Zander, R.

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1-71535
Ground-Based Infrared Solar Observations
for Early Detection of Stratospheric Changes
R. Zander - Institute of Astrophysics, University of Liege
B-4200 Liege-Ougree, Belgium
Over the last decades, spectroscoplc ground-based observations in the
infrared, using the sun as the source of radiation, have provided a large
amount of information about the composition and structure of the Earth's
atmosphere. Recognition of many advantages of that infrared absorption
spectroscopy technique for remote sensing of specific layers in the atmos-
phere led to subsequent investigations from on-board flying aircraft,
balloons, satellites and more recently from the shuttle platform. These
various "sites" of observation show obvious relative advantages, also
constraints and limitations; within the context of telluric researches
encompassing wide time and space spans, none of these "sites" has proven
obsolete yet. Worth recalling here is the fact that the absorption
spectroscopy technique for remote sensing is as good as the tools involved
in both the observation and the analysis phases: grating - and Fourier
transform spectrometers, heterodyne systems,..., associated to cryogenically
cooled detectors have reached some state-of-the-art operation (providing
high resolution and signal-to-noise ratios) and line parameters compilations
have, been supplemented significantly over the last years (major Improvements
are anticipated for OH, H02 , H202 and some HN03 bands).
Ground-based stations located favorably on high mountains and equipped .
with high performance instruments offer routine possibilities to:
(1) measure integrated column densities for a large number of atmos-
pheric constituents (e.g. N2, H20, C02, N20, CH^, CO, 03, NO, N02,
. HN03, HF, HC1, HCN, OCS , H2CO, HCOOH, C2H2, C2H6, CFC13, CF2C12,
CHF2C1,...), among which are all those gases playing an important
role in the radiation budget of the Earth's atmosphere and there-
fore of key importance in climatology related studies.
(2) provide information on diurnal variations (e.g. NO, N02...),
establish seasonal changes and secular trends (e.g. HC1, HF,
C02 , . . . )
For most of the measurements related to points (1) and (2) above, the
precision is very important. Using high quality solar spectra recorded at
the Jungfraujoch station (Switzerland, 3580m altitude, A6.5°N, 8°E) with
an FTS (resolution 0.005 cm"1; S/N > 1000), we have established that mod-
erately strong absorption lines with central depths between 10 and 50% can
be measured to better than +_ 2%; for this, use was made of solar lines as
well as temperature-independent lines of N2, C02 and N20.
https://ntrs.nasa.gov/search.jsp?R=19910073980 2020-03-17T14:52:12+00:00Z
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Further to the determination of integrated column densities, ground
observations carried out with spectral resolutions of 0.005 cm~* or better
and S/N ratios in excess of 1000 allow to extract information about the
concentration versus altitude, by fitting precisely the contours of series
of lines having various strengths and temperature dependences, recorded
over large zenith angle changes; such retrievals are relatively time con-
suming and not always unambiguous (they require a good knowledge of the
temperature profile prevailing during the observations).
Investigations are being carried out at the Jungfraujoch station
to assess the detectability limits of C10N02, H02N02 and CIO.
Workshop on Early Detection of Stratospheric Changes co-sponsored by NASA,
NOAA, WHO AND CMA.
Boulder, March 5 - 7, 1986.


Ground-based infrared solar observations for early detection of stratospheric changes

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