HR: 1340h
AN: A13D-1500    [Abstracts]
TI: Sensitivity Studies for a Space-based CO2 Laser Sounder
AU: * Mao, J
EM: Jianping.Mao@nasa.gov
AF: RSIS, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Kawa, S R
EM: Stephan.R.Kawa@nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Abshire, J B
EM: James.B.Abshire@nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Riris, H
EM: Haris.Riris-1@nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AB: NASA is developing a space-based CO2 Laser Sounder at Goddard Space Flight Center that is aimed at providing global CO2 measurement in the troposphere with an ultimate measurement precision goal of less than 1%. The laser technique uses a CO2 absorption band in the near infrared and has a number of laser wavelengths across one strong absorption line centered at 1572 nm. The focus of the laser measurement is lower atmosphere CO2. The lasers are pulsed and the surface return signal can be well separated from that returned by the atmosphere using time gating in the receiver. Atmospheric scattering effects on the returned signals can be greatly reduced by this method. In this paper, we report our line-by-line radiative transfer calculation results for the selection of laser frequencies used in this active technique, including the optimal selection of absorption line and laser frequencies at which the sensitivity to atmospheric temperatures is minimal and response to lower atmospheric CO2 is maximal. Other effects on this measurement, e.g., water vapor as the most variable atmospheric composition, will be also analyzed. In addition, the simultaneous measurement of surface pressure is fundamentally required in order to appropriately estimate the change of CO2 absorption corresponding to pressure fluctuation, to compute the CO2 mixing ratio relative to dry air, and to separate actual CO2 surface flux from variations in atmospheric density. The measurement technique for surface pressure will be similar to that for CO2 but uses the O2 A-band near 768 nm. Radiative transfer calculations for the surface pressure measurement will be also reported. Other information (e.g., temperature and water vapor estimates) required to go from differential absorption measurements to final CO2 concentration retrievals will be assessed and discussed.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0322 Constituent sources and sinks
DE: 0360 Radiation: transmission and scattering
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting