In this study we present and validate a simple empirical method to obtain bathymetry profiles using the geolocated photon data from the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission, which was launched by NASA in September 2018. The satellite carries the Advanced Topographic Laser Altimeter System (ATLAS), which is a lidar that can detect single photons and calculate their bounce point positions. ATLAS uses a green laser, causing some of the photons to penetrate the air–water interface. Under the right conditions and in shallow waters (<40 m), these photons are reflected back to ATLAS after interaction with the ocean bottom. Using ICESat-2 data from four different overflights above the Heron Reef, Australia, a comparison with SDB data showed a median absolute deviation of approximately 18 cm and Root Mean Square Errors (RMSEs) down to 28 cm. Crossovers between two different overflights above the Heron Reef showed a median absolute difference of 13 cm. For an area north-west of Sisimiut, Greenland, the comparison was done with multibeam echo sounding data, with RMSEs down to between 35 cm, and correspondingly showed median absolute deviations between 33 and 49 cm. The proposed method works well under good conditions with clear waters such as in the Great Barrier Reef; however, for more difficult areas a more advanced machine learning technique should be investigated in order to find an automated method that can distinguish between bathymetry and other signals and noise.

Denmark’s Depth Model (DDM) is a Digital Bathymetric Model based on hundreds of bathymetric survey datasets and historical sources within the Danish Exclusive Economic Zone. The DDM represents the first publicly released model covering the Danish waters with a grid resolution of 50 m. When modern datasets are not available for a given area, historical sources are used, or, as the last resort, interpolation is applied. The model is generated by averaging depths values from validated sources, thus, not targeted for safety of navigation. The model is available by download from the Danish Geodata Agency website. DDM is also made available by means of Open Geospatial Consortium web services (i.e., Web Map Service). The original datasets—not distributed with the model—are described in the auxiliary layers to provide information about the bathymetric sources used during the compilation.

&lt;p&gt;With the Advanced Topographic Laser Altimeter System (ATLAS), ICESat-2 is able to map underwater topography, i.e., bathymetry. The ICESat-2 altimeter uses a green laser with a wavelength of 532 nm, which can penetrate the water surface and provide information about the distance to the ocean bottom if the conditions allow it, i.e., preferably over clear and calm waters and for depths up to 40 m.&lt;/p&gt;&lt;p&gt;Precise bathymetry estimates for shallow water areas are important for industry and modelling of phenomena such as tides, currents and water temperature. Obtaining direct measurements of bathymetry using airborne lidar or echo soundings from ship can be a tedious and expensive task. The data from the Advanced Topographic Laser Altimeter System (ATLAS) carried by ICESat-2 offers a fast an inexpensive way to obtain accurate coastal bathymetry, which can be used alone or together with global satellite imagery, such as from Sentinel-2, to create bathymetric maps in areas where there are no available in situ data from ships or airborne lidars.&lt;/p&gt;&lt;p&gt;Here we present the validation of a simple empirical method (Ranndal, 2021) to obtain bathymetry profiles using the geolocated photon data (ATL03) from ICESat-2. The bathymetry profiles obtained with the statistical method are compared to other bathymetry data sets in the Great Barrier Reef, Australia, and in the area around Sisimiut, Greenland, such as echo soundings and satellite derived bathymetry from WorldView2 imagery. Comparisons with machine learning derived bathymetry profiles reveal that the statistical model provides similar results.&lt;/p&gt;&lt;p&gt;Some of the challenges concerning the extraction of bathymetry profiles from ICESat-2 photon data, such as apparent multiple sea surfaces and the difficulty of distinguishing between bathymetry and sea surface returns in very shallow waters are also discussed.&amp;#160;&lt;/p&gt;&lt;p&gt;Finally, the potential of using a similar method for extracting inland water bathymetry is addressed.&lt;/p&gt;