Appendix B
Characteristics of the NEXRAD Radar

Parameter or Feature

Value or Description

Radar System

 

Range of Observation

 

Reflectivity

460 km

Velocity

230 km

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-foot) 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°

Radome

 

Type

Fiberglass skin foam sandwich

Diameter

11.89 m (39 feet.)

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



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Flash Flood Forecasting Over Complex Terrain: With an Assessment of the Sulphur Mountain NEXRAD in Southern California Appendix B Characteristics of the NEXRAD Radar Parameter or Feature Value or Description Radar System   Range of Observation   Reflectivity 460 km Velocity 230 km 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-foot) 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° Radome   Type Fiberglass skin foam sandwich Diameter 11.89 m (39 feet.) 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

OCR for page 172
Flash Flood Forecasting Over Complex Terrain: With an Assessment of the Sulphur Mountain NEXRAD in Southern California Pulse Repetition Frequency   Long pulse 322–422 Hz ± 1.7% Short pulse 322–1282 Hz ± 1.7% Waveform types Contiguous and batch (phase-coded build 8.0) 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 Dynamic range 95 dB max; 93 dB at 1-dB compression Minimum detectable signal –113 dBm (ORDA) Noise temperature 450 K (ORDA) Intermediate frequency 57.6 MHz Sampling rate 600 kHz (This remains the same for the I/Q samples; IF samples will be at 72 MHz) Signal Processor   Type 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 Range Resolution   Reflectivity 1 km Velocity and spectrum width 0.25 km Azimuth Resolution   Reflectivity 1° Velocity and spectrum width 1° Clutter canceller Gaussian Model Adaptive Processing Filter, Spectral Domain Clutter suppression 30–50 dB max Radar Product Generator (RPG) RPG processor 64-bit reduced instruction set (RISC) digital computer Shared memory 512-MB semiconductor memory Wide-band communication 1.544 Mbit s–1 data rate Narrow-band communication Up to 13 of 14,400/4,800 bit s–1 4-wire (1 may be 33,600 bit s–1 capable) 8 of 14,400/4,800 bit s–1 2-wire Up to 9 Wide Area Network (WAN) connections RPG Graphic Display Processor   Principal user processor (PUP) 64-bit RISC digital computer

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Flash Flood Forecasting Over Complex Terrain: With an Assessment of the Sulphur Mountain NEXRAD in Southern California Communications 14,400/4,800 bit s–1; 2- and 4-wire (maximum: 28 lines) Video Color, with split-screen and zoom features Mass storage Up to two 40-GB disks Other National Climatic Data Center (NCDC) National archive for NEXRAD data and other meteorological and climatological data. Level II archive Network interface located at the RPG. Digital base data are output from the Base Data Dissemination System (BDDS), which includes base reflectivity, mean radial velocity, and spectrum width. Data are sent electronically to the NCDC for permanent storage. (Completed nationwide in September 2004) Level III archive Interface is located at the RPG. A set of predetermined products defined in FMH-11 Part A is sent electronically to NCDC for permanent storage. (Completed nationwide in September 2004) National Weather Radar Network Consists of WSR-88D sites dispersed throughout the conterminous United States (CONUS) plus Department of Defense sites or non-CONUS Department of Transportation sites.