A 35-GHz Scanning Doppler Radar for Fog Observations

To observe fog, a 35-GHz scanning Doppler radar was designed, assembled, and tested. The radar, mounted on a flatbed vehicle for portability, transmits peak powers of 100 kW in a pulse of 0.5-µs width and a beamwidth of 0.3°. Thus, a reflectivity factor Z of −20 dBZ at a range of 10 km generates a signal-to-noise ratio of 0 dB. Doppler velocity measurements are made by sampling the radio frequency phase within each pulse transmitted by a magnetron oscillator and referencing the phases of the received echoes to the transmitted phase. A Nyquist velocity of approximately 9.7 m s–1 is obtained in real time using the spaced pulse-pair method, and aliases of radial velocities are corrected using software. The three-dimensional structure of sea fog and its advection are depicted with the radar.