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Instrument: GOMOS : Global Ozone Monitoring by Occultation of Stars
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Description
The Global Ozone Monitoring by Occultation of Stars (GOMOS) experiment is
an Announcement of Opportunity (AO) European Space Agency (ESA) instrument
on the ENVISAT spacecraft (launched March 1, 2002). The GOMOS instrument
will monitor the global ozone in the 250-950 nm window by comparing
measurements with the spectrum of stars outside and through the
atmosphere. The GOMOS instrument also will measure H2O, NO2, ClO, NO3,
BrO, OClO, temperature, and aerosols. The GOMOS instrument consists of two
bore-sighted telescopes, each with its own spectrometer. The GOMOS optical
system consists of a Cassegrain telescope which simultaneously filtered
radiation through a 0.6 nm resolution U-Vis spectrometer for measurements
in the Huggins and Chappuis bands (0.25-0.45 micrometer and 0.425-0.65
micrometer) and through a near-IR high-resolution 0.07 nm spectrometer for
oxygen (O2) and water vapor (H2O) measurements in the 0.758-0.772
micrometer and 0.926-0.943 micrometer range. A CCD-based star tracker,
which operates in either dark limb or bright limb mode, shares the same
focal plane and provides pointing and tracking accuracy required to
maintain the star image at the center of the spectrometers entrance slits.
Stellar occulatations give a vertical resolution of 1.7 km. There were
about 25 occultations per orbit or about 350 observations during a single
24 hour period. Two blocks of CCD lines, above and below the stellar
spectrum, allows measurement of the atmospheric background which is
subtracted out of the stellar spectrum. The GOMOS instrument measures
atmospheric transmission in the stratosphere from 15-20 km altitude up to
60 km from the UV (250 nm) to near-IR (950 nm) with a spatial resolution
of 0.6 nm. Transmission is measured along the tangential line-of-sight
from the spacecraft to stars. The stellar spectrum is measured outside the
atmosphere and compared with the spectrum measured through the atmosphere.
The full UV-vis-Near-IR spectrum is recorded continuously in multispecral
mode. Atmospheric chemical species, such as ozone, are characterized by
the attenuation of the stellar spectrum and tangential column densities
are derived from a comparison of unattenuated stellar spectra with the
same instrument a few seconds before. Absolute concentrations of
atmospherc species are insulated from instrumental drifts using this
full-spectrum method and ensures long-term stability of the ozone
distribution.

For more information see:
GOMOS Home Page:
http://auc.dfd.dlr.de/info/AUC/GOMOS/

GOMOS Home Page at Finnish Meteorological Instituteinish:
http://sumppu.fmi.fi/~kyrola/gomos.html

For more information on ENVISAT, see:
http://envisat.esa.int/