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OCR for page 69
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°
OCR for page 70
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
OCR for page 71
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.
OCR for page 72
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.
Representative terms from entire chapter: