Radar imagery and display features

Radar imagery

Top: Because the earth curves out from beneath the radar's beam, a layer of migratory birds or insects that is limited in height (here represented as dashes) will be detectable only out to a certain range. Beyond this range, the beam passes entirely over the migratory layer. This largely defines the maximum range at which biological targets can be detected by radar.

Bottom: Colors show decreasing echo strength with increased range from the radar as the beam passes over the migratory layer. The conceptual cross-section above (not to scale) is matched to real echo typical of bird migration around the middle of the night. In this image, the radar, indicated by a black dot, is detecting birds out to about 150 km. This "range bias" is characteristic of nearly all surveillance radar imagery of biological targets.

Radar data
Nearly every radar image presentd here is comprised of radar data on the left and a panel describing those data on the right.

A. kind of data displayed, base reflectivity or base velocity

B. radar site, in this case ILX (Lincoln, Illinois)

C. universal date and time

D. range from the radar of these data in kilometers

E. spatial resolution of these data, more properly described as 1km x 1km

F. mode of data collection, either "clear air" or "precipitation"

G. volume coverage pattern, a numerical designation of mode

H. angle of elevation of the radar beam above the ground, the center of a nearly 1 degree beam is inclined 0.5 degrees relative to the ground

I. decibels of Z (dBZ), units by which the amount of echo is presented

J. color scheme used to depict the amount of echo in dBZ, the scheme varies depending on mode

K. maximum echo strength recorded

L. base velocity speed in knots

M. color scheme used to depict velocity in knots, the scheme varies, uncalculated velocities shown as purple (RF)

N. maximum recorded velocity toward and away

Display features

Several interactive features allow users to manipulate radar imagery to better understand the biology of migration through radar. Radar imagery is presented in ways that highlight different behaviors through space and time. Display features and imagery are described here.

County and range ring overlays can be superimposed over radar image data. Range rings are spaced every 50 km and rays every 30 degrees. The grey "+" indicates the location of the radar.

The "zoom" feature increases or decreases image magnification by integer multiples (1x, 2x, 3x, 4x, etc). The amount of magnification is essentially unlimited, but users will tire of waiting for highly zoomed images to load long before they reach limits on computer memory.Some behaviors, such as dawn ascent, occur over time and can not be appreciated in static imagery. This animation tool allows the user to display a series of images as a movie. (Note, longer movies require more time to download.) Features allow users to:

"Start/Stop" a movie, change direction ("<" or">") of a playing movie, step forward ">" or backward "<" through individual images when movie is stopped, vary the speed of play (slider), refresh the animation, "Zoom" to portion of imagery specified by mouse click (note, potentially time consuming), during play, left click sqaure to select frames to include (green) or exclude (red) in movie; when stopped, right click selects individual frames to display (blue).