NZ-BeachTopo30: A national-scale and full-coverage 30 m beach topography dataset for New Zealand reconstructed by fusing ICESat-2 and Sentinel-2

Abstract. Beaches provide essential ecological functions and support socio-economic resilience, yet accurate mapping is hindered by systematic limitations in global Digital Elevation Models (DEMs). A critical challenge remains in the intertidal zone, where frequent tidal inundation creates extensive data voids, disrupting the continuity of coastal topography. To bridge this fundamental data gap, we present NZ-BeachTopo30 which is a national-scale and full-coverage 30 m beach topography dataset for New Zealand constructed by fusing ICESat-2 photon-counting altimetry with Sentinel-2 multispectral time series. Using DeltaDTM as a high-precision baseline for the stable backshore, we trained an XGBoost model on ICESat-2 control points and Sentinel-2 spectral-geometric features to reconstruct the missing intertidal topography specifically. SHAP analysis was further employed to interpret the physical driving mechanisms of these predictors. Validation against airborne Lidar confirmed that the dataset accurately recovers elevations in previously void zones with an RMSE of 0.94 m. By integrating these predictions with the DeltaDTM baseline, the final national-scale product achieves robust accuracy with an R² of 0.75 and an RMSE of 1.17 m. This targeted integration significantly expanded valid topographic coverage by 145.8 % from 79.9 km² to 196.5 km². It delivers the first spatially continuous and full-coverage beach topography dataset for New Zealand. This product distinguishes itself by seamlessly bridging the critical intertidal gap that disconnects land and sea in existing global datasets. Given the global availability of ICESat-2 and Sentinel-2, NZ-BeachTopo30 offers a scalable solution for worldwide applications and provides a robust foundation for inundation modeling and coastal management.