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
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,
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.
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 .
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 Earth's 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.
Several organizations in the Netherlands are cooperating to develop user requirements and instrument concepts in the line of SCIAMACHY and OMI but with an increased focus on measuring tropospheric constituents from space. The concepts use passive spectroscopy in dedicated wavelength sections in the range of 300 to 2400 nm and wide angle, non-scanning, swath viewing.
To be able to penetrate into the troposphere small ground pixels are used to obtain a fair fraction of cloud-free pixels and to allow precise detection of the sources of polluting gases.
The trace gas products aimed for are O3, NO2, HCHO, H2O, SO2, Aerosol (optical depth, type and absorption index), CO and CH4, covering science issues on air quality and climate.
The main challenge in the instrument design is to obtain a good signal-to-noise for cloud free pixels and for low ground albedo and light levels. Also the retrieval of separated tropospheric and stratospheric column amounts from a nadir looking instrument is challenging.
The paper discusses the user requirements and compares alternative measurement strategies. It explains the selection of passive UV-Visible-NIR spectroscopy and comes with an instrument concept which provides the current best realisation of the user requirements.
We report on the use of laser based cavity ring down spectroscopy in the near UV. It is this part of the spectrum that is particulary well-suited for trace gas detection, as many molecules have strong, well characterized absorption bands in this region. We show that the detection limit for e.g. NH3 is in the order of 10 ppb, for OH below 1 ppb and for Hg at the ppt level. We propose a Fourier transform based cavity ring down spectrometer, in which the advantages of cavity ring down detection are combined with the multiplex advantage of a Fourier transform spectrometer. A theoretical description of this spectrometer, as well as a proposal for the construction of a prototype are worked out.