Data Products, Quality and Validation of the DLR Earth Sensing Imaging Spectrometer (DESIS)

Abstract

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.

PACO: Python-Based Atmospheric Correction

“…The relative difference in surface reflectance between RadCalNet and DESIS is below 5% for wavelengths above 600 nm, while the relative difference increases up to 10% for shorter wavelengths (∼ 400-600 nm). This is consistent with DESIS results reported in [18], and it is explained as an overestimation of the AOT in remote sensing (AOT DESIS ∼0.25) from arid sites with respect to the measured value (AOT RCN = 0.035). However, comparisons with Sentinel-2 data (<30 min.…”

“…In order to minimize the effect of the uncertainty of the scene AOT calculation, and its effect on the accuracy of the surface reflectance, the AOT value measured on the RadCalNet sites at the time of the BOA measurements might be used as input for PACO's atmospheric correction algorithms (for validation purposes). New software possibilities, like AOT input (already explored in [18]), are handy to compare the surface reflectance from different sensors from these types of homogeneous but arid sites, where DDV-based AOT extraction algorithms can not be applied or they are under low retrieved statistics. The results presented in this study are consistent with the same L2A validation study on the commissioning data of DESIS hyperspectral [18] camera system.…”

“…New software possibilities, like AOT input (already explored in [18]), are handy to compare the surface reflectance from different sensors from these types of homogeneous but arid sites, where DDV-based AOT extraction algorithms can not be applied or they are under low retrieved statistics. The results presented in this study are consistent with the same L2A validation study on the commissioning data of DESIS hyperspectral [18] camera system. Similar results were found when comparing DESIS surface reflectance results of scenes over the RadCalNet stations Gobabeb and Railroad Valley Playa [18].…”

“…As its predecessor ATCOR, PACO is developed as a multi-sensor atmospheric correction software package, easily portable and embeddable into any processing chain. Therefore, PACO is implemented as the current atmospheric correction of the L2A processor in the Ground Segment of DESIS [18] and EnMAP [19] hyperspectral sensors.…”

“…For this purpose, we use as an example the data acquired by DESIS and Sentinel-2 over one of the RadCalNet sites (Railroad Valley Playa) on 28 June 2019. The validation of DESIS surface reflectance for different RadCalNet sites is fully reported in [18]. Hence, we compare the results versus the corresponding Sentinel-2 scene.…”