Gijsbertus van den Oord

Ozone monitoring instrument (OMI)

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 NASAs 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.

The on-ground calibration of the ozone monitoring instrument from a scientific point of view

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.

Ozone monitoring instrument flight-model on-ground and inflight calibration

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.

EOS-aura Ozone Monitoring Instrument in-flight performance and calibration

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 instruments 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.

Sensitivity analysis of a new SWIR-channel measuring tropospheric CH4 and CO from space

In preparation for future atmospheric space missions a consortium of Dutch organizations is performing design studies on a nadir viewing grating-based imaging spectrometer using OMI and SCIAMACHY heritage. The spectrometer measures selected species (O3, NO2, HCHO, H2O, SO2, aerosols (optical depth, type and absorption index), CO and CH4) with sensitivity down to the Earths surface, thus addressing science issues on air quality and climate. It includes 3 UV-VIS channels continuously covering the 270-490 nm range, a NIR-channel covering the 710-775 nm range, and a SWIR-channel covering the 2305-2385 nm range. This instrument concept is, named TROPOMI, part of the TRAQ-mission proposal to ESA in response to the Call for Earth Explorer Ideas 2005, and, named TROPI, part of the CAMEO-proposal prepared for the US NRC decadal study-call on Earth science and applications from space. The SWIR-channel is optional in the TROPOMI/TRAQ instrument and included as baseline in the TROPI/CAMEO instrument. This paper focuses on derivation of the instrument requirements of the SWIR-channel by presenting the results of retrieval studies. Synthetic detector spectra are generated by the combination of a forward model and an instrument simulator that includes the properties of state-of-the-art detector technology. The synthetic spectra are input to the CO and CH4 IMLM retrieval algorithm originally developed for SCIAMACHY. The required accuracy of the Level-2 SWIR data products defines the main instrument parameters like spectral resolution and sampling, telescope aperture, detector temperature, and optical bench temperature. The impact of selected calibration and retrieval errors on the Level-2 products has been characterized. The current status of the SWIR-channel optical design with its demanding requirements on ground-pixel size, spectral resolution, and signal-to-noise ratio will be presented.

Toward the use of the Ozone Monitoring Instrument (OMI)

The Ozone Monitoring Instrument (OMI) is a UV/VISible spectrograph (270 - 500 nm). It employs two-dimensional arrays of CCD detectors for simultaneous registration of numerous spectra from ground pixels in the swath perpendicular to the flight direction. As a result, OMI provides (almost) daily global coverage in combination with small ground pixel sizes (nominally 13 X 24 km2 at nadir, minimum 13 X 12 km2 at nadir). The small ground pixels allow retrieval of tropospheric constituents. The OMI Flight Model is currently being integrated and will be launched on the Aura satellite in2003 as part of NASAs Earth Observing System. This paper discusses relationships between and the details of the on-ground calibration approach of OMI, the data processing of level 0 data (raw data) to level 1b data (geophysical data) and the foreseen activities for in-flight calibration.

Atmospheric data access for the geospatial user community

Historically the atmospheric and meteorological communities are separate worlds with their own data formats and tools for data handling making sharing of data difficult and cumbersome. On the other hand, these information sources are becoming increasingly of interest outside these communities because of the continuously improving spatial and temporal resolution of e.g. model and satellite data and the interest in historical datasets. New user communities that use geographically based datasets in a cross-domain manner are emerging. This development is supported by the progress made in Geographical Information System (GIS) software. The current GIS software is not yet ready for the wealth of atmospheric data, although the faint outlines of new generation software are already visible: support of HDF, NetCDF and an increasing understanding of temporal issues are only a few of the hints.

OMI flight model performance test results

Recently the performance verification phase of the Ozone Monitoring Instrument (OMI) was successfully completed and the calibration has started. The OMI is a next generation imaging spectrograph suitable for trace gas retrieval using the UV-Visible wavelength range. The instrument combines a wide field-of-view (114 degrees) with high spatial resolution enabling trace gas retrieval in the troposphere and providing continuous monitoring. The paper summarises the important performance aspects for the OMI such as the spectral, radiometric, polarisation, viewing and stray light properties of the instrument. It focuses on some aspects that we consider of particular importance such as polarisation scrambling and diffuser features. These features can potentially mix with trace gas absorption features and thereby form error sources. Historically an important issue is the spectral stray light at the steep gradient in the Earth shine radiance around 300 nm. In this paper we show that OMI has a very good stray light performance at these wavelengths. The OMI will be launched on NASAs EOS-AURA satellite early 2004.

Ozone monitoring with the OMI instrument

The Ozone Monitoring Instrument (OMI) is a UV/VIS spectrograph (270-500 nm) in the line of GOME3 and SCIAMACHY4. It employs two-dimensional CCD detectors for simultaneous registration of numerous spectra from ground pixels in the swath perpendicular to the flight direction. The OMI field of view is 13 ? 2600 km2 per two seconds nominal exposure time providing (almost) daily global coverage in combination with small ground pixel sizes (nominally 13 x 24 km2, minimum 13 x 12 km2). The small ground pixels will allow retrieval of tropospheric constituents. The OMI contains various new and innovative design elements such as a polarisation scrambler and programmable CCD read-out modes. This paper discusses the overall design of the OMI together with the instrumental capabilities.

In-flight calibration of the ozone monitoring instrument

This paper discusses various aspects of the on-ground and in-flight calibration of the OMI instrument.