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48 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING
2.3.1 Development and Application of a Versatile Balloon-Borne DOAS
Instrument for Skylight Radiance and Atmospheric Trace Gas Profile
Measurements
Participating scientists Weidner, F., H. Bösch, A. Butz, M. Dorf, U. Platt, C. von Friedeburg,
T. Wagner, and K. Pfeilsticker
Abstract A novel balloon-borne UV/vis DOAS instrument measuring limb scattered radiation was
developed, characterized in the laboratory and employed during 5 stratospheric balloon flights. Skylight
radiance and concentration profiles of O3, NO2, and BrO are retrieved and compared to radiative
transfer simulations and measurements of the same parameters.
Background In the past two decades remote
sensing of the atmosphere by optical methods
has evolved into a powerful tool for meteorology,
atmospheric photochemistry and climate studies.
Most recently, space-borne UV/vis limb observations
have also become available, e.g., through
the SME, SOLSE/LORE, Odin/OSIRIS, and EN-
VISAT/SCIAMACHY instruments. Quasi in-situ
UV/vis limb profiling from balloon may also offer
a new method for time resolved spectroscopy of
ozone harmful radicals in the stratosphere.
Scientific questions that can be tackled by
UV/vis limb measurements are:
(1) measurements of near horizon limb radiance
for different illumination conditions and validation
of radiative transfer codes.
(2) Monitoring profiles of stratospheric radical
species, such as O3, NO2, BrO, OClO, IO, ....
and studies of their photochemistry and budget,
e.g., for the systems NO2/N2O5 (see 2.2.3) or
BrO/OClO and its importance for ozone loss.
Methods UV/visible skylight radiances (330 −
550 nm) are measured from azimuth controlled
balloon payloads which are flying into the middle
stratosphere (∼ 32km). The spectra are analyzed
for along-the-sights column densities of O3,
NO2, BrO, H2O, and O4 by Differential Optical
Absorption Spectroscopy (DOAS). Radiative
Transfer (RT) calculations, e.g., with the lab programmed
Monte Carlo RT Model TRACY, are
used to (a) simulate the measured quantities and
(b) infer vertical profiles of O3, NO2, BrO and
OClO concentrations using the Maximum a Posteriori
(MAP) inversion technique. Subsequent
measurements of the profiles of these species allow
us to draw information on the temporal or
spatial variations (or both) of these species and
the related photochemistry.
Results Balloon-borne UV/vis limb scattered
measurements is tested against simultaneous measurements
of the same parameters available from
in-situ, or UV/vis/near IR solar occultation observations
performed on the same payload. Reasonable
agreement is found between (a) measured and
RT calculated limb radiances and (b) inferred limb
O3, NO2, and BrO (see Figure 2.20) and correlative
profile measurements when properly accounting
for all relevant atmospheric parameters (temperature,
pressure, aerosol extinction, and major
absorbing trace gases).
Figure 2.20: Comparison of retrieved BrO profiles
from mini-DOAS limb measurements (black line)
and direct sunlight DOAS measurements (red
line) during balloon ascent for an LPMA/DOAS
balloon flight in Kiruna, March 24 th , 2004 with a
priori profile in green.
Additionally, scanning limb observations provide
time-resolved profile information of radicals
during sunset.
Future work should concentrate on the application
of the method on photochemical studies addressing
the loss in stratospheric ozone at high,
middle, and low latitudes, including the tropical
tropopause region.
Main publication Weidner, F., Development
and Application of a Versatile Balloon-Borne
DOAS Instrument for Skylight Radiance and Atmospheric
Trace Gas Profile Measurements, Ph.D.
thesis, Universität Heidelberg, Heidelberg, 2005.