Title: Progress in developing the CO2 Sounder Lidar as a candidate for the ASCENDS Mission
Presenting Author: James B. Abshire
Organization: NASA GSFC
Co-Author(s): Haris Riris, Graham R. Allan, Jeffrey Chen, Anthony Yu, Xiaoli Sun, Anand Ramanathan

Abstract:
The lidar on NASA's planned ASCENDS mission will measure atmospheric CO2 and O2 column absorption and range, allowing calculation of the atmospheric CO2 mixing ratio needed for flux (surface exchange) estimates. The ASCENDS mission is quite important, because its lidar approach will permit, for the first time, global atmospheric CO2 concentration measurements, including those at night, at high latitudes, through hazy and thin cloud conditions and to cloud tops. None of these are possible using passive sensors. The CO2 Sounder team has made significant progress in developing of the CO2 Sounder approach and laser technology for the ASCENDS lidar. The team has demonstrated their airborne CO2 lidar prototype on airborne flights in 2010, 2011 and 2013. The team has used these measurements to improve the airborne instrument and to optimize the CO2 lidar retrieval approaches. The results show that airborne measurements made in 2011 and 2013 were accurate to ~1 ppm for airborne altitudes between 6 and 12 km. Analysis also highlighted a new capability to measure CO2 column absorption and range both to cloud tops and the ground. Differencing the retrievals allows estimating the CO2 in the column between the ground and cloud top, which in many cases allows a direct estimate of the CO2 concentrations in the boundary layer. Improved lidar measurements of the O2 column and atmospheric pressure were also demonstrated in 2013. The project has demonstrated a new step-locked laser diode source and a high power fiber laser preamplifier. A breadboard of a laser power amplifier using an initial planar waveguide gain element has been assembled at Raytheon and is being tested during the summer of 2014. The goal for this amplifier is to produce the space-needed power ~20W. Optimized planar waveguide optics for the laser power amplifier are being fabricated now via support from a 2014 ESTO QRS award. Delivery of the optimized power amplifier to Goddard is planned for March 2015. A new HgCdTe APD detector with 16 detector elements was also developed in collaboration with DRS RSTA. It passed proton radiation testing, and has been delivered to GSFC. Testing shows it has analog response, high linear dynamic range and ~x16 time more sensitivity than the IR-PMT detector previously used for the airborne lidar. Use of this detector reduces the laser power needed for the space lidar. The CO2 Sounder team is currently completing improvements to the airborne lidar. These include the step-locked laser source and HdCdTe APD detector. The CO2 Sounder team will participate in the 2014 ASCENDS flights during August on the NASA DC-8. Targeted measurement areas include the Pacific Ocean west of Baja California, the California Central Valley, the redwood forests along the northern California coast, the CO2 plume from Indianapolis IN, and the CO2 draw down above growing agriculture in Iowa. An under-flight of either the GOSAT or OCO-2 satellite track is also planned. A summary of all these results will be presented.