If detailed historical mapping of shorelines or inland areas is attempted, 

 care should be taken to reduce photographic distortion error. Aerial 

 photography should be corrected photogrammetrically to reduce sources of 

 error such as tilt, yaw, and parallax. If data are taken from maps using 

 different projections, the maps need to be geometrically corrected to conform 

 to the same grid. Once these corrections are made, allowance should be made 

 for tidal and seasonal changes. Good reference points should be chosen. 

 These are usually readily available in populated areas or areas with strong 

 human imprint, but can be difficult to establish along non-populated coasts. 

 Sampling intervals must also be chosen to avoid systematic errors associated 

 with rhythmic features. Extrapolation errors should also be avoided, so that 

 long-term erosion rates are not projected from short-term data sets. 



Airborne Scanners and Satellite Data 



Multispectral scanners and remote sensing devices mounted on aircraft and 

 satellites can provide various types of data that in some cases exceed the 

 capability of conventional photography. The resolution of scanner data is 

 generally not as good as aerial photography, with each data cell or pixel 

 (picture element) having a size from a few meters (on low-altitude aircraft 

 scanners) to several hundred meters on a side. Depending on the system and 

 flight altitude, the aerial coverage on one image is typically far more extensive 

 than on photographs. Also, the coverage may extend to parts of the electro- 

 magnetic spectrum invisible to the human eye, including the near and thermal 

 inft-ared and radar bands. With digital data collected from scanners, the 

 capability for quantitative analysis is far superior to aerial photography, and 

 the data in some cases may be suited to numerical modelling studies. Time- 

 sampling capabilities at a given location include several passes per month by 

 different satellites, allowing repetitive changes to be examined. The timing, 

 however, is not at the discretion of the user. 



Applications of satellite remote sensing are especially good for assessing 

 large-scale changes in the surface of the coastal zone. In the vicinity of del- 

 tas, estuaries, and other sediment-laden locations, the determination of spatial 

 patterns of suspended sediment concentration can be facilitated with remote 

 sensing. In shallow-water portions of non-turbid water bodies, some features 

 of the bottom, including the crests of submarine bars and shoals, can be 

 imaged. On a relatively crude level, satellites may assist in monitoring tidal 

 changes, particularly where the land-sea boundary changes by several 

 hundreds of meters. In deeper waters, satellites can also provide data on 

 ocean currents and circulation (Barrick, Evans, and Weber 1977). Aircraft- 

 mounted radar data also show promise in the analysis of sea state. 



Chapter 5 Investigation of Geomorphic Factors 



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