system block diagram
System Block Diagram

The NRL Eye-safe Volume Imaging Lidar (NEVIL) has three primary optical components: transmitter, receiver, and scanning system. The transmitter uses coupled deuterium cells that shift wavelength of the optical pulses from a Nd:YAG Laser at 1064 nm to the 1560 nm wavelength, allowing the lidar to operate in an eye-safe mode. The transmitted 1560 nm light is backscattered from the atmospheric aerosols, reflects off a dual mirror scanning system, is collected by a 0.3 m Cassegrainian telescope and is focused onto a 200 micro-meter diameter InGaAs avalanche photodiode (APD). A small drum lens is mounted directly above the APD and used to increase the APD collection efficiency. (Drum lens are machined from ball lens into a cylinders and are easier to align with cylindrical detector packages.) The receiver field of view is approximately 100 microradian.

The scanning system has two mirrors mounted on 18 inch diameter rotation stages. The rotation stages are mounted perpendicular to each other: the first stage is mounted horizontally controlling the azimuthal scans and the second stage is mounted vertically controlling the elevation scans. The rotation stages are driven by stepping motors, are computer controlled and can rotate at nearly 50 degree/s. The velocity and acceleration can be changed during measurement cycles.

The photograph shows the lidar in a shipping container. The scanning system is above the roof-line with the cover removed revealing the two mirrors. The lidar system is mounted on a scissor-jack. The system, which can be lowered into the shipping container and covered with a roof hatch, is easy to move.
The photograph shows the lidar in a shipping container. The scanning system is above the roof-line with the cover removed revealing the two mirrors. The lidar system is mounted on a scissor-jack. The system, which can be lowered into the shipping container and covered with a roof hatch, is easy to move.

The output from the optical detector is provided to a data acquisition system, which provides a real-time analysis and display of the signals received. The system determines the atmosphere's optical properties, provides maps of aerosol structures, measures wind speed, direction, and turbulence. NEVIL can be used to study atmospheric flows and dynamics remotely and in real time.