Canopy Penetration Research Articles

Improved Building Extraction With Integrated Decomposition of Time-Frequency and Entropy-Alpha Using Polarimetric SAR Data

Building extraction is one of the primary applications of urban remote sensing. Polarimetric synthetic aperture radar (POLSAR), with its all-weather day and night imaging, canopy penetration and full polarimetric information, provides a unique way to detecting and characterizing urban areas. In this study, the time-frequency decomposition technique and the entropy/alpha-Wishart classifier were integrated to improve building extraction. The entropy/alpha-Wishart classifier was able to extract ortho-oriented buildings. After time-frequency transformation, the variation of entropy, alpha, anisotropy differs for objects with different scattering mechanisms, and the alpha angle of subaperture images was optimal in delineating slant-oriented buildings. A comparison between the integrated approach and the conventional entropy/alpha-Wishart classifier was performed on both C- and L-band NASA/JPL AIRSAR datasets. The overall accuracy and kappa value of the integrated approach was about 20% higher than that of the entropy/alpha-Wishart classifier. The C-band output tends to show more detailed scattering properties whereas the extracted buildings from the L-band image reveal better overall visual results.

Land Cover and Soil Type Mapping From Spaceborne PolSAR Data at L-Band With Probabilistic Neural Network

This paper evaluates performance of fully polarimetric SAR (PolSAR) data in several land cover mapping studies in the boreal forest environment, taking advantage of the high canopy penetration capability at L-band. The studies included multiclass land cover mapping, forest-nonforest delineation, and classification of soil type under vegetation. PolSAR data used in the study were collected by the ALOS PALSAR sensor in 2006-2007 over a managed boreal forest site in Finland. A supervised classification approach using selected polarimetric features in the framework of probabilistic neural network (PNN) was adopted in the study. It has no assumptions about statistics of the polarimetric features, using nonparametric estimation of probability distribution functions instead. The PNN-based method improved classification accuracy compared with standard maximum-likelihood approach. The improvement was considerably strong for soil type mapping under vegetation, indicating notable non-Gaussian effects in the PolSAR data even at L-band. The classification performance was strongly dependent on seasonal conditions. The PolSAR feature data set was further modified to include a number of recently proposed polarimetric parameters (surface scattering fraction and scattering diversity), reducing the computational complexity at practically no loss in the classification accuracy. The best obtained accuracies of up to 82.6% in five-class land cover mapping and more than 90% in forest-nonforest mapping in wall-to-wall validation indicate suitability of PolSAR data for wide-area land cover and forest mapping.

Coherent structures detected in the unstable atmospheric surface layer above the Amazon forest

Some characteristics of the turbulence structure above primary forest localized in the south-western Amazon are analyzed. The data was collected in 60m height meteorological tower erected in Rebio-Jarú Reserve, Brazil. The Morlet’s wavelet is used to detect coherent structures (CS) “ramp” time scales from turbulent virtual temperature data measured above forest, under day-time conditions. It is shown that there is a close relationship between time scale of the coherent structure (TCS) and the height to the inflection point in the mean wind speed profile (IP). A time scale associated with the IP is used to provide useful information on inside canopy penetration flow in order to be compared with the CS time-scale. The results show a very robust correlation between these two time scales (for 144 half-hourly data sets, a correlation coefficient value of 0.9 have been obtained). Such results provide new insights regarding shear instability and turbulent eddy characteristics above tall vegetation, in the surface roughness sub-layer (SRS).

Predicting Surface Fuel Models and Fuel Metrics Using Lidar and CIR Imagery in a Dense, Mountainous Forest

We compared the ability of several classification and regression algorithms to predict forest stand structure metrics and standard surface fuel models. Our study area spans a dense, topographically complex Sierra Nevada mixed-conifer forest. We used clustering, regression trees, and support vector machine algorithms to analyze high density (average 9 pulses/m 2 ), discrete return, small-footprint lidar data, along with multispectral imagery. Stand structure metric predictions generally decreased with increased canopy penetration. For example, from the top of canopy, we predicted canopy height (r 2 0.87), canopy cover (r 2 0.83), basal area (r 2 0.82), shrub cover (r 2 0.62), shrub height (r 2 0.59), combined fuel loads (r 2 0.48), and fuel bed depth (r 2 0.35). While the general fuel types were predicted accurately, specific surface fuel model predictions were poor (76 percent and 50 percent correct classification, respectively) using all algorithms. These fuel components are critical inputs for wildfire behavior modeling, which ultimately support forest management decisions. This comprehensive examination of the relative utility of lidar and optical imagery will be useful for forest science and management.

A COMPARITIVE STUDY USING GEOMETRIC AND VERTICAL PROFILE FEATURES DERIVED FROM AIRBORNE LIDAR FOR CLASSIFYING TREE GENERA

Abstract. We present a comparative study between two different approaches for tree genera classification using descriptors derived from tree geometry and those derived from the vertical profile analysis of LiDAR point data. The different methods provide two perspectives for processing LiDAR point clouds for tree genera identification. The geometric perspective analyzes individual tree crowns in relation to valuable information related to characteristics of clusters and line segments derived within crowns and overall tree shapes to highlight the spatial distribution of LiDAR points within the crown. Conversely, analyzing vertical profiles retrieves information about the point distributions with respect to height percentiles; this perspective emphasizes of the importance that point distributions at specific heights express, accommodating for the decreased point density with respect to depth of canopy penetration by LiDAR pulses. The targeted species include white birch, maple, oak, poplar, white pine and jack pine at a study site northeast of Sault Ste. Marie, Ontario, Canada.

Interactive Effects of Fungicide, Application Timing, and Spray Volume on Peanut Diseases and Yield

Fungicide penetration of the peanut (Arachis hypogaea) canopy to target soilborne pathogens is difficult due to the dense foliage present when mid- to late-season applications are made. To assess the effect of application timing and volume on leaf spot and stem rot control as well as peanut yield, pyraclostrobin (0.21 kg a.i./ha) or chlorothalonil (1.26 kg a.i./ha), a systemic and a contact fungicide, respectively, were applied four times on cv. Georgia Green during the day (on unfolded leaves) or at night (on folded leaves) at 187, 243, or 355 liters/ha. Night application of pyraclostrobin, across spray volumes, gave the best stem rot control and pod yield increase. Pyraclostrobin applied during the day at higher spray volumes also slightly increased control of stem rot, apparently by improving canopy penetration. Neither application timing nor spray volume affected leaf spot control with pyraclostrobin. Higher spray volumes for the chlorothalonil applications tended to improve control of early and late leaf spot, possibly by increasing coverage of foliage and stems. Accepted for publication 10 January 2012. Published 20 April 2012.

Spatial variability of photosynthetically active radiation in European beech and Norway spruce

The vertical and horizontal variability of solar radiation within a mature European beech ( Fagus sylvatica L.)–Norway spruce ( Picea abies [L.] Karst) mixed stand in Southern Germany is investigated. A large dataset with more than one million spectral measurements of photon fluence rates at six vertical levels within the stand is analyzed with respect to tree species, meteorological sky conditions, and the influence of solar elevation angle on canopy penetration. Irradiance probability density functions of the photosynthetically active waveband are used to describe the three-dimensional radiation field. For a quantification of umbra, penumbra, and sunfleck frequencies, in-canopy fractions of photon fluence rates within the photosynthetically active waveband are investigated. Different phenological stages of beech and their effects on the in-canopy light climate are compared. The results show that during overcast conditions (OVC) fractions of photosynthetically active radiation (PAR) are higher at all canopy levels than during clear sky (CS) conditions due to their exclusively diffuse character. The lowest median PAR level of less than 1% of above-canopy PAR can be observed in the shade crown of beech and at ground level. More PAR can penetrate the canopy at a higher solar elevation under CS conditions. This effect is more pronounced for spruce than for beech due to the conical crown shape of the conifers that allows photons from higher angles to enter the gaps inbetween trees in contrast to the more homogeneously closed beech canopy. Solar elevation is not an important factor at uniformly overcast conditions. Differences in the vertical distribution of umbra and penumbra can be detected when comparing species or different sky conditions. The frequency of sunflecks differs more by species and by the vertical position within the canopy than by sky condition.

Mapping gap fraction, LAI and defoliation using various ALS penetration variables

Four alternative airborne laser scanning (ALS) canopy penetration variables were compared for their suitability for mapping of gap fraction, leaf area index and disturbances in a Scots pine forest. The variables were based on either echo counting or intensity, and on either first or first and last echoes. ALS data and field-measured gap fraction and effective leaf area index (LAIe) were gathered before and after a severe insect defoliation by pine sawflies. LAIe is a commonly used form of leaf area index that is mathematically derived from gap fraction, and includes the areas of foliage, branches and trunks, and which is not corrected for the clumping of foliage. The ALS penetration variables were almost equally strongly related to field-measured gap fraction and LAIe. The estimated slopes in the LAIe models varied from 0.94 to 2.71, and had coefficient of determination R 2 values of 0.92–0.94. They were strongly correlated to each other (R 2 values of 0.95–0.98) and agreed fairly well for temporal changes of LAIe during the summer and the insect defoliation (R 2 values of 0.82–0.95). Counting of first and last echoes produced penetration rates close to the gap fraction, and this penetration variable was able to penetrate tree crowns. Ground-only echoes represented mostly between-tree gaps, and canopy-first-ground-last pulses represented mostly within-canopy gaps. However, the penetration variables based on first and last echoes suffered from the problem that a second echo might be impaired both in low and in tall canopies. In low canopies, two adjacent echoes from the same pulse would be too close in time to be separated by the sensor, while in tall canopies the pulse might apparently be fragmented down through the canopy. The intensity-based penetration variables needed to be supplemented with reflectance values, or at least the ratio between reflectance of the canopy and the ground, and this ratio was estimated from the data. The study demonstrated that one might be able to distinguish between disturbance types, e.g. between defoliation and cutting, by comparing alternative ALS penetration variables. Insect defoliation was dominated by an increase in within-canopy gaps and, correspondingly, the fraction of partly penetrating canopy-first-ground-last pulses. Tree removals from cutting were dominated by increases in between-tree gaps and the corresponding fraction of ground-only pulses.

Greenhouse Evaluation of Air-Assist Delivery Parameters for Mature Poinsettias

Understanding the performance characteristics of application equipment is important for helping make the most efficacious applications. While handguns making high volume applications are common in greenhouse production, it is difficult to achieve uniform distribution of product in a timely manner. Broadcast applications made using air-assistance can help aid canopy penetration and the volume of carrier required to make applications. The objectives of this research were to determine how air-assist sprayer application parameters influence spray deposits on the undersides of leaves in a mature poinsettia canopy. Bench-top trials were conducted using a motorized boom inside a greenhouse to treat a mature and dense poinsettia canopy. Sprayer treatments applied a tank mix of water and fluorescent tracer. Nylon screen targets were secured to the underside surfaces of leaves in the upper and lower elevation of target plants. A five-port, air-assist nozzle with flat fan nozzle tips was used to make the applications. Three air outlet speeds, two travel speeds, and three nozzle flow rates were evaluated. Each treatment was replicated three times. Spray deposits were highly variable. Upper elevation spray deposits were significantly greater than lower elevation deposits. Individually, higher air outlet speed (36.0 m s-1), slower travel speed (3.2 km h-1), and higher nozzle flow rate (1.17 L min-1) tended to produce higher sprayer deposits on the underside surfaces of leaves. The combination of travel speed and nozzle flow rate that produced the highest application rate (900 L ha-1) also produced the highest deposits. There was a 500% increase in underside leaf surface deposits in the lower canopy area for a corresponding 500% increase in application rate. However, the main effects produced no significant differences in spray deposits in the lower canopy area. Further improvements in directing sprays or providing canopy turbulence are necessary to improve deposition and management of insect pests feeding on the underside of poinsettia leaves.

Canopy Penetration and Deposition of Barrier Sprays from Electrostatic and Conventional Sprayers1

An experimental study was conducted to investigate the usefulness of electrostatic and conventional sprayers for barrier applications. Two conventional and three electrostatic sprayers were used in the study. Usefulness of the sprayers was rated based on penetration of spray into and deposition onto 2 sides of leaves on natural vegetation. Bifenthrin (Talstar adulticide) was applied at labeled rate, fluorescent dye was added to the tank mix as tracer, and all sprayers applied the dye and insecticide at the same rate. The results indicated that sprayers producing larger droplets produced significantly higher deposition on vegetation in barrier applications than the sprayers producing smaller droplets. Sprayers with higher air velocity at the nozzle discharge proved significantly better for barrier sprays than the sprayers with lower air velocity. Electrostatic sprayers did not show any improvement in deposition on vegetation or in penetration into vegetation over the conventional sprayers. There was no difference in deposition between truck-mounted and backpack sprayers.

Characterizing L-Band Scattering of Paddy Rice in Southeast China With Radiative Transfer Model and Multitemporal ALOS/PALSAR Imagery

Rice is a major food supply in southeast China. With increased population and urbanization, reliable rice mapping is critical in this region. Because of frequent cloud cover and precipitation during the rice-growing season, it is difficult to conduct large-area rice monitoring with optical remote sensing techniques. L-band synthetic aperture radar (SAR), with its all-weather day and night imaging and canopy penetration capabilities, provides a unique alternative. In this study, a first-order radiative transfer model was developed to simulate L-band scattering properties of paddy rice. Three Advanced Land Observing Satellite (ALOS)/Phased-Array-Type L-band Synthetic Aperture Radar (PALSAR) images in dual-polarization mode (HH and HV) acquired in early tillering (June 28, 2007), tillering (August 13, 2007), and heading (September 28, 2007) stages were processed to test the temporal variation of rice backscatter. It was found that plant height and leaf mass amount were the two major structural parameters that contributed to rice backscatter in PALSAR images. The variation of the simulated HH backscatter matched with PALSAR observations in sample fields, although the simulated backscatter coefficients were around 3 dB lower than image-extracted values. Leaf volume scattering and leaf-ground double bounce were found as the two major scattering components in L-band HH polarization and increased with leaf layer height and density. This paper demonstrated that L-band HH backscatter was more sensitive to rice's structural variation than the VV backscatter and may therefore be more useful in rice mapping and modeling studies.

A comparison of lidar, radar, and field measurements of canopy height in pine and hardwood forests of southeastern North America

Forest canopy height is essential information for many forest management activities and is a critical parameter in models of ecosystem processes. Several methods are available to measure canopy height from single-tree to regional and global scales, but the methods vary widely in their sensitivities, leading to different height estimates even for identical stands. We compare four technologies for estimating canopy height in pine and hardwood forests of the Piedmont region of North Carolina, USA: (1) digital elevation data from the global Shuttle Radar Topography Mission (SRTM) C-band radar interferometry, (2) X- and P-band radar interferometry from the recently developed airborne Geographic Synthetic Aperture Radar (GeoSAR) sensor, (3) small footprint lidar measurements (in pine only), and (4) field measurements acquired by in situ forest mensuration. Differences between measurements were smaller in pine than in hardwood forests, with biases ranging from 5.13 to 12.17 m in pine (1.60–13.77 m for lidar) compared to 6.60–15.28 m in hardwoods and RMSE from 8.40 to 14.21 m in pine (4.73–14.92 m for lidar) compared to 9.54–16.84 in hardwood. GeoSAR measurements of canopy height were among the most comparable measurements overall and showed potential for successful calibration, with R 2 = 0.87 in pine canopies and R 2 = 0.38 in hardwood canopies from simple linear regression. An improved calibration based on differential canopy penetration is presented and applied to SRTM measurements, resulting in canopy height estimates in pine forests with RMSE and standard error <4.00 m. Each of the remotely sensed methods studied produces reasonable and consistent depictions of canopy height that can be compared with data of similar provenance, but due to differences in underlying sensitivities between the methods, comparisons between measurements from various sources require cross-calibration and will be most useful at broad scales.

Technical Note: Effect of Spray Rate and Method of Application in Spray Deposition

Field research in 2007 evaluated tracer deposition using different combinations of spray rates, vehicle speeds, and boom pressure using aerial and ground application in Louisiana. The objectives were to compare deposition and canopy penetration in soybean (Glycine max (L.) Merr.). Artificial mylar cards and a tracer (tartrazine) were used to quantify distribution and penetration. Results showed that total canopy deposition increases when spray rates are equal to or higher than 93.4 lha-1coupled with slower tractor speeds for ground-based systems (P < 0.05) or equal to or higher than 65.4 lha-1 for aerial-based systems (P < 0.0001). Regression analysis showed that air temperature and relative humidity did not influence tracer deposition during testing, but wind speed did ( r2 =0.38). Deposition throughout the canopy was highly variable; the top part of the canopy retained most of the spray regardless of application method or spray rate.

Field Evaluation of an Air-Assisted Sprayer Equipped with Two Reversed Rotation Fans

An air-assisted sprayer equipped with two reversed rotation fans was evaluated in a peach orchard. The effects on the spray deposition of the forward speed, the air volumetric flow rate, and the number of activated fans were analyzed. Spray mixtures contained manganese chelate as a tracer. Spray deposition was evaluated qualitatively through visual estimation of water-sensitive papers and quantitatively by analysis of filter papers using an atomic absorption spectrometer. Deposition and canopy penetration increased when the air volumetric flow was increased for most of the sampling points. The forward speed had no significant effect on the deposition and canopy penetration for most of the sampling points. The effect of the number of activated fans on the spray deposition was significant with increased deposition for the case of two activated fans.

Fungicide Application Timing and Row Spacing Effect on Soybean Canopy Penetration and Grain Yield

Foliar diseases, such as soybean rust (Phakopsora pachyrhizi) can cause severe defoliation and yield loss in soybean [Glycine max (L.) Merr.] and can be managed with an effective fungicide applied during the reproductive growth stages. The impact of soybean row spacing and fungicide application timing on canopy penetration and grain yield are unknown. The objectives of this experiment were (i) to quantify the impact of crop row spacing and spray application timing on penetration and coverage with a fungicide and (ii) to quantify the impact of sprayer wheel traffic during fungicide application on crop yield. The experiment was a split plot design with three replications conducted at the Northeast, Southeast, and Davis–Purdue Agricultural Centers (NEPAC, SEPAC, DPAC) in 2005 and 2006. The whole‐plot treatments were crop row spacing (19, 38, and 76 cm) and fungicide (azoxystrobin + propiconazole) [(methyl (E)‐2‐[2‐[6‐(2‐cyanophenoxy)pyrimidin‐4‐yl]oxyphenyl]‐3‐methoxy‐prop‐2‐enoate) + (1‐[[2‐(2,4‐dichlorophenyl)‐4‐propyl‐1,3‐dioxolan‐2‐yl]methyl]‐1,2,4‐triazole)] application timing (unsprayed or applications at growth stages R1, R3, R5, R3 + R5, or R1 + R3 + R5). Spray canopy coverage was quantified at 30‐cm increments within the soybean canopy. Crop row spacing affected spray canopy coverage at the R3 growth stage at the NEPAC location only. Application timing did not affect canopy coverage or spray penetration. Coverage decreased with depth in the canopy. Grain yield averaged 9% greater in the 19‐ and 38‐cm row spacing than in the 76‐cm row spacing. Fungicide application timing did not influence yield. Our research shows that fungicide application timing should not influence row spacing decisions. Growers should consider the effects of wheel‐track damage when planning spray applications during the reproductive growth stages of soybean.

High‐quality image matching and automated generation of 3D tree models

Image matching is a key procedure in the process of generation of Digital Surface Models (DSM). We have developed a new approach for image matching and the related software package. This technique has proved its good performance in many applications. Here, we demonstrate its use in 3D tree modelling. After a brief description of our image matching technique, we show results from analogue and digital aerial images and high‐resolution satellite images (IKONOS). In some cases, comparisons with manual measurements and/or airborne laser data have been performed. The evaluation of the results, qualitative and quantitative, indicate the very good performance of our matcher. Depending on the data acquisition parameters, the photogrammetric DSM can be denser than a DSM generated by laser, and its accuracy may be better than that from laser, as in these investigations. The tree canopy is well modelled, without smoothing of small details and avoiding the canopy penetration occurring with laser. Depending on the image scale, not only dense forest areas but also individual trees can be modelled.

Development of a Canopy Volume Reduction Technique for Easy Assessment and Harvesting of Valencia Citrus Fruits

The design and evaluation of a basic end-effector prototype for automated citrus harvesting was studied. The concept can be easily incorporated into the design of an automated or a robotic citrus harvester. The concept is based on a unique canopy volume reduction approach that takes advantage of the significant flexibility associated with citrus trees. The method provides a temporary reduction in the tree canopy volume, creating space for the action of simple and potentially fast three-axis Cartesian manipulators. The action of the device also creates fruit alignment that can simplify fruit quality assessment and picking. The prototype included a remotely controlled electro-pneumatic powered clipper to cut fruit stems, two remotely controlled pneumatic cylinders, and two hydraulic powered forks to reduce the canopy volume and to guide the cutting device to a specific location inside the tree canopy. The prototype performance was assessed by the quantification of its fruit removal success rate and damage to fruit and tree canopy. The fruit location of three Valencia orange trees was entirely mapped, and the device was operated on a forklift to evaluate its performance. Field trials were conducted in citrus groves located in Davis and Dinuba, California. This simple prototype end-effector successfully harvested an average of 84% of the fruit and caused no significant damage to harvested fruits during the harvest operations. The simple prototype end-effector, developed based on the canopy volume reduction technique, showed potential to reach significant citrus fruit removal. Based on these results, a future redesign of the system may improve the canopy penetration, increase successful removal rates, and maintain negligible fruit damage.

AERIAL OPTIMIZATION AND CANOPY PENETRATION STUDY OF DIBROM 14 CONCENTRATE1

This document describes the results of collaborative trials between St. Tammany Parish Mosquito Control, ADAPCO, Inc., and the Navy Disease Vector Ecology and Control Center, Naval Air Station, Jacksonville, FL. These tests provide data on the aerial optimization testing of Dibrom 14 Concentrate adulticide. During the week of June 17, 2002, 1 canopy penetration and 3 optimization studies were conducted in St. Tammany Parish, LA, using a Britton Norman twin turbine Islander equipped with 10-800067 flat fan nozzles. Dibrom 14 Concentrate (AMVAC Chemical Corp., Los Angeles, CA) was applied at 3.12 liter per min from a release height of 60.96 m above ground level (agl) at 140 kts indicated airspeed. This resulted in an application rate of 0.65 oz/acre.

HNO 3 fluxes to a deciduous forest derived using gradient and REA methods

Summertime nitric acid concentrations over a deciduous forest in the midwestern United States are reported, which range between 0.36 and 3.3 μg m −3. Fluxes to the forest are computed using the relaxed eddy accumulation technique and gradient methods. In accord with previous studies, the results indicate substantial uncertainties in the gradient-based calculations. The relaxed eddy accumulation (REA) derived fluxes are physically reasonable and are shown to be of similar magnitude to dry deposition estimates from gradient sampling. The REA derived mean deposition velocity is approximately 3 cm s −1, which is also comparable to growing season estimates derived by Meyers et al. for a similar deciduous forest. Occasional inverted concentration gradients and fluxes are observed but most are not statistically significant. Data are also presented that indicate substantial through canopy penetration of nitric acid.

Conditional Sampling Of Forest Canopy Gusts

Velocity measurements by a two-component laser-Doppler anemometer have been made in a wind-tunnel flow over a forest of aeroelastically scaled model trees. Mean velocity profiles close above three different model canopies exhibit typical ‘shear-layer’ inflections that are similar, as are the turbulence characteristics, when scaled by characteristic dimensions of the shear layer.A wavelet-based conditional sampling technique is used to generate pseudo-instantaneous flow-field vector maps that are concurrent with significant tree bending events. These diagrams show clear evidence of canopy penetration by coherent gusts.A discussion is offered, of the relationship between the development of coherent gusts and conventional descriptions of mixing layer instability.