The radiosonde may be on its way out. A new Doppler frequency-modulated, continuous-wave (FM-CW) radar has passed successive tests over the last year. The FM-CW developed by scientists at the National Oceanic and Atmospheric Administration uses two antennas. The first transmits a continuous microwave signal that sweeps up and down a range of frequencies, while the second simultaneously receives return signals.
Unlike conventional pulse radars, which measure the time delay between outgoing and return signals, the FM-CW measures the difference in frequency.