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The hyperspectral instrument ”DLR Earth Sensing Imaging Spectrometer” (DESIS) is a VNIR sensor on-board of the International Space Station (ISS) and operational since October 2019. DESIS acquires images of Earth on user request with a swath of about 30 km width and 235 bands with a Full Width at Half Maximum (FWHM) of 3.5 nm in the spectral range between 400 to 1000 nm.In this article we will present the basis of the atmospheric correction by PACO software, implemented inside the DESIS Ground Segment as L2A processor. The resulting L2A products will be validated against independent in-situ measurements.The aerosol optical thickness and water vapor will be compared with the Aerosol Robotic Network (AERONET) measurements and the surface reflectance will be validated with the Radiometric Calibration Network (RadCalNet) data.

Spectral unmixing represents both an application per se and a pre-processing step for several applications involving data acquired by imaging spectrometers. However, there is still a lack of publicly available reference data sets suitable for the validation and comparison of different spectral unmixing methods. In this paper, we introduce the DLR HyperSpectral Unmixing (DLR HySU) benchmark dataset, acquired over German Aerospace Center (DLR) premises in Oberpfaffenhofen. The dataset includes airborne hyperspectral and RGB imagery of targets of different materials and sizes, complemented by simultaneous ground-based reflectance measurements. The DLR HySU benchmark allows a separate assessment of all spectral unmixing main steps: dimensionality estimation, endmember extraction (with and without pure pixel assumption), and abundance estimation. Results obtained with traditional algorithms for each of these steps are reported. To the best of our knowledge, this is the first time that real imaging spectrometer data with accurately measured targets are made available for hyperspectral unmixing experiments. The DLR HySU benchmark dataset is openly available online and the community is welcome to use it for spectral unmixing and other applications.

The atmospheric correction of satellite images based on radiative transfer calculations is a prerequisite for many remote sensing applications. The software package ATCOR, developed at the German Aerospace Center (DLR), is a versatile atmospheric correction software, capable of processing data acquired by many different optical satellite sensors. Based on this well established algorithm, a new Python-based atmospheric correction software has been developed to generate L2A products of Sentinel-2, Landsat-8, and of new space-based hyperspectral sensors such as DESIS (DLR Earth Sensing Imaging Spectrometer) and EnMAP (Environmental Mapping and Analysis Program). This paper outlines the underlying algorithms of PACO, and presents the validation results by comparing L2A products generated from Sentinel-2 L1C images with in situ (AERONET and RadCalNet) data within VNIR-SWIR spectral wavelengths range.

Imaging spectrometry from aerial or spaceborne platforms, also known as hyperspectral remote sensing, provides dense sampled and fine structured spectral information for each image pixel, 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 ground sample distance is 30 m with 1024 pixels across track. In~this article, a~detailed review is given on the applicability of DESIS data based on the specifics of the instrument, the characteristics of the ISS orbit, and the methods applied to generate products. The~various DESIS data products available for users are described with the focus on specific processing steps. The results of the data quality and product validation studies show that top-of-atmosphere radiance, geometrically corrected, and bottom-of-atmosphere reflectance products meet the mission requirements. The limitations of the DESIS data products are also subject to a critical~examination.

Since end of August, 2018, the imaging spectrometer “DLR Earth Sensing Imaging Spectrometer” (DESIS) is integrated into the “Multi-User System for Earth Sensing” (MUSES) installed on the International Space Station ISS, which also marks the start of the commissioning phase. After commissioning phase, the data will be available for scientific purposes under certain restrictions. This presentation informs about available data products, the requirements to access these products and the data access process. L1B (at sensor radiance), L1C (georeferenced after L1B) and L2A (reflectance after L1C) products are generated and delivered to the DESIS science users. Further, different acquisition modes are available: 1) Image Strip Mode is the standard measurement for earth observation and 2) BRDF Mode (Bi-directional Distribution Function) can be used to generate image data from the same area on ground seen at different observation angles (acquisitions up to 3 images at different observations angles e.g. 15° forward, nadir, 15° backward are possible). The talk further informs about the specific latitude dependent orbit requirements. The irregular acquisition possibilities allow acquiring data at different sun-target-sensor geometries and open up new possibilities for data evaluation. Finally, the potential of common data acquisitions of all ISS Earth observing instruments such as NASA’s Lidar instrument GEDI or the thermal ECOSTRESS mission and the emerging initiative to coordinate this, will be presented.

When working with hyperspectral data, it is very important, that the data is properly pre-processed in terms of systematic radiometric and spectral correction, geometric correction as well as atmospheric correction. Airborne and spaceborne sensors show some similarities regarding the processing, but also some differences. In this paper, these similarities and differences are discussed on the example of the HySpex processing chain in the generic processing environment Catena and the EnMAP processor that is currently developed at DLR. The paper presents the different sensors and their properties and gives an overview of the different workflows and the used algorithms.

In 2014, the German Aerospace Center (DLR) and the US company Teledyne Brown Engineering (TBE) decided to collaborate and develop the hyperspectral instrument "DLR Earth Sensing Imaging Spectrometer" (DESIS) for integration into the "Multi-User System for Earth Sensing" (MUSES) installed on the International Space Station (ISS). Four years later, on 29 June 2018, the instrument was launched from Cape Canaveral with a SpaceX Dragon rocket. One month later, the instrument was robot-assisted integrated into MUSES and the commissioning phase started. First light images were available after 48 hours. The commissioning phase includes checkout for functional testing, End-to-End tests, processing parameter tuning, in-flight calibration tests and product validation. The operational phase of the mission has been entered several months later. From this point on, hyperspectral data will be available to the scientific and commercial user community. In this paper a summary of results from the commissioning phase will be presented including aspects of data quality, operational performance and first data evaluation results. The MUSES platform provides accommodations for two large and two small hosted payloads. MUSES is attached at the ELC-4 (EXPRESS Logistics Carriers) starboard of the ISS. It is a space-based, Earth-pointing platform providing position and attitude sensing, data downlink, and other core services common for each payload. DESIS has a mass of ~88 kg and is integrated in one of the large containers. Two gimbals allow a rotation of the whole MUSES platform around two axes resulting in ±25° forward / backward view, 45° backboard (port) view and 5° starboard view. The platform is equipped with a star tracker (sampling rate 10 Hz) and a MIMU (Miniature Inertial Measurement Unit) (sampling rate 50 Hz) providing a 10 Hz attitude measurement after filtering. ISS GPS data provide position and velocity vectors and time tags (sampling rate 1 Hz). The predicted viewing capability of MUSES, when operating at the ISS orbit inclination of 51.6°, will enable the DESIS instrument to scan greater than 90% of the populated Earth with an average cadence of about one week. The DESIS hyperspectral instrument is realized as a pushbroom imaging spectrometer and features 235 bands with 3.5-4.0 nm spectral resolution, covering a range from 400 nm to 1000 nm with 30 m spatial resolution employing a 2-dimensional back illuminated CMOS (Complementary Metal Oxide Semiconductor) detector array. The optical design is based on the Offner-type grating spectrometer widely used in hyperspectral imaging. DESIS is equipped with a Pointing Unit (POI) consisting of a rotating mirror in front of the entrance slit allowing a forward and backward viewing change up to ±15° w.r.t. the nominal (e.g. nadir) view. The POI can be operated in a static mode with 3° angle steps for the viewing direction and in a dynamic mode with up to 1.5° change in viewing direction per seconds. This allows, besides standard Earth data products, acquisition of Bidirectional Reflectance Distribution Function (BRDF) products and continuous observations of the same targets on ground (using forward motion compensation mode). DESIS has been characterized in laboratory and will be re-calibrated after launch employing measurements of internal light sources (bank of white and colored LED lamps) and globally distributed reference sites aiming to assess radiometric, spectrometric and geometric characteristics of the DESIS hyperspectral instrument in orbit. Vicarious validation activities will be performed at regular interval to ensure that a suitable data quality is met. This includes validation over well-known calibration sites, cross-comparisons with other simultaneous acquired data sets and analysis of homogenous areas. The Ground Segment at DLR has developed the operational processing chain to derive different types of DESIS products from tiled data takes of size 1024 x 1024 pixels (~30 x 30 km²). An identical processing chain is licensed to TBE running on a cloud based system (© Amazon Cloud) for commercial product generation. DESIS level 1A products (Earth image scenes, on-board calibration measurements, dark current measurements and experimental products) will be long-term archived together with the corresponding metadata, while level 1B products (systematically and radiometrically corrected data), level 1C products (geometrically corrected data employing global references) and level 2A products (atmospherically compensated data) will be processed on demand before being delivered to the user for further value-add product generation. For scientific purposes only, DLR can share DESIS scientific data with other scientific organizations. TBE distributes data on a commercial basis.

Whether for identification and characterization of materials or for monitoring of the environment, space-based hyperspectral instruments are very useful. Hyperspectral instruments measure several dozens up to hundreds of spectral bands. These data help to reconstruct the spectral properties like reflectance or emission of Earth surface or the absorption of the atmosphere, and to identify constituents on land, water, and in the atmosphere. There are a lot of possible applications, from vegetation and water quality up to greenhouse gas monitoring. But the actual number of hyperspectral space-based missions or hyperspectral space-based data is limited. This will be changed in the next years by different missions. The German Aerospace Center (DLR) Earth Sensing Imaging Spectrometer (DESIS) is one of the new currently existing space-based hyperspectral instruments, launched in 2018 and ready to reduce the gap of space-born hyperspectral data. The instrument is operating onboard the International Space Station, using the Multi-User System for Earth Sensing (MUSES) platform. The instrument has 235 spectral bands in the wavelength range from visible (400 nm) to near-infrared (1000 nm), which results in a 2.5 nm spectral sampling distance and a ground sampling distance of 30 m from 400 km orbit of the International Space Station. In this article, the design of the instrument will be described.