DTE-S2GOS Use Cases

Three Use Cases will be implemented to prototype this pre-operational DestnE service.

Synthetic satellite observations for ACIX-IV

The Atmospheric Correction Inter-comparison eXercise (ACIX) is an international initiative with the aim to analyse the Surface Reflectance (SR) products of various state-of-the-art atmospheric correction (AC) processors. The Aerosol Optical Thickness (AOT) and Water Vapour (WV) are also examined in ACIX as additional outputs of AC processing. The ACIX initiative went already through 3 phases and it now starting the fourth one.

The purpose of this use case is the simulation of synthetic satellite images, e.g., CHIME, at a spatial resolution of about 30 m over different types of land cover types and atmospheric conditions to benchmark atmospheric correction algorithms. The land cover types should include vegetated surfaces (e.g., forest, crop land), urban, arid or polar regions. The benchmarking will be performed in the framework of ACIX phase IV. Different atmospheric properties like aerosol and water vapour concentrations will be considered. Finally, simulation of bottom of atmosphere surface reflectance (HRDF) will also be performed for each pixel.

DTE-S2GOS will be used to simulate TOA reflectance or radiance (orthorectified L1c data) observed by a hyperspectral instrument like CHIME over the selected ROIs. The atmospheric correction algorithms will be benchmarked using these simulated data as input to derive the surface HDRF that will be compared with simulated HDRF. Simulated HDRF will be estimated for each pixel.

Byproducts will be made available during the result analysis such as the total column AOD and water vapour over each pixel. Prior information that should be make available to the users is still to be decided. A maximum of two seasons (winter and summer) will be simulated per ROI Atmospheric conditions will be taken from CAMS data.

Benchmarking of land parameter upscaling methods

Upscaling methods are essential in Earth observation for bridging the gap between high-resolution ground measurements and coarse-resolution satellite observations. These methods vary in complexity and underlying assumptions and can be broadly categorized into several types depending on whether they are empirical, statistical, deterministic, or hybrid. This Cal/Val activity is crucial for meaningful validation and comparison between field measurements and satellite-derived estimates as performed in the context of Ground-Based Observations for Validation (GBOV) of Copernicus Global Land Products. This service relies on a few upscaling procedures will be implemented to provide reference values (the so-called LPs) representative of areas large enough to cover over several pixels of typical mid-resolution satellite imagers. The GBOV service allows the quality control of the main land products Copernicus Gobal Land Service (CGLS) products (top-of-canopy reflectances, surface albedo, fAPAR, LAI, fCover, LST and soil moisture) providing collections of multiple years of ground-based RMs and derived land Products (LPs). Assessing the uncertainties resulting from upscaling method is thus challenging.

The purpose of this use case is to propose a rigorous framework for the evaluation of the uncertainties resulting from ground observation upscaling for land parameters such as surface albedo, LAI or FAPAR over two types of land cover types, simulating both ground and satellite observations.

Satellite image simulation over bright desert PICS

Bright desert Pseudo Invariant Calibration Sites (PICS) play a critical role for the routine monitoring of radiometric quality of EO data. These sites have stable and predictable reflectance properties over time. Traditionally, satellite images are acquired over this site. Pixels surrounding the site are averaged to estimate the mean TOA radiance or BRF and its standard deviation. These averaged observations are next compared with simulated calibration reference relying on 1D RTM. Within this use case, a new approach will be proposed by which pixel values are not averaged, meaning that each pixel individual value is kept.
Data acquired by the Gobabeb HYPERNETS Namibia (GHNA) will be used for that purpose . The site is well characterised as it is very close to an instrument already recognised as a radiometric calibration site (GONA) as part of the RadCalNet network. GONA and GHNA are 650 m apart. These simulated images will be compared with actual ones on a pixel-per-pixel basis, accounting for the uncertainties of both simulation and observations.

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