accumulate. If it is assumed that individual errors represent standard deviations, a root-mean- 

 square (rms) approach can be applied to provide a realistic assessment of combined potential 

 errors (Merchant 1987, Crowell, Leatherman, and Buckley 1991). In other words, if sources of 

 error are independent, there is some cancellation of error, resulting in a reduction of combined 

 potential errors. 



Table 3-2 summarizes estimates of potential positional error for the primary data sources 

 analyzed in this study. The rms error for 1875/79 topographic maps (T-sheets; 1:20,000 scale) is 

 about ±50 ft, whereas the 1928 and 1948 T-sheets (1:20,000) and the 1970 topographic 

 photomaps (TP-sheets; 1:10,000) contain about ±55 and ±27 ft of potential error, respectively. 

 The GPS survey provided the most accurate measurement of shoreline position, with an 

 estimated maximum rms error of ±14 ft. Table 3-3 provides a summary of maximum rms errors 

 for available shoreline change data for the study area. 



Table 3-1. Characteristics of shoreline data sources. 



Date 



Data Source 



Comments and Map Numbers 



1875/79 



USC&GS Topographic 

 Maps (1:20,000) 



First shoreline surveyed with standard engineering techniques; 

 1875- New Smyrna Beach to False Cape 



(T-sheets 1415a, 1415b, 1423); 

 1 877 - Cape Canaveral to Cocoa Beach 



(T-sheets 1450a, 1450b); 

 1878/79 - Indialanticto Sebastian Inlet (T-sheets 1460, 1478) 



April 29-30, 1928 



USC&GS Topographic 

 Maps (1:20,000) 



All maps produced from interpreted aerial photography 

 (T-sheets 4530, 4440b, 4441b, 4442b, 4554, 4555, 4556) 



April 1948 



USC&GS Topographic 

 Maps (1:20,000) 



All maps produced from interpreted aerial photography 

 (T-sheets 9162, 9164, 9165, 9168, 9171, 9174, 8880, 8882, 8884) 



February 1970 



USC&GS Topographic 



Photomaps in Cooperation 



with State of Florida 



(1:10,000) 



All photomaps produced from interpreted aerial photography 

 (TP-sheets 135, 136, 138, 140, 142, 143, 145, 146, 147, 149) 



May 20-22, 1996 



Differential GPS Survey 

 (1:1) 



North boundary of Cape Canaveral National Seashore to 

 Sebastian Inlet 



3-2 



Chapter 3 Assessment of Coastal Change 



