page_title: Pulse-Doppler signal processing
section_title: Sampling
hierarchical_section_title: Pulse-Doppler signal processing / Sampling
caption_attribution_description: English: Illustration of I and Q signal sampling required for coherent radar signal processing.
context_page_description: Pulse-Doppler signal processing is a radar and CEUS performance enhancement strategy that allows small high-speed objects to be detected in close proximity to large slow moving objects. Detection improvements on the order of 1,000,000:1 are common. Small fast moving objects can be identified close to terrain, near the sea surface, and inside storms.
  This signal processing strategy is used in pulse-Doppler radar and multi-mode radar, which can then be pointed into regions containing a large number of slow-moving reflectors without overwhelming computer software and operators. Other signal processing strategies, like moving target indication, are more appropriate for benign clear blue sky environments.
  It is also used to measure blood flow in Doppler ultrasonography.
context_section_description: The local oscillator is split into two signals that are offset by 90 degrees, and each is mixed with the received signal. This mixing produces I(t) and Q(t). Phase coherence of the transmit signal is crucial for pulse-Doppler operation. In the diagram, the top shows phases of the wave-front in I/Q.
  Each of the disks shown in this diagram represent a single sample taken from multiple transmit pulses, i.e. the same sample offset by the transmit period (1/PRF). This is the ambiguous range. Each sample would be similar but delayed by one or more pulse widths behind those that are shown. The signals in each sample are composed of signals from reflections at multiple ranges.
  The diagram shows a counterclockwise spiral, which corresponds with inbound motion. This is up-Doppler. Down-Doppler would produce a clockwise spiral.
caption: Pulse-Doppler signal processing begins with I and Q samples.
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