Pulsed Lidar for the ASCENDS Mission – Space Instrument Study
James
B
Abshire, NASA-Goddard, james.b.abshire@nasa.gov
(Presenting)
Haris
Riris, NASA-Goddard, haris.riris@nasa.gov
Graham
R.
Allan, NASA-Goddard, graham.r.allan@nasa.gov
Xiaoli
Sun, NASA-Goddard, xiaoli.sun@nasa.gov
Jeffrey
Chen, NASA-Goddard, jeffrey.chen@nasa.gov
Luis
Ramos-Izquierdo, NASA-Goddard, luis.a.ramos-izquierdo@nasa.gov
Our group is developing a pulsed dual wavelength lidar approach to measure tropospheric CO2 concentrations from space for the ASCENDS Mission. This work is ongoing and has been supported by the NASA ESTO ACT and IIP programs. Our laser sounder approach uses the 1570-nm CO2 band and a pulsed dual wavelength laser absorption spectrometer. This uses differential lidar absorption measurement in an altimeter mode, and 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, as well as surface height and aerosol backscatter in the same measurement path. It directs the narrow co-aligned laser beams toward nadir, and measures the energy of the pulsed laser echoes reflected from land and water surfaces. During the measurement, the lasers are tuned across a selected CO2 line and a region between two O2 lines near 765 nm. The lasers have spectral widths much narrower than the gas absorption lines and are wavelength tuned at kHz rates. 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 ratios of the on and off line signals. 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 in the path, which can otherwise bias retrievals.
We have recently completed a second design study for the ASCENDS space lidar. For the study, we selected a nominal sun-synchronous orbit with an altitude of 450 km and equator crossing time of 1:30 pm, and a 1.5 m diameter receiver telescope. The study went well and a summary of the results will be shown.
Presentation Type: Poster
Poster Session: Orbital and Suborbital Missions
NASA TE Funded Awards Represented:
NONE: Related Activity or Previously Funded TE Award