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C. E. Blom, T. Gulde, C. Keim, W. Kimmig, C.
Piesch, C. Sartorius, H. Fischer Institut für
Meteorologie und Klimaforschung Forschungszentrum
Karlsruhe GmbH / Universität Karlsruhe
MIPAS-STR a new instrument for stratospheric
aircraft
MIPAS-STR (Michelson Interferometer for Passive
Atmospheric Sounding - STRatospheric aircraft) is
a new instrument developed for remote sensing of
a large number of atmospheric trace compounds
(e.g. ClONO2, N2O5, NO, NO2 and HNO3) from
high-altitude aircraft. It will be operated from
the Russian M-55 Geophysica in the framework of
the APE-GAIA (Airborne Polar Experiment -
Geophysica Aircraft In Antarctica) in
September/October 1999. We used modules of the
Giessen diode laser system to test Braults
approach of time-equidistant sampling which was
implemented in the electronics of the
interferometer of MIPAS-STR.
Fig. 2 Linear representation of the optical
path. The IR-radiation propagates from the scan
mirror via the telescope and the interferometer
to the detector unit. The instrumental FOV is
defined by the lHe cooled apertures FS3 and AS3.
The apertures AS, FS1 and shields reduce the
radiation from outside the FOV as well as
scattered radiation reaching the front optics.
The radiation diffracted at the edges of the
front optics is suppressed by the Lyot and
aperture FS2.
Fig. 3 The detector system. The entire focal
plane with dichroic beam splitters, optical
filters, SiAs-detectors etc. is cooled to 4 K.
The division into 4 channels is necessary for
NESR improvement to facilitate the detection of
NO2 and NO (channels 3 and 4) and allows an
efficient data reduction.
Fig. 4 Scheme of the onboard electronics. The
electronics is structured hierarchically. A
transputer network connects the central computer
with the independent subsystems. The state of the
systems is defined by housekeeping and status
data. Access from the main computer enables full
control during operation of the instrument.
Table 1 Characteristic instrument data.
Fig. 5 Results from blackbody measurements with
scan velocities between 1.58 cm/s and 4.30 cm/s.
The mean of the phase spectra for forward and
backward scans shows the electrical contributions
to the phase.
Fig. 6a Spectrum of the diode laser. Low
current was applied to the TDL to obtain almost
monochromatic radiation. Fig. 6b Same as
fig. 6b but with expanded vertical scale. Since
no monochromator was used, weak secondary lines
(below 1) can be observed.
Fig 6c Spectrum obtained by sine modulating the
scan velocity. The modulation frequency was set
to 150 Hz, the amplitude (p-p) was 40 of the
nominal value of 3 cm/s. A time delay of 0 ?s was
used. Fig 6d Same as fig. 6c but with time
delay of 22 ?s derived from the phase spectra
shown in fig. 5. Note that the ghosts are reduced
to about 20. The non-vanishing part of the
ghosts may be due to simultaneous amplitude
modulation at the same frequency.
Fig. 5 The aircraft M-55 Geophysica. Left in
Pratica di Mare (November 1996). Right drawing
of the M-55 with the dorsal bay for MIPAS on
top.
August 1999