page_title: Pulse-Doppler signal processing
section_title: Detection
hierarchical_section_title: Pulse-Doppler signal processing / Detection
caption_attribution_description: English: Constant false alarm rate (CFAR)
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: Detection processing for pulse-Doppler produces an ambiguous range and ambiguous velocity corresponding to one of the FFT outputs from one of the range samples. The reflections fall into filters corresponding to different frequencies that separate weather phenomenon, terrain, and aircraft into different velocity zones at each range.
  Multiple simultaneous criteria are required before a signal can qualify as a detection.
  Constant false alarm rate processing is used to examine each FFT output to detect signals. This is an adaptive process that adjusts automatically to background noise and environmental influences. There is a cell under test, where the surrounding cells are added together, multiplied by a constant, and used to establish a threshold.
  The area surrounding the detection is examined to determine when the sign of the slope changes from  to , which is the location of the detection (the local maximum). Detections for a single ambiguous range are sorted in order of descending amplitude.
  Detection only covers the velocities that exceed the speed rejection setting. For example, if speed rejection is set to 75 mile/hour, then hail moving at 50 mile/hour inside a thunderstorm will not be detected, but an aircraft moving at 100 mile/hour will be detected.
  For monopulse radar, signal processing is identical for the main lobe and sidelobe blanking channels. This identifies if the object location is in the main lobe or if it is offset above, below, left or right of the antenna beam.
  Signals that satisfy all of these criteria are detections. These are sorted in order of descending amplitude (greatest to smallest).
  The sorted detections are processed with a range ambiguity resolution algorithm to identify the true range and velocity of the target reflection.
caption: Constant False Alarm Rate detection performed on FFT output.
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