The OMI instrument is an ultraviolet-visible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction with a 115° wide swath, which enables global daily ground coverage with high spatial resolution. This paper presents a number of examples of scientific results from the first two years in orbit, as well as a selection of in-flight radiometric, spectral and CCD detector performance and calibration results. The scientific results will show the OMI capability of measuring atmospheric phenomena with high spatial and temporal resolution. It will be shown that the OMI radiometric and spectral calibration are accurately understood. Radiation damage effects on the CCD detectors will be discussed in detail and it will be shown that it is possible to correct for the consequences to a large extent in order to minimise the impact on the scientific level-1 and level-2 data products.
The Ozone Monitoring Instrument (OMI) is an ultravioletvisible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a 114 degrees wide swath combined with an unprecedented small ground pixel (nominally 13 x 24 km2), which in turn enables global daily ground coverage with high spatial resolution. The OMI instrument is part of NASA’s EOSAURA satellite, which will be launched in the second half of 2004. The on-ground calibration of the instrument was performed in 2002. This paper presents and discusses results for a number of selected topics from the on-ground calibration: the radiometric calibration, the spectral calibration and spectral slit function calibration. A new method for accurately calibrating spectral slit functions, based on an echelle grating optical stimulus, is discussed. The in-flight calibration and trend monitoring approach and facilities are discussed.
In the December 2006 severe forest fires raged in south east Australia. We used the OMI instrument to study the
transport of the aerosols emitted by these fires. On 14 December a freshly released plume was lofted by a passing
weather system to high altitudes in the atmosphere and was transported around the planet in 10 days. We used the OMI
cloud product to retrieve the altitude of the aerosol plume, 8-10km. We compare our findings to CALIPSO observations
of the same plume, which yields 11-14km. We performed radiative transfer calculations to investigate the sensitivity of
the OMI cloud algorithm to the plume altitude.
In-flight performance and calibration results of the Ozone Monitoring Instrument OMI, successfully launched on 15 July
2004 on the EOS-AURA satellite, are presented and discussed. The radiometric calibration in comparison to the high-resolution
solar irradiance spectrum from the literature convolved with the measured spectral slit function is presented. A
correction algorithm for spectral shifts originating from inhomogeneous ground scenes (e.g. clouds) is discussed.
Radiometric features originating from the on-board reflection diffusers are discussed, as well as the accuracy of the
calibration of the instrument's viewing properties. It is shown that the in-flight performance of both CCD detectors shows
evidence of particle hits by trapped high-energetic protons, which results in increased dark currents and increase in the
Random Telegraph Signal (RTS) behaviour.
In July 2004 Nasa's AURA satellite was launched carrying the Dutch-Finnish Ozone Monitoring Instrument and since then it is producing high quality trace gas measurements of a.o. ozone and NO2. The OMI is a non-scanning nadir viewing spectrograph with a wavelength coverage of 270 to 500 nm and a spectral resolution of 0.4 to 0.7 nm. It has a large spatial field-of-view of 114 degrees perpendicular to the flight direction and uses the resulting swath of 2600 km to measure the complete globe in a single day with ground pixels of nominally 13 km × 24 km. After a brief instrument overview, this paper discusses a number of in-flight performance issues, such as the wavelength calibration and the stray light correction.
OMI's wavelength calibration is based on fitting the sun's Fraunhofer structures, both on sun irradiance spectra and Earth radiance spectra. For the latter the cloud structures impact the wavelength results via inhomogeneous illumination of the spectrometer slit. This is explained together with the basics of a correction algorithm.
OMI has a carousel with three on-board sun diffusers. Measurements with the quartz volume diffuser will be used to show remaining diffuser features in the data. The measured irradiances are compared to the results obtained by convolving the high-resolution solar reference spectrum with the accurately calibrated spectral slit functions.
In the in-flight measurement data in the wavelength range below 300 nm spatial stray light features are observed, resulting from clouds observed at wavelengths above 300 nm. These features are shown together with an explanation of the means to analyze the in-orbit stray light performance.
The Ozone Monitoring Instrument (OMI) was launched on 15 July 2004 on NASA's EOS AURA satellite. The OMI instrument is an ultraviolet-visible imaging spectrograph that uses two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction with a 115 degrees wide swath, which enables global daily ground coverage with high spatial resolution. This paper presents a number of in-flight radiometric and spectral instrument performance and calibration results.
Launched on 15 July 2004 aboard the EOS AURA satellite, the Ozone Monitoring Instrument (OMI) is intended as the successor to the Total Ozone Mapping Spectrometer (TOMS). OMI's improved horizontal spatial resolution and extended wavelength range (264-504nm) will provide total column ozone, surface reflectance, aerosol index, and ultraviolet (UV) surface flux as well as ozone profiles and tropospheric column ozone, trace gases, and cloud fraction and height. We present results from a variety of calibration techniques that have been developed over the years to assess the calibration accuracy of backscatter UV sensors. Among these are comparisons of OMI solar measurements with external solar reference spectra and radiances measured over Antarctica and Greenland. OMI UV measured irradiances show wavelength dependencies and spectral features on order of 5% when compared to external solar spectra while all channels exhibit a nearly wavelength independent 1% seasonal goniometric error. No instrument throughput degradation has been identified beyond this level and has been confirmed through ice radiance comparisons. A 3% OMI radiance cross-track swath dependence is seen when comparing radiances over ice fields to radiative transfer results. Reflectances derived at low latitudes show the same cross-track swath dependence with an additional 5% offset.
The Ozone Monitoring Instrument is an UV-Visible imaging spectrograph using two-dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a wide swath (114 degrees) combined with a small ground pixel (nominally 13 x 24 km2). The instrument is planned for launch on NASA’s EOS-AURA satellite in January 2004. The on-ground calibration measurement campaign of the instrument was performed May-October 2002, data is still being analyzed to produce the calibration key data set. The paper highlights selected topics from the calibration campaign, the radiometric calibration, spectral calibration including a new method to accurately calibrate the spectral slitfunction and results from the zenith sky measurements and gas cell measurements that were performed with the instrument.
The Ozone Monitoring Instrument (OMI) is an UV-Visible imaging spectrograph using two dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a wide swath (114 degrees) combined with a small ground pixel (nominally 13 x 24 km). The instrument is planned for launch on NASA's EOS-AURA satellite in June 2003. Currently the OMI Flight Model is being build. This shortly follows the Instrument Development Model (DM) which was built to, next to engineering purposes, verify the instrument performance. The paper presents measured results from this DM for optical parameters such as distortion, optical efficiency, stray light and polarization sensitivity. Distortion in the spatial direction is shown to be on sub-pixel level and the stray light levels are very low and almost free from ghost peaks. The polarization sensitivity is presently demonstrated to be below 10-3 but we aim to lower the detection limit by an order of magnitude to make sure that spectral residuals do not mix with trace gas absorption spectra. Critical detector parameters are presented such as the very high UV quantum efficiency (60 % at 270 nm), dark current behavior and the sensitivity to radiation.