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A Comparison of Potential IM-CW Lidar Modulation Techniques for ASCENDS CO2 Column Measurements From SpaceGlobal atmospheric carbon dioxide (CO2) measurements through the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) Decadal Survey recommended space mission are critical for improving our understanding of CO2 sources and sinks. IM-CW (Intensity Modulated Continuous Wave) lidar techniques are investigated as a means of facilitating CO2 measurements from space to meet the ASCENDS science requirements. In previous laboratory and flight experiments we have successfully used linear swept frequency modulation to discriminate surface lidar returns from intermediate aerosol and cloud contamination. Furthermore, high accuracy and precision ranging to the surface as well as to the top of intermediate clouds, which is a requirement for the inversion of the CO2 column-mixing ratio from the instrument optical depth measurements, has been demonstrated with the linear swept frequency modulation technique. We are concurrently investigating advanced techniques to help improve the auto-correlation properties of the transmitted waveform implemented through physical hardware to make cloud rejection more robust in special restricted scenarios. Several different carrier based modulation techniques are compared including orthogonal linear swept, orthogonal non-linear swept, and Binary Phase Shift Keying (BPSK). Techniques are investigated that reduce or eliminate sidelobes. These techniques have excellent auto-correlation properties while possessing a finite bandwidth (by way of a new cyclic digital filter), which will reduce bias error in the presence of multiple scatterers. Our analyses show that the studied modulation techniques can increase the accuracy of CO2 column measurements from space. A comparison of various properties such as signal to noise ratio (SNR) and time-bandwidth product are discussed.
Document ID
20140006238
Acquisition Source
Langley Research Center
Document Type
Presentation
Authors
Campbell, Joel F. (NASA Langley Research Center Hampton, VA, United States)
Lin, Bing (NASA Langley Research Center Hampton, VA, United States)
Nehrir, Amin R. (NASA Langley Research Center Hampton, VA, United States)
Harrison, F. Wallace (NASA Langley Research Center Hampton, VA, United States)
Obland, Michael D. (NASA Langley Research Center Hampton, VA, United States)
Ismail, Syed (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
May 27, 2014
Publication Date
April 27, 2014
Subject Category
Earth Resources And Remote Sensing
Instrumentation And Photography
Report/Patent Number
NF1676L-18158
Meeting Information
Meeting: 2014 European Geosciences Union General Assembly
Location: Vienna
Country: Austria
Start Date: April 27, 2014
End Date: May 2, 2014
Funding Number(s)
WBS: WBS 432938.09.02.07.02.01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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