Continuous canopy status monitoring is an essential factor to support and precisely apply orchard management actions such as pruning, pesticide and foliar treatment applications, or fertirrigation, ...among others. For that, this work proposes the use of multispectral vegetation indices to estimate geometric and structural orchard parameters from remote sensing images (high temporal and spatial resolution) as an alternative to more time-consuming processing techniques, such as LiDAR surveys or UAV photogrammetry. A super-intensive almond (
Prunus dulcis
) orchard was scanned using a mobile terrestrial laser (LiDAR) in two different vegetative stages (after spring pruning and before harvesting). From the LiDAR point cloud, canopy orchard parameters, including maximum height and width, cross-sectional area and porosity, were summarized every 0.5 m along the rows and interpolated using block kriging to the pixel centroids of PlanetScope (3 × 3 m) and Sentinel-2 (10 × 10 m) image grids. To study the association between the LiDAR-derived parameters and 4 different vegetation indices. A canonical correlation analysis was carried out, showing the normalized difference vegetation index (NDVI) and the green normalized difference vegetation index (GNDVI) to have the best correlations. A cluster analysis was also performed. Results can be considered optimistic both for PlanetScope and Sentinel-2 images to delimit within-field management zones, being supported by significant differences in LiDAR-derived canopy parameters.
•We developed a 100 m resolution urban morphological dataset for 36 major cities in China.•We proposed a framework to extract morphological parameters from building vectors.•City center showed larger ...building height and FAI, but smaller street width and SVF.•Southern cities showed larger building height and FAI, but smaller street width and SVF.
Characterizing urban morphology is critical for urban climate examination and modeling. However, high-resolution urban morphological datasets are lacking, especially in Chinese cities that undergoing fast-urbanization. We proposed a two-step rasterization method to develop an urban morphological dataset at a resolution of 100 m for 36 major cities in China. The morphological dataset includes building height, width, fraction, and street width as well as sky view factor and frontal area index. We then characterized the spatial patterns of these morphological parameters within and across cities. In general, the derived morphological parameters match the raw vector data well in terms of both magnitude and spatial distribution at the block, district, and city scales. The morphological parameters show large spatial variations within and across cities. On the city scale, the city center shows a larger building height and frontal area index, but smaller street width and sky view factor, compared to the city edge. Across cities, the morphological parameters generally show latitudinal variations, with higher building height and frontal area index, but smaller street width and sky view factor in the south. This new morphological dataset provides fundamental data to examine urban climate mechanism, classify urban land use, and drive urban climate model.
The structural characteristics of the canopy are a key consideration for improving the efficiency of the spray application process for tree crops. However, obtaining accurate data in an easy, ...practical, and efficient way is an important problem to be solved. This paper describes the technical characteristics of a sprayer prototype developed for vineyards, following the principles and previous laboratory tests described in the complementary paper Variable rate sprayer. Part 1 – Orchard prototype: design, implementation and validation. This prototype can modify the sprayed volume application rate according to the target geometry by using an algorithm based on the canopy volume inspired by the tree row volume (TRV) model. Variations in canopy width along the row crop are electronically measured using several ultrasonic sensors placed on the sprayer and used to modify the emitted flow rate from the nozzles in real time; the objective during this process is to maintain the sprayed volume per unit canopy volume (Lm⁻³). Field trials carried out at different crop stages for Merlot and Cabernet Sauvignon vines (Vitis vinifera) indicated a good relationship between the applied volume and canopy characteristics. The potential pesticide savings were estimated to be 21.9% relative to the costs of a conventional application. This conclusion is in accordance with the results of similar research on automated spraying systems.
Restoring riparian shade to formerly forested streams in cleared land is an important step in the restoration of stream ecological health. In a companion paper, we validated a numerical model for ...diffuse non-interceptance (difn) against measurements made in precisely-constructed physical models for two simplified geometries ‘canyon’ and ‘cylinder’ with trees lacking canopy ‘shape’. In this paper, we extend the model to include canopy ‘shape’ by representing trees as ellipses or kites, and quantifying shading from canopy overhang of the channel. The ratio of tree height (h) to stream width (w) strongly influences stream shade and is a key parameter when scoping riparian revegetation. Canopy width, overhang and viewpoint affect stream shade and could profitably be included in water temperature and aquatic plant growth models. Tree shape has a second-order effect on shade, most noticeably near the stream banks. The model predicts shade assuming a sky of uniform radiance (viz., it predicts shade to diffuse radiation) on the premise that difn is a useful index of long-term averaged light exposure. The model successfully reproduced the trajectory of shade reductions following riparian restoration predicted using a published physically-based model, confirming its suitability for scoping riparian shade restoration. While it would be feasible to include direct radiation in the model, this would require additional input data and computational effort.
ABSTRACT Laser sensor applications associated with LiDAR (Light Detection and Ranging) technology on platforms allow the evaluation of crop and forest biomass in a non-invasive way. This study ...presents the development of a measurement system based on LiDAR technology aimed at the proposed assessment of the height of sugarcane plants during the pre-harvest period. A laser sensor, a GNSS (Global Navigation Satellite System) receiver, and an inertial unit compose the measurement system. The equipment was integrated with a computer for data acquisition and installed on an agricultural tractor platform. The GNSS receiver with a real-time kinematic signal was synchronized to the laser sensor to obtain the point cloud and to the inertial unit to evaluate the intensity of the vibration from platform oscillation. Data acquisition was carried about 10 days before sugarcane harvest. The developed steps of acquisition and data processing enabled the generation of point clouds with a density of about 2,000 points m−2 and the extraction of metrics related to the height of sugarcane plants. The influence of vibration in the dataset was more significant in one of the experimental fields due the high-amplitude spectral power observed.
As a major part of the urban green space system, street trees play a corresponding role in adjusting the thermal comfort of the environment and alleviating heat island effects. The correlation ...between the morphological structure and microclimate factors in the lower canopy of street trees was studied, using data that were captured with vehicle-borne LiDAR to model the morphological structure and geometric canopy features of six key street tree species in the built-up area of Zhumadian City, Henan Province. The regulating ability and differences of canopy geometry on cooling, humidification, shading, and Physiologically Equivalent Temperature (PET) were studied. Research shows that: (1) Canopy Volume (CV), Canopy Area (CA), Canopy Diameter (CD), and Tree Height (TH) have a linear negative correlation with air temperature, relative humidity, and luminosity. TH had significant effects on the air temperature and relative humidity (R2 = 0.90, 0.96), and CV and CD had significant effects on luminosity (R2 = 0.70, 0.63). (2) The oval-shaped plant (Platanus acerifolia (Aiton) Willdenow) had a strong cooling and shading ability, with an average daily cooling of 2.3 °C and shading of 318 cd/m2. The spire-shaped plant (Cedrus deodara (Roxb.) G. Don) had a strong ability to humidify, with an average daily humidification of 4.5%. (3) The oval-shaped and spire-shaped plants had a strong regulation ability on PET, and the daily average regulation values were 40.5 °C and 40.9 °C, respectively. (4) The CD of the oval-shaped plant had a significant effect on PET (R2 = 0.49), and the TH of the spire-shaped plant had a significant effect on PET (R2 = 0.80), as well as a significantly higher CV and Leaf Area Index (LAI) than other street tree species. Therefore, selecting oval and spire canopy-shaped plants with a thick canopy, dense leaves, and high CD and TH values as street trees can provide significant advantages in cooling, humidifying, and shading, and can effectively adjust human comfort in the lower canopy understory. This study is the first to apply LiDAR technology to the regulation of urban microclimate. The research results provide a theoretical basis and quantitative reference for street tree design from the perspective of outdoor thermal comfort evaluation and play a guiding role in the application of LiDAR to urban forestry research.
One of the challenges in orchard management, in particular of hedgerow tree plantations, is the delineation of management zones on the bases of high-precision data. Along this line, the present study ...analyses the applicability of vegetation indices derived from UAV images to estimate the key structural and geometric canopy parameters of an almond orchard. In addition, the classes created on the basis of the vegetation indices were assessed to delineate potential management zones. The structural and geometric orchard parameters (width, height, cross-sectional area and porosity) were characterized by means of a LiDAR sensor, and the vegetation indices were derived from a UAV-acquired multispectral image. Both datasets summarized every 0.5 m along the almond tree rows and were used to interpolate continuous representations of the variables by means of geostatistical analysis. Linear and canonical correlation analyses were carried out to select the best performing vegetation index to estimate the structural and geometric orchard parameters in each cross-section of the tree rows. The results showed that NDVI averaged in each cross-section and normalized by its projected area achieved the highest correlations and served to define potential management zones. These findings expand the possibilities of using multispectral images in orchard management, particularly in hedgerow plantations.
Sunlight exposure of streams controls their thermal regime and light availability for photosynthesis. Restoring riparian shade to formerly forested streams in cleared land is an important step in the ...restoration of stream ecological health. Methods exist for measuring existing stream shade, but management tools are needed for predicting future shade as riparian plantings grow. We refine an existing geometrically-based numerical model for diffuse lighting which can be linked to models of tree growth to investigate how shade changes over time. The model predicts ‘diffuse non-interceptance’ (difn) which is an index of long-term averaged lighting. Shade of real (meandering) streams is bounded by two computationally straightforward cases: a perfectly straight channel (canyon model) and a channel meandering so tightly that its shade geometry ‘collapses’ to that of a circular pool (cylinder model). In this paper, we verify model results against measurements of shading made with a canopy analyzer instrument in precisely-constructed physical models of both the cylinder and canyon cases. For both canyon and cylinder geometries the observed and predicted difn matched closely (over a wide range of the ratio tree height to stream width, h/w) corroborating the numerical model. As expected, light exposure at the channel mid-point was higher than at channel edges, highlighting the need to consider variations in lighting across the channel when predicting water temperature and aquatic plant growth. Over the range of h/w where difn changes rapidly, shade was appreciably higher for the cylinder than the canyon case.
Abstract
One-dimensional light models using the Beer–Lambert equation (BL) with the light extinction coefficient k are simple and robust tools for estimating light interception of homogeneous ...canopies. Functional–structural plant models (FSPMs) are powerful to capture light–plant interactions in heterogeneous canopies, but they are also more complex due to explicit descriptions of three-dimensional plant architecture and light models. For choosing an appropriate modelling approach, the trade-offs between simplicity and accuracy need to be considered when canopies with spatial heterogeneity are concerned. We compared two light modelling approaches, one following BL and another using ray tracing (RT), based on a framework of a dynamic FSPM of greenhouse cucumber. Resolutions of hourly step (HS) and daily step (DS) were applied to simulate light interception, leaf-level photosynthetic acclimation and plant-level dry matter production over growth periods of 2–5 weeks. Results showed that BL-HS was comparable to RT-HS in predicting shoot dry matter and photosynthetic parameters. The k used in the BL approach was simulated using an empirical relationship between k and leaf area index established with the assistance of RT, which showed variation up to 0.2 in k depending on canopy geometry under the same plant density. When a constant k value was used instead, a difference of 0.2 in k resulted in up to 27 % loss in accuracy for shoot dry matter. These results suggested that, with the assistance of RT in k estimation, the simple approach BL-HS provided efficient estimation for long-term processes.
•Canopies showing efficiency in light interception and distribution is a must for any tree orchard.•A method to assess efficiency in light use was tested on three different canopy shapes in ...peach.•Canopy-intercepted photon flux (QC) is derived from ground-monitoring of light-shadow windows.•QC was very closely correlated (r>0.90) to whole-canopy net photosynthesis in all canopy shapes.•QC was also closely correlated (r=0.87) to whole-canopy transpiration in the Y trellis.
Functionality of training systems different in size, shape and geometry are primarily a function of their ability to intercept and distribute light effectively within the canopy. In peach, methodologies for a rapid and reliable assessment of such features are still lacking. In this study we propose a systemic approach that as unique data entry requires diurnal ground monitoring of the light-shadow windows of a tree canopy. Case studies for canopy shapes were a pyramid (▴, Delayed Vase), a parallelogram (♦, Palmette) and a Y (Tatura trellis) chosen within a 3-year-old peach orchard. Canopy geometrical and structural parameters calculated from above and below canopy radiation readings taken at full canopy development include Silhouette (S) as sunlit canopy area projected orthogonal to the sunbeam, leaf layer index (LLI), canopy leaf projection coefficient computed orthogonal to sunbeam direction (K⌋), instantaneous canopy photon influx (QCA), instantaneous canopy intercepted photon flux in the 300–1100nm waveband (QC) and canopy photon influx capture efficiency (εQCA→QC).
Whole-tree gas exchange was also continuously monitored for a week on each canopy shape to gain a direct measurement of canopy net assimilation rate (AC) and canopy transpiration rate (EC). A positive QC vs. AC correlation was shown by any canopy type, with r=0.93, 0.97 and 0.92 for ▴, ♦ and Y, respectively. By contrast, while QC and EC were weakly correlated in ▴ and ♦, a close positive correlation (r=0.87) was found between these two variables in Y. The Tatura trees also showed, regardless of timing of the day, the highest EC/AC, hence better water use efficiency. This study validates the hypothesis that a systemic assessment of canopy quantum flux absorption (QC) leads to reliable prediction of actual net canopy photosynthetic rates paving the way to: (a) easier and faster evaluation of efficiency of canopy systems differing in size and shape and (b) simplification in whole-canopy photosynthetic models.
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