The CRS is a 94 GHz (W-band; 3 mm wavelength) Doppler radar developed for autonomous operation in the NASA ER-2 high-altitude aircraft and for ground-based operation. It will provide high-resolution profiles of reflectivity and Doppler velocity in clouds and it has important applications to atmospheric remote sensing studies. The CRS was designed to fly with the Cloud Lidar System (CLS), in the tail cone of an ER-2 superpod. There are two basic modes of operation of the CRS: 1) ER-2 with reflectivity, Doppler, and linear-depolarization measurements, and 2) ground-based with full polarimetric capability. The overall radar system parameters are listed in the attached table.

The CRS consists of subsystems including the transmitter/receiver, antenna, processor/radar controller, and disk data storage. The transmitter/receiver subsystem utilizes an Extended Interaction Amplifier (EIA) Varian transmitter tube that transmits 1.7 kW peak power. This subsystem has a custom modulator, power supply, and timing and control designed for ER-2 autonomous operation and with flexibility to transmit a wide variety of modulation schemes with range pulse widths between 0.25 and 3.0 ms at pulse repetition frequencies (PRF) up to 42 kHz (limited to £ 1% duty cycle), and with capability to perform multiple PRF’s. For Doppler measurements on the ER-2, the range-Doppler ambiguity at 94 GHz necessitates using a dual-PRF (5 kHz and 10 kHz) approach to extend the unambiguous range and Nyquist interval. The two channel receiver downconverts signals to a 60 MHz IF which is then processed by the digital-IF/processor subsystem. The data system is similar to that of the 9.6 GHz EDOP system; it has a high degree of flexibility and performs all the signal processing from bandpass filtering to calculation of the Doppler velocities through the autocovariance method. Switching of the transmit polarization by the radar controller provides measurement of the linear depolarization ratio, LDR, differential reflectivity, ZDR, and differential phase measurements. The radar has two antennas; one antenna is used for ground-based operation and has 55 dBi gain. The other antenna designed for the ER-2 installation is an offset parabolic reflector antenna with 47 dBi gain. Both antennas are novel designs utilizing Flat Parabolic Surface (FLAPS) technology developed under an SBIR contract.

Absolute calibration of the transmitter and receiver is performed externally using standard methodologies. Internal calibration of the CRS receiver is performed continuously through consecutive looks at a single noise source. IF calibration is performed by injecting the IF phase-locked oscillator signal at the output of the mixer/preamplifier stages. Digitally-stepped attenuators are used to step the calibration signal over the receiver full dynamic range during flight. Phase calibration of the coherent detector is achieved by varying the phase of the reference signal. Transmitter power is monitored continuously through a detector. So far the radar has not participated in any field experiments but has operated successfully from the rooftop laboratory at NASA Goddard.