Abstract:
Passive Light Detection and Ranging (LIDAR) has successfully been used for observing insects
and their activities. It was reported that such techniques are more efficient compared to traditional
approaches. Quadrant Photo Detectors (QPDs) are widely used at the image plane with the use of
a modified eye-piece to detect both wing-beats and heading angles of insects. In these systems,
knowing the exact orientation of the QPD in the image plane is an imperative task. This study
was carried out to propose a method to calibrate the rolling angle of a QPD mounted in the image
plane of a Newtonian telescope in a dark-field passive LIDAR system using a Hamamatsu S4349
Silicon QPD. Each segment of the QPD was connected to a data acquisition card through four
Trans-impedance amplifiers and programmable gain amplifiers. A white coloured inverted
pendulum oscillated across the Field of View (FOV) of the QPD at a known distance was used
for calibration. Intensities registered at the individual segments of the QPD were recorded at a
rate of 10 kHz while the pendulum swept the FOV. Thirty-six of such measurements were
obtained by changing the rolling angles by 10-degree at a time. The four filtered and normalized
signals were used to calculate the activation times (full width at 10%) and four unique sinusoidal
functions were fitted to the whole range of angles. These coefficients can be used to estimate the
rolling angle of the QPD using a test oscillation. It was found that the accuracy of the estimate
was ± 6.04 degrees. A ray tracing-based simulation was conducted to simulate this activity and
findings from the activity agrees with the theoretical simulation results. It was noted that the
highest performance can be obtained when the pendulum oscillates in a plane normal to the optical
axis.
