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from NorthWest Research Associates, Inc.
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Argus Beach Monitoring Stations (ABMS)

Quantitative Video Monitoring Services for Coastal Zone

Management and Engineering

 

  Glossary  

Listed below are definitions for some common terms related to applications of the ABMS technology.

 

daytimex An image where individual pixel intensities are averaged over all visible sampling times to reveal mean daily features, such as the locations of bars and rip channels.
ground control points Ground Control Points (GCP's) are fixed targets in the field of view of each ABMS camera that are used to calibrate the geometry solutions of each image before further analysis is performed.  GCP's can be "targets of opportunity" in an image (e.g., light pole) or they can be markers placed at the time of station installation.  A typical station installation will use three GCP's for each camera.
digital image A digital video image consists of an array of 640 by 480 picture elements (pixels), where the light intensity of each pixel is resolved to 256 (0-255) individual values (i.e., one byte per pixel).
photogrammetry The science of making reliable measurements by the use of photographic or video imagery.

To learn more about the application of photogrammetry to ABMS data, click here.

pixel Acronym for "picture element," the basic unit of measurement in a digital image.  Pixel values are resolved into red, green, and blue (RGB) values on a scale of 0-255, where 0 is no intensity and 255 is full intensity.

The real-world size of the volume contained in a pixel (width, depth, height) is determined by lens focal length and the geometry of the camera, notably height, tilt, azimuth, and yaw (camera roll).

rectification The process of converting from image coordinates to real world coordinates using appropriate algorithms.  A rectified image is often presented as a plan (x-y) view.
snap image A single individual ABMS image where no averaging is applied.
time stack A data set containing the time history of pixel intensities along a transect.  Time stacks are especially useful for tracking features such as shoreline migration, wave run-up and swash excursion, and wave phase speed and direction.
timex

 

An image where individual pixel intensities are averaged over some suitable interval, such as 10 minutes (mean  Iu,v  = SIu,v/n ).  Timex's help to remove visual "noise" and reveal the location of key coastal zone features such as shoreline location, dry beach width, and sand bar location.
variance image An image that displays the variance of light intensity (sI2) calculated over some suitable averaging period, usually the same as that used to calculate a timex image.  Dark areas indicate little change in light intensity, light areas the opposite.  Variance images are used to better define shoreline location and shoreline features such as cusps.
 

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Last updated August 2001