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Processing Multiple Reflections
It is possible to receive multiple valid return signals from a single measurement if the beam illuminates more
than one surface along the beam path. This situation may be encountered when the beam clips or passes
through an object in the foreground. Because of the inverse square law behavior of the return signal (double
the distance get four times less signal) a very small illuminated area near the sensor may produce a much
stronger signal than that from the desired target. Ranging objects through a window can produce a strong
shorter range signal masking the longer target or conversely it may be desirable to detect a window in the
foreground that may only produce a small reflective signal relative to a larger distant reflection.
The sensor has the capability to process two distinct reflections as long as they are separated by more than
3.5 meters and the reflection at the shorter distance does not saturate the correlation record masking the
more distant object. The "Secondary return" flag in bit position 4 in the status register [1] indicates that a
second pulse has been detected. The figure below shows an example of two reflections in the signal
correlation record (record address locations greater than 64) separated by approximately 3.5 meters.
The sensor detection criteria may be selected to pick the nearer signal, the more distant signal or the
strongest signal strength. In addition, when a second pulse is encountered the other reflection can be read
from the system without having to perform a new measurement with different detection criteria. Control
register 75, summarized below, sets up the criteria for selection of the desired return when two are present.
LIDARLite v1 "Silver Label" Manual , Updated: 08/13/15
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