Description Spatial Attributes

Theme: imageryBaseMapsEarthCover
Place: Connecticut, CT

The Connecticut 1981 Coastal Aerial Photography Tile Index is a polygon feature class that defines the approximate extent of the geographic area covered by each Connecticut 1981 Coastal Photograph. The 1981 Coastal Photography data for Connecticut is comprised of 773 non-georeferenced 1:12,000 scale 9" by 9" vertical color infrared aerial images. The extent of all the polygons comprise a project area described by: * all land areas within one-thousand (1000) feet of Mean High Water (MHW) and within one-thousand (1000) feet of state-regulated tidal wetlands; * an area of at least two-thousand (2000) feet waterward of the immediate shoreline of Long Island Sound; * all offshore islands within the territorial borders of the State of Connecticut including Goose Island and Falkner Island (offshore of Branford); Calf Islands and Great Captain Island (offshore of Greenwich); Norwalk Islands (offshore of Norwalk); Thimble Islands (offshore of Branford); Sandy Point (offshore of Stonington); and all islands in the Connecticut part of Fishers Island Sound; and * the main stem of the Connecticut River up to the Massachusetts State line. The Connecticut 1981 Coastal Aerial Photography Tile Index is organized in a non-regular grid pattern that reflects the orientation of the flight lines used to photograph the project area. The tiles have an approximate sidelap (overlap between tiles in adjacent flightlines) of 30% and an approximate endlap (overlap between adjacent tiles within a flightline) of 60% in order to achieve well defined stereo pairs. Each feature is identified by a unique PHOTONAME value, to match the filename of the corresponding digital photo image as well as a PHOTO_NO value to match the hardcopy prints and transparencies maintined by the State of Connecticut Department of Environmantal Protection. PHOTO_NO is combination of the ROLL number and a unique ID number for the tiles in that roll. In addition, each polygon feature also contains the unique flight line, film roll, photo exposure numbers, and date recorded on the original film transparency and hardcopy print as well as basic information on the flight including the year, photography type, tide control, vegetation state, scale, etc. NOTE: 1981 Coastal Aerial Photography represents a reflight of the preceeding 1980 flight to address QA/QC problems that forced the rejection of numerous photos.

These data serve as a polygon index to the set of 1981 Coastal Aerial Photographs for Connecticut.  They cartographically descibe the location and orientation of the photographs and also serve as a way to access digital versions (scanned images) of the original hardcopy transparencies and/or prints.

While the index provides scaling information for the hardcopy photos and digital images, care should be taken when using these to measure distances or calculate areas.  Any measurements should be considered approximate as the photography has not been corrected to account for the physical characterisitcs of the flight or the ground topography.

Supplementary Information
While the polygon index is referenced to the CT State Plane Coordinate System (NAD83); the associated digital versions of the Connecticut 1981 Coastal Aerial Photography is neither orthorectified nor georeferenced to any real-world coordinate sytem.

To maximize the quality of the images and their contents, photography was specified to conform to the following environmental conditions: 
* photos were only taken during times of no/minimal cloud cover when lighting and weather conditions optimized the color infrared film; 
* solar altitude was more than thirty (30) degrees; 
* the ground detail was not obscured by flooding; 
* the foliage (salt marsh vegetation in particular) was fully developed; 
* seasonal conditions (summer) favored maximum human use/recreation activities (e.g., boats & temporary docks/structures in water, etc.); 
* photo times were planned within one (1) hour window before or after a predicted low tide based on National Oceanic & Atmospheric Administration (NOAA) predicted tide tables; and 
* no photography was flown between the hours 1100 and 1300 Eastern Standard Time (EST) to minimize specular reflection.

The photos exist as 1:12,000 vertical color infrared images.  Color infrared photography, often called false color photography because it renders the scene in other than the normal colors seen by the human eye, is widely used for interpretation of natural resources.  Atmospheric haze does not interfere with the acquisition of the image, therefore is well suited to aerial photography.  Because the film is high speed and subject to degrees of degradation in handling before exposure, the aerial photographs can vary in overall tone.  This variability can complicate the interpretation of color tones between photographs, but some general guidelines can be given to aid the inexperienced interpreter. 

* The red tone of color infrared aerial photographs is almost always associated with live vegetation. Very intense reds indicate vegetation which is growing vigorously and is quite dense.  Knowledge of the vigor and density of vegetation is important to the interpretation of the red colors on color infrared aerial photography. 

* As the vigor and density of vegetation decreases, the tones may change to light reds and pinks. If plant density becomes low enough the faint reds may be overcome by the tones of the soils on which the plants are growing. The ground areas in this case will appear in shades of white, blue, or green depending on the kind of soil and its moisture content. As plant vigor decreases, the vegetation will show as lighter shades of red and pink, various shades of greens, and possible tans.  Dead vegetation will often be shades of greens or tans. 

* Bare soils will appear as shades of white, blue, or green in most agricultural regions.  In general, the more moist the soil the darker the shade of that particular soil color. Composition of the soil will affect the color tones shown on the photographs.  Dry sand will appear white and, with more moisture, may be very light gray or possibly light tan.  Clayey soils will generally be darker in color than sands and tend toward tans and bluegreens.  Again, wetter clays will be darker shades of the same tones.  Soils high in organic matter, like silts and loams will be even darker in color, and usually in shades of blues and greens.  Wet organic soils can be very dark blue or green in the aerial photographs. 

* Man-made features will show in the tones that relate to the materials they are made of.  Asphalt roads, for example, will be dark blue or black, gravel or dirt roads will show as lighter colors, depending on the soil materials involved in their composition, and concrete roads will appear light in tone, assuming clean concrete.  The buildings and streets of towns can be considered in a similar manner, their color dependent on the material they are made of. 

* Water will appear as shades of blue, varying from nearly black to very pale blue.  Clear, clean water will appear nearly black.  As the amount of sediment increases, the color becomes increasingly lighter blue.  Very shallow water will often appear as the material present in the bottom of the stream.  For example, a very shallow stream with a sandy bottom will appear white due to the high level of reflection of the sand. 

* Degraded film will result in photographs which have an overall blue or green cast.  When that occurs, the interpretation must consider what that overall cast will do to a "normal" rendition of the scene. 

(Description and guidelines for color infrared photography taken from the United States Geological Survey Aerial Photo FAQ web page, http://edc.usgs.gov/guides/news/aerialfaq.htmlt#A10)


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