observed during which waves strike the beach with almost equal frequency 

 from all directions, resulting in frequent reversals in the direction of 

 littoral transport. During the summer, waves are more likely to come 

 from the southeast and south and produce northward drift (U.S. Army Engi- 

 neer District, Wilmington, 1969). Although on an annual basis the pre- 

 dominant direction of wave attack is from the northeast and east, shoaling 

 and accretion on the south side continue because of the occasional contri- 

 bution made by currents moving northward. Moreover, when the waves are 

 coming from the northeast and east, the shoal is protected by the weir 

 jetty. 



Wave diffraction is another factor that may contribute to the shoaling. 

 Waves approaching the end of the jetty are diffracted, and the resulting 

 loss in wave energy causes the sediment load to be deposited in the 

 shoaled area. This phenomenon of wave diffraction around the end of the 

 jetty is visible in Figure 11. 



5. Wrightsville Beach . 



No discernible change was noted in the ERTS-1 imagery on Wrightsville 

 Beach. Like Masonboro Beach, the amount of sand lost approximately 

 equaled the amount gained during the time interval under consideration. 

 Some accretion was visible on the north side of the Masonboro jetty, but 

 like the rest of the beach, it remained stable during the time interval 

 between ERTS-1 observations. 



VII 1. SUMMARY AND CONCLUSIONS 



This study was undertaken to determine how satellite imagery may be 

 applied to specific coastal engineering problems. The study analyzed 

 unenhanced imagery recorded by the four spectral channels of the ERTS-1 

 multispectral scanner. Problems encountered with analysis of the ERTS-1 

 imagery and the advantages offered by examination of each spectral band 

 separately were discussed. A number of coastal features seen in ERTS-1 

 films, including sediment plumes discharged from inlets, a change in 

 water coloration, inlet bars, and cape bars were also examined and dis- 

 cussed. These features were correlated with ground-truth data. Morpholo- 

 gical changes in selected coastal land features were determined by com- 

 paring ERTS-1 films obtained about 1 year apart. The observations 

 presented in this report should provide a significant input to other 

 coastal studies being conducted along the study area. 



Two characteristics of satellite imagery are considered essential 

 attributes when applied to coastal engineering problems. The first 

 characteristic is adequate water depth penetration; depth of water pene- 

 tration by light increases as wavelength decreases. This property of 

 light allows an examination of certain underwater features in the lower 

 MSS bands of the ERTS-1 imagery. As inferred from the imagery presented 

 in this report, specifically in reference to the shoals and bars, depth 

 penetration in MSS channel 4 is estimated to be tens of feet. Actual 

 depth penetration by light of a given wavelength can vary greatly. 



38 



