Satellite-derived bathymetry

It depends on the water. In turbid, temperate water at Jervis Bay in New South Wales, our depths agree with an airborne LiDAR survey to about a metre across the shallows. Over a clear lagoon in the Bahamas, they land within 38 centimetres of ICESat-2 laser measurements that we held back from calibration. Every pixel also carries its own uncertainty value, so you can see how far to trust each depth instead of relying on one figure for the whole map.

Water depth read from satellite imagery. Some sunlight passes through the water, reflects off the seabed and returns to the satellite. The deeper the water, the more of that light is absorbed on the way, so the colour of the water carries information about its depth. Satellite-derived bathymetry turns that signal into a seabed map without a boat, an aircraft or an in-water survey.

Mostly from the imagery processing. The seabed signal is faint, and the atmosphere, sun glint and suspended sediment all distort it. We remove those effects with the same imagery processing behind every Geopera order, then calibrate against ICESat-2 laser depths. We publish the validation results; the method stays with us.

As deep as light reaches the seabed and comes back, which depends on water clarity rather than on the satellite. In clear water that is roughly 15 to 20 metres. In murky water it is shallower. Where the seabed stops being visible, the map marks it with a bottom-visibility flag instead of reporting a depth it could not see.

Airborne LiDAR fires a laser from an aircraft and measures depth directly along its flight lines. It is accurate, and every survey needs an aircraft and crew. Satellite bathymetry reads depth from imagery over a whole coastline and can be repeated as new satellite passes come in. Use satellites to cover a wide area, find where to look and track change. Use LiDAR or multibeam sonar where you need survey-grade depths. That is why we validate our maps against LiDAR.

It can inform a chart, and it does not replace a hydrographic survey. The international hydrographic community treats satellite-derived bathymetry as reconnaissance and chart-update data. The per-pixel uncertainty is what lets a hydrographer decide which confidence category an area can support: clear, shallow water supports a higher one than turbid water. Inferred depths are marked as inferred, never presented as surveyed.

Yes, with a larger error than in clear water. Sediment scatters light, so the seabed signal is weaker and fades out at shallower depths. At Jervis Bay our depths stay within about a metre of an airborne LiDAR survey across the shallow margin, and the error grows gradually as the water deepens.

Send us the area. We search the Sentinel-2 archive for clear captures over it, process them and deliver a GeoTIFF with depth, uncertainty and bottom visibility for every pixel. Turnaround depends on the size of the area and on how recently the water was clear enough to see the seabed, so we give you a date when we scope the job. There is no vessel or aircraft to schedule.