Underwater altimetry &amp;#8211; Extracting ICESat-2 bathymetry in shallow water areas

Heidi Ranndal,Philip S Christiansen,Ole B Andersen

doi:10.5194/egusphere-egu22-701

Abstract

&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;

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