Black and white aerial photography was obtained from a fixed-wing plane at 

 an altitude of 183 m (600 ft), resulting in a contact scale of 1:1,200. The photo- 

 graphy was obtained with a precision cartographic camera, a Zeiss RMK A 

 15/23. Photographic stereo pairs were obtained during the flights. Aerial 

 photography was obtained for the south jetty on 9 January 1982, 29 January 

 1983, 15 September 1983, 27 March 1984, and 9 May 1984. For the north jetty, 

 aerial photography was obtained on 29 January 1983, 15 September 1983, 

 27 March 1984, and 9 May 1984. The photography was obtained after signifi- 

 cant storm events during the course of the initial Manasquan Inlet monitoring 

 program. 



Prior to obtaining aerial photography, primary targets were established on 

 stable portions of the jetties. They were surveyed in from nearby geodetic and 

 vertical control benchmarks and were visible in the aerial photography. The pri- 

 mary targets on the jetties were located along the center lines of the concrete 

 caps. 



Photogrammetric analysis of armor unit movement 



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 

 overlap area can be positioned under an instrument called a stereoscope and 

 viewed in extremely sharp three-dimensional detail. If properly selected survey 

 points on the ground have previously been targeted and are visible in the over- 

 lapping photography, accurate measurements can be obtained of any point 

 appearing in the photographs. This technique is called photogrammetry. 



The stereo pair images obtained during aerial photography at Manasquan 

 Inlet were viewed through a Kern PG 2-AT stereo restitution instrument, and 

 stereo models were oriented to the target data previously obtained. The stereo 

 models were used for compilation and development of plan view outlines of the 

 dolosse and concrete cap. These features were superimposed on a grid based on 

 the New Jersey State Plane Coordinate System, which graphically defined loca- 

 tion and orientation of the features in the horizontal plane. Vertical data were 

 recorded numerically at selected points on the dolosse. Photogrammetric maps 

 developed from the stereo models were enlarged 20 times that of the contact 

 scale, to a scale of 1:60. 



The photogrammetric maps were plotted on transparent drafting material. 

 The stability of dolosse from one flight to the next was determined by overlaying 

 the two maps and visually comparing the location of individual dolosse. If a 

 dolos moved during the time interval, the horizontal component of movement 

 was evident, as a displacement of the outline occurred that was scaled from the 

 l:60-scale maps. The vertical component of movement was determined by com- 

 parison of spot elevations at selected points. 



The initial maps of the north and south jetties were the most detailed prepared 

 during the monitoring program. They documented the location, orientation, and 



16 



Chapter 2 Prior Monitoring of the Site 



