Linyuan Li

Linyuan Li
Beijing Forestry University · College of Forestry

Ph.D

About

24
Publications
19,464
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325
Citations

Publications

Publications (24)
Article
Full-text available
Remote sensing via unmanned aerial vehicles (UAVs) is becoming a very important tool for augmenting traditional spaceborne and airborne remote sensing techniques. Commercial RGB cameras are often the payload on UAVs, because they are inexpensive, easy to operate and require little data processing. RGB images are increasingly being used for mapping...
Article
Full-text available
The canopy bidirectional reflectance distribution function (BRDF) plays a pivotal role in estimating the biophysical parameters of plants, whereas soil background anisotropy creates challenges for their retrieval. Soil optical properties affect canopy anisotropic characteristics, especially in open-canopy areas. However, the remote sensing of backg...
Article
Full-text available
The clumping effect is the main issue causing the heterogeneity in vegetation canopies and the underestimation of leaf area index (LAI) obtained using indirect measurement methods. Significant efforts have been exerted to correct for the clumping effect and derive the true LAI. Recent research has shown that the fractal dimension (FD) is directly r...
Article
Full-text available
Fire disturbance has been one of the main reasons for the alteration of forest succession trajectory and forest composition in the Daxing’anling Mountain of Inner Mongolia. Therefore, predicting the dynamic process of post-fire regrowth is critical for understanding the specific forest succession trajectory of this region. The 3-PGmix model (i.e.,...
Article
Full-text available
Pine wilt disease (PWD) is a global destructive threat to forests which has been widely spread and has caused severe tree mortality all over the world. It is important to establish an effective method for forest managers to detect the infected area in a large region. Remote sensing is a feasible tool to detect PWD, but the traditional empirical met...
Article
Full-text available
Accurate wall-to-wall estimation of forest crown cover is critical for a wide range of ecological studies. Notwithstanding the increasing use of UAVs in forest canopy mapping, the ultrahigh-resolution UAV imagery requires an appropriate procedure to separate the contribution of understorey from overstorey vegetation, which is complicated by the spe...
Article
Canopy radiative transfer (RT) modeling is critical for the quantitative retrieval of vegetation biophysical parameters and has been under intensive research over the decades. RT models of discontinuous canopies, such as three-dimensional (3D) RT models, posed challenges for the early one-dimensional (1D) hypothesis. Although 3D RT models have high...
Article
Full-text available
The demand for Leaf Area Index (LAI) retrieval from spaceborne full-waveform LiDAR increases due to its direct sampling of the three-dimensional forest structure at a near-global scale. However, the nonrandomness (i.e., clumping effect) of canopy composition limits the reliability of LAI derived from two common methods. They either assume a homogen...
Article
Full-text available
Forest canopy cover (FCC) plays an important role in many ecological, hydrological and forestry applications. For large-scale applications, FCC is usually estimated from remotely sensed data by inverting radiative transfer models (RTMs) or using data-driven regressions. In this study, we proposed a hybrid model, which combines 3D RTMs and transfer...
Article
Full-text available
Terrain reflected solar radiation in snow‐covered mountains is nonnegligible in investigations of the energy budget. However, it has so far not been investigated thoroughly, especially with regard to the influence of snow cover. Several parameterization approaches have been raised but not yet evaluated in a more uniform and quantitative manner. Bas...
Article
Accurate and rapid estimation of canopy cover (CC) is crucial for many ecological and environmental models and for forest management. Unmanned aerial vehicle-light detecting and ranging (UAV-LiDAR) systems represent a promising tool for CC estimation due to their high mobility, low cost, and high point density. However, the CC values from UAV-LiDAR...
Article
Full-text available
Leaf angle distribution (LAD) is an important attribute of forest canopy architecture and affects the solar radiation regime within the canopy. Terrestrial laser scanning (TLS) has been increasingly used in LAD estimation. The point clouds data suffer from the occlusion effect, which leads to incomplete scanning and depends on measurement strategie...
Article
Full-text available
Accurate estimates of canopy cover (CC) are central for a wide range of forestry studies. As direct measurements are impractical, indirect optical methods have often been used to estimate CC from the complement of gap fraction measurements obtained with restricted-view sensors. In this short note we evaluated the influence of the image pixel resolu...
Article
Full-text available
Occlusion effect, an inherent problem of terrestrial laser scanning (TLS) measurements, limits the potential of TLS data in tree attribute estimation. Multiple scans seek to mitigate this effect to provide enhanced scan completeness. However, the numbers and locations of the scans (i.e., the scan design) are usually determined via a subjective asse...
Article
Full-text available
Vegetation cover estimation for overstory and understory layers provides valuable information for modeling forest carbon and water cycles and refining forest ecosystem function assessment. Although previous studies demonstrated the capability of light detection and ranging (LiDAR) in the three-dimensional (3D) characterization of forest overstory a...
Article
Full-text available
Accurate and efficient measurement of leaf angle distribution (LAD) is important for characterizing canopy structures and understanding solar radiation regimes within the plant canopy. The main challenge for obtaining LAD is measuring the orientations of individual leaves rapidly and accurately in complex field conditions. In this letter, we propos...
Article
Full-text available
Three-dimensional (3D) radiative transfer modeling of the transport and interaction of radiation through earth surfaces is challenging due to the complexity of the landscapes as well as the intensive computational cost of 3D radiative transfer simulations. To reduce computation time, current models work with schematic landscapes or with small-scale...
Article
Full-text available
Estimation of daily downward shortwave radiation (DSR) is of great importance in global energy budget and climatic modeling. The combination of satellite-based instantaneous measurements and temporal extrapolation models is the most feasible way to capture daily radiation variations at large scales. However, previous studies did not pay enough atte...
Article
Normalized difference vegetation index (NDVI) of highly dense vegetation (NDVIv) and bare soil (NDVIs), identified as the key parameters for Fractional Vegetation Cover (FVC) estimation, are usually obtained with empirical statistical methods However, it is often difficult to obtain reasonable values of NDVIv and NDVIs at a coarse resolution (e.g.,...
Article
Full-text available
A novel method for registering imagery with Light Detection And Ranging (LiDAR) data is proposed. It is based on the phenomenon that the back-projection of LiDAR point cloud of an object should be located within the object boundary in the image. Using this inherent geometrical constraint, the registration parameters computation of both data sets on...

Questions

Questions (6)
Question
Dear all,
I would like to find a solution to separate green tree pixels from background using UAV images taken over forest area. Generally, forest floor/background is complex with containing soil, rocks, grass/shrub, moss and so forth. Moreover, many shaded ground areas casted by trees introduce more difficulty for image segmentation. All above mentioned induce big challenges for extracting green tree pixels from RGB even multispectral images.
Question
I want to conduct Ground synchronization of VIIRS. unfortunatelly,I don't know how to acquire its overpass. Please help me .
Thanks
Li
Question
Hi, Guys,
 Anyone who could recommend a website consisting of global ground validation site distribution map of some satellite  product.
Thanks a lot
Question
Dear all, I want to discuss how much error caused by central projection of extracting vegetation cover using the method of photograph.  As we all known, the definition of vegetation cover points that parallel projection is necessary for assessing veg cover. However, central projection will bring error for evaluating veg cover. Could anyone recommend some papers about this topic. Thanks a lot.
Question
First, I can estimate LAI at several viewing zenith angles by the equation of Nilson 1971,utilizing digital photos taken from different angles . of course, it needs some assumption. Second, I would like to calculate the final LAI as the output value through above, however, I don't konw how to do this. Please someone help me .

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Projects

Projects (2)
Project
The recent technological advancement in the UAVs, light-weight imaging sensors (RGB, multispectral and hyperspectral camera) and image processing provides new operational systems for quantitative remote sensing of plants at very fine resolution. Accurate and efficient estimation of biophysical variables/traits is essential especially for high-throughput phenotyping and ecosystem monitoring. UAV also offers new insights into characterization of the canopy and background anisotropy using multi-angular observation, which will facilitate the canopy radiative transfer modelling and validation. Besides, the UAVs have potentials to revolutionize the geometric modelling with its flexibility.
Project
The projects aims to develop an efficient ray-tracing based 3D radiative transfer model to simulate various remote sensing datasets. For using this model, please refer to: http://lessrt.org/