Dear authors,

I have reviewed the manuscript “NZ-BeachTopo30: Bridging the Intertidal Data Gap by Fusing ICESat-2 and Sentinel-2”. Overall, this paper presents a novel and valuable dataset for New Zealand beach topography, filling an important data gap. The manuscript is generally well structured, and the methodology is clearly described. However, some revisions are still required to enhance the quality of the manuscript, and my specific comments are detailed as follows.

1 In the introduction, the authors discuss the characteristics and limitations of airborne LiDAR and spaceborne LiDAR together. I recommend discussing them separately to better distinguish between the two in the manuscripts.

2 I suggest the authors ensure the completeness of information for all datasets used, as I noticed that some data sources do not have corresponding URLs provided. This is essential to guarantee data accessibility and the reproducibility of the methodology.

3 Sentinel-2 composite images serve as the foundation for beach topography modeling in this study. Hence, I recommend that the authors provide a more detailed explanation of the meaning of different quantiles derived from Sentinel-2 optical imagery.

4 I suggest the authors supplement the paper with an explanation of the applicability of the SMOGN algorithm to regression tasks, or add relevant clarifications.

5 I suggest the authors also provide the latitude and longitude information for the beaches corresponding to panels a-f in Figure 5.

6 It is suggested that the authors add relevant discussion and outlook in the discussion section regarding whether the proposed approach can be applied to the inversion of muddy tidal flat topography in the future.

Dear authors,

The study titled “NZ-BeachTopo30: A national-scale and full-coverage 30 m beach topography dataset for New Zealand reconstructed by fusing ICESat- 2 and Sentinel-2” presents a novel and robust methodology for generating topography for beaches and then develop a useful and national-scale dataset across New Zealand. Please find my revision suggestions below.

• I suggest adding one sentence at the end of the second paragraph in the introduction to summarize the current status and limitations of remote sensing techniques for beach topography reconstruction. Moreover, The first sentence of the third paragraph in the introduction should be revised to provide a general overview of mainstream DEM datasets, so as to improve the logical coherence of the paragraph;
• I suggest that ICESat-2 track information should be added in Figure 1 to better illustrate its spatial distribution across the study area;
• In Figure 2 workflow diagram, I suggest that the authors explicitly indicate that airborne LiDAR was used for validation; otherwise, it could easily be confused with the spaceborne ICESat-2 LiDAR data also employed in this study;
• The authors used composite remote sensing imagery of different quantiles to represent states at various tidal levels and claimed that this method can achieve denoising effects. I recommend the authors provide more quantitative evidence to demonstrate the rationality of this approach used in this study;
• I suggest the authors add boxplots for the X-axis and Y-axis corresponding data in panels a and b of Figure 14 in Section 5.2, to enable a more intuitive comparison. In addition, In Figure 14, it is evident that DeltaDTM systematically omits low-lying areas of beaches as well as regions adjacent to the ocean. I suggest that the authors emphasize this point in their discussion;
• I suggest that the authors add a discussion in this section addressing potential limitations of this study. For example, the use of OSM data to delineate beach extents may introduce errors inherent to the baseline data itself. Beaches undergo long-term evolution, and their temporal changes are also critical. Additionally, the 10 m spatial resolution may be insufficient for accurately representing narrower beaches. In summary, I would like to see the authors expand the discussion to include these considerations in the manuscript；
• This study presents a useful and large-scale dataset that fills an important gap in coastal elevation data for New Zealand. Hence, I suggest that the authors provide a more systematic explanation regarding the advantages, significance, and potential application scenarios of the data.

This manuscript by Wang et al. presents NZ-BeachTopo30, a 30 m beach topography dataset for New Zealand that fills intertidal data voids in DeltaDTM by fusing ICESat-2 photon-counting altimetry with Sentinel-2 multispectral composites via XGBoost. The problem is well-motivated — intertidal voids in global coastal DEMs are a genuine and widely recognised obstacle for coastal hazard assessment — and the dataset itself is a welcome contribution. The production workflow is clearly described, the validation framework is multi-layered, and the sea-level rise demonstration nicely illustrates the practical value of improved intertidal coverage. I have only a few minor comments.

The manuscript positions NZ-BeachTopo30 as "the first spatially continuous and full-coverage beach topography dataset for New Zealand." The national-scale application and the specific integration strategy with DeltaDTM are clearly valuable. That said, the ICESat-2 + Sentinel-2 + ML approach for coastal elevation estimation has been demonstrated in several publications, and XGBoost for structured regression is well established. The authors might consider framing the novelty more precisely around the data product and the fusion design rather than the methodology itself — this would make the contribution stand out more clearly on its own merits.

The 4,392 valid ICESat-2 pixels span 340 of 1,576 beach units (~22%). The transferability analysis in Section 4.4 is a real strength of the paper, and the modest degradation in accuracy (RMSE 0.93 → 1.02 m) is reassuring. It may be worth noting that this assessment can only be carried out where airborne Lidar is available, which itself tends to be concentrated in more accessible or higher-priority coastal segments. A brief acknowledgement of whether performance on remote, unsampled beaches might differ would give readers a more complete picture.

The internal model evaluation (Fig. 3) against ICESat-2 train/val/test splits usefully demonstrates model consistency, while the independent Lidar comparison (Fig. 4) provides the more informative accuracy diagnostic. It might be worth giving slightly more prominence to Fig. 4(f) — the accuracy specifically within the newly predicted intertidal voids (R² = 0.61, RMSE = 0.94 m) — since this is the metric most directly relevant to the paper's core contribution. The combined-product metrics (R² = 0.75, RMSE = 1.17 m) include the high-quality DeltaDTM backshore pixels and could, on their own, give readers a somewhat optimistic impression of the ML prediction component. Relatedly, the Lidar DEM was resampled from 1 m to 30 m via mean aggregation; on steeper beach faces this could introduce representativeness differences that inflate apparent disagreement. A brief note on this point would be helpful.

The SHAP analysis is well executed and adds useful transparency to the modelling. The main findings — NIR reflectance correlating positively with elevation, distance-to-coast tracking the cross-shore gradient — align with established coastal remote sensing understanding. The analysis is valuable precisely as confirmation that the model has learned physically sensible relationships. The authors might consider framing it in those terms rather than as a discovery of "physical driving mechanisms," which could slightly overstate what the interpretability exercise reveals.

Finally, the conversion from NZVD2016 to EGM2008 orthometric heights (lines 188–190) is an important step but is described only briefly. The difference between these two vertical reference surfaces varies spatially across New Zealand. It would be helpful if the authors could indicate the approximate magnitude and spatial pattern of this offset, so that readers can judge whether residual datum inconsistencies contribute meaningfully to the reported error budget.

I think the authors have answer all questions well. The manuscript has meet the requirements of ESSD and can be published.