On this project, WMD manufactured an entirely new receiver for NASA's Differential Absorption LiDAR (DIAL ) instrument, integrating High Spectral Resolution LiDAR (HSRL) measurement capability into the existing DIAL ozone system for deployment on the NASA DC-8 aircraft. This needed to be accomplished without increasing the overall instrument footprint or weight, a requirement which was achieved by WMD. The upgraded DIAL system takes highly accurate nadir and zenith measurements of aerosol and cloud aerosol properties, in addition to ozone profiles.
The DIAL system consists of nadir and zenith telescopes provided by NASA, and nadir and zenith optical systems provided by WMD. Each WMD optical system consists of a lightweight breadboard, numerous optics, and detector subsystems for the 295-nm, 355-nm, 532-nm, and 1064-nm channels. The two breadboards are mounted facing one another using a unique two-piece, high-precision post design that enables the nadir and zenith breadboards to be easily separated for optical alignment operations. There is also a shutter controlled bore-sight system which collects rays from from both the nadir and zenith systems, then passes them through the zenith breadboard and a motorized filter wheel into a detector camera. The entire assembly is light tight, with thin panels covering the outer edges.
One of the biggest challenges on this project was the lack a real estate for all the parts that needed to be incorporated. We had a specific breadboard size that needed to be maintained, and the breadboards had to be easily separated from one another for maintenance. There are hundreds of parts attached to each breadboard, and the breadboards needed to be spaced a precise distance apart with light-tight panels all around. Structural posts around the outer perimeter were not possible because of the spacing of the components and the placement of the light-blocking panels so WMD engineered high-strength, precision two-piece hollow posts that fit into gaps between the components and allow easy separation of the two breadboards.
Another challenge was placement of the numerous optics and detectors on each breadboard, while maintaining correct optical offsets and alignment. As a testament to our accuracy, the client stated that they received the system "basically pre-aligned mechanically" and had to make very few adjustments for perfect optical alignment. The lessons learned from this alignment accuracy have been applied to all subsequent breadboard projects.