A characterization of the data, including its intended use and limitations.
Abstract: The 2010 Connecticut Multispectral Coastal Digital Orthophotography is 1:12,000-scale, 4-band (red, green, blue, and near infrared) tide controlled orthorectified imagery. These data were compiled from a set of 821 individual vertical aerial images taken over 3 distinct days during a June 15 to September 15, 2010 flight window. The indivudual orthophotos have been subsequently mosaicked into a composite that can be configured to show either true color or color infrared versions of the coastal landscape.
The geographic extent (~320 sq mi) of the photography includes:
* 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 in order to clearly depict the interface between the shorelands and coastal waters;
* 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.
To maximize the quality of the images and their contents, photography also conformed to the following flight specifications:
* photos were only taken during times of no/minimal cloud cover when lighting and weather conditions optimized the data collection;
* solar altitude was no more than 65 degrees and no less than 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 1 hour window before or after a predicted low tide based on National Oceanic & Atmospheric Administration (NOAA) predicted tide tables.
* Forward overlap is 60% and side image overlap is 30%
* Crab and Tilt do not exceed 5 degrees.
The individual aerial photos were first orthorectifed and mosaicked into grid-based system provided by the State of Connecticut Department of Environmental Protection. Adjacent tiles are edgematched with no gaps. Temporal and seasonal differences between source images were minimized to avoid incongruence across join lines. When a mosaic of source images was made, the image judged by visual inspection to have the best contrast was used as the reference image. The brightness values of the other images were adjusted to match that of the reference image. The join lines between the overlapping images were hosen to minimize tonal variations. Localized adjustment of the brightness values were performed to minimize tonal differences between join areas.
Subsequent mocaicking took the individual orthophotos and combined them into a project-wide composite.
The ground resolution of the imagery is approximately 1 ft per pixel. Data is compiled at 1:12,000 scale. This data is not updated.
Purpose: The 2010 Connecticut Multispectral Coastal Digital Orthophotography is 1:12,000-scale 4 band (red, green, blue, & near infrared) tide controlled imagery. It depicts land use, natural resources, vegetation, and other features and characteristics in the immediate shoreline areas of Connecticut during the summer of 2010 within one hour of a predicted low tide both in true color or color infrared, depending on the band configuration. Use this layer as photo representation for depicting coastal features/landscapes or to analyze the landscape, features, or activities of the coastal area.
NOTE: This data is georeferenced, so it can be combined with other GIS data with real world coordinates. An un-rectified version of this data (2010 Connecticut Multispectral Coastal Imagery) constituting the source data for the orthophtography is also available for use.
Supplemental information: The imagery exists as 1:12,000 4-band (red, green, blue, near infrared) multispectral images. When bands are configured as follows: red = 1, green = 2, blue = 3, the imagery will render as true color - the same color the human eye naturally discerns. When bands are configured as follows: red = 4, green = 1, blue = 2, the imagery will render as color infrared.
A digital orthophoto is a digital image of an aerial photograph in which displacements caused by the camera and the terrain have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map. A digital orthophoto has the same scale throughout and can be used as a map for measuring distances, calculating areas, determining the shape of features, and reading coordinate locations, for example. Digital orthophotos provide the necessary background (base map) layer information to which other spatial data layers are registered or created. The process of creating an orthophoto, orthorectification, corrects the geometry of a aerial photo image so that it appears as though each pixel were acquired from directly overhead. Orthorectification uses elevation data to correct terrain distortion in aerial or satellite imagery.
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)
Dataset credit: Photoscience, Inc., of Lexington, KY performed the 2010 Connecticut Multispectral Coastal Imagery Project via an MOU between the State of Connecticut Department of Environmental Protection and the NOAA Coastal Services Center as part of the Coastal Geospatial Services Contract (CGSC), a FAR Part 36, Architectural and Engineering Contract vehicle to provide geospatial services.