- 

 ter battery, and temperature 

 measuring probe (Figure D-1). 

 Two types of AXBT's are avail- 

 able: the standard AN/SSQ-36 

 AXBT with a probe depth of 300 

 meters and the "deep" AXBT's 

 with a depth of 760 meters. The 

 performance of the AXBT is 

 documented in Boyd (1987), and 

 Bane and Session (1984). 



After deployment from the aircraft 

 (Figure D-2), a wind flap separates 

 from the AXBT cannister, pulling 

 out a parachute which stabilizes 

 the AXBT and ensures it enters 

 the water correctly. Once in the 

 water, the package containing the 

 transmitter, antenna, electronics, 

 battery, and temperature probe 

 separates from the outer cannis- 

 ter. A dead-air space in this 

 package provides flotation to bring 

 it back to the surface. The sea 

 water battery activates, the 

 transmitter turns on, and an 

 unmodulated RF signal is trans- 

 mitted to the aircraft on one of 

 three possible VHF carrier fre- 

 quencies: 170.5, 172.0, or 173.5 

 MHz. Thirty to forty seconds later, 

 the temperature probe is released. 



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