8.1 A-scope, B-scope, PPI
A-scope: B-scope: PPI:
amplitude vs range azimuth vs range plan position
amp range ____
│ │ * * / \
│ * * │ * / * \
│ * * │ * * | * * |
│_________*_*___ R │_________________ az | |
\ * /
\____/A-scope. The oldest display: a single trace showing returned amplitude versus range, with the antenna locked to one direction. A simple oscilloscope wired to the receiver. Used in early WWII radars and still used in some niche applications like ground-penetrating radar where you analyze a single direction at a time.
B-scope. Range on one axis, azimuth on the other. The screen is a 2D rectangle with targets as bright spots. Used in fire-control and aircraft radars. It distorts true geometry (objects further away occupy more angular space), but it scans efficiently.
PPI (Plan Position Indicator). The most familiar radar display: a circular plot with the radar at the center and targets shown at their true azimuth and range. Antenna scans round and round, the trace sweeps with it, and targets appear as bright dots that fade with persistence. This is what every airport tower and ship radar shows. The classic green-phosphor PPI of the 1960s movies has been replaced by full-color LCD displays, but the geometric layout is unchanged.
8.2 Modern processed displays
Modern radars rarely show raw echoes. After matched filter, CFAR, MTI, and tracking, the operator sees synthesized icons: track symbols at the predicted target position, with attached labels showing speed, altitude, and identification. The raw radar video is usually dimmed or hidden. A modern air-traffic controller sees a stable flat picture annotated with ICAO call signs, not a swirling green PPI.
Weather radars, by contrast, show colored maps of intensity (and, with dual polarization, additional layers showing precipitation type and rotation). NEXRAD's familiar green-yellow-red precipitation map is the processed output of a coherent S-band pulse-Doppler radar with full I/Q processing.