Global Fair‐Weather Bias in Remotely Sensed Coastal Suspended Sediment Concentration

Satellite estimates of suspended‐sediment concentration (SSC) are widely used to understand ecosystem functions and resilience of coastal environments. Yet, they rely largely on fair‐weather observations. Combining continuous in situ time series with multi‐decadal satellite records and reanalysis products, we quantify a systematic fair‐weather bias that misrepresents coastal SSC in both magnitude and sign. Negative biases dominate where cloudy conditions coincide with energetic sediment mobilization, causing satellites to miss high‐SSC events and underestimate long‐term means by up to ∼20%. In contrast, positive biases arise where clear‐sky conditions align with elevated wave energy. Bias magnitude and direction are driven by local couplings among cloud cover, wave energy and sediment mobilization, enabling prediction and correction. Climate‐model projections indicate only modest changes in cloudiness over this century, suggesting the bias will persist in the future. Ignoring fair‐weather limitations distorts sediment budgets and biogeochemical fluxes, underscoring the need for bias‐aware algorithms in global coastal assessments.