Typical temperature protiles from 

 the deployments are shown in 

 Figures D-4 through D-7. There is 

 a great variation in the quality of 

 the temperature profiles from the 

 twelve AXBT's. The profiles from 

 the three AXBT's deployed on 3 

 May 1988 were of the best quality 

 (Figure D-4). All three tempera- 

 ture profiles had some spikes in 

 the profile, and the frequency of 

 spikes increased with depth (time). 

 There were many white caps 

 observed on the sea surface when 

 the AXBT's were deployed. 



The quality of the temperature 

 profiles from the three AXBT's 

 deployed on 18 May 1988 was 

 very poor (Figure D-5). These 

 AXBT's were deployed from a 

 relatively low altitude (2000-2500 

 feet). The temperature profiles 

 were, overall, much noisier than 

 the temperature profiles from 3 

 May, despite the fact that the sea 

 conditions were much calmer on 

 18 May than 3 May. Static noise 

 interference made the temperature 

 profiles unreadable after 170-250 

 meters. The temperature profile 

 which was readable down to 250 

 meters (deployment 3) was from 

 an AXBT deployed at the end of a 

 search leg and shortly before a 

 turn. 



The six AXBT's deployed on 4 

 June exhibited a wide variation in 

 quality of performance, although 

 the deployment altitude and sea 

 conditions were constant through- 

 out (Figures D-6 and D-7). All six 

 temperature profiles were in 

 general noisier than the tempera- 

 ture profiles of the AXBT's de- 

 ployed on 3 May, which were also 

 deployed from 8000 feet, although 

 the sea conditions were much 

 calmer on 4 June than on 3 May. 



Conclusions 



• AXBT's are an excellent means 

 of gathering ocean temperature 

 information at a relatively low cost 

 to the U. S. Coast Guard and IIP. 



• AXBT data can successfully be 

 collected using a portable, low 

 cost, easy to operate, commer- 

 cially available system such as the 

 one presented here. 



• IIP can conduct AXBT opera- 

 tions from either the HC-1 30 or 

 HU-25 without airframe modifica- 

 tions. 



• Optimum AXBT drop conditions 

 are 4000-8000 feet and 150 knots. 

 The aircraft should maintain 150 

 knots for the entire 3.3 minute 

 drop time. 



• If local weather conditions 

 dictate dropping at other than 

 optimum conditions, the following 

 guidelines should be used in 

 making a drop decision: 



a. As altitude decreases 

 or aircraft speed increases, the 

 quality of the AXBT temperature 

 profile decreases, particularly 

 towards the end of the profile. 



b. A drop from 3000 feet, 

 at 150 knots, and on a steady 

 heading will be unreadable after 

 150 meters. If the aircraft turns or 

 circles around the drop site after a 

 drop from 3000 feet, the tempera- 

 ture profile will be readable to 200- 

 250 meters, or the amount of data 

 gathered is essentially doubled. 



• The quality of the temperature 

 profile decreases with increasing 

 sea state. 



• The quality of the temperature 

 profile decreases with time (depth) 

 because the distance between the 

 aircraft and AXBT increases. 



• The loss of quality at low 

 altitudes and at distance from the 

 AXBT is due to poor transmission 

 angle. A loss of line of sight 

 occurs more frequently at low 

 transmission angles due to wave 

 and swell action, particularly in 

 high sea states. This causes 

 interference of the AXBT signal 

 and spiking in the temperature 

 profile. 



96 



