scholarly journals Simulation of Ku-Band Profile Radar Waveform by Extending Radiosity Applicable to Porous Individual Objects (RAPID2) Model

2020 ◽  
Vol 12 (4) ◽  
pp. 684 ◽  
Author(s):  
Kai Du ◽  
Huaguo Huang ◽  
Yuyi Zhu ◽  
Ziyi Feng ◽  
Teemu Hakala ◽  
...  
Keyword(s):  
Penetration Depth ◽  
Forest Canopy ◽  
Stem Density ◽  
Forest Stands ◽  
Area Index ◽  
Single Tree ◽  
Crown Shape ◽  
Band Profile ◽  
Ku Band ◽  
Individual Objects

Similar to light detection and ranging (lidar), profile radar can detect forest vertical structure directly. Recently, the first Ku-band profile radar system designed for forest applications, called Tomoradar, has been developed and evaluated in boreal forest. However, the physical relationships between the waveform and forest structure parameters such as height, leaf area index (LAI), and aboveground biomass are still unclear, which limits later forestry applications. Therefore, it is necessary to develop a theoretical model to simulate the relationship and interpret the mechanism behind. In this study, we extend the Radiosity Applicable to Porous IndiviDual objects (RAPID2) model to simulate the profile radar waveform of forest stands. The basic assumption is that the scattering functions of major components within forest canopy are similar between profile radar and the side-looking radar implemented in RAPID2, except several modifications. These modifications of RAPID2 mainly include: (a) changing the observation angle from side-looking to nadir-looking; (b) enhancing the ground specular scattering in normal direction using Fresnel coefficient; (c) increasing the timing resolution and recording waveform. The simulated waveforms were evaluated using two plots of Tomoradar waveforms at co- and cross- polarizations, which are collected in thin and dense forest stands respectively. There is a good agreement (R2 ≥ 0.80) between the model results and experimental waveforms in HH and HV polarization modes and two forest scenes. After validation, the extended RAPID2 model was used to explore the sensitivity of the stem density, single tree LAI, crown shape, and twig density on the penetration depth in the Ku-band. Results indicate that the backscattering of the profile radar penetrates deeper than previous studies of synthetic aperture radar (SAR), and the penetration depth tends to be several meters in Ku-band. With the increasing of the needle and twig density in the microwave propagation path, the penetration depth decreases gradually. It is worth noting that variation of stem density seems to have the least effect on the penetration depth, when there is no overlapping between the single tree crowns.

scholarly journals Using Microwave Profile Radar to Estimate Forest Canopy Leaf Area Index: Linking 3D Radiative Transfer Model and Forest Gap Model

2021 ◽  
Vol 13 (2) ◽  
pp. 297
Author(s):  
Kai Du ◽  
Huaguo Huang ◽  
Ziyi Feng ◽  
Teemu Hakala ◽  
Yuwei Chen ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Forest Canopy ◽  
Parameters Estimation ◽  
Forest Gap ◽  
Gap Model ◽  
Area Index ◽  
Forest Gap Model ◽  
Band Profile ◽  
Ku Band

Profile radar allows direct characterization of the vertical forest structure. Short-wavelength, such as Ku or X band, microwave data provide opportunities to detect the foliage. In order to exploit the potential of radar technology in forestry applications, a helicopter-borne Ku-band profile radar system, named Tomoradar, has been developed by the Finnish Geospatial Research Institute. However, how to use the profile radar waveforms to assess forest canopy parameters remains a challenge. In this study, we proposed a method by matching Tomoradar waveforms with simulated ones to estimate forest canopy leaf area index (LAI). Simulations were conducted by linking an individual tree-based forest gap model ZELIG and a three-dimension (3D) profile radar simulation model RAPID2. The ZELIG model simulated the parameters of potential local forest succession scene, and the RAPID2 model utilized the parameters to generate 3D virtual scenes and simulate waveforms based on Tomoradar configuration. The direct comparison of simulated and collected waveforms from Tomoradar could be carried out, which enabled the derivation of possible canopy LAI distribution corresponding to the Tomoradar waveform. A 600-m stripe of Tomoradar data (HH polarization) collected in the boreal forest at Evo in Finland was used as a test, which was divided into 60 plots with an interval of 10 m along the trajectory. The average waveform of each plot was employed to estimate the canopy LAI. Good results have been found in the waveform matching and the uncertainty of canopy LAI estimation. There were 95% of the plots with the mean relative overlapping rate (RO) above 0.7. The coefficients of variation of canopy LAI estimates were less than 0.20 in 80% of the plots. Compared to lidar-derived canopy effective LAI estimation, the coefficient of determination was 0.46, and the root mean square error (RMSE) was 1.81. This study established a bridge between the Ku band profile radar waveform and the forest canopy LAI by linking the RAPID2 and ZELIG model, presenting the uncertainty of forest canopy LAI estimation using Tomoradar. It is worth noting that since the difference of backscattering contribution is caused by both canopy structure and tree species, similar waveforms may correspond to different canopy LAI, inducing the uncertainty of canopy LAI estimation, which should be noticed in forest parameters estimation with empirical methods.

scholarly journals Erratum: Du, K., et al. Simulation of Ku-Band Profile Radar Waveform by Extending Radiosity Applicable to Porous Individual Objects (RAPID2) Model. Remote Sensing 2020, 12, 684

2020 ◽  
Vol 12 (17) ◽  
pp. 2830
Author(s):  
Kai Du ◽  
Huaguo Huang ◽  
Yuyi Zhu ◽  
Ziyi Feng ◽  
Teemu Hakala ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Band Profile ◽  
Ku Band ◽  
Individual Objects

The authors wish to make the following corrections to this paper [...]

Inverting a forest canopy reflectance model to retrieve the overstorey and understorey leaf area index for forest stands

2011 ◽  
Vol 32 (22) ◽  
pp. 7591-7611 ◽  
Author(s):  
Jianxi Huang ◽  
Yuan Zeng ◽  
Andres Kuusk ◽  
Bingfang Wu ◽  
Lixin Dong ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Forest Canopy ◽  
Canopy Reflectance ◽  
Forest Stands ◽  
Area Index ◽  
Reflectance Model

scholarly journals Single tree crown shape and volume models for Pinus nigra planted forests in Italy to support forest management strategies in artificial stands

2020 ◽  
Author(s):  
Umberto Di Salvatore ◽  
Maurizio Marchi ◽  
Paolo Cantiani
Keyword(s):  
Forest Management ◽  
Field Data ◽  
Light Transmittance ◽  
Black Pine ◽  
Tree Crown ◽  
Area Index ◽  
Additional Tool ◽  
Single Tree ◽  
Crown Volume ◽  
Crown Shape

Abstract Background Tree crown can be considered the engine of trees whose size is a key variable to understand the most important ecological and physiological processes that occur in forest ecosystem. The shape and dimension of single-tree crown are affected by a combination of multiple factors such as lateral competition, fertility as well as forest management practices. Anyway, few models are provided in literature to derive their shape and volume from sampled data except the light transmittance or light measurements under canopy closure (Photosynthetic Active Radiation or Leaf Area Index). The main goal of the study is to present a simple and effective method to predict crown shape and crown volume in artificial black pine plantations in Italy from simple field data. Two key parameters involved in crown volume calculation in literature were here modelled. Such parameters were the distance from the top where the crown expresses its the maximum radius (L 0 ) and the radius at crown base height (r cb ). The analysis of crown profile and volume is based on available knowledge we found in literature (Pretzsch 2009) and where the considered species was not included. Results The nonlinear equation results the most adequate for the fitting and able to characterise the ecological processes more properly. Even if just slightly different, the mean absolute error was lower and statistically significant and around 84 cm for L 0 and 36 cm for r cb . Then the use of a modelling procedure also allowed the calculation of confidence intervals and was more powerful than a single multiplier, which is the most common method available in literature. Once compared with field data collected during thinning harvesting, the calculated volumes were correlated with thinning intensities and able to characterise the number of trees removed in each treatment and the increased amount of PAR on the ground. Conclusions The proposed model results useful to evaluate the spatial structure of forest stand without sophisticated and time-consuming surveys and could be an additional tool to support the practical management of artificial black pine stands.

scholarly journals UAV Based Estimation of Forest Leaf Area Index (LAI) through Oblique Photogrammetry

2021 ◽  
Vol 13 (4) ◽  
pp. 803
Author(s):  
Lingchen Lin ◽  
Kunyong Yu ◽  
Xiong Yao ◽  
Yangbo Deng ◽  
Zhenbang Hao ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Point Cloud ◽  
Forest Canopy ◽  
Estimation Method ◽  
Vertical Direction ◽  
Estimation Accuracy ◽  
3D Point Cloud ◽  
Area Index ◽  
Better Than

As a key canopy structure parameter, the estimation method of the Leaf Area Index (LAI) has always attracted attention. To explore a potential method to estimate forest LAI from 3D point cloud at low cost, we took photos from different angles of the drone and set five schemes (O (0°), T15 (15°), T30 (30°), OT15 (0° and 15°) and OT30 (0° and 30°)), which were used to reconstruct 3D point cloud of forest canopy based on photogrammetry. Subsequently, the LAI values and the leaf area distribution in the vertical direction derived from five schemes were calculated based on the voxelized model. Our results show that the serious lack of leaf area in the middle and lower layers determines that the LAI estimate of O is inaccurate. For oblique photogrammetry, schemes with 30° photos always provided better LAI estimates than schemes with 15° photos (T30 better than T15, OT30 better than OT15), mainly reflected in the lower part of the canopy, which is particularly obvious in low-LAI areas. The overall structure of the single-tilt angle scheme (T15, T30) was relatively complete, but the rough point cloud details could not reflect the actual situation of LAI well. Multi-angle schemes (OT15, OT30) provided excellent leaf area estimation (OT15: R2 = 0.8225, RMSE = 0.3334 m2/m2; OT30: R2 = 0.9119, RMSE = 0.1790 m2/m2). OT30 provided the best LAI estimation accuracy at a sub-voxel size of 0.09 m and the best checkpoint accuracy (OT30: RMSE [H] = 0.2917 m, RMSE [V] = 0.1797 m). The results highlight that coupling oblique photography and nadiral photography can be an effective solution to estimate forest LAI.

scholarly journals Optimizing smartphone-based canopy hemispherical photography

2021 ◽  
Author(s):  
Gastón Mauro Díaz
Keyword(s):  
Large Scale ◽  
Forest Canopy ◽  
Accuracy Assessment ◽  
Low Cost ◽  
R Package ◽  
Coefficient Of Determination ◽  
Native Forest ◽  
Hemispherical Photography ◽  
Area Index ◽  
Plant Area Index

1) Hemispherical photography (HP) is a long-standing tool for forest canopy characterization. Currently, there are low-cost fisheye lenses to convert smartphones into high-portable HP equipment; however, they cannot be used whenever since HP is sensitive to illumination conditions. To obtain sound results outside diffuse light conditions, a deep-learning-based system needs to be developed. A ready-to-use alternative is the multiscale color-based binarization algorithm, but it can provide moderate-quality results only for open forests. To overcome this limitation, I propose coupling it with the model-based local thresholding algorithm. I call this coupling the MBCB approach. 2) Methods presented here are part of the R package CAnopy IMage ANalysis (caiman), which I am developing. The accuracy assessment of the new MBCB approach was done with data from a pine plantation and a broadleaf native forest. 3) The coefficient of determination (R^2) was greater than 0.7, and the root mean square error (RMSE) lower than 20 %, both for plant area index calculation. 4) Results suggest that the new MBCB approach allows the calculation of unbiased canopy metrics from smartphone-based HP acquired in sunlight conditions, even for closed canopies. This facilitates large-scale and opportunistic sampling with hemispherical photography.

scholarly journals Electromagnetic Induction Is a Fast and Non-Destructive Approach to Estimate the Influence of Subsurface Heterogeneity on Forest Canopy Structure

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3218
Author(s):  
Simon Damien Carrière ◽  
Nicolas K. Martin-StPaul ◽  
Claude Doussan ◽  
François Courbet ◽  
Hendrik Davi ◽  
...  
Keyword(s):  
Forest Structure ◽  
Electromagnetic Induction ◽  
Forest Canopy ◽  
Soil Depth ◽  
Soil Conditions ◽  
Mediterranean Forests ◽  
Area Index ◽  
Edaphic Conditions ◽  
Plant Area Index ◽  
Plant Area

The spatial forest structure that drives the functioning of these ecosystems and their response to global change is closely linked to edaphic conditions. However, the latter properties are particularly difficult to characterize in forest areas developed on karst, where soil is highly rocky and heterogeneous. In this work, we investigated whether geophysics, and more specifically electromagnetic induction (EMI), can provide a better understanding of forest structure. We use EMI (EM31, Geonics Limited, Ontario, Canada) to study the spatial variability of ground properties in two different Mediterranean forests. A naturally post-fire regenerated forest composed of Aleppo pines and Holm oaks and a monospecific plantation of Altlas cedar. To better interpret EMI results, we used electrical resistivity tomography (ERT), soil depth surveys, and field observations. Vegetation was also characterized using hemispherical photographs that allowed to calculate plant area index (PAI). Our results show that the variability of ground properties contribute to explaining the variability in the vegetation cover development (plant area index). Vegetation density is higher in areas where the soil is deeper. We showed a significant correlation between edaphic conditions and tree development in the naturally regenerated forest, but this relationship is clearly weaker in the cedar plantation. We hypothesized that regular planting after subsoiling, as well as sylvicultural practices (thinning and pruning) influenced the expected relationship between vegetation structure and soil conditions measured by EMI. This work opens up new research avenues to better understand the interplay between soil and subsoil variability and forest response to climate change.

scholarly journals Hydrological effects of Norway spruce and European beech on snow cover in a mid-mountain region of the Polana mts., Slovakia / Hydrologický vplyv smreka obyčajného a buka lesného na snehovú pokrývku v stredohorských polohách pohoria poľana na slovensku

2012 ◽  
Vol 60 (4) ◽  
pp. 319-332 ◽  
Author(s):  
Matus Hribik ◽  
Tomas Vida ◽  
Jaroslav Skvarenina ◽  
Jana Skvareninova ◽  
Lubomir Ivan
Keyword(s):  
Snow Cover ◽  
Norway Spruce ◽  
Forest Canopy ◽  
Biosphere Reserve ◽  
European Beech ◽  
Mountain Region ◽  
Runoff Generation ◽  
Forest Stands ◽  
Snow Melting ◽  
Beech Stand

The paper evaluates the results of a 6-year-monitoring of the eco-hydrological influence of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus silvatica L.) forest stands on the hydro-physical properties of snow cover. The experiment was carried out in the artificially regenerated 20-25-year-old forest stands approaching the pole timber stage in the middle mountain region of the Polana Mts. - Biosphere reserve situated at about 600 m a.s.l. during the period of maximum snow supply in winters of years 2004 - -2009. Forest canopy plays a decisive role at both the snow cover duration and spring snow melting and runoff generation. A spruce stand is the poorest of snow at the beginning of winter. High interception of spruce canopy hampers the throughfall of snow to soil. During the same period, the soil surface of a beech stand accumulates greater amount of snow. However, a spruce stand accumulates snow by creating snow heaps during the periods of maximum snow cumulation and stand´s microclimate slows down snow melting. These processes are in detail discussed in the paper. The forest stands of the whole biosphere reserve slow down to a significant extent both the snow cover melting and the spring runoff of the whole watershed.

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