As discussed in the next section of this report, logistical problems were 
encountered during attempts to obtain aerial photography. Additional ground 
survey data were obtained on two occasions while attempting to secure aerial 
survey data. These data were obtained on 16 March and 7 June 1997. 
Positions and elevations of representative targets obtained during the March 
1997 survey are shown in Table 3. The absolute values of differences in posi- 
tions and elevations between the March 1997 and the October 1996 survey also 
are presented in Table 3. Differences between the values ranged from 0.0 to 
11.0 cm (0.0 to 0.36 ft) in the horizontal direction and from 0.3 to 7.0 cm (0.1 to 
0.23 ft) in the vertical direction. The average of the differences in the x, y, and z 
directions was 1.4, 1.2, and 1.2 cm (0.047, 0.038, and 0.040 ft), respectively. 
Based on the surveys, 75 percent of the targets moved less than 1.5 cm (0.05 ft) 
in the horizontal direction, and 75 percent of the targets moved less than 1.5 cm 
(0.05 ft) in the vertical direction. 
Position and elevation data obtained for the tribar targets during the June 
1997 survey are presented in Table 4 as well as the absolute values of the differ- 
ences in positions and elevations between this and the October 1996 survey. 
Differences between the values ranged from 0.0 to 14.6 cm (0.0 to 0.48 ft) 
horizontally and from 0.0 to 11.6 cm (0.0 to 0.38 ft) vertically. The average of 
the differences in the x, y, and z directions was 1.3, 1.5, and 0.9 cm (0.043, 
0.048, and 0.029 ft), respectively. Of the targeted points, 73 percent moved less 
than 1.5 cm (0.05 ft) horizontally, and 90 percent moved less than 1.5 cm 
(0.05 ft) vertically based on the survey results. 
Forty targets were surveyed during March 1997, and 94 targets were surveyed 
during the June 1997 deployment. Based on the survey results, tribar 113 
(located on the breakwater head) had the greatest horizontal movement, and 
tribar 127 (on the breakwater trunk) had moved the greatest vertical distance. 
With the exception of these two tribars, only four additional ones (tribars 114, 
118, 130, and 133) had moved more than 3 cm (0.1 ft) in any direction (horizon- 
tal or vertical). 
Aerial Photography 
Aerial photography is a very effective means of capturing images of large 
areas for later analysis, study, visual comparison to previous or subsequent 
photography, or measurement and mapping. Its chief attribute is the ability to 
freeze a moment in time, while capturing extensive detail. 
A manned, propane-powered, blimp/balloon-type aircraft was proposed to 
obtain aerial photography for the remote Ofu Harbor breakwater, since no per- 
manent aircraft are based on the island. The equipment was shipped to Pago 
Pago, Tutuila, and then to Ofu Harbor aboard the open deck of a World War II 
landing craft. Shipping the equipment proved to be extremely difficult, as new 
Federal Aviation Administration regulations regarding shipping of gas containers 
or gasoline-powered engines were very stringent. Both the propane tanks and 
Chapter 2 Monitoring Plan and Data 
21 
