The Copernicus missions Sentinel-4 (S4) and Sentinel-5 (S5) will carry out atmospheric composition observations on an operational long-term basis to serve the needs of the Copernicus Atmosphere Monitoring Service (CAMS) and the Copernicus Climate Change Service (C3S). Building on the heritage from instruments such as GOME, SCIAMACHY, GOME-2, OMI and S5P, S4 is an imaging spectrometer instruments covering wide spectral bands in the ultraviolet and visible wavelength range (305-500nm) and near infrared wavelength range (750-775 nm). S4 will observe key air quality parameters with a pronounced temporal variability by measuring NO2, O3, SO2, HCHO, CHOCHO, and aerosols over Europe with an hourly revisit time. A series of two S4 instruments will be embarked on the geostationary Meteosat Third Generation-Sounder (MTG-S) satellites. S4 establishes the European component of a constellation of geostationary instruments with a strong air quality focus, together with the NASA mission TEMPO (to be launched end 2022) [9] and the Korean mission GEMS (launched 19 February 2020) [8]. This paper addresses the result of the final and crucial phase for the end to end performance of the PFM instrument: the extensive on-ground Characterization and Calibration of the instrument that is happening during the summer/fall 2022. The paper presents an overview of the calibration campaign objectives, the main performance verification and calibration measurements and preliminary performances of the PFM as-built instrument.
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 selection of in-flight radiometric and CCD detector calibration and performance monitoring results since the launch in July 2004. From these examples it will be shown that OMI is performing very well after more than four years in orbit. It is shown how the OMI irradiance measurement data have been used to derive a high resolution solar reference spectrum with good radiometric calibration, good wavelength calibration and high spectral sampling. The surface reflectance climatology derived from three years of in-orbit OMI measurement data is presented and discussed. The OMI mission may possibly be extended in 2009 for another two or four years, depending on the performance of the instrument. By 2013-2014 OMI on EOS-Aura and SCIAMACHY on ENVISAT will have reached more that twice their anticipated lifetimes. In order to guarantee continuity of Earth atmosphere tropospheric and climate measurement data new instrumentation shall be available around that time. A successor of OMI and SCIAMACHY, named TROPOspheric Monitoring Instrument (TROPOMI), scheduled for launch by the end of 2013, is discussed in this paper.
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.
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 Tropospheric Monitoring Instrument (TROPOMI) is currently planned for launch on ESA's Sentinel 5 precursor
satellite in the time frame of 2014. TROPOMI is an ultraviolet-to-SWIR wavelengths imaging spectrograph that uses
two-dimensional detectors to register both the spectrum and the swath perpendicular to the flight direction. The swath is
about 110 degrees wide to allow daily global coverage from the polar orbit of the Sentinel 5 precursor satellite. The
instrument follows the heritage of SCIAMACHY (ENVISAT, launch 2002) and OMI (AURA, launch 2004), but it has
been improved in several ways: the ground resolution is down to 7 x 7 km2, the instrument is fit for low albedo scenes
and the wavelength bands are optimized using the SCIAMACHY and OMI heritages to have the best trace gas products.
The first two improvements basically mean that the instrument aperture is much larger for TROPOMI and, related to
this, the reading of the detectors much faster. The selected wavelength bands for TROPOMI are UV1 (270-310 nm),
UV2 (310 - 370 nm), VIS (370 - 500 nm), NIR (675 - 775 nm) and SWIR (2305 - 2385 nm). The first three bands are
very similar to the OMI bands, the NIR has been added to improve on clouds and air mass corrections and the SWIR
allows measuring CH4 and CO. The paper discusses the development status on several topics, such as detector selection
and polarization scrambler performance simulations using the TIDE grid based level 2 scene simulator.
The TROPOMI instrument concept is part of the TRAQ mission proposal to ESA in response to the Call for Ideas in
2005. TRAQ (TRopospheric composition and Air Quality) has been accepted for a further pre-phase A study for the
next Earth Explorer core Mission. A very similar instrument has been proposed for the CAMEO platform to the US
National Research Council decadal study, which has also been accepted for further study.
TROPOMI is a nadir-viewing grating-based imaging spectrometer using the Dutch OMI and SCIAMACHY heritage. It
includes an UV-VIS-NIR module that consists of three UV-VIS channels continuously covering the 270-490 nm range
to determine O3, NO2, HCHO, SO2, aerosols and a NIR-channel covering 710-775 nm for cloud detection and
information on the aerosol height distribution using the oxygen A band. TROPOMI also includes a SWIR module
covering 2305-2385 nm that mainly focuses on determination of CO and CH4 total columns. All species are measured
with sensitivity down to the Earth's surface, thus addressing issues of anthropogenic emissions and their impact on air
quality and climate. In the TRAQ mission, unique diurnal time sampling with up to 5 daytime observations over midlatitude
regions (Europe, North-America, China) is foreseen by using a non-sun-synchronous, medium-inclination
drifting orbit and a 2600 km wide observational swath.
Several more general aspects related to the TROPOMI instrument are discussed in a separate paper in this conference.
This paper focuses on the development of the SWIR module. A breadboard model (BBM) has been designed and
constructed which is as much as possible functionally flight representative. Critical technologies to be demonstrated
with the BBM are the SWIR HgCdTe-based 2D focal plane array, the on-board SWIR calibration LED, and in
particular, the SRON/TNO developed silicon-based immersed grating that allows a hugely reduced instrument volume.
In the presentation the results of a performance analysis of the TROPOMI-SWIR channel will be discussed, as well as
results of the detector characterization program on a representative off-the-shelf FPA, and details of the
photolithographic production of the immersed grating.
TROPOMI is a nadir-viewing grating-based imaging spectrograph in the line of OMI and SCIAMACHY. TROPOMI is
part of the ESA Candidate Core Explorer Mission proposal TRAQ and also of the CAMEO satellite proposed for the US
NRC decadal study. A TROPOMI-like instrument is part of the ESA/EU Sentinel 4&5 pre-phase A studies.
TROPOMI covers the OMI wavelengths of 270-490 nm to measure O3, NO2, HCHO, SO2 and aerosols and adds a NIR
channel and a SWIR module. The NIR-channel (710-775 nm) is used for improved cloud detection and aerosol height
distribution. The SWIR module (2305 - 2385 nm) measures CO and CH4 and forms a separate module because of its
thermal requirements.
TROPOMI is a non-scanning instrument with an OMI-like telescope but optimized to have smaller ground pixels (10 x
10 km2) and sufficient signal-to-noise for dark scenes (albedo 2 %). TROPOMI has the same wide swath as OMI (2600
km). In TRAQ's mid-inclination orbit, this allows up to 5 daytime observations over mid-latitude regions (Europe,
North-America, China).
The paper gives a description of the TROPOMI instrument and focuses on several important aspects of the design, for
example the sun calibration and detector selection status.
KEYWORDS: Short wave infrared radiation, Aerosols, Calibration, Ozone, Diffusers, Carbon monoxide, Near infrared, Sensors, Spectroscopy, Signal to noise ratio
TROPOMI (Tropospheric Ozone-Monitoring Instrument) is a five-channel UV-VIS-NIR-SWIR non-scanning nadir
viewing imaging spectrometer that combines a wide swath (114°) with high spatial resolution (10 × 10 km2 ). The
instrument heritage consists of GOME on ERS-2, SCIAMACHY on Envisat and, especially, OMI on EOS-Aura.
TROPOMI has even smaller ground pixels than OMI-Aura but still exceeds OMI's signal-to-noise performance. These
improvements optimize the possibility to retrieve tropospheric trace gases. In addition, the SWIR capabilities of
TROPOMI are far better than SCIAMACHY's both in terms of spatial resolution and signal to noise performance.
TROPOMI is part of the TRAQ payload, a mission proposed in response to ESA's EOEP call. The TRAQ mission will
fly in a non-sun synchronous drifting orbit at about 720 km altitude providing nearly global coverage. TROPOMI
measures in the UV-visible wavelength region (270-490 nm), in a near-infrared channel (NIR) in the 710-775 nm range
and has a shortwave infrared channel (SWIR) near 2.3 μm. The wide swath angle, in combination with the drifting orbit,
allows measuring a location up to 5 times a day at 1.5-hour intervals. The spectral resolution is about 0.45 nm for UVVIS-
NIR and 0.25 nm for SWIR. Radiometric calibration will be maintained via solar irradiance measurements using
various diffusers. The instrument will carry on-board calibration sources like LEDs and a white light source. Innovative
aspects include the use of improved detectors in order to improve the radiation hardness and the spatial sampling
capabilities. Column densities of trace gases (NO2, O3, SO2 and HCHO) will be derived using primarily the Differential
Optical Absorption Spectroscopy (DOAS) method. The NIR channel serves to obtain information on clouds and the
aerosol height distribution that is needed for tropospheric retrievals. A trade-off study will be conducted whether the
SWIR channel, included to determine column densities of CO and CH4, will be incorporated in TROPOMI or in the
Fourier Transform Spectrometer SIFTI on TRAQ.
The TROPI instrument is similar to the complete TROPOMI instrument (UV-VIS-NIR-SWIR) and is proposed for the
CAMEO initiative, as described for the U.S. NRC Decadal Study on Earth Science and Applications from Space.
CAMEO also uses a non-synchronous drifting orbit, but at a higher altitude (around 1500 km). The TROPI instrument
design is a modification of the TROPOMI design to achieve identical coverage and ground pixel sizes from a higher
altitude. In this paper capabilities of TROPOMI and TROPI are discussed with emphasis on the UV-VIS-NIR channels
as the TROPOMI SWIR channel is described in a separate contribution [5].
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.
The OMI instrument that flies on the EOS Aura mission was launched in July 2004. OMI is a UV-VIS imaging
spectrometer that measures in the 270 - 500 nm wavelength range. OMI provides daily global coverage with high
spatial resolution. Every orbit of 100 minutes OMI generates about 0.5 GB of Level 0 data and 1.2 GB of Level 1 data.
About half of the Level 1 data consists of in-flight calibration measurements. These data rates make it necessary to
automate the process of in-flight calibration. For that purpose two facilities have been developed at KNMI in the
Netherlands: the OMI Dutch Processing System (ODPS) and the Trend Monitoring and In-flight Calibration Facility
(TMCF). A description of these systems is provided with emphasis on the use for radiometric, spectral and detector
calibration and characterization.
With the advance of detector technology and the need for higher spatial resolution, data rates will become even higher
for future missions. To make effective use of automated systems like the TMCF, it is of paramount importance to
integrate the instrument operations concept, the information contained in the Level 1 (meta-)data products and the inflight
calibration software and system databases. In this way a robust but also flexible end-to-end system can be
developed that serves the needs of the calibration staff, the scientific data users and the processing staff. The way this
has been implemented for OMI may serve as an example of a cost-effective and user friendly solution for future
missions. The basic system requirements for in-flight calibration are discussed and examples are given how these
requirements have been implemented for OMI. Special attention is paid to the aspect of supporting the Level 0 - 1 processing with timely and accurate calibration constants.
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.
For the calibration of OMI a slit function measurement stimulus has been developed. The slit function is the monochromatic image of the entrance slit of the spectrometer on the detector. Accurate knowledge of this slit function for all wavelengths and field angles is very important both for the spectral calibration and for the DOAS retrieval algorithm. Determination of this function with a spectral line source is inaccurate, because of the detector resolution and incomplete, because of the limited number of discrete spectral lines, that are available. For accurate and complete measurement of the slit function an echelle monochromator has been developed, that offers a number of spectral lines, that can be scanned with a small wavelength step over the entire spectral range of OMI. The spectral bandwidth of these lines is about 0.1 x the spectral resolution of OMI and the wavelength step during scanning is even smaller. The wavelength scanning is performed by accurate rotation of the echelle. In this paper the scientific background of the slit function measurement, the stimulus and first OMI slit function calibration measurements are described.
This document describes the calibration and performance of the SCIAMACHY instrument, to be launched on ESA-ENVISAT in 2000, after the main on-ground calibration and performance verification phases. A number of calibration and performance parameters will be discussed and results will be shown.
The atmospheric spectrometer SCIAMACHY to be launched on board ESA's Envisat satellite in 2000 will measure UV, visible and IR spectra from nadir, limb and occultation with spectral resolution between 0.2 and 1.4 nm. SCHIAMACHY's channel 8 covering the wavelength range 2265-2380 nm will allow the global determination of concentrations of methane, carbon monoxide and nitrous oxide. Sensitivity studies using the most recent values for the instrument parameters show that the minimum values for the accuracies for total vertical columns are of order 5 Dobson units (DU) for carbon monoxide, 3 DU for methane, and 6 DU for nitrous oxide, for a 1 s SCIAMACHY nadir observation. The detection of the IR spectra features novel InGaAs detectors, specially developed for the SCIAMACHY project. While providing the required sensitivity in this wavelength domain, these detectors are limited by noise levels that vary strongly from pixel to pixel. This poses special challenges to the retrieval of molecule concentrations from the measured detector signals. Ways to overcome this problem are discussed.
In-flight monitoring of the optical response of GOME revealed a number of instrumental features that drift or change with time. Some of these observed features are related to outgassing of the instrument in space. In particular outgassing of optical coatings, e.g. the dichroic mirror in GOME, can result in a change of the optical characteristics and thereby changing the response of the GOME instrument. Another feature is related to the etalon effect which results in a spectral modulation of the GOME spectra. This modulation varies in time due to a varying contamination layer, most likely ice, on the cooled detectors. Through the GOBELIN project the GOME breadboard model has been made available to us by ESA. The GOME breadboard model has been fully upgraded to represent the GOME flight mode and therefore offers a unique opportunity to study the above phenomenon under controlled laboratory conditions. First results are presented addressing in particular the effect of outgassing on instrument optical response, including the polarization response, and the etalon effect.
The scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY), to be launched on the European polar platform ENVISAT at the end of 1999, will measure sun- and moonlight which is either transmitted, reflected or scattered by the Earth atmosphere. The double spectrometer is designed for the ultraviolet, visible and near IR wavelength region, covering that range with a resolution of 0.24 nm to 1.5 nm. It was conceived to improve our knowledge and understanding of a variety of issues of importance to chemistry and physics of the Earth atmosphere. Scientific objectives are to study ozone hole chemistry, troposphere- stratosphere exchange and tropospheric pollution. This will be achieved by a combined limb, nadir and occultation observation strategy. The SCIAMACHY instrument and operational concept is finalized approaching now the on- ground calibration phase. The planned wavelength and radiometric calibration measurements, including a detailed characterization of the instrument polarization behavior, will be fundamental for the required high data accuracy. Additionally the in-flight calibration and monitoring concept will allow a proper correction of instrument ageing effects. This study describes pre-flight and in-flight calibration the approaches to be employed to maintain a high radiometric and spectral accuracy of the SCIAMACHY measurements throughout its life are reported.
In this paper the sun and moon spectra observed by GOME are examined in detail. For the moon observations this paper presents the first analysis of spectra and all factors that contribute to the measured signal are analyzed in detail. It is shown that the moon spectra, like the sun spectra, can be used for monitoring of the instrument performance. The geometrical moon albedo over the complete 240 - 800 nm wavelength range as measured by GOME is presented and discussed. The polarization properties of sunlight and moonlight measured by GOME are investigated.
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