Abstract
In the last decade, full-waveform airborne laser scanning (ALSFW) has proven to be a promising tool for forestry applications. Compared to traditional discrete airborne laser scanning (ALSD), it is capable of registering the complete signal going through the different vertical layers of the vegetation, allowing for a better characterization of the forest structure. However, there is a lack of ALSFW software tools for taking greater advantage of these data. Additionally, most of the existing software tools do not include radiometric correction, which is essential for the use of ALSFW data, since extracted metrics depend on radiometric values. This paper describes and presents a software tool named WoLFeX for clipping, radiometrically correcting, voxelizing the waves, and extracting object-oriented metrics from ALSFW data. Moreover, extracted metrics can be used as input for generating either classification or regression models for forestry, ecology, and fire sciences applications. An example application of WoLFeX was carried out to test the influence of the relative radiometric correction and the acquisition scan angle (1) on the ALSFW metric return waveform energy (RWE) values, and (2) on the estimation of three forest fuel variables (CFL: canopy fuel load, CH: canopy height, and CBH: canopy base height). Results show that radiometric differences in RWE values computed from different scan angle intervals (0°–5° and 15°–20°) were reduced, but not removed, when the relative radiometric correction was applied. Additionally, the estimation of height variables (i.e., CH and CBH) was not strongly influenced by the relative radiometric correction, while the model obtained for CFL improved from R2 = 0.62 up to R2 = 0.79 after applying the correction. These results show the significance of the relative radiometric correction for reducing radiometric differences measured from different scan angles and for modelling some stand-level forest fuel variables.
Highlights
Laser scanning has been used in the last several decades for a wide range of applications, such as climate change monitoring through biomass estimation [1,2], carbon sequestration [3,4] and wildlife protection [5,6]
In this manuscript we presented and described a software tool named WoLFeX, designed to process ALSFW data, which includes a wide range of new and previously proposed ALSFW metrics
We assessed the influence of radiometric correction on ALSFW metrics and on estimates of forest fuel variables through WoLFeX
Summary
Laser scanning has been used in the last several decades for a wide range of applications, such as climate change monitoring through biomass estimation [1,2], carbon sequestration [3,4] and wildlife protection [5,6]. In forestry applications, laser scanning is capable of registering accurate data from the different vertical strata, providing complementary information to other remote sensing techniques for a better characterization of forest structure [7]. Discrete airborne laser scanning (ALSD) can register larger areas, and it has been widely used to estimate some forest variables at stand- and individual-tree-level by tree segmentation approaches (e.g., [10,11]). The forest fuel variables mentioned (i.e., canopy bulk density, canopy fuel load, canopy base height, and dominant tree height) describe the forest fuel load as well as the horizontal and vertical structure. These are key inputs for fire behavior models, since they describe amount of fuel and its vertical and horizontal continuity [28]
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