Scattered Ultraviolet Radiation in the Upper Stratosphere, I:
Observations
K. Minschwaner, R. J. Thomas, and D. W. Rusch
Abstract
We present observations of scattered solar near UV radiation
in the upper stratosphere taken during a 1983 balloon flight
at 31 deg N latitude. The instrument design was
patterned after the UV ozone spectrometer
on board the Solar Mesosphere Explorer satellite. The
measurements cover the wavelength range
175 to 325 nm at a spectral
resolution of 1.5 nm, spanning a range of viewing angles
from -3.3 deg to 14.6 deg above the horizon
with a field of view 1.65 x 10{-5} sr.
Observations commenced at mid-day near 46 km and continued to
approximately 1700 LT near an altitude of 40 km.
Calibrated radiances are determined from the raw data
using measured sensitivity characteristics
of the spectrometer. A correction
to account for the polarized nature of Rayleigh
scattered radiation is included which employs the
measured polarization response of the instrument and
assumes single scattering of solar radiation.
The single pass spectrometer was susceptible to a small, but in some cases
important, contamination by stray light. This effect is quantified
using observations obtained at low altitudes and low solar
elevation angles, i.e., large optical paths.
The uncertainty in radiances is determined by statistical
and systematic errors (efficiency, polarization,
and stray light determinations) and ranges typically from
15 to 30%. In contrast to previous observations,
scattered radiances decrease rapidly
at wavelengths shortward of 210 nm.
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