Oral Session 2

Evaluation of Sentinel-3A and 3B OLCI reflectance products over dynamic coastal waters of Salish Sea, Canada

This research encompasses 61 and 39 days of coincident occurrences of Sentinel-3A and 3B – OLCI cloud-free images and in situ measured reflectance data, covering various seasonal dynamics, in 2016, 2018, 2019, and 2020 in the Salish Sea, west coast of Canada. We used Sentinel-3 Level-2 remote sensing reflectance [Rrs(λ)] processed with POLYMER (v4.9), 3×3-pixel grid box with a time difference of ±3h between satellite and in situ observations. In situ hyperspectral reflectance data [Rrs(λ)in situ] were acquired using autonomous shipborne radiometric sensors (SAS-Solar Tracker) installed on British Columbia Ferries. Along transact Rrs(λ)in situ, with a spatial resolution of 13m, were spatially binned to a 900m resolution, equivalent to the size of a 3×3-pixel grid box of S3A-OLCI, ship superstructure, wind speed-dependent sky radiance, bi-directional reflection distribution function (BRDF), and spectral quality assurance and spatial variability corresponding to inhomogeneous transitional water masses, resulting in 80% of high-quality data (N = 1791). The matchup analysis yielded correlation statistics for S3A and S3B as r = 0.90, 0.81; 0.94, 0.90, and 0.89, 0.85 at the blue, green, and red spectral bands, respectively. Prior to the spatial quality assurance, the matchup results showed a decline in statistics for S3A and S3B OLCI as r = 0.75, 0.41, 0.78, 0.70, and 0.70, 0.64, respectively. Our results suggest that high-quality Rrs(λ)in situ data is essential for evaluating satellite Rrs(λ) in coastal dynamic waters and that POLYMER-derived S3A and S3B Rrs(λ) have low BIAS for all visible wavelengths.

Maycira Costa, University of Victoria, Canada

Hussain Nasiha, University of Victoria, Canada

Ziwei Wang, University of Victoria, Canada

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