Diffuse Light Intensity Research Articles

Optical tactile sensor using scattering inside sol-gel-derived flexible macroporous monoliths

Tactile sensors are an essential technology for robots, and various types have been developed. This paper reports on a new optical tactile sensor based on multiple scattering in a porous material with a viscoelastic phase-separated structure fabricated by a sol–gel method. When a macroporous silicone monolith with a few micrometer diameter skeletons was compressed, the diffuse light intensity near the light source was reduced due to Mie multiple scattering. This light intensity change was opposite to the behavior of conventional polymer foams (cellular structures), which have a large structural scale. A simple tactile sensor using a macroporous monolith and a photo reflector was fabricated based on this finding. The skeleton diameter was an important factor for the sensor. In the case of macroporous silicones, the voltage-strain curve showed an almost hysteresis-free clear response. However, the response of macroporous polymethylmethacrylate monolith with a smaller skeleton diameter was weak due to low Mie scattering intensity. Sensors using sol–gel derived macroporous materials have the potential to be thinner and provide improved surface tactile sensation compared to foam materials.

Simultaneous measurements of tissue blood flow and oxygenation using a wearable fiber-free optical sensor.

.Significance: There is an essential need to develop wearable multimodality technologies that can continuously measure both blood flow and oxygenation in deep tissues to investigate and manage various vascular/cellular diseases.Aim: To develop a wearable dual-wavelength diffuse speckle contrast flow oximetry (DSCFO) for simultaneous measurements of blood flow and oxygenation variations in deep tissues.Approach: A wearable fiber-free DSCFO probe was fabricated using 3D printing to confine two small near-infrared laser diodes and a tiny CMOS camera in positions for DSCFO measurements. The spatial diffuse speckle contrast and light intensity measurements at the two different wavelengths enable quantification of tissue blood flow and oxygenation, respectively. The DSCFO was first calibrated using tissue phantoms and then tested in adult forearms during artery cuff occlusion.Results: Phantom tests determined the largest effective source–detector distance (15 mm) and optimal camera exposure time (10 ms) and verified the accuracy of DSCFO in measuring absorption coefficient variations. The DSCFO detected substantial changes in forearm blood flow and oxygenation resulting from the artery occlusion, which meet physiological expectations and are consistent with previous study results.Conclusions: The wearable DSCFO may be used for continuous and simultaneous monitoring of blood flow and oxygenation variations in freely behaving subjects.

Growth dynamics of the Norway spruce and silver fir understory in continuous cover forestry

The conversion to uneven-aged, mixed-species stands represents one possible way to mitigate the consequences of disturbances in Norway spruce forests in Central Europe. A better understanding of the establishment and growth dynamics of the understory can contribute to a more effective conversion process. Here we investigate the structure of understory, light climate and growth of natural regeneration of Norway spruce and silver fir in two forest stands undergoing conversion to continuous cover forestry. Stand-wise forest inventory was conducted in 1993 and 2013. The natural regeneration was surveyed, and the light conditions and inter-tree competition were quantified in 51 sample plots established across the stands in 2013. Our results suggest that the diffuse radiation strongly affects the height growth of fir and spruce natural regeneration. We do not confirm the effect of local sapling density on the regeneration dynamics. The results further show that fir trees grow faster than spruce under less intensity of diffuse light. Most of the spruce and fir trees reached the upper limit of the lower overstory (DBH 12 cm) at approximately 50 years of age. Thus, more substantial reductions in stand density can lead to a well-differentiated structure in less than five decades. To control the prospective representation of spruce and fir in mixed-species forests undergoing the conversion, managing of light conditions is crucial.

Polarization-based extracting diffuse reflection from light-field of object surface

<sec>The reflection light field of surface of the Non-Lambertian body in nature has both specular reflection and diffuse reflection components. In the process of three-dimensional(3D) reconstruction, image matching and pattern recognition are based on the ideal Lambert body. The imaging effect is limited due to the presence of specular reflection components, and the accuracy of feature recognition is low. In order to obtain the diffuse reflection component accurately, a large number of studies have been conducted for a long time, which can be mainly divided into two parts: intensity- and polarization-based separation techniques. The intensity-based separation algorithm is limited in many aspects due to the prior knowledge, such as light source chromaticity, direction and image color information. With the maturity of detection technology, the acquisition and interpretation of multi-dimensional physical properties of light-field have made great progress of the utilization of polarization characteristics of light wave. Compared with traditional intensity imaging technology, the polarization imaging technology has strongr and many advantages in highlighting targets. However, in traditional polarization-based separation techniques, it is often necessary to assume that the diffuse light is completely unpolarized, which is used in some specific cases but not universally.</sec><sec>In this work, we report a method to obtain the diffuse reflection components of the target surface based on the polarization characteristics of the light-field. According to Fresnel's law and Lawrence B. Wolff's reflection model, the reflected light-field on the target surface can be divided into diffuse and specular components with partial polarization. The partial polarization characteristics of diffuse and specular components are explored in depth and the Stokes vector is used to calculate the minimum light intensity of each pixel modulated by polarizer, which is completely unpolarized light. By subtracting completely unpolarized light from the obtained polarized sub-images, the diffuse and specular components in the polarized part satisfy the linear constraint model. Based on the independent component analysis (ICA) model, the diffuse and specular components in the polarized part are regarded as independent and non-interfering additive vectors. The singular value decomposition method and optical relevancy of mutual information are used to determine the optimal mix coefficients matrix of the subcomponents in the linear constrained model. Thus, the diffuse components are accurately acquired and explained from the complex reflected light-field. </sec><sec>Simulation and experimental results show that the algorithm mentioned above can accurately obtain the optimal mix coefficients’ matrix without the prior knowledge of illuminant chromaticity, or direction or image chromatic information, or others. This technique can accurately obtain and remove the specular reflection part, at the same time, restore the diffuse light intensity which is covered by the specular reflection and conforms to the change trend of the surface shape. Meanwhile, the pretty good results also demonstrate that the proposed separation method has the strong stability and wide applicability. This technology does not have to make the assumption that 3D imaging technology and computer vision algorithms such as pattern recognition rely on natural objects as ideal Lambert bodies, and it can eleminate the influence of complex reflected light-field on target results, which makes passive remote 3D imaging technology more applicable and more robust.</sec>

Specialized source-detector separations in near-infrared reflectance spectroscopy platform enable effective separation of diffusion and absorption for glucose sensing.

We present an approach for accurate glucose sensing in turbid media using a spectrally resolved reflectance setup. Our proposed reflectance setup uses specialized source-detector separations (SDSs) to enable an effective separation of diffusion and absorption signals. Additionally, we adjust the selected SDSs to their optimal values to acquire maximum sensitivity to glucose in the two signals. The separation can help to enhance the sensitivity to glucose both for the diffusion and absorption signals, as they always suppress each other by causing opposite effects on the reflected diffuse light intensity. Monte Carlo simulations and experiments for glucose sensing are used to test the method. The acquired optimal SDSs could provide a reference for noninvasive blood glucose sensing.

Ultra-violet imaging of the night-time earth by EUSO-Balloon towards space-based ultra-high energy cosmic ray observations

The JEM-EUSO (Joint Experiment Missions for the Extreme Universe Space Observatory) program aims at developing Ultra-Violet (UV) fluorescence telescopes for efficient detections of Extensive Air Showers (EASs) induced by Ultra-High Energy Cosmic Rays (UHECRs) from satellite orbit. In order to demonstrate key technologies for JEM-EUSO, we constructed the EUSO-Balloon instrument that consists of a ∼1 m2 refractive telescope with two Fresnel lenses and an array of multi-anode photo-multiplier tubes at the focus. Distinguishing it from the former balloon-borne experiments, EUSO-Balloon has the capabilities of single photon counting with a gate time of 2.3 µs and of imaging with a total of 2304 pixels. As a pathfinder mission, the instrument was launched for an 8 h stratospheric flight on a moonless night in August 2014 over Timmins, Canada. In this work, we analyze the count rates over ∼2.5 h intervals. The measurements are of diffuse light, e.g. of airglow emission, back-scattered from the Earth’s atmosphere as well as artificial light sources. Count rates from such diffuse light are a background for EAS detections in future missions and relevant factor for the analysis of EAS events. We also obtain the geographical distribution of the count rates over a ∼780 km2 area along the balloon trajectory. In developed areas, light sources such as the airport, mines, and factories are clearly identified. This demonstrates the correct location of signals that will be required for the EAS analysis in future missions. Although a precise determination of count rates is relevant for the existing instruments, the absolute intensity of diffuse light is deduced for the limited conditions by assuming spectra models and considering simulations of the instrument response. Based on the study of diffuse light by EUSO-Balloon, we also discuss the implications for coming pathfinders and future space-based UHECR observation missions.

Empirical base solar reflective array accumulator design simulator

Sun energy in Indonesia is 5Kwh/m2/day average per year. This alternative energy can be convert to solar thermal up to 80% efficiency, the percentage is highly significant compare to electric conversion that only has 20%. To provide any process requirement for heating, an empirical research of reflective array accumulator has been done, so that a design simulation for the accumulator has to be held. The accumulator can be used as a heat energy supplier for drying, egg hatching, food oven and other requirement. The sun energy trapping method is a reflective array. This method aims to maximize the energy captured and stored in an accumulator and has to be maintained for 24 hours by opening and closing the array. This simulator will calculated and control some input such as water mass, accumulator temperature, environment temperature, humidity and sun intensity. The array control performance to watch diffuse solar light intensity by time. The result of the simulation will give absorption storage capability, insulation capability to watch sun energy performance per day. It is expected that with the simulation, it can simplify the design of the accumulator and improve the efficiency of heat energy storage. The absorption capability perform 72%.

Determination of fat content in goat milk using annular photoelectric sensor system

In this paper, a new method for quantitative determination of fat content in goat milk at room temperature (25°C), based on the annular photoelectric sensor system, has been developed. The measurement system consists of an annular photoelectric sensor, thermoelectric cooler (TEC), amplifier, A/D converter, microprocessor and other components. Based on Mie theory, the diffuse reflection light intensity is adopted as the optical parameter representing the fat content in goat milk. In this way, the standard model of the system can be established and loaded into the processor to realize data acquisition, processing and output. The proposed method has been tested on goat milk samples with variable fat content in the prediction experiment. The results show that the fitting equation is y=−0.366 x+0.295 ( R2=0.987) and measurement errors are within ±3%, which indicates that the presented method has high prediction performance and can measure the fat content in goat milk accurately and in real time.

A Novel Method of Measuring Fat Content in Soybean Milk Based on Y-Type Optical Fiber Sensor

Abstract A new method of measuring fat content in soybean milk at room temperature (25°C) based on the Y-type optical fiber sensor is presented. The measurement system consists of a light source, Y-type optical fiber sensor, detector, thermoelectric cooler (TEC), preamplifier, second-level amplifier, A/D converter, and microprocessor. Based on the Mie theory, the diffuse reflection light intensity is adopted as the optical parameter representing the fat content in soybean milk. In this way the standard model of the system was established based on the diffuse reflection light intensity (the output voltage) of 40 soybean milk samples with different fat content. A prediction was also made to verify the measurement accuracy of the system (the prediction errors are within ±3 % of results). Results of this study indicate the feasibility of using this technology for soybean milk fat analysis that is suitable for the milk laboratory or field analysis.

Effects of cumulus clouds on microclimate and shoot-level photosynthetic gas exchange in Picea engelmannii and Abies lasiocarpa at treeline, Medicine Bow Mountains, Wyoming, USA

Here we describe the dynamic effects of cumulus clouds on microclimate and shoot-level photosynthetic gas exchange in saplings of two treeline conifer species—Picea engelmannii and Abies lasiocarpa. Measurements were made during both clear-sky and partly cloudy conditions (∼10–70% cumulus cloud cover) throughout the 2012 growing season within an alpine-treeline ecotone. Cumulus clouds generated dynamic fluctuations in photosynthetically active radiation (PAR), higher maximum PAR (>2500μmolm−2s−1), 2–4 fold increases in diffuse PAR, reduced daily mean and cumulative PAR, lower needle temperatures, and reduced leaf-to-air vapor pressure differences relative to clear-sky conditions. Onset of cloud-shade corresponded with declines in photosynthesis, needle temperatures, and evapotranspiration, which were proportional to cloud duration and opacity. Despite increased diffuse light and greater sunlight intensity during cloud-gaps, photosynthesis was never higher on partly cloudy days compared to clear days in either species, during cloud-gaps or cloud-shade. However, reduced transpiration paired with photosynthesis comparable with clear-sky levels during cloud-gaps resulted in greater instantaneous water use efficiency relative to clear-sky measurements. There was no apparent photoinhibition of photosynthesis reflected in gas exchange measurements in response to abrupt and dramatic changes in PAR levels caused by cumulus clouds. We conclude that cumulus clouds reduce instantaneous and daily carbon gain, although lower needle temperatures and associated reductions in transpirational water loss may alleviate daily and seasonal water stress, thereby enhancing carbon gain over the growing season.

Effect of Ren meridian acupoints moxibustion on light propagation along the pericardium meridian at human wrist.

To explore the relationship between acupoints and meridians. Researches were performed on 45 healthy people under the same conditions. The diffuse light intensity of the Pericardium meridian and its surrounding areas were measured before and after warming moxibustion on three acupoints [Shimen (RN5), Qihai (RN6), and Yinjiao (RN7)] of Ren meridian below umbilicus in the same way. Then two sets of data of each sample were used for statistics and analysis, as well as the three-dimensional distribution figures. Statistical definition of probability value was used to evaluate the effect made by moxibustion. After moxibustion, the diffuse light intensity presented significant changes in 25 samples (P<0.05), enhanced in 15 people (P<0.05) and decreased in 10 (P<0.05). It was consistent with the classification by questionnaire interviews of somatotypes. In addition, diffuse light changed more obviously on Pericardium than non-meridian areas. It was distinct in the three-dimensional distribution figures. Diffuse light changes happened in entire measure sites demonstrated that acupoints of Ren meridian moxibustion could affect the light propagation of wrist, especially on the Pericardium meridian. It gave an expression to meridians interconnection as said in the Chinese medicine theory. The two classifications made by light propagation changes were experimental corroboration of that personal physical differences affected the manipulation of Chinese acupuncture and moxibustion treatment. These above provided some implications or new directions to future meridian researches.

Effect of optical panel distance in a photobioreactor for nutrient removal and cultivation of microalgae

The aim of present investigation is to assess the effect of illumination area and distance of an optical panel (OP) on the growth of microalgae with simultaneous removal of nutrients. Four different distances of OPs were used i.e. 225 mm OP (Run 1), 150 mm OP (Run 2), 112.5 mm OP (Run 3) and 90 mm distance OP (Run 4) in the photobioreactor (PBR) operations. The PBR was equipped with an OP and operated with a total volume of 37-l. A batch culture was prepared using an initial cell concentration of 1.12 ± 0.05 g l(-1). The experiments were conducted at neutral pH (7.2 ± 0.3) under dark and light cycles of 8 and 16 h, respectively. The diffuse light intensity was recorded as 91, 93, 95 and 98% for Run 1, Run 2, Run 3 and Run 4, respectively, at a 300 mm depth level in the PBR. The chlorophyll content per cell was found to be an average of 701, 721, 785 and 808 fg for Run 1, Run 2, Run 3 and Run 4, respectively. High chlorophyll content per cell and diffuse light intensity was observed for Run 4 compared to other fractions. However, Run 3 sample possessed approximately 10.51% higher biomass growth along with 15.22% chemical oxygen demand, 18.15% total nitrogen 2.37% NH4-N, 15.1% total phosphorus and 15.05% PO4-P more removal than the Run 1. These findings suggest that in terms of economic consideration and efficiency of nutrients removal, Run 3 is found to be more effective than other samples. Moreover, an enhanced growth of Chlorella vulgaris could further be utilized as a potential biodiesel source.

DESIGN AND DEVELOPMENT OF A LINEAR VARIABLE DIFFERENTIAL OPTICAL SENSOR FOR SMALL RANGE LINEAR DISPLACEMENT MEASUREMENT

In this present paper, we have illustrated the deve lopment of a novel linear displacement sensor utili zing the intensity of light. This sensor is based on temporal changes in the intensit y of diffuse light beam for the movement of a solid metallic obstacle between the source and detector instead of traditional reflecto r. An obstacle is moved over open surface of a holl ow shaped channel, where light beams impinged vertically into the channel. Two pho to detectors has been used to sense the variation o f diffuse light intensity at the covered & uncovered area of channel surface due to the movement of obstacle over its open surface. Thi s movement of an obstacle represents the actual target displacement by differ entiating the output transformation of two photo de tectors; this phenomenon is reported as linear variable differential optical se nsor (LVDOS). The measured displacement recorded in terns of voltage by the signal processing circuit (SPC). Experimental results are shown a satisfactory performance of the sensor for small range displacement measurement.

Surface Finish Assessment of Polishing Process of Tool Steels by Abrasion, Using Diamond and Alumina Particles

The present work investigates the surface finishing of two mould tool steels (WNr 1.2738~P20 and WNr 1. 4305) after polishing by conventional method and automatic laboratory equipment. These steels are employed in the fabrication of polymer injection moulds due to its good machinability, homogeneous microstructure and hardness. The polishing process was performed in laboratory by manual and automated processes. The surface finishing was measured by mechanical and optical methods. In the manual polishing, SiC paper grit 320, 600 and 1200 was used. Final polishing was carried out with polishing cloth containing 0.3 μm alumina suspension or 6 μm and 1 μm diamond suspension. Alternately, polishing of steel specimens in the specially developed laboratory automatic equipment was performed using a large rotating disc at 140 rpm, nominal pressures of 0.013 Pa, 0.139 Pa and 0.244 Pa and diamond paste with particle size 1 μm. Surface finish of specimens were compared as a function of the particle size and polishing time by three methods: the roughness parameter Rz (mean of maximum roughness depth) using a stylus probe, light reflectance with an integrating sphere connected to a spectrophotometer, and reflected diffuse light intensity analysis of a He-Ne laser. Specimen surface images were also obtained by an optical microscope to compare the topography after polishing. From the plot of roughness measurements versus particle size and intensity of diffuse light versus particle size, it was observed that both roughness parameter Rz and the intensity of diffuse light decreased linearly with the abrasive particle size for the manual polishing method. The method of light reflectance measurements shows an approximately constant value of 55 % for all particle size. Therefore, the better methods to assess surface finish of tool steels are the roughness parameter Rz and the intensity of diffuse light by laser method. For the automatic polishing, the results show that there is an optimized time for minimum roughness which is 5 minute. Other relevant aspects of surface finish by particle abrasion are also discussed.

DIFFUSE GALACTIC LIGHT IN THE FIELD OF THE TRANSLUCENT HIGH GALACTIC LATITUDE CLOUD MBM32

We have conducted B, g, V, and R-band imaging in a 45x40 arcmin^2 field containing part of the high Galactic latitude translucent cloud MBM32, and correlated the intensity of diffuse optical light S_\nu(\lambda) with that of 100 micron emission S_\nu(100um). A chi^2 minimum analysis is applied to fit a linear function to the measured correlation and derive the slope parameter b(\lambda)= \Delta S_\nu(\lambda) / \Delta S_\nu(100um) of the best-fit linear function. Compiling a sample by combining our b(\lambda) and published ones, we show that the b(\lambda) strength varies from cloud to cloud by a factor of 4. Finding that b(\lambda) decreases as S_\nu(100um) increases in the sample, we suggest that a non-linear correlation including a quadratic term of S_\nu(100um)^2 should be fitted to the measured correlation. The variation of optical depth, which is A_V = 0.16 - 2.0 in the sample, can change b(\lambda) by a factor of 2 - 3. There would be some contribution to the large b(\lambda) variation from the forward-scattering characteristic of dust grains which is coupled to the non-isotropic interstellar radiation field (ISRF). Models of the scattering of diffuse Galactic light (DGL) underestimate the b(\lambda) values by a factor of 2. This could be reconciled by deficiency in UV photons in the ISRF or by a moderate increase in dust albedo. Our b(\lambda) spectrum favors a contribution from extended red emission (ERE) to the diffuse optical light; b(\lambda) rises from B to V faster than the models, seems to peak around 6000 \AA, and decreases towards long wavelengths. Such a characteristic is expected from the models in which the DGL is combined with ERE.

Root distribution of under-planted European beech (Fagus sylvatica L.) below the canopy of a mature Norway spruce stand as a function of light

Aboveground and belowground biomass of 15-year-old under-planted European beech seedlings (Fagus sylvatica L.) in Norway spruce stand were studied along a light gradient in three plots, in the northern part of Slovenia. Differences in soil water content, aboveground and fine root biomass distribution were confirmed between studied plots. Light had significant effect on the total biomass, root-shoot ratio (0.388 ± 0.076 under canopy, 0.549 ± 0.042 in the edge, 0.656 ± 0.047 in the open), specific root length (SRL) of fine beech roots (561.9 ± 42.2 under canopy, 664.3 ± 51.2 in the edge, 618.2 ± 72.8 in the open) and specific leaf area in beech, indicating morphological adjustment to shade. However, SRL of beech fine roots indicated no change between plots. The correlation between total aboveground and root biomass and light below the mature stand canopy was higher in the case of diffuse light intensity. Most fine roots of spruce were concentrated in the top (0–20 cm) soil layer. Beech fine roots under canopy and edge conditions were also concentrated in top (0–20 cm) soil layer and exhibited shift downwards to deeper soil horizons in open plot. Root proportion between beech and spruce changed with light toward beech with increasing light intensity for both fine and coarse roots.

A low level of extragalactic background light as revealed by γ-rays from blazars

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources-in particular from the first stars formed. This result also indicates that intergalactic space is more transparent to gamma-rays than previously thought.

Etiological and epidemiological studies on the red leaf disease of pineapple in Ghana

Possible cause(s) of red leaf disease (RLD) of pineapple (Ananas comosus L.) in Ghana were examined through field observations, isolation of suspected organisms from roots of diseased plants, growing plants in potted steam-sterilised and unsterilised natural field soils. Others included detection of the pineapple closterovirus (PCV) from symptomatic and healthy pineapple leaves using tissue blot immunoassay (TBIA). Effects of soil moisture, soil fertility, sucker condition and light intensity on the disease were studied in pots while some factor combinations were studied in mini plots in the field. Diseased plants from the field had reduced root systems and had Neosartorya fischeri. Nematodes of the genera Aphelenchus, Pratylenchus and Helicotylenchus were recovered from roots and infrequently from the rind of the underground stem. Pineapple plants grown outdoors in steam-sterilised field soil reddened just as those grown in unsterilised soil. The PCV was detected in only 53% of all typically symptomatic leaves examined. All non-symptomatic leaves also tested positive for PCV. Plants grown from symptomatic suckers in a plant house with diffuse light intensity (7,440 lm m-2) and at 29 oC, recovered from RLD within 6 months. These plants, however, reddened when grown outdoors with intense light (39,751 lm m-2) at 30 oC. Significantly (P

Effect of light availability on the carbon gain of beech (Fagus crenata) seedlings with reference to the density of dwarf bamboo (Sasa kurilensis) in an understory of Japan Sea type beech forest

AbstractIn the understory of Japan Sea type beech (Fagus crenata Bl.) forests, a beech seedling bank persists at the forest floor where the seedlings are shaded by dwarf bamboo (Sasa kurilensis Makino et Shibata). The culm density of dwarf bamboo is reduced by shading from the overstory. To determine the effect of the dwarf bamboo on the photosynthetic productivity of beech seedlings, we evaluated the leaf carbon gain of the beech seedlings with respect to the spatiotemporal variation in light regimes and CO2 concentration in a forest at Buna‐Daira, Fukushima Prefecture, central Japan. In midsummer, we measured photosynthetic photon flux density (PPFD) and air CO2 concentration (Camb) at the beech seedling height in the understory beneath the forest canopy with less dwarf bamboo, and in a canopy gap with dense dwarf bamboo. A frequency distribution of log10‐transformed PPFD showed that the mode PPFD class was greater beneath the closed canopy patch than in the gap (51–109 µmol/m2 per s vs 24–52 µmol/m2 per s), which was close to the estimated mean background PPFD (diffuse light) in each understory. The total sunfleck period during the midday hours and the mean PPFD of each sunfleck were also greater beneath the closed canopy than in the gap. From the diurnal course of PPFD and Camb, we simulated the midday carbon gain of beech seedlings using the CO2 assimilation (A)–PPFD and A–CO2 curves of beech leaves in the closed canopy patch. The total carbon gain of beech leaves beneath the canopy was 2.35‐fold greater than that in the gap, whether the simulation incorporated photosynthetic induction responses to sunflecks or not. High Camb at the forest floor (380–420 µmol/mol) enhanced the total carbon gain 1.12‐fold. The simulation indicated that an increase in diffuse light under sparse dwarf bamboo, which could accelerate the photosynthetic responses to sunflecks and high Camb, contributed to the photosynthetic carbon gain of beech leaves beneath the forest canopy. These findings suggest that the light environment of the understory can be determined by the effects of forest canopy structure on the density of understory dwarf bamboo and that the photosynthetic productivity of beech seedlings mainly depends on the diffuse light intensity.

A non-touch sensor for local scour measurements

A diffuse light intensity photocell coupled with a fiber optic was tested as a non-touch switch sensor for bottom profiling. The device is inexpensive and robust. When mounted on a mechanical positioning carriage it allows continuous scour measurements underwater. Only the fiber optic is immersed in water; therefore the sensor is little intrusive and can be easily used in proximity of side walls. Control tests on a fixed shape showed that the accuracy of the system is appropriate for measurements of local scours. The apparatus was successfully used during mobile bed scour experiments, allowing highly detailed measurements.