2
Methods
This study was based on analyses of a series of aerial photographs, taken on
roughly a yearly basis from 1987 to 1999. A set of aerial photography taken in
1982 provides a base map of preinlet conditions. Bathymetric survey data is
limited, but historic preinlet NOAA data and a Scanning Hydrographic Opera-
tional Airborne Lidar Survey (SHOALS) from 11/1998 will be used to charac-
terize the vertical component. Aerial photography has been scanned from 22 sets
of color and black and white prints (Table 1). The original study on the effects of
the new breach at Chatham (Weishar, Stauble, and Gingerich 1989) compared the
first eight sets of photography taken approximately every 4 months for the first
2 years after inlet formation. The first postinlet vertical aerials were not flown
until May 1987, 5 months after the breach occurred. The 1989 study ended with
the analysis of changes as of the May 1989 photography.
For the present long-term study, one set of aerial photographs from every year
was chosen from the 22 photo sets in the archive. This subset of 14 photo groups
were deemed sufficient to show yearly change. Most of the annual photo sets
chosen were collected in the summer months of May, June, July, or August. This
temporal coverage reduced the seasonal bias in the analysis. For 1991 and 1996,
winter photos were all that were available and had to be used to complete the
annual study. The photographs were taken by various aerial photography com-
panies and were collected at several different scales. All photo prints were 9 9 in
format. Some of the photographs were in color, but all sets were scanned in black
and white at 600 dpi to reduce digital file space.
GIS Analysis
A base map was constructed from AutoCad files supplied by the Town of
Chatham that contained detailed positioning of streets, buildings, and other
physical features. Five sheets covering portions of the mainland coast were
supplied and imported into ArcView. The AutoCad base map was in Massa-
chusetts State Plane NAD 83 coordinates. Using the ArcView Image Analysis
package, it was possible to import each scanned photo and register them against
the control points on the base map. Geo-referenced photo mosaics were con-
structed from the three or four photographs in each set on a common scale. As a
minimum, four control points were used to register each print.
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Chapter 2 Methods
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