photogrammetrist was that line at the time of the survey or the date of 

 photography. 



60. With the advent of precision aerial photography, the compilation 

 of a "T-sheet" for photohydro support opened a new dimension in shoreline 

 compilation. When stereoscopic instruments and known tide data were used, the 

 MHWL could be accurately determined by aerial photography. This method was 

 supplemented, when possible, by profile points run from vertical bench marks 

 to verify the photointerpretation. When beach profiles were run on the more 

 contemporary surveys, they were referenced to the nearest tide station. If 

 this was a tertiary (i.e., temporary) station, the readings were referenced 



to a primary station. 



Methods Used to Revise the 1980 Mean High Water Line 



61. To make this study as current as possible, USGS quadrangle maps 

 were revised to show a 1980 MHWL. The revision was made using 1980 color 

 aerial photographs flown for this study. Date and time of the photography 

 were correlated with the stage of the tide, and a detailed stereoscopic ex- 

 amination of the photographs was made to determine the 1980 MHWL. This pro- 

 cess was completed by the Cartographic Revision Section of the Photogrammetry 

 Division of NOS. Their method was by direct transfer of the photointerpreted 

 line (see paragraph 60) from l:24,000-ratioed film positives to the USGS base 

 maps. Using the ratioed photography, the base maps (manuscripts) were held 

 planimetrically to local physical features. In absence of triangulation sta- 

 tions to position the manuscript accurately against the photographs, it is 

 possible to use "hard" planimetric features, such as road intersections or 

 other permanent physical structures without great relief, to assure good photo- 

 graphic positioning. In areas where there were not enough features to assure 

 proper positioning, stereomodels were set on the National Ocean Survey Analyt- 

 ical Plotter (NOSAP) . NOSAP is a high-precision stereoscopic plotter that 

 allows the operator to bridge over areas of sparse control and accurately 

 determine the correct relationship between photographic models and the base 

 maps. Due to time restraints, no field check of the office-determined 1980 

 MHWL was made. All shorelines compiled by this method were reviewed to assure 

 a uniformity of the photointerpreted shoreline, accuracy of compilation, and 



50 



