Testing a near-infrared Lidar mounted with a large incidence angle to monitor the water level of turbid reservoirs

It is sometimes difficult to monitor the water level of reservoirs with a sloping bank – such as many lakes and earth-dam embankment – using terrestrial techniques or airborne instruments. A proposed alternative is a new technique using a terrestrial near-infrared Lidar mounted with a large incidence angle (at least between 40° and 70°). This technique assumes that the Lidar can detect the (sub-)surface of a water body provided that it contains enough suspended particles to backscatter the light emitted by the instrument to its detector. Tests performed with a commercial Lidar show that the technique can be used to estimate the water level of a reservoir with moderate accuracy (within ±0.05 m [p = 0.95]) when the water is very turbid (Secchi depth < 0.5 m). The versatility and accuracy of the technique is expected to improve in the future with the use of current Lidar that are more sophisticated than the tested one.