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16 June 1995 Practical low-cost high-range-resolution ladar
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This paper treats a practical adaptation of frequency modulation (FM) radar ranging principles to an incoherent laser radar (ladar). In the simplest sense, the ladar's laser transmitter output is amplitude modulated with a radio-frequency subcarrier which itself is linearly frequency modulated. The subcarrier signal may have a start frequency in the tens to low hundreds of megahertz and stop frequency in the hundreds of megahertz to low gigahertz. The difference between the start and stop frequency, (Delta) F, is chosen to establish the desired range resolution,(Delta) R, according to usual equation from FM radar theory, (Delta) R equals c/(2(Delta) F), where c is the velocity of light. The target-reflected light is incoherently detected with a photodiode and converted into a voltage waveform. This waveform is then mixed with an undelayed sample of the original modulation waveform. The output of the mixer is processed to remove `self-clutter' that is commonly generated in FM ranging systems and obscures the true target signals. The clutter-free waveform is then processed coherently using the discrete Fourier transform to recover target amplitude and range. A breadboard of the ladar architecture was developed around a 30-mW GaAlAs diode laser operating at 830 nm. Imagery and range responses obtained show that the theoretical range resolution of 0.25 m was attained for a (Delta) F of 600 MHz. Embodiments of this ladar are likely to be practical and economical for both military and commercial applications because low-cost continuous wave laser diodes are used, coherent optical mixing is not required, and the post- mixing processor bandwidth is low.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Barry L. Stann, William C. Ruff, and Zoltan G. Sztankay "Practical low-cost high-range-resolution ladar", Proc. SPIE 2472, Applied Laser Radar Technology II, (16 June 1995);


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