Analyzing the Angle Effect of Leaf Reflectance Measured by Indoor Hyperspectral Light Detection and Ranging (LiDAR)

Abstract

Hyperspectral light detection and ranging (LiDAR) (HSL) combines the characteristics of hyperspectral imaging and LiDAR techniques into a single instrument without any data registration. It provides more information than hyperspectral imaging or LiDAR alone in the extraction of vegetation physiological and biochemical parameters. However, the laser pulse intensity is affected by the incident angle, and its effect on HSL has not yet been fully explored. It is important for employing HSL to investigate vegetation properties. The aim of this paper is to study the incident angle effect of leaf reflectance with HSL and build a model about this impact. In this paper, we studied the angle effect of leaf reflectance from indoor HSL measurements of individual leaves from four typical tree species in Beijing. We observed that (a) the increasing of incident angle decreases the leaf reflectance; (b) the leaf spectrum observed by HSL from 650 to 1000 nm with 10 nm spectral resolution (36 channels) are consistent with those that measured by Analytica Spectra Devices (ASD) spectrometer (R2 = 0.9472 ~ 0.9897); (c) the specular reflection is significant in the red bands, and clear non-Lambertian characteristics are observed. In the near-infrared, there is little specular reflection, but it follows the Lambert-scattering law. We divided the whole band (650–1000 nm) into six bands and established an empirical model to correct the influence of angle effect on the reflectance of the leaf for HSL applications. In the future, the calibration of HSL measurements applied for other targets will be studied by rigorous experiments and modelling.

Radiometric Calibration for Incidence Angle, Range and Sub-Footprint Effects on Hyperspectral LiDAR Backscatter Intensity

“…The relationship between the backscatter intensity of the HSL and the incident angle and range is explored. The incidence angle and range experiments' results, carried out with different targets, demonstrated that the backscatter intensity recorded by the HSL (Figures 6 and 9) cannot follow the theoretical model, including the Lambertian model and the 1/R 2 relation model, which is consistent with some previous studies [27,46,47]. The laser backscatter intensities of targets with isotropically reflecting reflectance surfaces share a similar trend in the incidence angle and distance behavior and there seems to be no wavelength dependency on the scanning geometry effect.…”

Application of Hyperspectral LiDAR on 3-D Chlorophyll-Nitrogen Mapping of Rohdea Japonica in Laboratory

“…The distribution density of leaf angle, one of canopy structure parameter, is highly related to the reflectance signals of HSL. Some relevant scholars have carried out preliminary exploration in the correction of factors such as distance and incident angle [45,50,53], but the impact assessment and model correction of complex canopy reflection characteristics need to be further studied.…”

“…Thus, we set the angle threshold as 60° for the incidence angle calibration in this study during the scanning experiment. Hu et al [53] conducted the similar experiments on different leaves from 0° to 80° and they found the specular reflection was significant in red band, and its non-Lambertian characteristics are obvious. However, the reflectance characteristic in NIR band followed the Lambertscattering law, but little specular reflection was observed.…”

Survey of Datafusion Techniques for Laser and Vision Based Sensor Integration for Autonomous Navigation

“…2. Continuous/Full waveform LiDAR: When the entire waveform is saved as one unit, its a continuous or full form LiDAR [108]. A lot of LiDARs use this form of recording.…”