Development of Laser, Detector, and Receiver Systems for an Atmospheric CO2 Lidar Profiling System

A ground-based Differential Absorption Lidar (DIAL) is being developed with the capability to measure range-resolved and column amounts of atmospheric CO₂. This system is also capable of providing high-resolution aerosol profiles and cloud distributions. It is being developed as part of the NASA Earth Science Technology Office's Instrument Incubator Program. This three year program involves the design, development, evaluation, and fielding of a ground-based CO₂ profiling system. At the end of a three-year development this instrument is expected to be capable of making measurements in the lower troposphere and boundary layer where the sources and sinks of CO₂ are located. It will be a valuable tool in the validation of NASA Orbiting Carbon Observatory (OCO) measurements of column CO₂ and suitable for deployment in the North American Carbon Program (NACP) regional intensive field campaigns. The system can also be used as a test-bed for the evaluation of lidar technologies for space- application. This DIAL system leverages 2-mum laser technology developed under a number of NASA programs to develop new solid-state laser technology that provides high pulse energy, tunable, wavelength-stabilized, and double-pulsed lasers that are operable over pre-selected temperature insensitive strong CO₂ absorption lines suitable for profiling of lower tropospheric CO₂. It also incorporates new high quantum efficiency, high gain, and relatively low noise phototransistors, and a new receiver/signal processor system to achieve high precision DIAL measurements. Atmospheric tests of the laser have been conducted by operating it locked to the CO₂ absorption line center, with off-set locking in the side-line mode, and in the off-line position. The reference laser is locked to center of absorption line within 390 kHz. This improves the level of stabilization by factor of 10 compared to earlier configuration. The detector has been characterized in the laboratory and by conducting atmospheric tests at The National Center of Atmospheric Research (NCAR), Boulder, Colorado. The receiver uses an F2.2 all aluminum 40 cm diameter telescope and the system is designed to focus light onto a 200 μm size detector. Subsystem level integration and testing has been completed in the second year. System level testing is planned in the third year along with validation in the late spring of 2008 that involves comparisons with ground-based and aircraft in situ CO₂ sensors.