Of the numerous advanced environmental sensors under development, many are based on lidar instruments. One of them is NASA's Mobile Aerosol and Temperature Lidar System, shown here emitting a visible output beam. The Nd:YAG-based system is designed to measure atmosphere temperature and aerosols from the ground. Housed in a 48-ft trailer, the lidar system has been transported to the Mauna Loa, Hawaii, Observatory. As part of the International Network for Detection of Stratospheric Change project, this lidar system is undergoing final testing before its performance is compared to existing instruments.
Designed and built by Continuum (Santa Clara, CA), the custom Nd:YAG laser produces 15 W of fundamental (1064-nm) and second-harmonic (532-nm) frequencies in 10-ns pulses while operating at a 50-Hz repetition rate. According to principal scientist Upendra Singh at NASA Goddard subcontractor Hughes STX (Greenbelt, MD), these two wavelengths are suited for aerosol measurements that yield information about the size distribution of particles in the stratosphere. The 532-nm wavelength is also used for temperature measurements in the altitude range of 25-90 km.
The lidar instrument is designed to transmit three wavelengths (1064 and 532 nm from the Nd:YAG laser and 351 nm from a xenon chloride excimer laser) and to receive four wavelengths (backscattered infrared, visible, ultraviolet, and a Raman scattered signal from the excimer laser). The combination of these wavelengths gives aerosol property information, while vertical temperature profiling is performed with the 532 and 351 nm beams. "Initial results are promising," said principal investigator Thomas McGee of the Atmospheric Chemistry and Dynamics Branch at the NASA Goddard Space Flight Center. So far in the Hawaii tests, temperatures have been tracked to elevations of 85-87 km with the 532-nm beam and up to 95 km with the excimer beam.