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Titel |
Retrieval of Temperature and Water Vapour From Multiple Channel Lidar Systems Using an Optimal Estimation Method |
VerfasserIn |
Robert Sica, Alexander Haefele |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250104021
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Publikation (Nr.) |
EGU/EGU2015-3441.pdf |
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Zusammenfassung |
While the application of optimal estimation methods (OEMs) is well-known for the retrieval
of atmospheric parameters from passive instruments, active instruments have typically not
employed the OEM. For instance,Âthe measurement of temperature in the middle atmosphere
with Rayleigh-scatter lidars is an important technique for assessing atmospheric change.
Current retrieval schemes for these temperatures have several shortcomings which can be
overcome using an OEM. Forward models have been constructed that fully characterize the
measurement and allow the simultaneous retrieval of temperature, dead time and background.
The OEM allows a full uncertainty budget to be obtained on a per profile basis that includes,
in addition to the statistical uncertainties, the smoothing error and uncertainties due
to Rayleigh extinction, ozone absorption, the lidar constant, nonlinearity in the
counting system, variation of the Rayleigh-scatter cross section with altitude, pressure,
acceleration due to gravity and the variation of mean molecular mass with altitude.
The vertical resolution of the temperature profile is found at each height, and a
quantitative determination is made of the maximum height to which the retrieval
is valid. A single temperature profile can be retrieved from measurements with
multiple channels that cover different height ranges, vertical resolutions and even
different detection methods. The OEM employed is shown to give robust estimates of
temperature consistent with previous methods, while requiring minimal computational
time.
Retrieval of water vapour mixing ratio from vibrational Raman scattering lidar
measurements is another example where an OEM offers a considerable advantage over
the standard analysis technique, with the same advantages as discussed above for
Rayleigh-scatter temperatures but with an additional benefit. The conversion of the
lidar measurement into mixing ratio requires a calibration constant to be employed.
Using OEM the calibration constant can be retrieved if additional water vapour
measurements, such as those provided by a radiosonde or microwave radiometer, are
included.
The success of lidar temperature and composition retrievals using an OEM opens new
possibilities in atmospheric science for measurement integration between active and passive
remote sensing instruments. This presentation will highlight some of these possibilities, as
well as show temperature and water vapour retrievals from the MétéoSuisse Raman Lidar for
Meteorological Observations and The University of Western Ontario’s Purple Crow Lidar. |
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