Abstract
The Communications Research Laboratory is studying spaceborne cloud-profiling radar with Doppler measurement capability. This study uses pulse-pair operation, based on the polarization-diversity technique, to measure Doppler velocity. The error in the measured Doppler velocity was analyzed using simulation technique as a parameter of pulse-pair intervals at several signal to noise ratios. The optimal pulse-pair interval (TS) is investigated in this paper because it is a key parameter in determining the dynamic range of the Doppler velocity and its accuracy. Moreover, it was found that the terminal fall velocity of cloud drops in still air could be measured.
Two TS’s (10 μsec and 60 msec) were used as the optimal values. The dynamic range of Doppler velocity for TS = 60 msec is 13.3 m/sec. If this dynamic range for Doppler velocity is enough to avoid the aliasing of Doppler velocity, TS = 60 msec will be suitable for spaceborne cloud-profiling radar because it effectively reduces the error of mean Doppler velocity (<υ>). If the accuracy of the beam-alignment of the antenna is not within 0.1 degrees as a general requirement, a wider dynamic range of Doppler velocity is required to avoid the aliasing of Doppler velocity. It was found that TS of 10 msec gives a wide dynamic range of Doppler velocity. It is thus expected that use of TS = 10 μsec is an optional way for spaceborne cloud-profiling radar, though it does not give good accuracy. Selecting TS ranging from 10 to 60 μsec is also a possible way of optimizing the expansion of the dynamic range of Doppler velocity and reducing the error of <υ>.
