LiDAR technology emits two laser light beams from a sensor on-board an airplane. One beam reaches the water surface and is reflected, while the second beam penetrates the water, hits the seabed and is then reflected back. The difference in time between the two returning beams allows the water depth to be calculated. Digital photographs are also taken with a geo-referenced digital camera. INFOMAR uses LiDAR data to produce a bathymetry chart of very shallow, intertidal areas that boats cannot reach. In Ireland the typical depth penetration is 15 metres depending on sediment or biological material (seaweed) in the water. LiDAR can establish seaweed biomass to enable sustainable harvesting.