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

Stage Monitoring in Turbid Reservoirs with an Inclined Terrestrial Near-Infrared Lidar

“…No attempt was made to describe this phenomenon known as "volume scattering" during the experimental study described herein. Equation (1) was used empirically during the field experiment, that is, both parameters H 0 and cos(θ) were adjusted through a simple calibration. Therefore, and strictly speaking, the present form of the proposed technique does not provide a stage "measurement" but rather a stage "surrogate".…”

“…Although unexplained (due to manufacturing secrets), it seems that the least expensive Lidar instruments perform better than others with similar features [7]. As a matter of fact, tests by Tamari et al [1] of two models of the same brand (Optech Inc., Vaughan, ON, Canada) found that the "3100-SR Watchman" (firmware 35-AWLX-2.0) provides better results than the more expensive "Sentry SR" (firmware SR-V2.8). Similarly, two models by another brand (Laser Technology Inc., Centennial, CO, USA) were tested during this study (Figure 2a,b), finding that the "TruSense S200" (firmware 1.11.4) provided better results than the more expensive "ULS" (firmware 1.0.5).…”

“…Thus, the test Lidar can measure a distance with three modes, which are well-known in ALB (at least, when analyzing the bottom returns of a green Lidar) as [10]: "first pulse", "strongest pulse" and "last pulse". These three Lidar modes of operation were sequentially used by the present study (unlike Tamari et al [1] who could only use one mode).…”

“…As discussed by Tamari et al [1], it is sometimes difficult to use the current terrestrial techniques or airborne instruments for monitoring the stage of reservoirs with a sloping bank (such as many lakes and earth-dam embankments). Therefore, it would be useful to develop techniques that can monitor the stage using non-contact terrestrial instruments mounted at the edge and that look at the water surface with a large incidence angle (typically larger than ≈ 60 • ).…”

“…Therefore, it would be useful to develop techniques that can monitor the stage using non-contact terrestrial instruments mounted at the edge and that look at the water surface with a large incidence angle (typically larger than ≈ 60 • ). In the particular case of turbid reservoirs, Tamari et al [1] have proposed a new technique using a (time-of-flight) inclined near-infrared Lidar. This technique is based on two simple assumptions about the so-called "volume scattering" (e.g., [2]): (1) the main feature that can be detected by a Lidar looking with a large incidence angle (between ≈ 30 • and 70 • ) at a turbid water body (with no floating objects) are suspended particles (due to the Tyndall effect) and (2) those detected particles-if any-should be slightly below the water surface (due to the strong absorption of the near-infrared light by water, if compared to other Lidar wavelengths).…”