Ghost radiance suppression using backward ray path analysis for a Risley prism scanner of an active laser ranging...

Area of Science:

• Optics and Photonics
• Remote Sensing Technology
• Image Processing

Background:

• Laser Detection and Ranging (LADAR) systems can produce ghost patterns due to internal reflections.
• The presence of multiple wedge prisms in the LADAR system contributes to complex light paths and potential ghosting.

Purpose of the Study:

• To establish an efficient and thorough analysis method for identifying and mitigating ghost patterns in LADAR imagery.
• To improve the resolution and clarity of images generated by the LADAR system.

Main Methods:

• Backward ray tracing was employed to analyze instantaneous ray paths and their flux.
• Ray path histories were accumulated and categorized to understand ghost reflection origins.
• Neutral density (ND) filters and mechanical vignettes were systematically used to reduce ghost radiance.

Main Results:

• The backward ray tracing method, combined with ND filter adjustments, effectively minimized ghost radiance to below a 5° tilt angle.
• Replacing the ND filter with a mechanical vignette resulted in ghost flux being 21% of the total point cloud, closely matching the measured 19%.
• The final LADAR images exhibited significantly improved resolution with no ghost reflections in previously affected areas.

Conclusions:

• The developed ray tracing analysis method is effective in identifying and resolving ghost patterns in LADAR systems.
• The implementation of ND filters and mechanical vignettes offers a practical solution for ghost reflection mitigation.
• This approach enhances the quality and reliability of LADAR imaging for various applications.