Spectrometers
GOMOS
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/"