HAMLET - Hypstar-based Angular Measurements for hyperspectraL Earth-observation validaTion

Abstract. The advent of hyperspectral missions such as DESIS, EMIT, PRISMA and EnMAP increases the need for robust calibration and validation frameworks. While Pseudo Invariant Calibration Sites support vicarious calibration, validation of L2 products requires Fiducial Reference Measurements over real, diverse landscapes. ESA’s HYPERNETS initiative addresses this goal by deploying continuous, automated spectroradiometric measurements across multiple sites. In this context, agricultural targets pose major challenges due to strong seasonal dynamics, non-Lambertian behavior, and viewing geometry effects, further complicated by off-nadir acquisitions. To analyze such targets, two crop seasons of HYPSTAR®-XR multi-angular spectroradiometer (ranging from 380 nm up to 1680 nm) and satellite data were collected at the Jolanda di Savoia agricultural site, located in northern Italy (JSIT). Constrained match-ups between satellite and JSIT reflectances were analysed through HAMLET, an ad-hoc R package developed to support improved validation practices for hyperspectral reflectance products in complex targets.