| 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. |
