2.6.3测量多普勒频移：空间多普勒
2.6.3. Measuring Doppler Shift: Spatial Doppler
在大多数情况下，雷达观测到的多普勒频移太小，无法从单个脉冲回波中测量。
The Doppler shiftsobserved in radar are too small to be measured from a single pulse echo in mostcases.
即使对于10 kHz的高多普勒频移和30 dB的信噪比（χ = 1000），Tobs也必须大于123 μs。
Even for a ratherhigh Doppler shift of 10 kHz and a very good SNR of 30 dB (χ = 1000), Tobsmust be much larger than 123 μs.
因此，用单脉冲测量多普勒频移要求脉冲长度大于1 ms，远大于通常使用的亚毫秒（通常小于100μs）脉冲长度。
To measure theDoppler shift with a single pulse would therefore require pulse lengths greaterthan 1 ms, much longer than the submillisecond (usually less than 100 μs) pulselengths typically used.
对于1-kHz多普勒频移和20分贝信噪比，则需要一个持续时间超过10毫秒的脉冲。
For a 1-kHz Dopplershift and 20-dB SNR, a pulse longer than 10 ms would be needed.
由于这个原因，大多数雷达不在脉冲内测量多普勒频移，尽管一些专为超高速目标（卫星和导弹）设计的长脉冲可以做到这一点。
For this reason, mostradars do not measure Doppler shift on an intrapulse basis, although a fewdesigned for very high speed targets (satellites and missiles) and using verylong pulses can do so.
利用多脉冲可以获得所需的长观测时间。
The long observationtime needed can be obtained by using multiple pulses.
假设在t = mT时刻发射一系列M个持续时间为τ的脉冲，其中T为脉冲重复间隔（PRI）。
Suppose a series of Mdistinct pulses of duration τ are transmitted beginning at times t = mT, whereT is the pulse repetition interval (PRI).
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
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