85 research outputs found
Design of an imaging spectrometer for Earth observation using freeform mirrors
Design of an imaging spectrometer for earth observation using freeform mirrors
Thomas Peschel1, Christoph Damm1, Matthias Beier1, Andreas Gebhard1, Stefan Risse1, Ingo Walter2, Ilse Sebastian2, David Krutz2
1 Fraunhofer Institut für Angewandte Optik und Feinwerktechnik, Jena
2 DLR, Institut für Optische Sensorsysteme, Berlin
In 2017 the new hyperspectral DLR Earth Sensing Imaging Spectrometer (DESIS) will be integrated in the Multi-User-System for Earth Sensing (MUSES) platform /1/ installed on the International Space Station (ISS).
The DESIS instrument is developed under the responsibility of the DLR. It will deliver images of the earth with a spatial resolution of 30 m on ground in 235 spectral channels in the wavelength range from 400 nm to 1 µm.
As partner of the development team Fraunhofer IOF is responsible for the optical system of the imaging spectrometer.The optical system is made of two primary components: A compact Three-Mirror-Anastigmat (TMA) telescope images the ground strip under observation onto a slit. The following spectrometer reimages the slit onto the detector and performs the spectral separation using a reflective grating.
The whole optical system is realized using metal-based mirrors the surfaces of which are made by Single-Point-Diamond Turning (SPDT). Since the spectral range is in the visible, a post-processing of the surfaces by Nickel plating is necessary. The final surface shape and roughness are realized by a second SPDT step and subsequent Magneto-Rheological Finishing.
The TMA provides a focal length of 320 mm and an aperture of F/2.8. Its mechanical design relies on the Duolith-technology of IOF as well as optical and mechanical reference structures on the mirrors /2/ manufactured in the same SPDT run. This strategy allows for a significantly simplified adjustment of the optical system /3/.
The spectrometer was designed on the basis of the so-called Offner scheme. Because of the high aperture of the system a freeform mirror had to be introduced in order to provide a good imaging quality over the whole spectral range.
The above optical design requires a grating on a curved surface. Technologies are developed in order to fabricate the grating either by SPDT or, alternatively, by laser lithography.
The mechanical design uses light-weight housing elements which wrap the optical path to suppress stray light. An athermal design is provided by using the same metal for mirrors and housing. To provide high adjustment precision, the housing elements carry reference and mounting features made by SPDT as well. This approach allows for a stiff mechanical set-up of the system, which is compatible with the harsh requirements of a space flight.
References:
1 N. Humphrey, “A View From Above: Imaging from the ISS”, Teledyne DALSA 2014, http://possibility.teledynedalsa.com/a-view-from-above/
2 S. Scheiding, e.a., “Ultra-precisely manufactured mirror assemblies with well-defined reference structures“, Proc. SPIE 7739, 2010.
3 T. Peschel, e.a., “Anamorphotic telescope for earth observation in the mid-infrared range”, ICSO 201
Vicarious Calibratipon of the DESIS Imaging Spectrometer: Status and Plans
The DLR Earth Sensing Spectrometer (DESIS) on board the International Space Station (ISS) has been providing high quality hyperspectral data to the scientific community and commercial users since the start of operations in September 2018. After almost 4 years in orbit, the DESIS instrument continues to operate correctly and to deliver hyperspectral data products for a wide variety of applications. In order to support this successful activity, the calibration team regularly analyzes the instrument data and provides updates using vicarious calibration. We present here the latest results from the DES IS vicarious calibration and our plans for future improvements
CO2 Image: The design of an imaging spectrometer for CO2 point source quantification
CO2Image is a satellite demonstration mission, now in Phase B, to be launched in 2026 by the German Aerospace Center (DLR). The satellite will carry a next generation imaging spectrometer for measuring atmospheric column concentrations of Carbon Dioxide (CO2). The instrument concept reconciles compact design with fine ground resolution (50-100 m) with decent spectral resolution (1.0-1.3 nm) in the shortwave infrared spectral range (2000 nm). Thus, CO2Image will enable quantification of point source CO2 emission rates of less than 1 MtCO2/a. This will complement global monitoring missions such as CO2M, which are less sensitive to point sources due to their coarser ground resolution and hyperspectral imagers, which suffer from spectroscopic interference errors that limit the quantification
The Spaceborne Imaging Spectrometer DESIS: Mission summary and potential for scientific developments
The DLR Earth Sensing Imaging Spectrometer (DESIS) is a spaceborne instrument installed and operated on the International Space Station (ISS). The German Aerospace Center (DLR) has developed the instrument and the full pre-processing chain up to L2A, while the US company Teledyne Brown Engineering (TBE) provided the Multi-User System for Earth Sensing (MUSES) platform and the infrastructure for operations and data tasking.
DESIS is equipped with an on-board calibration unit and a rotating pointing mirror (POI). The POI can change the line of sight in the forward/backward direction (independently of the MUSES orientation), allowing the observation of the same area with different pointing angles within an overflight. About four years after the mission’s kick-off, the DESIS spectrometer was integrated into MUSES in August 2018, marking the start of the commissioning phase. The DESIS on-orbit functional tests were successful, and the DLR-built processing chain installed at DLR for scientific users and at Amazon Web Service for commercial users started to generate operational L1B, L1C and L2A DESIS products.
In October 2019 the operational phase started the distribution of the data to scientific and commercial users. Since then, the instrument performance has been constantly evaluated. In a continuous monitoring process, the data quality is controlled and, if necessary, the calibration algorithms and tables are adjusted. This is essential for the later data application by scientists. In particular, the monitoring approaches emphasize the need for high and consistent data quality over long time periods. In autumn 2021, the first DESIS user workshop demonstrated the widespread use of DESIS data for topics like water and terrestrial resource monitoring, biodiversity and forest management.
This presentation will give an overview of the DESIS mission, data quality, data access, and provides examples and perspectives on the scientific exploitation of the mission. The contribution for the CHIME mission is presented exemplarily for the CHIME test sites that are constantly observed by DESIS since 2020. DESIS data acquisition opportunities rely on the non-sun-synchronous ISS orbit, resulting in observation and illumination conditions difficult to reproduce. On the other hand, DESIS time series contain images of different day times, sensor incident angles as well as sun zenith angles and thus, can open up new opportunities for the monitoring of Earth system processes that have a daily variability such as photosynthesis. Finally, DESIS multitemporal data stacks can be an essential data base for algorithm and operational processor developments that shall be able to handle massive data amounts. The DESIS data archive is open for such research and developments and thus, is a valuable imaging spectroscopy data source
The Spaceborne Imaging Spectrometer DESIS: Data Access and Scientific Applications
The DLR Earth Sensing Imaging Spectrometer (DESIS) is a space-based instrument installed and operated on the International Space Station (ISS). This space mission is the achievement of the collaboration between the German Aerospace Center (DLR) and the US company Teledyne Brown Engineering (TBE). DLR has developed the instrument and the software for data processing, while TBE provides the Multi-User System for Earth Sensing (MUSES) platform, where DESIS is installed, and the infrastructure for operation and data tasking
Data Validation of the DLR Earth Sensing Imaging Spectrometer DESIS
Imaging spectrometry provides densely sampled and finely
structured spectral information for each image pixel over
large areas, enabling the characterization of materials on the
Earth's surface by measuring and analyzing quantitative
parameters allowing the user to identify and characterize
Earth surface materials such as minerals in rocks and soils,
vegetation types and stress indicators, and water
constituents. The recently launched DLR Earth Sensing
Imaging Spectrometer (DESIS) installed on the International
Space Station (ISS) closes the long-term gap of sparsely
available spaceborne imaging spectrometry data and will be
part of the upcoming fleet of such new instruments in orbit.
DESIS measures in the spectral range from 400 and 1000
nm with a spectral sampling distance of 2.55 nm and a Full
Width Half Maximum (FWHM) of about 3.5 nm. The
various DESIS data products available for users are
described with the focus on specific processing steps. A
summary of the data quality results are given. The product
validation studies show that top-of-atmosphere radiance,
geometrically corrected, and bottom-of-atmosphere
reflectance products meet the mission requirements
The Evolution of New Catalytic Mechanisms for Xenobiotic Hydrolysis in Bacterial Metalloenzymes
Comparative Study of Transport Processes of Nitrogen, Phosphorus, and Herbicides to Streams in Five Agricultural Basins, USA
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