orthographic projection by processing each image pixel. The image is free from 

 skewness and distortion, and therefore, precise horizontal measurements may be 

 obtained with an engineer scale. Orthophotos were prepared for the dolos armor 

 unit fields on the seaward ends of both the north and south jetties at Humboldt Bay. 

 An example of an orthophoto for a portion of the north jetty is shown in Figure 15. 

 Orthophotos were produced on mylar sheets at a scale of 1 :240. 



A photogrammetric analysis of the armor unit targets was conducted and x, y, 

 and z (easting, northing, and el) coordinates were obtained. Data from the dolosse 

 which had three targets were compared to corresponding data derived during the 

 ground surveys to establish the accuracy of the photogrammetric work. Ground 

 survey data and aerial survey data are compared in Table 1 . The table shows very 

 close comparison between ground and aerial survey data. Differences between 

 ground and aerial values, for the majority of the targets, were 0.61 cm (0.02 ft) or 

 less. Maximum differences were 1.52 cm (0.05 ft) for both the horizontal and ver- 

 tical positions; however, this level of difference occurred for only 5.4 percent of the 

 targets for the horizontal and 6.5 percent of the targets for the vertical position. 

 Seventy-eight percent of all horizontal target positions, and 80 percent of all vertical 

 target positions, were within 0.91 cm (0.03 ft). As a result of the photogrammetric 

 analysis, aerial data obtained for the dolosse with single targets are shown in 

 Table 2. 



Additional analysis was conducted for the dolosse with three targets. With the x, 

 y, and z (easting, northing, and el) coordinates defined for each target on the various 

 armor units, the centroids of each targeted armor unit were computed. In addition, 

 the position of each armor unit relative to the x, y, and z axes was determined. Fig- 

 ure 16 shows the orientation of representative armor units to the three axes. The 

 centroid of each targeted dolos and each armor unit's orientation (rotation angle 

 relative to x, y, and z) are presented in Table 3 for the aerial survey results. These 

 are base level conditions from which comparisons can be made in future surveys. 



Full-scale hardcopies of aerial photographs and orthophotos are on file at the 

 authors' offices at WES and CESPN. In addition, all photogrammetric compilations 

 and analyses have been stored on diskettes in Intergraph files for future use. In 

 summary, very detailed and accurate information relative to the dolos armor unit 

 positions for the Humboldt Bay jetties have been captured by means of aerial photo- 

 graphy and photogrammetric analysis. Data are stored and can be retrieved and 

 compared against data obtained during subsequent monitoring. Thus, armor unit 

 movement may continue to be quantified precisely in future years. 



Broken Armor Unit Survey 



On 17-18 September 1996, a survey of broken/cracked dolos armor units above 

 the waterline was conducted on the seaward portions of the north (sta 84+00 - 

 89+93) and south (sta 67+00 -74+00) jetties. During the inspection, each broken 

 armor unit was identified and photographed, and its approximate location relative to 

 breakwater station and distance from a baseline was recorded. The baseline was the 



Chapter 2 Monitoring Plan and Data 23 



