22 
gas tanks had to be purged and certified as empty prior to shipment to Pago 
Pago. The balloon's gas tanks were to be filled with propane in Pago Pago and 
shipped on the barge to Ofu. When they arrived, however, it was found that they 
had been filled with low-pressure butane. At this point it was determined that 
propane was not available in American Samoa, and that the terms propane and 
butane were used interchangeably. Because of the pressure differences, butane 
could not be used in the balloon. Strong winds and heavy rain contributed to 
delay of the balloon flight, but the discovery of the improper fuel canceled the 
low-altitude balloon flight entirely. 
In an attempt to complete the mission, a twin-engine otter aircraft was 
chartered from Samoa Air. The baggage door was removed, and an oblique 
mount was constructed to allow the mapping camera to be placed in the opening. 
The oblique photography that was obtained provided visual imagery of the struc- 
ture and the harbor. At some point, the camera began malfunctioning, plus the 
speed of the aircraft at the low altitude and the very rough air caused by the 
vertical rise of the adjacent mountain, prevented the collection of a series of 
high-quality exposures. Figures 19 and 20 are aerial photos of the breakwater 
looking shoreward and seaward, respectively. The aerial photography was 
obtained on 20 October 1996. 
In an attempt to obtain improved imagery for higher accuracy photogrammet- 
ric measurement purposes, arrangements were later made to charter a helicopter 
and again photograph the structure. The helicopter was based on a tuna clipper 
operating out of Pago Pago. While the contractor was enroute to American 
Samoa in March 1997 to complete the work, the helicopter left aboard its mother 
ship for the fishing grounds and was not available. The only other helicopter 
located was inoperative. As mentioned earlier, a ground survey of representative 
targets was completed. 
In a final attempt to obtain low-altitude aerial photography, the contractor 
again arranged to charter a helicopter based on one of the tuna clippers in Pago 
Pago. The helicopter arrived on Ofu as scheduled, on 7 June 1997. The aircraft, 
however, had encountered very strong headwinds on the flight and used more 
fuel than estimated. No fuel is available on Ofu. Because of fuel considerations 
and the weight of the mapping camera equipment, the pilot would not allow the 
heavy mapping camera in the helicopter and limited his flight time on the island 
to 30 min. A backup 70-mm hand-held aerial camera was used to obtain views 
of the jetty from the open doorway of the aircraft, but due to damage in ship- 
ment, exposures were unacceptable for high-accuracy photogrammetric measure- 
ments. Additional ground-based surveys were conducted during this 
deployment. 
Photogrammetric Analysis of Armor Unit Targets 
When aerial photography is planned and conducted so that each photo image 
overlaps the next by 60 percent or more, the two photographs comprising the 
Chapter 2 Monitoring Plan and Data 
