Validation of satellite water products based on HYPERNETS in situ data using a Match-up Database (MDB) file structure

Abstract

A Match-up Database (MDB) file structure and tools were developed to ease thevalidation analysis of satellite water products and to improve the exchange andprocessing of match-up data from different sites, missions and atmosphericcorrection processors. In situ remote sensing reflectance (Rrs) measurementswere available from the HYPSTAR® (HYperspectral Pointable System forTerrestrial and Aquatic Radiometry), a new automated hyperspectralradiometer. An MDB file is a NetCDF file containing all the potential matchupsbetween satellite and in situ data on a specific site and within a given timewindow. These files are generated and manipulated with three modulesdeveloped in Python to implement the validation protocols: extract satellitedata, associate each extract with co-located in situ radiometry data, and thenperform the validation analysis. This work provides details on the implementationof the open-source MDB file structure and tools. The approach is demonstratedby a multi-site matchup comparison based on satellite data from the Sentinel-2MSI and Sentinel-3 OLCI sensors, and HYPSTAR® data acquired over six watersites with diverse optical regimes from February 2021 to March 2023.The analysisof Sentinel-3 OLCI matchups across the six sites shows consistency with previouscomparisons based on AERONET-OC data over extended reflectance range. Weevaluated Sentinel-2 MSI reflectance data corrected with two atmosphericcorrection processors (ACOLITE and C2RCC) over four sites with clear tohighly turbid waters. Results showed that the performance of the processorsdepends on the optical regime of the sites. Overall, we proved the suitability of theopen-source MDB-based approach to implement validation protocols andgenerate automated matchup analyses for different missions, processorsand sites.