Published on November 28, 2007
Slide1: Mona Houcheime San Jose State University Dr. Richard Ulrich University of Arkansas Department of Chemical Engineering Arkansas Center for Space and Planetary Science July 28, 2005 Fayetteville, AR Feasibility of Using Orbital LIDAR to Measure Methane in the Martian Atmosphere Purpose of this Project: This project evaluates the feasibility of orbital LIDAR to map CH4 in the Martian atmosphere. What is LIDAR Instrument Characteristics: detection limits spatial resolution (column abundance) hardware requirements orbital considerations Absorption of Photons by Atmospheric Species System Configurations Purpose of this Project Methane in the Martian Atmospherefrom ESA Mars Express: Methane in the Martian Atmosphere from ESA Mars Express 10 +/- 5 ppbv about 300 years lifetime Major sink = photolysis Sources may be biogenic! LIDAR can provide much higher sensitivity and spatial resolution Methane mixing ratios: Red high Yellow medium Blue low What is LIDAR: What is LIDAR LIght Detection And Ranging In Vacuum Ranging t=? Atmospheric Characterization l =? LIDAR as a Rangefinder : LIDAR as a Rangefinder Digital elevation models (DEMs) Ranging time 1 ns round trip time = 15 cm MOLA (Mars Orbiter Laser Altimeter) topographic map of Mars: LIDAR for Atmospheric Characterization: LIDAR for Atmospheric Characterization Can determine: Aerosol characteristics (clouds, dust particles) Wind speeds (temperature profile and air circulation) H2O(v) concentrations (humidity) Chemical composition (major/minor constituents) tune LIDAR to l at strongest absorption cross-section Our Goal: global mapping of methane on Mars even at low abundance (ppb) Terrestrial Results from LIDAR Studies of the Atmosphere: Terrestrial Results from LIDAR Studies of the Atmosphere Methane plume imaging from aircraft LIDAR Aerosols Water Vapor Beer-Lambert’s Law: Beer-Lambert’s Law To analyze and quantify absorption Id = I° e-(sCH4 * NCH4)L I°≠ I initial Id < I° (photons/sec) DIAL – eliminates scattering due to particles Take two measurements at two closely-spaced frequencies One tuned to absorption l of species ~3.32 mm and non- absorbing ~3.34 mm Chemical Analysis using Photon Absorption: Chemical Analysis using Photon Absorption CH4 Absorption Cross Sections: Absorption Cross Sections CH4 Absorption coefficient b=N * s LIDAR: Bistatic vs. Monostatic: LIDAR: Bistatic vs. Monostatic CH4 Bistatic Monostatic CH4 Orbital Consideration for Bistatic LIDAR: Orbital Consideration for Bistatic LIDAR For a circular orbit and the optical path tangential to the surface, the spacecraft separation would be: Close/tangential to the surface Larger T-R separation lower SNR Conclusions: LIDAR could be effectively used to map methane in the Martian atmosphere Optimal laser wavelength 3.32 mm if there is no interference with water absorption lines Bistatic might be preferable to monostatic better sensitivity, but requires two spacecraft DIAL would be effective at eliminating scattering contribution Conclusions References: Hanel, R.A., et al., Exploration of the Solar System by Infrared Remote Sensing, Cambridge University Press, Second edition, Cambridge, UK 2003 Lewis, John S., Physics and Chemistry of the Solar System, Academic Press, San Diego, California, 1995 Spectral Database http://vpl.ipac.caltech.edu/spectra Laser sensing tutorial http://www.swsciences.com/technology/sensors.html Laser Technology http://oea.larc.nasa.gov/PAIS/LaserTech.html Pictures: http://www.nature.com/news/2004/041025/images/laser.jpg http://www.bol.ucla.edu/~jberle/med_atmosphere2.jpg http://scirealm.netfirms.com/gallery/planets_comets_asteroids/mars/mars.html http://ltpwww.gsfc.nasa.gov/tharsis/mola.html http://www.esrin.esa.it/export/esaLP/ESA40MPV16D_campaigns_3.html http://virl.gsfc.nasa.gov/gif/0411933a.gif http://www.geointelmag.com/geointelligence/article/articleDetail.jsp?id=151575&&pageID=2 References Thanks to Dr. Ulrich for his assistance in the research
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