ENMAP data product standards

Abstract

EnMAP (Environmental Mapping and Analysis Program; www.enmap.org) is a German, Earth observing, imaging spectroscopy, spaceborne mission planned for launch in 2017. In order to ensure data product standards during the complete mission lifetime operational workflows are established. These cover all activities for pre-and in-flight spectral, radiometric, and geometric characterization and calibration as well as for the independent product validation of the quality controlled images. Spectral and radiometric calibration of the hyperspectral imager covering the wavelength range from 420 nm to 2450 nm is especially based on satellite onboard sources and a full aperture diffuser. Geometric calibration and validation is based on acquisitions of selected reference sites, but also compared to further ground-truth, air-, and spaceborne missions. Standardized products including geometric and/or atmospheric corrections are generated by a fully-automatic hyperspectral image processing chain.

Estimating the Influence of Spectral and Radiometric Calibration Uncertainties on EnMAP Data Products—Examples for Ground Reflectance Retrieval and Vegetation Indices

“…For EnMAP, the requirement for the absolute radiometric calibration accuracy is better than 5%, having a radiometric stability of ±2.5% (standard deviation) between two consecutive calibrations. The targeted spectral calibration accuracy is 0.5 nm for the VNIR and 1 nm for the SWIR, and a spectral stability of better than 0.5 nm [10]. Note that the spectral smile requirement (i.e., the change in centre wavelength of a band as a function of the spatial cross-track position) is below 20% of a spectral pixel.…”

“…Having this tool available, studies on the expected uncertainty related to EnMAP data can be conducted. As the instrument is yet to be completed and launched, requirements on an instrument level (e.g., the ground sampling distance or the spectral bandwidth) and requirements related to the laboratory calibration as well as requirements for the in-orbit operation (e.g., [10]) can be used for the uncertainty estimation.…”

Calibration and Validation for the Surface Biology and Geology (SBG) Mission Concept: Challenges of a Multi-Sensor System for Imaging Spectroscopy and Thermal Imagery

“…Vicarious calibration is any radiometric calibration method that uses stable materials on the Earth's surface as a reference. Earth's surface may be well-characterized pseudo-invariant, sites that are actively instrumented in situ (e.g., RadCalNet;Bouet et al, 2019), or sites that are episodically measured during field campaigns, for example, during a commissioning phase or later evaluation period (Storch et al, 2014). The modifier 'vicarious' is used because a spaceborne instrument is being indirectly calibrated using instruments on the ground, i.e., transferring radiometric scales from instruments on Earth to a spaceborne instrument using the Earth's surface as an intermediate reference.…”

“…Because potential variation in the Earth's atmosphere increases uncertainty, care must be taken to avoid adjusting a time-dependent calibration as a result of atmospheric variations. For this reason, onboard or celestial references are preferred for calibration (Storch et al, 2014), especially with mission objectives such as change detection, monitoring, and trending, while vicarious measurements are employed for validation of data products (Masek et al, 2020). On the other hand, for aquatic remote sensing, vicarious calibration is primarily used to optimize accuracy of surface radiometry, not at-sensor accuracy, so biases in the atmospheric radiative transfer model are incorporated in the adjustments applied to the production of water-leaving reflectance (Clark et al, 1997).…”

Mapping the relative abundance of soil microbiome biodiversity from eDNA and remote sensing

“…To address this shortfall requires fundamentally new approaches for rapidly quantifying and understanding the complexity and changes in global biodiversity, including the relative abundance of species and community composition. Exciting actual and planned innovations in next-generation hyperspectral satellites (viz., the Environmental Mapper and Analysis Programme EnMAP (Storch, 2022) from DLR-Germany, PRecursore IperSpettrale della Missione Applicativa PRISMA (PRISMA, 2022) from ASI-Italy , Copernicus Hyperspectral Imaging Mission for the Environment CHIME (ESA, 2022) from ESA-Europe, and Surface Biology and Geology SBG (Nastal and Pavlick, 2022) from NASA-USA) further our abilities to upscale biodiversity products to a global level and further understanding of how biodiversity responds to stress and environmental change (Lausch et al, 2016).…”