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RASL
Time period
January 2000 to Present
Project description
The Raman Airborne Spectroscopic Lidar (RASL) consists of a 15W ultraviolet laser, a 24-inch (61-centimeter) diameter Dahl-Kirkham telescope, a custom receiver package, and a structure to mount these components inside an aircraft. Both the DC-8 at NASA Dryden and the P3 at NASA/Wallops are aircrafts that could carry RASL. The system is unique because it requires the largest window ever put into either of these aircraft. A fused-silica window, diameter of 27 inches (68.6 centimeters) and 2.375 inches (6 centimeters) thick is needed to withstand the pressure and temperature differentials at a 50,000-foot (15.2-kilometer) altitude.
The atmospheric returns for a Raman Lidar are orders of magnitude weaker than for systems using other Lidar techniques. This makes the RASL receiver package very sensitive to stray light since the signal collected by the telescope is already very weak. We have designed multiple levels of light blocking into the receiver package to minimize the number of stray photons reaching the sensitive photo multiplier tubes (PMTs). There are also many features to speed the calibration process and allow future automation. This should improve the quality and quantity of data collected compared to previous Raman Lidars.
For scale reference, the telescope outer diameter is 28"
Previous Iteration of RASL design