pOptical Earth observation satellites provide vast amounts of data on a daily basis. The top-of-atmosphere radiance measured by these satellites is usually converted to bottom-of-atmosphere radiance or reflectance which is then used for deriving numerous higher level products used for monitoring environmental conditions, climate change, stock of natural resources, etc. The increase of available remote sensing data impacts decision-making on both regional and global scales, and demands appropriate quality control and validation procedures. A HYperspectral Pointable System for Terrestrial and Aquatic Radiometry (HYPSTAR$^®$) has been designed to provide automated, italicin-situ/italic multiangular reflectance measurements of land and water targets. HYPSTAR-SR covers 380–1020 nm spectral range at 3 nm spectral resolution and is used at water sites. For land sites the HYPSTAR-XR variant is used with the spectral range extended to 1680 nm at 10 nm spectral resolution. The spectroradiometer has multiplexed radiance and irradiance entrances, an internal mechanical shutter, and an integrated imaging camera for capturing snapshots of the targets. The spectroradiometer is mounted on a two-axis pointing system with 360° range of free movement in both axes. The system also incorporates a stable light emitting diode as a light source, used for monitoring the stability of the radiometric calibration during the long-term unattended field deployment. Autonomous operation is managed by a host system which handles data acquisition, storage, and transmission to a central WATERHYPERNET or LANDHYPERNET server according to a pre-programmed schedule. The system is remotely accessible over the internet for configuration changes and software updates. The HYPSTAR systems have been deployed at 10 water and 11 land sites for different periods ranging from a few days to a few years. The data are automatically processed at the central servers by the HYPERNETS processor and the derived radiance, irradiance, and reflectance products with associated measurement uncertainties are distributed at the WATERHYPERNET and LANDHYPERNET data portals./p
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RBINS Staff Publications 2025
pThis paper describes a prototype network of automated italicin situ/italic measurements of hyperspectral water reflectance suitable for satellite validation and water quality monitoring. Radiometric validation of satellite-derived water reflectance is essential to ensure that only reliable data, e.g., for estimating water quality parameters such as chlorophyll italica/italic concentration, reach end-users. Analysis of the differences between satellite and italicin situ/italic water reflectance measurements, particularly unmasked outliers, can provide recommendations on where satellite data processing algorithms need to be improved. In a massively multi-mission context, including Newspace constellations, hyperspectral missions and missions with broad spectral bands not designed for “water colour”, the advantage of hyperspectral over multispectral italicin situ/italic measurements is clear. Two hyperspectral measurement systems, PANTHYR (based on the mature TRIOS/RAMSES radiometer) and HYPSTAR$^®$ (a newly designed radiometer), have been integrated here in the WATERHYPERNET network with SI-traceable calibration and characterisation. The systems have common data acquisition protocol, data processing and quality control. The choice of validation site and viewing geometry and installation considerations are described in detail. Three demonstration cases are described: 1. PANTHYR data from two sites are used to validate Sentinel-2/MSI (A&B); 2. HYPSTAR$^®$ data at six sites are used to validate Sentinel-3/OLCI (A&B); 3. PANTHYR and HYPSTAR$^®$ data in Belgian North Sea waters are used to monitor phytoplankton parameters, including italicPhaeocystis globosa/italic, over two 5 month periods. Conclusion are drawn regarding the quality of Sentinel-2/MSI and Sentinel-3/OLCI data, including indications where improvements could be made. For example, a positive bias (mean difference) is found for ACOLITE\_DSF processing of Sentinel-2 in clear waters (Acqua Alta) and clues are provided on how to improve this processing. The utility of these italicin situ/italic measurements, even without accompanying hyperspectral satellite data, is demonstrated for phytoplankton monitoring. The future evolution of the WATERHYPERNET network is outlined, including geographical expansion, improvements to hardware reliability and to the measurement method (including uncertainty estimation) and plans for daily distribution of near real-time data./p
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This study assesses hydrogeological hazards in the Saint-Vaast region, Belgium, impacted by three decades of deformation post-coal mine closure. Using Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) applied to 30 years of Synthetic Aperture Radar (SAR) data along with geological investigations and 13 years of piezometric well data, we analysed subsurface dynamics leading to environmental hazards in the region. We focused on identifying key periods of significant deformation pattern changes. The soft Wealden terrains (Lower Cretaceous) are characterized by alternating sandstones, clay, and sand facies, composing the sedimentary roof of an old mine drainage adit dug at 30 m depth. The presence of this mined adit structure is contributing to the current vulnerability of the region. Especially, when the abandoned mine drainage adit was filled with water following the cessation of pumping. Due to an increase in the water level in the Wealden aquifer below the gallery, natural groundwater flow paths and pressures have increased over time. At least two significant mudflow outbursts, in 2009 and 2018, occurred. This study shows that both events were correlated with changes in water level and deformation. Moreover, results suggest a new phase of rising water levels and ground uplift due to increased pressure in the Wealden aquifer. A crucial outcome of this research is the assessment of the potential for another similar incident soon, informed by the correlation analysis of water level and ground displacement time series.
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RBINS Staff Publications 2024
