Mapping hydraulic biotopes using terrestrial laser scan data of water surface properties

Abstract

For more than a decade, habitat mapping using biotopes (in-channel hydraulically-defi ned habitats) has underpinned aquatic conservation in the UK through (a) providing baseline information on system complexity and (b) allowing environmental and ecological change to be monitored and evaluated. The traditional method used is the subjective river habitat or corridor survey. This has recently been revised to include the fl oodplain via GeoRHS, but issues still exist concerning development of a national database due to the labour intensive nature of the data collection, subjectivity issues between samplers, temporal changes, the fuzzy nature of perceived habitats and habitat boundaries. This paper takes an innovative approach to biotope defi nition using high resolution spatial data to defi ne water surface roughness for two representative reaches of the River South Tyne, Cumbria, and the River Rede, Northumberland, UK. Data was collected using a terrestrial laser scanner (TLS) and hydraulic variability simply expressed through assigning a local standard deviation value to a set of adjacent water surface values. Statistical linkage of these data with biotope locations defi ned visually in the fi eld allowed complete mapping of the surveyed reach defi ning habitat and biotope areas to the fi ne scale resolution of the TLS data. Despite issues of data loss due to absorption and transmission through the water, the refl ected signal generated an extremely detailed and objective map of the water surface roughness, which may be compared with known biotope locations as defi ned by visual identifi cation in the fi eld. The TLS accuracy achieved in the present study is comparable with those obtained using hyperspectral imagery: with 84% of the pool/glide/marginal deadwater amalgamated biotope, 88% of riffl es, 57% of runs and 50% of the amalgamated cascade/rapid biotope successfully plotted. It is clear from this exercise that biotope distribution is more complex than previously mapped using subjective techniques, and based upon the water surface roughness delimiters presented in this study, the amalgamation of pools with glides and marginal deadwaters, riffl es with unbroken standing waves, and cascades with rapids, is proposed.

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

“…As a matter of fact, it attempts to estimate each stage data independently of what had been estimated previously. In addition, and contrary to findings by Mandlburger et al [12], its performances were not found to be significantly different when computing the third (or the first) quartile of the raw distance data instead of the median during step (3).…”

“…Therefore, and strictly speaking, the present form of the proposed technique does not provide a stage "measurement" but rather a stage "surrogate". However, a few field [3] and laboratory [6,7] observations suggest that for a given Lidar configuration (which includes the laser wavelength, power and distance) and water turbidity, it can be roughly assumed that the emitted laser pulses penetrate through water up to a constant distance (please, note that such a distance must be seen as an effective property). If so, the bias in the stage estimation can be simply deduced as [4] (please, note that the Lidar "ignores" that its beam is refracted and travels slower into water):…”

“…In this context, it is worth noting that a growing number of experimental studies are showing the usefulness of commercial Terrestrial Lidar Scanning (TLS) systems to map the water surface of some rivers [3,4] and coastal areas [25,26]. Although this technique appears to be similar to the one described in this study, it is not explicitly based on the same physical principle: as a matter of fact, studies suggest that TLS systems are mostly able to detect water surface due to "glint noise" after a very large number of attempts and provided that the surface is agitated enough.…”

Terrestrial Laser Scanning Reveals Seagrass Microhabitat Structure on a Tideflat

“…Pools of standing water greatly reduced TLS return density, and introduced occasional reflection artifacts. This phenomenon has been described in TLS studies of river beds [41], and even capitalized upon to map the water surface in such studies [42]. Point return density may be useful in classifying the TLS image into pools and mounds, particularly by using object-based image analysis to delineate distinct contiguous regions of low point density.…”

The Use of Terrestrial Laser Scanning for Measurements in Shallow-Water: Correction of the 3d Coordinates of the Point Cloud

“…Therefore, more recent research focuses on the use of Terrestrial Laser Scanning (TLS) from either a fixed or static position (STLS) or from a mobile platform (MTLS). [3] Notwithstanding data loss due to the reflection of the laser beam at the water surface and the absorption and the dispersion of the laser beam passing through the water, TLS has the potential to produce high density point clouds of shallow-water riverbeds with a high level of detail [4], [5].…”