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presence of a valid second reflection such as from a window or from a shorterrange object illuminated by
the beam. The onboard processing of secondary returns is limited to weaker target reflections in the
foreground. The correlation record can be downloaded by the user to examine target details in post
processing.
Processing the Correlative Pulse
The calculation of the effective delay is based on the coarse location within the correlation record and the
interpolated crossing between sample points. For the full resolution correlation record used in the
LIDARLite processor, each sample represents 2nsec in time or roughly one foot or .3 meters. To obtain a
result in cm requires 30 resolution points obtained by interpolating between data points. The figure below
illustrates a single correlation pulse obtained by processing either the reference or signal.
The correlation waveform on the left shows a zero crossing on the falling edge around the location 185. The
detail of the crossing on the right shows a linear fit from the upper crossing point at 185 with a value of 26
and a value at 186 of 44. The calculation of the crossing is equal to (26/ (26 44))*30 or 11.14cm.
To get the total delay we multiply the index of the upper point 185 and multiply by 30 to get the coarse delay
in cm. The total delay is then 30 * 185 + 10 = 5560. If we have a delay for the reference waveform, with a
crossing at 30*30 +15 or 915cm we get a measured delay of 5560915 = 46.45 meters.
Processing
A module within the processor analyzes the correlation record looking for the largest peak waveform within
the record. As it moves through the record, the crossing characteristics of each new larger peak is sampled.
At each peak, the coarse delay to the positive sample prior to the zero crossing along with correlation values
above and below the crossing and the peak value are stored. With each new peak sample, the previous
LIDARLite v1 "Silver Label" Manual , Updated: 08/13/15
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