Data Quality Assessment, Representativeness, and External Consistency of a Coastal Oceanographic Buoy Using Copernicus Marine and ERA5 Products

Coastal oceanographic buoys provide high-frequency observations, but their scientific use requires channel-specific quality assessment and explicit treatment of representativeness. This study evaluates a coastal buoy deployed off Cabo de Gata, southeastern Spain, during two non-contiguous observation windows in 2025 and 2026. Buoy records were standardized, screened with quality-control tests, aggregated daily without gap filling, and compared with Copernicus Marine and ERA5 products as an external-consistency assessment. Gridded products were interpolated to the mean buoy position using inverse-distance weighting, and Copernicus Marine temperature was vertically interpolated to the 5 m and 10 m buoy-sensor depths. Completeness was 88.1–88.3% in 2025 and 99.9–100.0% in 2026, with no gross-range failures. Significant wave height and atmospheric pressure showed strong external consistency, with root mean square errors of 0.15/0.14 m and 0.63/0.59 hPa, respectively. Temperature at 5 m showed moderate-to-strong agreement, with errors of 0.98/0.64 °C. Wave-spectrum-derived wind speed showed larger, sea-state-dependent differences, although disagreement decreased under higher wave steepness. The workflow distinguishes channels suitable for daily environmental interpretation from those requiring additional metadata or independent field verification.