GOMOS
GOMOS (Global Ozone Monitoring by Occultation of Stars) is a stellar occultation instrument onboard the European Space Agency's Envisat satellite. The wavelength region is ultraviolet-visible, 250-675 nm, and there are also two infrared channels at 756-773 nm and at 926-952 nm. The species covered by GOMOS are O3, NO2, NO3, H2O, O2. In addition, aerosols and temperature are retrieved. Measurements cover altitude region 5-150 km. Atmospherically valid data are obtained in 15-100 km. GOMOS makes several hundred occultations per day and it can measure in both day and night conditions. The self-calibration means that GOMOS measurements can be used to create long time series and data from any new similar instrument can be joined with the GOMOS data without calibration questions. The limb viewing geometry, the point source nature of stars and short enough measurement integration time provide good vertical resolution. The vertical sampling distance is 0.5-1.6 km.
The GOMOS instrument has a large scanning mirror controlled by a star tracker. Light is forwarded through a slit to the two holographic gratings and to two fast photometers. During nighttime measurements the slit is not needed but during daytime measurements the slit restricts the intrusion of scattered solar light into the instrument. The spectrally resolved light is recorded by CCD detectors. Three spatial bands are read from the CCDs: the stellar band and the upper and lower limb bands. In dark limb occultations only the stellar band is used to calculate the transmission function. In bright limb occultations the upper and lower bands are used to estimate the magnitude of the scattered solar light in the stellar band. The two photometers work at blue and red wavelengths at a frequency of 1kHz. Data are used to make the scintillation correction for the spectrometer data. From the photometer data it is also possible to retrieve high resolution (resolution of 200 m) temperature profiles in the range of 15-40 km.
GOMOS is operated by ESA and the Level 1 and near real time data processing takes place at ESA facilities in Esrin and Kiruna. Level 2 off-line data processing takes place at in Sodankylä at FMI’s Arctic Research Centre (ESA’s Fin-CoPac facility).
GOMOS data levels are L0, L1b, and L2. L0 is raw data, L1 calibrated
radiances and transmissions, and L2 profiles. The geophysical products:
L1b: GOM_TRA: Transmissions, photometer radiances
L1b; GOM_LIM: Limb radiances
L2: GOM_EXT: Refraction corrected transmissions
L2: GOM_NL: Local profiles and tangential column profiles
GOMOS facts
Mass = 160 kg
Power = 220 W
Data = 226 kbit/s
Operated since 1.3. 2002
Presentations: Gomos1108.ppt
See also: ESA Advanced atmospheric training course
Overviews:
Kyrölä, E., et al., GOMOS on Envisat: An overview, Adv. Space Res. Volume 33, Issue 7, p. 1020-1028, 2004.
Bertaux, J.L, et al., First results on GOMOS/Envisat. Adv. Space Res., Volume 33, pp. 1029-1035. 2004
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