HR: 09:30h
AN: A11F-07    [Abstracts]
TI: Laser Sounder for Measuring Atmospheric CO2 Concentrations: Demonstrations and Analysis
AU: * Abshire, J B
EM: james.abshire@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Mail Code 690, Greenbelt, MD 20771, United States
AU: Riris, H
EM: Haris.Riris@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Mail Code 690, Greenbelt, MD 20771, United States
AU: Allan, G R
EM: Graham.Allan@gsfc.nasa.gov
AF: Sigma Space, NASA Goddard Space Flight Center, Mail Code 694, Greenbelt, MD 20771, United States
AU: Sun, X
EM: Xiaoli.Sun@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Mail Code 690, Greenbelt, MD 20771, United States
AU: Stephen, M A
EM: Mark.Stephen@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Mail Code 690, Greenbelt, MD 20771, United States
AU: Burris, J F
EM: John.Burris@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Mail Code 690, Greenbelt, MD 20771, United States
AU: Krainak, M A
EM: Michael.Krainak@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Mail Code 690, Greenbelt, MD 20771, United States
AB: Accurate measurements of tropospheric CO2 abundances with global-coverage and monthly temporal resolution are needed to quantify processes that regulate CO2 exchange with the land and oceans. The NASA Orbiting Carbon Observatory (OCO) is a space mission focused on atmospheric CO2 for measuring total column CO2 and O2 by measuring the spectral absorption in reflected sunlight. The recent Decadal Survey for Earth Science by the US National Research Council has recommended a subsequent laser-based CO2 mission called ASCENDS. We have been developing a laser technique for the remote measurement of tropospheric CO2 concentrations from space. Our immediate goal is to develop and demonstrate the lidar technique and instrument technology that will permit measurements of the CO2 column abundance over horizontal paths and from aircraft at the few- ppmv level. Our longer-term goal is to demonstrate the needed capabilities of the technique, develop an approach and instrument design for ASCENDS. Our approach is to use the 1570-nm band and a two channel laser absorption spectrometer (ie DIAL used in altimeter mode), which continuously measures at nadir from a near-polar circular orbit. It uses several tunable fiber laser transmitters allowing simultaneous measurement of the absorption from a CO2 absorption line in the 1570 nm band, O2 extinction in the oxygen A-band, and aerosol backscatter in the same measurement path. It directs the narrow co-aligned laser beams toward nadir, and measures the energy of the laser echoes reflected from land and water surfaces. During the measurement, the lasers are tuned on and off a selected CO2 line and an O2 line (near 765 nm) at kHz rates. The lasers have spectral widths much narrower than the gas absorption lines. The receiver uses a telescope and photon counting detectors, and measures the background light and energies of the laser echoes from the surface along with scattering from any clouds and aerosols in the path. The gas extinction and column densities for the CO2 and O2 gases are estimated from the ratio of the on and off line signals via the DIAL technique. We use pulsed laser signals and time gating to isolate the laser echo signals from the surface, and to reject photons scattered from thin clouds and aerosols. Generally for laser measurements high SNRs are required, the CO2 estimates can be sensitive to small drifts or other errors in the instrument, and the absorption estimates need to be quite stable for hours. We have constructed a breadboard version of the CO2 sensor, which uses a low-power fiber laser and a 20 cm diameter telescope. We have used it to make measurements of CO2 absorption in the laboratory and over 206 and 400-m long open horizontal paths. These have been in several sessions extending over multiple days, and have allowed us to assess the measurement stability and to compare its estimates to readings from an external CO2 sensor. We have also calculated several characteristics of the technique for space including its expected measurement performance for different modulation types, and have performed an initial space mission accommodation study. We will describe these results in the presentation.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0394 Instruments and techniques
DE: 0490 Trace gases
DE: 1610 Atmosphere (0315, 0325)
DE: 1694 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting