Abstract:
Application of dark-field passive LIDAR in entomological studies has been an emerging
technology which is capable of identifying insects and detecting their activities in situ. With
the use of simplistic instrumentation, passive LIDAR is capable of producing results
comparable to more sophisticated technologies such as RADAR and Active LIDAR, although
range resolving in passive LIDAR is a challenging task. Moreover, it has a minimal impact on
the targeted flora and fauna, and no associated health hazards. One promising method of range
estimation is to use a passive LIDAR range equation developed based on ray tracing. The
objective of this study is to experimentally evaluate the passive LIDAR range equation (under
its linear mode). The intensity variation of the probe volume was recorded by using a quadrant
photodetector (QPD) attached to the image plane of a Newtonian telescope (f=1200 mm, ∅tel =
20 cm). The system was calibrated by observing the time domain parameters of the intensity
variations of adjacent QPD segments corresponding to a pendulum oscillation. These were
conducted at different locations along the probe volume with 10 m increments. System
parameters were adjusted to comply with the passive LIDAR range equation’s linear mode.
This was done by matching the width of the QPD image on the dark terminator with the
diameter of the telescope aperture. It was observed that the range can be estimated with an
accuracy of ± 3.29 m for a maximum range of 80 m. The observations were aligned with
previously published simulated insect signal-based retracing. It was also noted that the
deviations in range estimation accuracy is due to the finite thickness of the pendulum and it
can be minimized by using a thinner pendulum. This method can be applied to resolve the range
information on daytime insects.
