Radiometric Validation of Sentinel-3AB by the WATERHYPERNET, including 2023 expansion sites

RUDDICK, K.; DOGLIOTTI, A. I.; ET AL.

Encuentro; 8th Sentinel-3 Validation Team Meeting 2023; 2023

TheWATERHYPERNET network of hyperspectral radiometers has been designed forradiometric validation of satellite missions. The network provides waterreflectance data for all visible and near infrared bands of all optical imagingmissions, including Sentinel-3A&B&C&D,Sentinel-2A&B&C&D, PROBA-V, MODIS-AQUA&TERRA, VIIRS, Landsat-8,Pléiades, CHRIS-PROBA, MSG-SEVIRI, PlanetDove,PRISMA … ENMAP, PACE, CHIME, SBG,MTG and ... any future optical missions, including Newspacecubesats. Thisnetwork follows closely the AERONET-OC federation concept [Zibordi et al, 2009]but uses hyperspectral radiometers. Two instrument systems have been developed:a) the PANTHYR system [Vansteenwegen et al, 2019] consists of one radiance andone irradiance TRIOS/RAMSES sensor, a mature high performance radiometer b) theprototype HYPSTAR® system, based on a newly designed hyperspectral radiometer with asingle spectrometer and both radiance and irradiance fore-optics and anintegrated camera. Both systems including a pointing robot, data acquisitioncomputer and 2G/3G/4G data transmission, and are or can be supplemented withGPS, inclinometer, rain sensor and camera auxiliary sensors. The measurementmethod is based on the abovewater method of [Mobley, 1999 and 2015], but allowsadditional scenarios for different viewing zenith and azimuth configurations.Bothsystems provide measurements every 20-30 mins for validation of all visible andnear infrared Sentinel-3AB bands (400nm to 900nm inclusive).The first PANTHYRsystems have been deployed in the Italian Adriatic Sea (September 2019 -present) offshore of Oostende North Sea (December 2019 - August 2020 andSeptember 2021 - present) and Thornton Bank North Sea (May 2023 –present). The first HYPSTAR® systemshave been deployed in Blankaart Reservoir (Belgium), the Etang de Berre(France), Adriatic Sea (Italy), La Plata Estuary (Argentina), Gironde estuary(France), Lake Garda (Italy), offshore of Zeebrugge (Belgian North Sea) andLakeVortsjävn (Estonia) as well as at land-based sites. One more PANTHYR and onemore HYPSTAR®deploymentsare planned for2023Q4 with further international expansion in 2023-24.This presentation will provide results fromthese deployments, comparing matchups with Sentinel-3A and -3B, illustratingthe usefulness for validation of Sentinel-3 and outlining the next steps asregards hardware improvements, measurement method refinements, radiometercalibration and characterisation and quantification of the in situ measurementuncertainties. Results will be sorted to demonstrate any performance issues ofthe S3/OLCI products including turbid water cases, cloud shadow outliers,adjacency effects, etc. Comparisons will be made with AERONET-OC data whereco-located.