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Weather Radar Technology: Beyond Nexrad
APPENDIX A
NEXRAD WSR-88D System Characteristics
Parameter/Feature
Value/Description
Radar System
Range of observation
Reflectivity
460km
Velocity
230km
Angular Coverage
Azimuth
Full circle or sector
Elevation
Operational limits; -1° to +20°
Antenna
Type
S-Band, center-fed, parabolic dish
Reflector aperture
8.54-m (28-ft) diameter; circular
Beamwidth (one-way, 3 dB)
0.96° at 2.7 GHz; 0.88° at 3.0 GHz
Gain
45.8 dB at 2.85 GHz (midband)
Polarization
Linear horizontal
First side-lobe level
-29 dB
Steerability
360° azimuth; -1° to +45° elevation
Mechanical limits
-1° to +60°
Rotation rate
30° s-1 (azimuth and elevation)
Angular acceleration
15° s-2 (azimuth and elevation)
Pointing accuracy
±0.2°
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Weather Radar Technology: Beyond Nexrad
Radome
Type
Fiberglass skin foam sandwich
Diameter
11.89m (39 ft.)
RF Loss (two-way)
0.3 ± 0.06 dB over 2.7–3.0 GHz band
Transmitter
Type
Master Oscillator Power Amplifier (MOPA)
Frequency range
2.7–3.0 GHz
Peak power output (nominal)
500 kW into antenna
Pulsewidth (nominal)
1.57 µs (short pulse); 4.5 µs (long pulse) ± 4%
RF duty cycle (maximum)
0.002
Pulse Repetition Frequency
Long pulse
322–422 Hz ± 1.7%
Short pulse
322–1282 Hz ± 1.7%
Waveform types
Contiguous and batch
Receiver
Type
Linear
Tunability (frequency range)
2.7–3.0 GHz
Bandwidth (3 dB)
0.63 MHz (short pulse); 0.22 MHz (long pulse)
Phase control
Selectable
Receiver channels
Linear output I/Q; log output
Dynamic range
95 dB max; 93 dB at 1 dB compression
Minimum detectable signal
-113 dBm
Noise temperature
450 K
Intermediate frequency
57.6 MHz
Sampling rate
600 kHz
Signal Processor
Type
Hardwired/programmable
Parameters derived
Reflectivity; mean radial velocity; Doppler spectral width
Algorithms (respective)
Power averaging; pulse-pair; single-lag correlation
Accuracy (Standard Deviation)
Reflectivity
< 1 dB
Velocity and spectrum width
< 1 m s-1
Number of Pulses Averaged
Reflectivity
6–64
Velocity and spectrum width
40–200
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Weather Radar Technology: Beyond Nexrad
Range Resolution
Reflectivity
1 km
Velocity and spectrum width
0.25 km
Azimuth Resolution
Reflectivity
1°
Velocity and spectrum width
1°
Clutter canceller
Digital, infinite impulse response (IIR), 5-pole
Clutter suppression
30–50 dB
Filter notch half-width
0.5–4 m s-1
Radar Product Generator (RPG)
RPG processor
32-bit general purpose digital computer
Shared memory
32-MB semiconductor memory, expandable to 96 MB
Wide band communication
1.544 Mbits s-1 data rate
Narrow band communication
Up to 21 of 9,600/4,800 bits s-1 4-wire
Up to 26 of 9,600/4,800 bits s-1 2-wire (will have 14,400/9,600/4,800 bits s-1 capability)
RPG Graphic Display Processor
Principal user processor (PUP)
Fixed point: 32-bit general purpose digital computer
Communications
9600/488 bits s-1; 2- and 4-wire (maximum: 10 lines)
RS449/RS2332 converters
Video
Color, with split-screen and zoom features
Mass storage
Up to two 600 MB disks
Other
National Climatic Data Center (NCDC)
National archive for NEXRAD data and other meteorological and climatological data.
Level II archive
Interface located at the Radar Data Acquisition (RDA). Digital base data output from the signal processor that includes base reflectivity, mean radial velocity, and spectrum width. Other data include information on synchronization, calibration, date, time, antenna position, and operational mode. Recorded on 8-mm magnetic tape and sent to NCDC for permanent storage.
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Weather Radar Technology: Beyond Nexrad
Level III archive
Interface is located at the Radar Product Generator (RPG). A set of pre-determined products defined in FMH-11 Part A. Data are archived on WORM Optical Disk and sent to NCDC for permanent storage.
National Weather Radar Network
Consists of WSR-88D sites dispersed throughout the conterminous United States plus Department of Defense sites or non-CONUS Department of Transportation sites.
