Diode-Laser-Based Differential Absorption Lidar (DIAL) for Long Term Autonomous Field Deployment

Abstract:

The rapidly changing spatial and temporal distribution of water vapor in the planetary boundary layer influences dynamical and physical processes that drive weather phenomena, general circulation patterns, radiative transfer, and the global water cycle. The ability to measure the water vapor distribution continuously within the lower troposphere has been identified as a high priority measurement capability needed by both the weather forecasting and climate science communities. This presentation provides an update on an economical and compact diode-laser-based differential absorption lidar (DIAL) which has demonstrated the capability of meeting these high priority measurement needs.

The DIAL instrument utilizes two continuous wave distributed feedback diode lasers to injection seed a current modulated tapered semiconductor optical amplifier. An improved switching time between the on-line and off-line wavelength, on the order of 16.7 ms, allows the instrument to retrieve water vapor profiles in rapidly changing atmospheric conditions. A shared telescope design based on a 40.64 cm diameter Dobsonian telescope allows the outgoing beam to be eye-safe at the exit of the telescope. The DIAL receiver utilizes the Dobsonian telescope to collect the scattered light and direct it through an optical narrow bandpass filter (NBF) and a Fabry-Perot etalon with a free spectral range of 0.1 nm which is equal to the wavelength difference between the on-line and off-line DIAL wavelengths. A beam splitter directs 90% of the scattered light through a second NBF, and couples it onto a fiber coupled avalanche photodiode (APD), providing a far field measurement. The remaining 10% of the light passing through the beam splitter is incident on a free space coupled APD, providing a wider field of view for water vapor measurements at lower altitudes. The two channel receiver allows water vapor measurement between 500 m and 4 km/6km during daytime/nighttime operation, respectively. The DIAL instrument layout will be described in this presentation along with data sets demonstrating the long term data collection capabilities of this instrument.