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PubMed2002

Canopy light transmittance in Douglas-fir--western hemlock stands.

We measured vertical and horizontal variation in canopy transmittance of photosynthetically active radiation in five Pseudotsuga menziesii (Mirb.) Franco-Tsuga heterophylla (Raf.) Sarg. (Douglas-fir-western hemlock) stands in the central Cascades of southern Washington to determine how stand structure and age affect the forest light environment. The shape of the mean transmittance profile was related to stand height, but height of mean maximum transmittance was progressively lower than maximum tree height in older stands. The vertical rate of attenuation declined with stand age in both the overstory and understory. A classification of vertical light zones based on the mean and variance of transmittance showed a progressive widening of the bright (low variance and high mean) and transition (high variance and rapid vertical change) zones in older stands, whereas the dim zone (low variance and mean) narrowed. The zone of maximum canopy surface area in height profiles, estimated by inversion of transmittance profiles, changed from relatively high in the canopy in most young stands ("top-heavy") to lower in the canopy in older stands ("bottom-heavy"). In the understory, all stands had similar mean transmittances, but the spatial scale of variation increased with stand age and increasing crown size. The angular distribution of openness was similar in all stands, though the older stands were less open at all angles than the younger stands. Understory openness was generally unrelated to transmittance in the canopy above. Whole-canopy leaf area indices, estimated using three methods of inverting light measurements, showed little correspondence across methods. The observed patterns in light environment are consistent with structural changes occurring during stand development, particularly the diversification of crowns, the creation of openings of various sizes and the elaboration of the outer canopy surface. The ensemble of measurements has potential use in distinguishing forests of differing ages that have similar stature.

Light↗

PubMed1989

Comparative mucosal microvasculature of the mammalian stomach.

The comparative morphology of the gastric mucosal microvasculature was investigated using the corrosion casting technique. The vascular pattern consisted of a hexagonally arranged capillary plexus surrounding the gastric glands and terminating in venules running perpendicular to the mucosal axis. Vessels of the pyloric antrum demonstrated an acute angle between capillaries and venules, whereas vessels of the gastroduodenal junction changed from a honeycomb pattern to a leaf-like arrangement.

Animals↗

PubMed2002

A simulation study on the importance of size-related changes in leaf morphology and physiology for carbon gain in an epiphytic bromeliad.

This study addresses the question of how size-related changes in leaf morphology and physiology influence light absorption and carbon gain of the epiphytic bromeliad Vriesea sanguinolenta. A geometrically based computer model, Y-plant, was used for the three-dimensional reconstruction of entire plants and for calculation of whole plant light interception and carbon gain. Plants of different sizes were reconstructed, and morphological and physiological attributes of young and old leaves, and small and large plants were combined to examine the individual effects of each factor on light absorption and carbon gain of the plant. The influence of phyllotaxis on light absorption was also explored. Departure of measured divergence angles between successive leaves from the ideal 137.5 degrees slightly decreased light absorption. The only morphological parameter that consistently changed with plant size was leaf shape: larger plants produced more slender foliage, which substantially reduced self-shading. Nevertheless, self-shading increased with plant size. While the maximum rate of net CO(2) uptake of leaves increased linearly with plant size by a factor of two from the smallest to the largest individual, the potential plant carbon gain (based on total foliage area) showed a curvilinear relationship, but with similar numerical variation. We conclude that leaf physiology has a greater impact on plant carbon gain than leaf and plant morphology in this epiphytic bromeliad.

Bromeliaceae↗

PubMed2004

Commissioning and quality assurance for intensity modulated radiotherapy with dynamic multileaf collimator: experience of the Pontificia Universidad Católica de Chile.

The objective of this paper is to present our experience in the commissioning and quality assurance (QA) for intensity modulated radiotherapy (IMRT) using dynamic multileaf collimator (dMLC), sliding window technique. Using Varian equipment solution, the connectivity and operation between all IMRT chain components was checked. Then the following test were done: stability of leaf positioning and leaf speed, sensitivity to treatment interruptions (acceleration and deceleration), evaluation of standard field patterns, stability of dMLC output, segmental dose accuracy check, average leaf transmission, dosimetric leaf separation, effects of lateral disequilibrium between adjacent leaves in dose profiles and multiple carriage field verification. Standard patterns were generated for verification: uniform field, pyramid, hole, wedge, peaks and chair. Weekly QA Protocol include: sweeping gap output, Garden Fence Test (narrow bands, 2 mm wide, of exposure spaced at 2-cm intervals) and segmental dose accuracy check. Monthly QA include: sweeping gap output at multiple gantry and collimator angle, sweeping gap output off-axis, Picket Fence Test (eight consecutive movements of a 5-cm wide rectangular field spaced at 5-cm intervals), stability of leaf speed and leaf motor current test (PWM test). Patient QA procedure consists of an absolute dose measurement for all treatments fields in the treatment condition, analysis of actual leaf position versus planned leaf position (dynalog files) for each treatment field, film relative dose determination for each field, film relative dose determination for the plan (all treatment fields) in two axial planes and patient positioning verification with orthogonal films. The tests performed showed acceptable result. After more than one year of IMRT treatment the routine QA machine checks confirm the precision and stability of the IMRT system.

Chile↗

PubMed2006

Evaluation of MLC leaf positioning using a scanning liquid ionization chamber EPID.

A method was developed to determine the accuracy of multileaf collimator (MLC) positioning using transmitted dose maps measured by a scanning liquid ionization chamber electronic portal imaging device (SLIC-EPID). Several MLC fields were designed, using the Varian C-series standard MLC-80, as reference fields for open fields. The MLC leaves were then shifted from the reference positions along the direction of MLC leaf movement towards the central axis from 0.1 to 1.6 mm. The electronic portal images (EPIs), acquired for each case, were converted to two-dimensional dose maps using an appropriate calibration method and the relative dose difference maps were then calculated. The experiment was then performed at non-zero gantry angles in the presence of an anthropomorphic phantom for typical prostate and head and neck fields. Several standard edge detection algorithms were also used in order to find the shifted MLC leaf position. In addition, the short-term reproducibility of MLC leaf positioning was evaluated using the above-mentioned methods. It was found that the relationship between the relative dose difference and MLC leaf spatial displacement is linear. A variation of 0.2 mm in leaf position leads to approximately 4% change in the relative dose values for open fields. The variation of the relative dose difference for phantom studies depends on the phantom positioning and the EPI normalization. From the standard edge detection algorithms, used in the current study, the 'Canny' algorithm was found to be the optimum method to identify the minimum detectable MLC leaf displacements with a precision of approximately 0.1 mm for all cases. However, the result of edge detection algorithms generally is binary and there is no additional information compared to the relative dose maps. The reproducibility of MLC positions was found to be within 0.3 mm. In conclusion, a SLIC-EPID can be used for regular quality assurance (QA) of MLC leaf positioning. Despite significant difference in the pixel size of the acquired SLIC-EPIs, it can be concluded that the SLIC-EPID can be used for MLC quality assurance protocols with similar accuracy compared to amorphous silicon (a-Si) EPID results.

Algorithms↗

PubMed2005

Radiotherapy of prostate cancer with multileaf collimators (MLCs) optimization of the undulating dose distribution at the MLC edge.

BACKGROUND AND PURPOSE: A technical modification for radiotherapy of prostate cancer is presented to smooth the scalloped dose pattern that occurs at treatment field edge, when a multileaf collimator (MLC) has been used. MATERIAL AND METHODS: Ten patients with prostate cancer receiving postoperative, adjuvant irradiation were studied prospectively. By a three-dimensional planning system (TMS, Helax 6.1B) the irradiation was planned for an 18-MV linear accelerator (Primus 1, Siemens). The volumes of interest (VOI) were the planning target volume (PTV; the region of the prostate including the seminal vesicles), the volume of rectum (V(rectum)) and urinary bladder (V(bladder)). Two four-field techniques (0 degrees , 90 degrees , 180 degrees , 270 degrees ) were planned using "beam's eye view" for setting the leaf position of the MLC. For technique A the MLC was adapted to the PTV using a 0 degrees collimator angle for the lateral fields. For technique B the collimator angle of the lateral fields was optimized to compensate the cascade field shape. Dose-volume histograms of PTV, V(rectum) and V(bladder) were analyzed. The dose was prescribed for the reference point according to ICRU 50. Film dosimetry was used to show the dose pattern at the field edge produced by the two techniques. RESULTS: Dose to PTV did not differ between technique A and B. Median dose to V(rectum) was 82.6% for technique A and 77.3% for technique B (p < 0.001). Technique A irradiates a larger V(rectum) than technique B being significant for all isodose levels tested. Median dose to V(bladder) did not differ for technique A and B (p > 0.05). CONCLUSION: The presented technical modification is an effective method to blur the staggered dose distribution that results, when the MLC is conventionally stepped to adapt to the dorsal, irregular PTV border in irradiation of prostate. Especially for irradiation to escalated dose levels, this modification may reduce the dose to the rectum and thus the rectal side effects in comparison to the conventional MLC fields.

Algorithms↗

PubMed2001

New vegetation indices for remote measurement of chlorophylls based on leaf directional reflectance spectra.

Directional reflectance (R) spectra from 380 to 780 nm for nadir illuminated leaves of four different plants (croton, Codiaeum variegatum; spotted eleagnus, Eleagnus pungens Maculata; Japanese pittosporum, Pittosporum tobira and Benjamin fig, Ficus benjamina Starlight) were acquired at a viewing angle of 30 degrees from the nadir direction. Chlorophyll-a and -b content of leaves covered a range of 1-60 and 0.5-21 microg/cm(2), respectively. In contrast with previous results from hemispherical reflectance measurements, directional reflectance data does not correlate well with chlorophyll concentration. This is mainly due to the external reflectance (R(E)) at the leaf epidermis, caused by the mismatch of the refractive index at the air-epidermis and epidermis-inner layer boundary. The external reflectance can be identified with the blue flat reflectance between 380 and 480 nm. The inner reflectance (R(I)), obtained by subtracting the external reflectance from the measured spectra, was found to be linearly related to the logarithm of the chlorophyll content. Good fitting of the log (Chl) versus R(I)(lambda) curves were obtained for R(I) in the green band (around 550 nm) and close to the inflection point in the red edge (around 700 nm). The coefficient of determination, r(2), of curve fitting improved (up to 0.97) when the normalised inner reflectance NR(I)(lambda)=R(I)(lambda)/R(I)(lambda(0)), with lambda(0)>or=750 nm, was used instead of the absolute reflectance. The best indices for Chl, Chl-a and Chl-b determination were R(I)(542)/R(I)(750), R(I)(706)/R(I)(750) and R(I)(556)/R(I)(750), respectively. However, since the content of Chl-a relative to Chl-b was almost constant for the plants investigated, the two last indices must be further validated on leaves with a high variability in the Chl-a:Chl-b ratio. The error in the determination of chlorophyll content was found to be of the order of 10%. This value was lower than those obtained by applying the vegetation indices previously suggested. Therefore, the normalised inner reflectance in the green and in the red edge represents a more suitable index for the chlorophyll determination than those up to now used.

Chlorophyll↗

PubMed1999

A method of beam-couch intersection detection.

At the time of treatment planning it would be useful to know whether part of the treatment beam passes through the patient/couch support assembly before it passes through the patient. In the previous work of Yorke, the range of gantry angles leading to beam-couch intersection was found as a function of couch translation for symmetric field sizes and for zero couch rotation. Yorke's method has been extended to include couch rotation, dual independent jaws, and multi-leaf collimator (MLC) field shapes. In addition, the new method is also applicable in the situation of the couch top located above the isocenter. For a clinically treatable, 20 x 20 cm field configuration in a linac, the range of gantry angles leading to beam-couch intersection are different by 6.7 degrees for a couch rotation angle of 25 degrees when compared to no couch rotation. The new method agrees with data within the setup and measurement uncertainties for a variety of field sizes including an oval shaped MLC field, and various couch locations, couch, and collimator rotation angles.

Humans↗

PubMed1977

[Gold drainage as a glaucoma operation (author's transl)].

A glaucoma operation is described in which a piece of gold leaf 0.05 mm thick, 1.5 mm wide and 4 mm long is laid into a trepanation opening or into an anterior chamber angle incision after preparation of a scleral flap. The tendency of rejecting of large gold leaves was considerable. A diverticulum of the anterior chamber formed round all gold leaves through the scarred walls of which a reasonable regulation of pressure by drainage of the aqueous was apparently not possible. A real wick or drainage effect was not seen in any case.

Adult↗

PubMed2006

[Iridoschisis and angle-closure glaucoma: a case report].

INTRODUCTION: Iridoschisis is a rare condition where a localized area of iris stroma is cleaved in two, with the anterior atrophic portion disintegrating into fibrils. It is frequently associated with angle closure glaucoma and with cataract. CASE REPORT: A 70-year-old male presented with reduction of visual acuity in the left eye. Visual acuity was 20/25 OD and 20/70 OS. He had suffered acute angle-closure glaucoma in the right eye 10 years before, treated with laser iridotomy and topical antiglaucomatous therapy. Intraocular pressure was 12 mmHg OD and 46 mmHg OS. Slit lamp biomicroscopic examination revealed bilateral shallow anterior chamber, iris atrophy, and leaf degeneration of the iris stroma. A-scan and B-scan standardized echography in both eyes showed shortening of the anterior chamber, a thickened and more anteriorly located lens, the presence of a few hyperechogeneous flocculated masses floating in the vitreous, and optic disc excavation. CONCLUSION: The mechanism by which iridoschisis causes angle closure is unclear. A pupillary block could be favored by the thickening and anteriorization of the lens and the ciliary processes. Both the presence of strings of iris stroma occluding the trabecula and pupillary block could cause an elevation in intraocular pressure.

Aged↗

PubMed2001

Pre-treatment dosimetric verification by means of a liquid-filled electronic portal imaging device during dynamic delivery of intensity modulated treatment fields.

BACKGROUND AND PURPOSE: Although intensity modulated radiation therapy is characterized by three-dimensional dose distributions which are often superior to those obtained with conventional treatment plans, its routine clinical implementation is partially held back by the complexity of the beam verification. This is even more so when a dynamic multileaf collimator (dMLC) is used instead of a segmented beam delivery. We have therefore investigated the possibility of using a commercially available, liquid-filled electronic portal imaging device (EPID) for the pre-treatment quality assurance of dynamically delivered dose distributions. METHODS AND MATERIALS: A special acquisition mode was developed to optimize the image acquisition speed for dosimetry with the liquid-filled EPID. We investigated the accuracy of this mode for 6 and 18 MV photon beams through comparison with film and ion chamber measurements. The impact of leaf speed and pulse rate fluctuations was quantified by means of dMLC plans especially designed for this purpose. Other factors influencing the accuracy of the dosimetry (e.g. the need for build-up, remanence of the ion concentration in the liquid and bulging of the liquid at non-zero gantry angles) were studied as well. We finally compared dosimetric EPID images with the corresponding image prediction delivered without a patient in the beam. RESULTS: The dosimetric accuracy of the measured dose distribution is approximately 2% with respect to film and ion chamber measurements. The accuracy declines when leaf speed is increased beyond 2 cm/s, but is fairly insensitive to accelerator pulse rate fluctuations. The memory effect is found to be of no clinical relevance. When comparing the acquired and expected distributions, an overall agreement of 3% can be obtained, except at areas of steep dose gradients where slight positional shifts are translated into large errors. CONCLUSIONS: Accurate dosimetric images of intensity modulated beam profiles delivered with a dMLC can be obtained with a commercially available, liquid-filled EPID. The developed acquisition mode is especially suited for fast and accurate pre-treatment verification of the intensity modulated fields.

Dose-Response Relationship, Radiation↗

PubMed1995

Variation in the ratio of shoot silhouette area to needle area in fertilized and unfertilized Norway spruce trees.

We compared the range and variation in shoot silhouette area to projected leaf area ratio (SPAR) in fertilized and unfertilized (control) Norway spruce (Picea abies (L.) Karst.) trees. We measured SPAR for several view directions of 169 shoots at different depths in the crown of fertilized and control trees. There was an increase in SPAR with depth in the crown in both control and fertilized trees. In the fertilized trees, however, mean SPAR was larger overall, the increase with depth in the crown was steeper, and there was a larger variation in SPAR with inclination and rotation angle of the shoot (relative to the view direction). In particular, shoots in the lower crown of fertilized trees were rotationally asymmetrical ("flat") and had high values of the maximum ratio of shoot silhouette area to projected leaf area (SPAR(max)). Differences in SPAR between fertilized and control trees were explained by changes in shoot structure in response to fertilization and shading. Shoots of fertilized trees were larger and had more needle area than shoots of control trees. However, the ratio of needle area to shoot size was smaller in fertilized trees than in control trees, implying less within-shoot shading and, consequently, a larger SPAR. Also, the increase in SPAR with increased shading (depth in the crown) could be explained by a decrease in the ratio of needle area to shoot size. In addition, because fertilized trees had more needle area than control trees, the effect of shading at a given depth in the crown was more pronounced in fertilized trees than in control trees.

Journal Article↗

PubMed2006

Crown development in a pioneer tree, Rhus trichocarpa, in relation to the structure and growth of individual branches.

Based on an allometric reconstruction, the structure and biomass-allocation patterns of branches and current-year shoots were investigated in branches of various heights in the pioneer tree Rhus trichocarpa, to evaluate how crown development is achieved and limited in association with height. Path analysis was conducted to explore the effects of light availability, basal height and size of individual branches on branch structure and growth. Branch angle was affected by basal height, whereas branch mass was influenced primarily by light availability. This result suggests that branch structure is strongly constrained by basal height, and that trees mediate such constraints under different light environments. Previous-year leaf area and light availability showed positive effects on current-year stem mass. In contrast, branch basal height and mass negatively affected current-year stem mass. Moreover, the length of stems of a given diameter decreased with increasing branch height. Therefore the cost of biomass investment for a unit growth in length is greater for branches of larger size and at upper positions. Vertical growth rate in length decreased with increasing height. Height-dependent changes in stem allometry and angle influenced the reduction in vertical growth rate to a similar degree.

Biomass↗

PubMed2005

Degradation of Alyssum murale biomass in soil.

The Ni-hyperaccumulating plant Alyssum murale accumulates exceptionally high concentrations of nickel in its aboveground biomass. The reasons for hyperaccumulation remain unproven; however, it has been proposed that elemental alelopathy might be important. High-Ni leaves shed by the plant may create a "toxic zone" around the plant where germination or growth of competing plants is inhibited. The efficacy of this argument will partially depend upon the rate at which leaves degrade in soil and free metals are released, and the subsequent rate at which metals are bound to soil constituents. To test the degradation of biomass of hyperaccumulators, A. murale was grown on both high- and low-Ni soils to achieve high- (12.0 g Ni/kg) and low- (0.445 g Ni/kg) Ni biomass. Shredded leaf and stem biomass were added to a serpentine soil from Oregon that was originally used to grow high-Ni biomass and a low-Ni control soil from Maryland. Biomass Ni was readily soluble and extractable, suggesting near immediate release as biomass was added to soil Extractable nickel in soil amended with biomass declined rapidly over time due to Ni binding in soil These results suggest that Ni released from biomass of Ni hyperaccumulators may significantly affect their immediate niche only for short periods of time soon after leaf fall, but repeated application may create high Ni levels under and around hyperaccumulators.

Biodegradation, Environmental↗

PubMed1990

Crown architecture of Populus clones as determined by branch orientation and branch characteristics.

Crown architecture, including branching pattern, branch characteristics and orientation of proleptic and sylleptic branches was studied in five poplar clones (Populus deltoides, P. trichocarpa and P. trichocarpa x P. deltoides hybrids), grown under intensive culture in the Pacific Northwest, USA. Branch characteristics measured were number, length, diameter, biomass and the angles of origin and termination. The results suggest that genotype has a major influence on crown architecture in Populus. Clonal differences in branch characteristics and branching patterns were found that resulted in striking differences in crown form and architecture. Branch angle and curvature differed significantly among clones, and among height growth increments within clones. Branch length and diameter were significantly correlated in all clones. Sylleptic branches and the considerable leaf area they carry have important implications for whole tree light interception, and thus, play a critical role in the superior growth and productivity of certain hybrid poplar clones. The considerable variation in branch characteristics implies a strong justification for including them in selection and breeding programs for Populus.

Journal Article↗

PubMed1990

Human endothelial actin-binding protein (ABP-280, nonmuscle filamin): a molecular leaf spring.

Actin-binding protein (ABP-280, nonmuscle filamin) is a ubiquitous dimeric actin cross-linking phosphoprotein of peripheral cytoplasm, where it promotes orthogonal branching of actin filaments and links actin filaments to membrane glycoproteins. The complete nucleotide sequence of human endothelial cell ABP cDNA predicts a polypeptide subunit chain of 2,647 amino acids, corresponding to 280 kD, also the mass derived from physical measurements of the native protein. The actin-binding domain is near the amino-terminus of the subunit where the amino acid sequence is similar to other actin filament binding proteins, including alpha-actinin, beta-spectrin, dystrophin, and Dictyostelium abp-120. The remaining 90% of the sequence comprises 24 repeats, each approximately 96 residues long, predicted to have stretches of beta-sheet secondary structure interspersed with turns. The first 15 repeats may have substantial intrachain hydrophobic interactions and overlap in a staggered fashion to yield a backbone with mechanical resilience. Sequence insertions immediately before repeats 16 and 24 predict two hinges in the molecule near points where rotary-shadowed molecules appear to swivel in electron micrographs. Both putative hinge regions are susceptible to cleavage by proteases and the second also contains the site that binds the platelet glycoprotein Ib/IX complex. Phosphorylation consensus sequences are also located in the hinges or near them. Degeneracy within every even-numbered repeat between 16 and 24 and the insertion before repeat 24 may convert interactions within chains to interactions between chains to account for dimer formation within a domain of 7 kD at the carboxy-terminus. The structure of ABP dimers resembles a leaf spring. Interchain interactions hold the leaves firmly together at one end, whereas intrachain hydrophobic bonds reinforce the arms of the spring where the leaves diverge, making it sufficiently stiff to promote high-angle branching of actin filaments. The large size of the leaves, their interruption by two hinges and flexible actin-binding site, facilitate cross-linking of widely dispersed actin filaments.

Amino Acid Sequence↗

PubMed2000

Patterns and determinants of potential carbon gain in the C3 evergreen Yucca glauca (Liliaceae) in a C4 grassland.

Yucca glauca is a C(3) evergreen rosette species locally common in the C(4)-dominated grasslands of the central Great Plains. Most congeners of Y. glauca are found in deserts, and Y. glauca's morphological similarities to desert species (steeply angled leaves, evergreen habit) may be critical to its success in grasslands. We hypothesized that the evergreen habit of Y. glauca, coupled with its ability to remain physiologically active at cool temperatures, would allow this species to gain a substantial portion of its annual carbon budget when the C(4) grasses are dormant. Leaf-level gas exchange was measured over an 18-mo period at Konza Prairie in northeast Kansas to assess the annual pattern of potential C gain. Two short-term experiments also were conducted in which nighttime temperatures were manipulated to assess the cold tolerance of this species. The annual pattern of C gain in Y. glauca was bimodal, with a spring productive period (maximum monthly photosynthetic rate = 21.1 ± 1.97 μmol·m·s) in March through June, a period of midseason photosynthetic depression, and a fall productive period in October (15.6 ± 1.25 μmol·m·s). The steeply angled leaves resulted in interception of photon flux density at levels above photosynthetic saturation throughout the year. Reduced photosynthetic rates in the summer may have been caused by low soil moisture, but temperature was strongly related (r = 0.37) to annual variations in photosynthesis, with nocturnal air temperatures below -5°C in the late fall and early spring, and high air temperatures (>32°C) in the summer, limiting gas exchange. Overall, 31% of the potential annual carbon gain in Y. glauca occurred outside the "frost-free" period (April-October) at Konza Prairie and 43% occurred when the dominant C(4) grasses were dormant. Future climates that include warmer minimum temperatures in the spring and fall may enhance the success of Y. glauca relative to the C(4) dominants in these grasslands.

Journal Article↗

PubMed2005

Spatial variability of leaf wetness duration in different crop canopies.

The spatial variability of leaf wetness duration (LWD) was evaluated in four different height-structure crop canopies: apple, coffee, maize, and grape. LWD measurements were made using painted flat plate, printed-circuit wetness sensors deployed in different positions above and inside the crops, with inclination angles ranging from 30 to 45 degrees. For apple trees, the sensors were installed in 12 east-west positions: 4 at each of the top (3.3 m), middle (2.1 m), and bottom (1.1 m) levels. For young coffee plants (80 cm tall), four sensors were installed close to the leaves at heights of 20, 40, 60, and 80 cm. For the maize and grape crops, LWD sensors were installed in two positions, one just below the canopy top and another inside the canopy. Adjacent to each experiment, LWD was measured above nearby mowed turfgrass with the same kind of flat plate sensor, deployed at 30 cm and between 30 and 45 degrees. We found average LWD varied by canopy position for apple and maize (P<0.05). In these cases, LWD was longer at the top, particularly when dew was the source of wetness. For grapes, cultivated in a hedgerow system and for young coffee plants, average LWD did not differ between the top and inside the canopy. The comparison by geometric mean regression analysis between crop and turfgrass LWD measurements showed that sensors at 30 cm over turfgrass provided quite accurate estimates of LWD at the top of the crops, despite large differences in crop height and structure, but poorer estimates for wetness within leaf canopies.

Coffea↗