A Dual-frequency Dual-polarized Doppler Radar (D3R) was developed with funding from NASA's Global Precipitation Measurement (GPM) Project. The D3R is a fully polarimetric, scanning weather radar system operating at the nominal frequencies of 13.91 GHz and 35.56 GHz covering a maximum range of 30 km. The frequencies chosen allow close compatibility with the GPM Dual-frequency Precipitation Radar system, which was selected for flight on the GPM core spacecraft that launched in February 2014.
The D3R is part of GPM Ground Validation activities. These activities support GPM pre-launch algorithm development and contribute to post-launch precipitation product validation. Pre-launch, the D3R provides independent estimation of hydrometeor classification and drop size distribution retrievals. The radar thus offers an insight into the microphysical processes that dominate the retrieval (and associated measurement error) of precipitation types and rates from satellite data. While the GPM DPR radar presents a global picture of precipitation through observations at Ku- and Ka-band, the ground-based D3R yields detailed, fine-scale local statistics of the microphysical interpretation.
The D3R takes advantage of several innovative technologies to achieve its design goals as a relatively compact, transportable system. Chief among these are the use of solid state power amplifiers and a novel waveform composed of three consecutive, frequency modulated, frequency separated pulses. Using these methods, blind ranges and range sidelobes are minimized, and the radar meets its sensitivity requirement of -10 dBZ at 15 km (clear air, single pulse, with 150 m range resolution).
A government-industry-academic consortium developed the D3R. NASA's Goddard Space Flight Center has overall management and lead engineering responsibility for the radar. Remote Sensing Solutions, Inc. is responsible for the solid-state transceivers and intermediate frequency electronics; Orbital Systesm, Ltd.. developed the radar pedestal and positioner. Colorado State University (CSU) developed the data product and archive software, and has a wide range of responsibilities related to the radar electronics (including the digital receiver and waveform generation), electronic integration, and test. The D3R was field tested alongside of CSU's S band CHILL radar. D3R's first deployment was the Mid-Latitude Continental Convective Clouds Experiment (MC3E) field campaign, which took place in April and May 2011.
D3R Radar Parameters
Ku: 13.91GHz ± 25 MHz
Ka: 35.56GHz ± 25MHz
|Minimum detectable signal (Ku, Ka)||-10dBZ at 15 km for a single pulse at 150m range resolution|
|Minimum operational range||450 m|
|Operational range resolution||150 m (nominal)|
|Maximum range||30 km|
|Angular coverage||0-360o Az, -0.5-90o El (full hemisphere)|
|Parabolic reflector (diameter)||6ft/72in (Ku), 28in (Ka)|
|Gain||44.5 dB (Ku, Ka)|
|HPBW||~1o (Ku, Ka)|
|Polarization||Dual linear simultaneous and alternate (H and V) (Ku, Ka)|
|Maximum sidelobe level||~ -25 dB (Ku, Ka)|
|Cross-polarization isolation||< -32 dB (on axis)|
|Ka-Ku beam alignment||Within 0.2o|
|Scan capability||0-24o/s Az, 0-12o/s El|
|Scan types||PPI sector, RHI, Surveillance, Vertical pointing|
|Transmitter architecture||Solid state power amplifier modules|
|Peak power/Duty cycle||160 W (Ku), 40 W (Ka) per H and V channel, Max duty cycle 30%|
|Receiver noise figure||4.6 (Ku), 5.5 (Ka)|
|Receiver dynamic range||³ 90 dB (Ku, Ka)|
Equivalent reflectivity factor Zh (Ku, Ka),
Doppler velocity (unambiguous: 25 m/s)
|Dual-polarization products (Ku, Ka) (LDR only in alternate transmit mode)||
Differential reflectivity Zdr
Differential propagation phase _dp
Copolar correlation coefficient _hv
Linear depolarization ratios LDRh, LDRv