Stelios Mertikas (Technical University of Crete, Greece); Craig Donlon (European Space Agency, European Space and Technology Centre, The Netherlands); Achilles Tripolitsiotis (Space Geomatica, Greece); Kristine Larson (Germany, Greece); Simon Williams (United Kingdom, Greece); Panagiotis Mertikas (Technical University of Crete, Greece); Xenophon Frantzis (Greece, Greece); Costas Kokolakis (Space Geomatica, Greece); Dimitrios Piretzidis (Space Geomatica, Greece)

Sea state variability remains a primary source of uncertainty in satellite radar altimetry, influencing radar waveform shape, electromagnetic bias, and the Sea State Bias. Current sea-state bias parameterizations rely largely on empirical models with significant wave height and wind speed. The European Space Agency Permanent Facility for Altimetry Calibration in Crete requires independent and spatially representative observations of sea surface roughness to better determine altimetry uncertainty budgets. This work investigates the use of optical observations acquired under sun-glitter conditions to characterize sea state variability relevant to altimetry calibration.

An integrated imaging approach combining satellite and ground-based optical systems, covering Crete and Gavdos, is developed to: (a) retrieve Mean Square Slope from sun-glint radiometry, (b) reconstruct three-dimensional sea surface geometry through stereo photogrammetry, and (c) derive wave dispersion characteristics from time-resolved video imagery. Collocation with satellite altimeter overpasses of Sentinel-6MF and Sentinel-6B is implemented to establish a robust methodology to correlate optical roughness metrics with sea state. The proposed framework provides a physically based, spatially resolved methodology to support FRM uncertainty assessment and advance sea state characterization for present and future satellite altimetry missions.