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| Titel |
Retrievability of atmospheric water vapour, temperature and vertical windspeed profiles from proposed sub-millimetre instrument ORTIS. |
| VerfasserIn |
Jane Hurley, Patrick Irwin, Nicholas Teanby, Remco de Kok, Simon Calcutt, Ranah Irshad, Brian Ellison |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035220
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| Zusammenfassung |
| The sub-millimetre range of the spectrum has been exploited in the field of Earth observation
by many instruments over the years and has provided a plethora of information
on atmospheric chemistry and dynamics — however, this spectral range has not
been fully explored in planetary science. To this end, a sub-millimetre instrument,
the Orbiter Terahertz Infrared Spectrometer (ORTIS), is jointly proposed by the
University of Oxford and the Rutherford Appleton Laboratory, to meet the requirements
of the European Space Agency’s Cosmic Visions Europa Jupiter System Mission
(EJSM).
ORTIS will consist of an infrared and a sub-millimetre component; however in this study
only the sub-millimetre component will be explored. The sub-millimetre component of
ORTIS is projected to measure a narrow band of frequencies centred at approximately
2.2Â THz, with a spectral resolution varying between approximately 1Â kHz and
1 MHz, and having an expected noise magnitude of 2 nW/cm2 sr cm-1. In this
spectral region, there are strong water and methane emission lines at most altitudes on
Jupiter.
The sub-millimetre component of ORTIS is designed to measure the abundance of
atmospheric water vapour and atmospheric temperature, as well as vertical windspeed
profiles from Doppler-shifted emission lines, measured at high spectral resolution. This study
will test to see if, in practice, these science objectives may be met from the planned design, as
applied to Jupiter.
In order to test the retrievability of atmospheric water vapour, temperature and windspeed
with the proposed ORTIS design, it is necessary to have a set of "measurements” for which
the input parameters (such as species’ concentrations, atmospheric temperature, pressure -
and windspeed) are known. This is accomplished by generating a set of radiative transfer
simulations using radiative transfer model RadTrans in the spectral range sampled by ORTIS,
whereby the atmospheric data pertaining to Jupiter have provided by Cassini-CIRS. These
simulations are then convolved with the ORTIS field-of-view response function, yielding
"measurements” of Jupiter as would be registered by ORTIS about which all atmospheric
parameters are known.
A standard optimal estimation retrieval code, the Non-Linear Optimal Estimator for
Multivariate Spectral Analysis (NEMESIS), shall be used to retrieve atmospheric water
vapour and temperature from such nadir "measurements” taken by ORTIS. The vertical
windspeed profiles, as determined from Doppler-shifted emission lines taken at
extremely high spectral resolution from limb (or near-limb, 80- emission angle) ORTIS
"measurements”, shall be determined using an implementation of standard optimal estimation
theory. Preliminary analysis indicates that ORTIS should be able to retrieve atmospheric
water vapour and temperature, as well as Doppler windspeed profiles on Jupiter to a high
degree of accuracy over a large range of altitudes using single nadir or limb/near-limb
measurements, respectively. |
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