Automatic detection for ICESat-2 shallow-water seabed candidate segments by along-track continuity constraints

The shallow-water bathymetric use of ICESat-2 ATL03 photon data depends on whether stable seabed responses can be identified along satellite ground tracks. In reef and nearshore environments, seabed photons often occur locally, become discontinuous along track and vary with water depth, bottom reflectance, water optical properties, sea-surface state and beam strength. Afterpulse responses and thick near-surface photon tails may also form pseudo-linear structures below the sea surface, which can be confused with shallow seabed returns. This study proposes an automatic method for detecting shallow-water seabed candidate segments from full-track ICESat-2 ATL03 data using along-track continuity constraints. A local sea-surface reference is first constructed to normalize photon elevations into relative depths. A depth-gated underwater candidate space is then generated, followed by along-track peak-chain connection, continuity assessment, morphology-based window constraints, pseudo-signal suppression and segment-level boundary refinement. A total of 52 effective ATL03 subsets selected from 75 ATL03 HDF5 files were evaluated. The proposed method produced spatially explicit candidate segments that corresponded well with visible shallow-water geomorphology. Segment-level evaluation against 170 manually interpreted seabed-response reference slices yielded a precision of 97.81%, a recall of 78.82%, an F1-score of 87.30%, a false discovery rate of 2.19% and an intersection over union of 77.46%. These results indicate that the proposed method can provide candidate spatial constraints for subsequent fine seabed-photon extraction, shallow-water range identification and active-passive bathymetric analysis by reducing the search space of potential seabed-response areas.