3D leaf water content mapping using terrestrial laser scanner backscatter intensity with radiometric correction

Zhu, Xi; Wang, Zhihui; Darvishzadeh, Roshanak; Skidmore, A.K.; Niemann, K. Olaf

doi:10.1016/j.isprsjprs.2015.10.001

Cited by 61 publications

(65 citation statements)

References 56 publications

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“…Gaulton et al [31] showed somewhat similar results (R 2 = 0.65), with only five leaf samples employing a laser wavelength at 1545 nm. Zhu et al [29] also presented a significant correlation (R 2 = 0.74) between laser intensity at 1550 nm and EWT with a wide range of leaf structures, but there was wide variability in the correlation between the species.…”

Section: Discussionmentioning

confidence: 95%

“…Additionally, the limitations of the ranging device should be noted since the incidence angle was approximated from the point clouds; thus, any measuring error in ranging can cause an error in the calculation of the surface normal and the resulting incidence angle. The accuracy of the ranging measurements may not be sufficient to account for small wrinkles and curvatures of leaves, but when a wider range of leaf angles and larger surfaces are present (i.e., scanning a tree), the incidence angle correction could be able to improve the estimation of EWT, as was found in Zhu et al [29]. Also, the surface properties of the target affect the effect of incidence angle on the measured intensity, thus rough surfaces are less influenced by the incidence angle if the surface scattering is highly diffuse [20].…”

Section: Discussionmentioning

confidence: 99%

“…Spruce and pine needle samples were found to dry relatively slowly during the experiment; therefore, they were dried in an oven at 65 • C in 10-min time periods after 44 h of drying naturally to capture a wider range of EWT values than would have been possible without drying, similar to the approach used by Zhu et al [29]. The relative humidity in the laboratory was about 45% during the experiment.…”

Section: Experiments Designmentioning

confidence: 99%

“…The mapping of EWT has recently been studied at leaf level using a single wavelength full-waveform TLS operating at 1550 nm, resulting in a significant correlation between backscattered intensity and EWT (R 2 = 0.74), with eight broadleaf species exhibiting a variety of leaf surface types [29]. However, the achieved correlation was a result of a number of intensity correction methods including the removal of the specular reflection component, and correction of incidence angle.…”

Section: Introductionmentioning

confidence: 99%

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Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners

et al. 2016

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Decreased leaf moisture content, typically measured as equivalent water thickness (EWT), is an early signal of tree stress caused by drought, disease, or pest insects. We investigated the use of two terrestrial laser scanners (TLSs) employing different wavelengths for improving the understanding how EWT can be retrieved in a laboratory setting. Two wavelengths were examined for normalizing the effects of varying leaf structure and geometry on the measured intensity. The relationship between laser intensity features, using red (690 nm) and shortwave infrared (1550 nm) wavelengths, and the EWT of individual leaves or groups of needles were determined with and without intensity corrections. To account for wrinkles and curvatures of the leaves and needles, a model describing the relationship between incidence angle and backscattered intensity was applied. Additionally, a reflectance model describing both diffuse and specular reflectance was employed to remove the fraction of specular reflectance from backscattered intensity. A strong correlation (R 2 = 0.93, RMSE = 0.004 g/cm 2 ) was found between a normalized ratio of the two wavelengths and the measured EWT of samples. The applied intensity correction methods did not significantly improve the results of the study. The backscattered intensity responded to changes in EWT but more investigations are needed to test the suitability of TLSs to retrieve EWT in a forest environment.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Section: Experiments Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners

et al. 2016

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“…Intensity, which is insensitive to ambient light and shadowing [5], is initially used to improve point cloud separability. Apart from visualization purposes, intensity data can be used as a major or complementary data source in various studies, such as vegetation and forest investigation [6,7], road traffic marking identification [8,9], water content extraction [6,[10][11][12][13], metro tunnel inspection [10,14], and lithological differentiation [5,15,16].…”

Section: Introductionmentioning

confidence: 99%

Specular Reflection Effects Elimination in Terrestrial Laser Scanning Intensity Data Using Phong Model

Tan

Cheng

2017

Remote Sensing

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Abstract:The intensity value recorded by terrestrial laser scanning (TLS) systems is significantly influenced by the incidence angle. The incidence angle effect is an object property, which is mainly related to target scattering properties, surface structures, and even some instrumental effects. Most existing models focus on diffuse reflections of rough surfaces and ignore specular reflections, despite that both reflections simultaneously exist in all natural surfaces. Due to the coincidence of the emitter and receiver in TLS, specular reflections can be ignored at large incidence angles. On the contrary, at small incidence angles, TLS detectors can receive a portion of specular reflections. The received specular reflections can trigger highlight phenomenon (hot-spot effects) in the intensity data of the scanned targets, particularly those with a relatively smooth or highly-reflective surface. In this study, a new method that takes diffuse and specular reflections, as well as the instrumental effects into consideration, is proposed to eliminate the specular reflection effects in TLS intensity data. Diffuse reflections and instrumental effects are modeled by a polynomial based on Lambertian reference targets, whereas specular reflections are modeled by the Phong model. The proposed method is tested and validated on different targets scanned by the Faro Focus 3D 120 terrestrial scanner. Results imply that the coefficient of variation of the intensity data from a homogeneous surface is reduced by approximately 38% when specular reflections are considered. Compared with existing methods, the proposed method exhibits good feasibility and high accuracy in eliminating the specular reflection effects for intensity image interpretation and 3D point cloud representation by intensity.

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Monitoring small pioneer trees in the forest-tundra ecotone: using multi-temporal airborne laser scanning data to model height growth

Hauglin

Bollandsås

Næsset

2017

Environ Monit Assess

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Monitoring of forest resources through national forest inventory programmes is carried out in many countries. The expected climate changes will affect trees and forests and might cause an expansion of trees into presently treeless areas, such as above the current alpine tree line. It is therefore a need to develop methods that enable the inclusion of also these areas into monitoring programmes. Airborne laser scanning (ALS) is an established tool in operational forest inventories, and could be a viable option for monitoring tasks. In the present study, we used multi-temporal ALS data with point density of 8-15 points per m, together with field measurements from single trees in the forest-tundra ecotone along a 1500-km-long transect in Norway. The material comprised 262 small trees with an average height of 1.78 m. The field-measured height growth was derived from height measurements at two points in time. The elapsed time between the two measurements was 4 years. Regression models were then used to model the relationship between ALS-derived variables and tree heights as well as the height growth. Strong relationships between ALS-derived variables and tree heights were found, with R values of 0.93 and 0.97 for the two points in time. The relationship between the ALS data and the field-derived height growth was weaker, with R values of 0.36-0.42. A cross-validation gave corresponding results, with root mean square errors of 19 and 11% for the ALS height models and 60% for the model relating ALS data to single-tree height growth.

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3D leaf water content mapping using terrestrial laser scanner backscatter intensity with radiometric correction

Cited by 61 publications

References 56 publications

Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners

Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners

Specular Reflection Effects Elimination in Terrestrial Laser Scanning Intensity Data Using Phong Model

Monitoring small pioneer trees in the forest-tundra ecotone: using multi-temporal airborne laser scanning data to model height growth

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