Applicability of personal laser scanning in forestry inventory.
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ABSTRACT:
SUBMITTER: Chen S
PROVIDER: S-EPMC6392439 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Background and aimsTerrestrial laser scanners (TLSs) have successfully captured various properties of individual trees and have potential to further increase the quality and efficiency of forest surveys. However, TLSs are limited to line of sight observations, and forests are complex structural environments that can occlude TLS beams and thereby cause incomplete TLS samples. We evaluate the prevalence and sources of occlusion that limit line of sight to forest stems for TLS scans, assess the impacts of TLS sample incompleteness, and evaluate sampling strategies and data analysis techniques aimed at improving sample quality and representativeness.MethodsWe use a large number of TLS scans (761), taken across a 255 650-m2 area of forest with detailed field survey data: the Harvard Forest Global Earth Observatory (ForestGEO) (MA, USA). Sets of TLS returns are matched to stem positions in the field surveys to derive TLS-observed stem sets, which are compared with two additional stem sets derived solely from the field survey data: a set of stems within a fixed range from the TLS and a set of stems based on 2-D modelling of line of sight. Stem counts and densities are compared between the stem sets, and four alternative derivations of area to correct stem densities for the effects of occlusion are evaluated. Representation of diameter at breast height and species, drawn from the field survey data, are also compared between the stem sets.Key resultsOcclusion from non-stem sources was the major influence on TLS line of sight. Transect and point TLS samples demonstrated better representativeness of some stem properties than did plots. Deriving sampled area from TLS scans improved estimates of stem density.ConclusionsTLS sampling efforts should consider alternative sampling strategies and move towards in-progress assessment of sample quality and dynamic adaptation of sampling.
| S-EPMC8557379 | biostudies-literature
Project description:Adaptive optics (AO) describes a set of tools to correct or control aberrations in any optical system. In the eye, AO allows for precise control of the ocular aberrations. If used to correct aberrations over a large pupil, for example, cellular level resolution in retinal images can be achieved. AO systems have been demonstrated for advanced ophthalmoscopy as well as for testing and/or improving vision. In fact, AO can be integrated to any ophthalmic instrument where the optics of the eye is involved, with a scope of applications ranging from phoropters to optical coherence tomography systems. In this article, I discuss the applications and advantages of using AO in a specific system, the AO scanning laser ophthalmoscope. Since the Borish award was, in part, awarded to me because of this effort, I felt it appropriate to select this as the topic for this article. Furthermore, users of AO scanning laser ophthalmoscope continue to appreciate the benefits of the technology, some of which were not anticipated at the time of development, and so it is time to revisit this topic and summarize them in a single article.
| S-EPMC2911957 | biostudies-literature
Project description:To develop and test the application of an adaptive optics scanning laser ophthalmoscope (AOSLO) with eye tracking for high-resolution microperimetric testing.An AOSLO was used to conduct simultaneous high-resolution retinal imaging and visual function testing in six normal subjects. Visual sensitivity was measured at test locations between the fovea and 5.0° eccentricity via an increment threshold approach using a 40-trial, yes-no adaptive Bayesian staircase procedure (QUEST). A high-speed eye tracking algorithm enabled real-time video stabilization and the delivery of diffraction-limited Goldmann I-sized stimuli (diameter = 6.5 arc min = ?32 ?m; ? = 680 nm) to targeted retinal loci for 200 ms. Test locations were selected either manually by the examiner or automatically using Fourier-based image registration. Cone spacing was assessed at each test location and sensitivity was plotted against retinal eccentricity. Finally, a 4.2 arc min stimulus was used to probe the angioscotoma associated with a blood vessel located at 2.5° eccentricity.Visual sensitivity decreases with eccentricity at a rate of -1.32 dB/deg (R = 0.60). The vertical and horizontal errors of the targeted stimulus delivery algorithm averaged 0.81 and 0.89 arc min (?4 ?m), respectively. Based on a predetermined exclusion criterion, the stimulus was successfully delivered to its targeted location in 90.1% of all trials. Automated recovery of test locations afforded the repeat testing of the same set of cones over a period of 3 months. Thresholds measured over a parafoveal blood vessel were 1.96 times higher (p < 0.05; one-tailed t-test) than those measured in directly adjacent retina.AOSLO-based microperimetry has the potential to test visual sensitivity with fine retinotopic precision. Automated recovery of previously tested locations allows these measures to be tracked longitudinally. This approach can be implemented by researchers interested in establishing the functional correlates of photoreceptor mosaic structure in patients with retinal disease.
| S-EPMC3348404 | biostudies-literature
Project description:PurposeDual wavelength retinal oximetry has been developed for adults, but is not available for infants. Retinal oximetry may provide insight into the pathophysiology of oxygen-mediated diseases like retinopathy of prematurity. More insight in the oxygen metabolism of the retina in infants may provide valuable clues for better understanding and subsequent prevention or treatment of the disease. The measurements of oxygen saturation are obtained with two fundus images simultaneously captured in two different wavelengths of light. The comparison in light absorption of oxygenated and deoxygenated hemoglobin can be used to estimate the oxygen saturation within the retinal vessels by means of a software algorithm. This study aims to make retinal oximetry available for neonates. The first step towards estimating retinal oxygen saturation is determining the optical density ratio. Therefore, the purpose of this study is to image healthy newborn infants with a scanning laser ophthalmoscope and determine the optical density ratio for retinal oximetry analysis.MethodsImages of the retina of full-term healthy infants were obtained with an SLO, Optomap 200Tx (Optos), with two laser wavelengths (532nm and 633nm). The infant lay face down on the lower arm of the parent, while the parent supported the chest and chin with one hand, and stabilized the back with the other hand. No mydriatics or eyelid specula were used during this study. The images were analyzed with modified Oxymap Analyzer software for calculation of the Optical Density Ratio (ODR) and vessel width. The ODR is inversely and approximately linearly related to the oxygen saturation. Measurements were included from the superotemporal vessel pair. A paired t-test was used for statistical analysis.ResultsFifty-nine infants, (58% female), were included with mean gestational age of 40 ± 1.3 weeks (mean ± SD) and mean post-natal age of 16 ± 4.8 days. A total of 28 images were selected for retinal oximetry analysis. The ODR was 0.256 ± 0.041 for the arterioles and 0.421 ± 0.089 for the venules (n = 28, p < 0.001). The measured vessel-width for the arterioles was 14.1 ± 2.7 pixels and for the venules 19.7 ± 3.7 pixels (n = 28, p < 0.001).ConclusionsRetinal oximetry can be performed in newborn infants by combining an SLO and a dual-wavelength algorithm software. Sensitivity of the approach is indicated by the fact that the ODR measurements are significantly different between the arterioles and the venules. However, more variability in ODR is seen with the SLO approach in babies than is seen with conventional oximetry in adults. This approach is completely non-invasive, non-contact and even avoids the use of mydriatics or eyelid specula.
| S-EPMC4740427 | biostudies-literature
Project description:In conventional confocal/multiphoton fluorescence microscopy, images are typically acquired under ideal settings and after extensive optimization of parameters for a given structure or feature, often resulting in information loss from other image attributes. To overcome the problem of selective data display, we developed a new method that extends the imaging dynamic range in optical microscopy and improves the signal-to-noise ratio. Here we demonstrate how real-time and sequential high dynamic range microscopy facilitates automated three-dimensional neural segmentation. We address reconstruction and segmentation performance on samples with different size, anatomy and complexity. Finally, in vivo real-time high dynamic range imaging is also demonstrated, making the technique particularly relevant for longitudinal imaging in the presence of physiological motion and/or for quantification of in vivo fast tracer kinetics during functional imaging.
| S-EPMC4821995 | biostudies-literature
Project description:The uniform energy distribution of top-hat laser beams is a very attractive property that can offer some advantages compared to Gaussian beams. Especially, the desired intensity distribution can be achieved at the laser spot through energy redistribution across the beam spatial profile and, thus, to minimize and even eliminate some inherent shortcomings in laser micro-processing. This paper reports an empirical study that investigates the effects of top-hat beam processing in micro-structuring and compares the results with those obtainable with a conventional Gaussian beam. In particular, a refractive field mapping beam shaper was used to obtain a top-hat profile and the effects of different scanning strategies, pulse energy settings, and accumulated fluence, i.e., hatch and pulse distances, were investigated. In general, the top-hat laser processing led to improvements in surface and structuring quality. Especially, the taper angle was reduced while the surface roughness and edge definition were also improved compared to structures produced with Gaussian beams. A further decrease of the taper angle was achieved by combining hatching with some outlining beam passes. The scanning strategies with only outlining beam passes led to very high ablation rates but in expense of structuring quality. Improvements in surface roughness were obtained with a wide range of pulse energies and pulse and hatch distances when top-hat laser processing was used.
| S-EPMC7074761 | biostudies-literature
Project description:Bessel beams have been successfully used in two-photon laser scanning fluorescence microscopy to extend the depth of field (EDF), which makes it possible to observe fast events volumetrically. However, the depth information is lost due to integration of fluorescence signals along the propagation direction. We describe the design and implementation of two-photon lasers scanning stereomicroscopy, which allows viewing dynamic processes in three-dimensional (3D) space stereoscopically in real-time with shutter glasses at the speed of 1.4 volumes per second. The depth information can be appreciated by human visual system or be recovered with correspondence algorithms for some cases.
| S-EPMC5173245 | biostudies-literature
Project description:PurposeTo evaluate the feasibility and reliability of a standardized approach for quantitative measurements of fundus autofluorescence (AF) in images obtained with a confocal scanning laser ophthalmoscope (cSLO).MethodsAF images (30°) were acquired in 34 normal subjects (age range, 20-55 years) with two different cSLOs (488-nm excitation) equipped with an internal fluorescent reference to account for variable laser power and detector sensitivity. The gray levels (GLs) of each image were calibrated to the reference, the zero GL, and the magnification, to give quantified autofluorescence (qAF). Images from subjects and fixed patterns were used to test detector linearity with respect to fluorescence intensity, the stability of qAF with change in detector gain, field uniformity, effect of refractive error, and repeatability.ResultsqAF was independent of detector gain and laser power over clinically relevant ranges, provided that detector gain was adjusted to maintain exposures within the linear detection range (GL < 175). Field uniformity was better than 5% in a central 20°-diameter circle but decreased more peripherally. The theoretical inverse square magnification correction was experimentally verified. Photoreceptor bleaching for at least 20 seconds was performed. Repeatability (95% confidence interval) for same day and different-day retests of qAF was ±6% to ±14%. Agreement (95% confidence interval) between the two instruments was <11%.ConclusionsQuantitative AF imaging appears feasible. It may enhance understanding of retinal degeneration, serve as a diagnostic aid and as a sensitive marker of disease progression, and provide a tool to monitor the effects of therapeutic interventions.
| S-EPMC3250263 | biostudies-literature
Project description:High-throughput laser micro-machining demands precise control of the laser beam position to achieve optimal efficiency, but existing methods can be both time-consuming and cost-prohibitive. In this paper, we demonstrate a new high-throughput micro-machining technique based on rapidly scanning the laser focal point along the optical axis using an acoustically driven variable focal length lens. Our results show that this scanning method enables higher machining rates over a range of defocus distances and that the effect becomes more significant as the laser energy is increased. In a specific example of silicon, we achieve a nearly threefold increase in the machining rate, while maintaining sharp side walls and a small spot size. This method has great potential for improving the micro-machining efficiency of conventional systems and also opens the door to applying laser machining to workpieces with uneven topography that have been traditionally difficult to process.
| S-EPMC6060055 | biostudies-literature
Project description:A new approach to quantitative single-molecule imaging by confocal laser scanning microscopy (CLSM) is presented. It relies on fluorescence intensity distribution to analyze the molecular occurrence statistics captured by digital imaging and enables direct determination of the number of fluorescent molecules and their diffusion rates without resorting to temporal or spatial autocorrelation analyses. Digital images of fluorescent molecules were recorded by using fast scanning and avalanche photodiode detectors. In this way the signal-to-background ratio was significantly improved, enabling direct quantitative imaging by CLSM. The potential of the proposed approach is demonstrated by using standard solutions of fluorescent dyes, fluorescently labeled DNA molecules, quantum dots, and the Enhanced Green Fluorescent Protein in solution and in live cells. The method was verified by using fluorescence correlation spectroscopy. The relevance for biological applications, in particular, for live cell imaging, is discussed.
| S-EPMC2587633 | biostudies-literature