Radiation Regime Research Articles

An algorithm for the retrieval of the clumping index (CI) from the MODIS BRDF product using an adjusted version of the kernel-driven BRDF model

The clumping index (CI) characterizes the grouping of foliage relative to a random spatial distribution of leaves and is an important structural parameter for plant canopies that can influence canopy radiation regimes. Consequently, the CI is very useful for ecological and meteorological models. One method used to retrieve the CIs of plant canopies is to construct a linear relationship between the CI and the normalized difference between hotspot and dark spot (NDHD) angular index. This method requires a particularly accurate reconstruction of hotspot signatures, which are difficult to measure. In this study, we propose a framework to retrieve CIs from Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF) parameters, which are generally based on linear CI-NDHD equations. The main algorithm is designed to retrieve CIs in the closed interval [0.33, 1.00]. This range is derived from the CI-NDHD equations and is thus called as the physical range here, although a modified lower boundary can be implemented in the future if necessary. If CIs are outside of this range, then a backup algorithm is designed to reprocess these so-called outlier CIs. The hotspot-adjusted version of the RossThick-LiSparseReciprocal (RTLSR) model (i.e., the RTCLSR model) is employed to reconstruct the hotspot signatures for the MODIS BRDF parameters. This method simplifies the hotspot reconstruction by using two hotspot parameters that are not distinctly scale-dependent particularly in the context of an inhomogeneous coarse spatial resolution. To evaluate this algorithm framework, we collect dozens of global field-measured CIs and calculate their determination coefficient (R2), root mean square error (RMSE) and bias relative to MODIS CIs derived using both the main algorithm and the backup algorithm. Our results show that this framework can derive MODIS CIs with a high accuracy (i.e., R2 = 0.80 (0.72), RMSE = 0.07 (0.12), bias = −0.03 (−0.10)) using the main (backup) algorithms and that it shows promise for various ecological applications, especially in combination with the leaf area index (LAI).

Effects of winter weather and mixing regime on the restoration of a deep perialpine lake (Lake Lugano, Switzerland and Italy)

Long-term (1987–2015) monitoring data from Lake Lugano (Switzerland/Italy) were used to examine the effects of winter weather, solar radiation and mixing regime on the recovery of the trophic state of a lake undergoing nutrient management. Main hypotheses were that (H1) trends in trophic state were influenced not only by nutrient management, but also by winter weather and solar radiation, and (H2) the effects of management were more pronounced in the holomictic South basin than in the meromictic North basin of the lake. External loadings of phosphorus were strongly reduced during the study period, but key indicators of trophic state, including phosphorous concentration, primary production, chlorophyll a and deep-water oxygenation, showed inconsistent responses. Supporting H1, winter weather (parameterized using an index of the East Atlantic pattern) influenced temporal variation in phosphorus concentration and primary production in the North basin. Supporting H2, the effects of management on trophic state were clearer in the South basin, where most trophic-state indicators declined. Meromixis affected the restoration of the North basin lake by transmitting effects of climatic variation on trophic state. The added variability obscured the effects of restoration and caused sudden deteriorations in water quality, indicating that the restoration of meromictic lakes presents unique challenges.

Identification of solar radiation effect on climatic indicators of the territory of Ukraine

Formulation of the problem. Understanding that solar energy is the main source of the majority of biological, chemical and physical processes on Earth, investigation of its influence on different climatic fields allows us to define the features of its space and hour fluctuations. To define radiation and temperature regime of the territory it is necessary to determine climatic features of the spreading surface, which absorbs and will transform solar energy. Considering the fact that modern climatic changes and their consequences cover all components of the system, today there is a problem of their further study for comprehension of atmospheric processes, modeling weather conditions on different territories depending on the properties. The purpose of the article is to determine interrelations between indexes of solar radiation (the Wolf's number) and air temperature, atmospheric pressure on the territory of Ukraine during 1965-2015, their change in space and time. Methods. Correlative method is one of the main methods of a statistical analysis which allows us to receive correlation coefficients of solar radiation variability indexes, air temperature, atmospheric pressure on the territory of the research. This technique estimates the extent of solar radiation influence on temperature regime of the territory and distribution of atmospheric pressure. Results. Coefficients of correlation, which characterize variability of solar radiation indexes, air temperature and atmospheric pressure on the explored territory have been received by means of statistical correlation analysis method. This technique allows us to estimate the degree and nature of solar radiation influence on a temperature regime of the territory and distribution of atmospheric pressure. It has been defined that direct correlative connection between indexes of solar radiation is characteristic of air temperature and atmospheric pressure fields. Significant statistical dependence between incoming solar radiation on the territory of Ukraine and atmospheric pressure has been noted during the spring and autumn periods mainly at the majority of stations. Between indexes of solar radiation and air temperature the inverse correlative connection in winter will be transformed to a direct connection during the spring and summer periods. Scientific novelty and practical significance. Physical processes, which happen in the atmosphere, are characterized by complex interrelations. For further research it is important to define solar radiation value and the extent of influence on climatic conditions.

Testing of the SOLPS-ITER code at Globus-M2 spherical tokamak with detached divertor

In according to a present understanding of Scrape-Off Layer (SOL) physics, future thermonuclear devices like ITER, DEMO and beyond, require high radiation regimes in order to reduce heat loads on tokamak divertor. Recent experiments at ASDEX Upgrade, JET and other tokamaks demonstrated that such regimes might be achieved by the seeding of the radiative impurities. In the present paper the modeling of the high radiation regimes and the transition to the detachment at the Globus-M2 spherical tokamak is performed by the SOLPS-ITER transport code. The obtained modeling results for GLobus-M2 tokamak demonstrate the trend similar to what is observed at larger machines, e.g. AUG and JET. The significant reduction of peak power density at the outer target plate and transition to the detachment with High Field Side High Density (HFSHD) formation at the inner plate was achieved with impurity seeding rate almost equal to the deuterium puff (in el/sec). However, unlike AUG, further increasing of the seeding rate leads not to a formation of the radiative X-point, but to a radiative collapse. This is caused by smaller machine size, which allows the impurity neutrals to penetrate easier into the confined region. It was noticed that starting with attached divertor the inner target transits to the detachment earlier than the outer one.

Dietary Photoprotective Compounds Ameliorate UV Tolerance in Shrimp (Pleoticus muelleri) through Induction of Antioxidant Activity

AbstractThe aim of this study was to determine the effects of ultraviolet radiation (UVR) on bioaccumulation of UV‐absorbing compounds acquired through the diet, in larvae and postlarvae of Pleoticus muelleri, and to assess tissue antioxidant activity, survival, and development. Mysis stage I were exposed to two artificial radiation treatments: M‐PAR (photosynthetically active radiation, range = 400–700 nm) and M‐PAR + UVR (280–700 nm). The experimental larvae received a mixed dietary treatment of Artemia persimilis and the microalga Pavlova lutheri, reared under two radiation regimes: PAR (D‐PAR) and PAR + UVR (D‐PAR + UVR). Shrimp from all treatments reached 8 d postlarval stage (PL8), except those under M‐PAR + UVR treatment fed the D‐PAR‐cultured algae, which had 0% survival. Larvae in M‐PAR + UVR and M‐PAR treatments fed with D‐PAR + UVR diet presented the highest survival rates (70 and 75%, respectively), with 37 and 41% increase in PL size. UV‐absorbing compounds were detected in microalgae and PL subject to PAR + UVR treatments. Antioxidant activity, quantified by measuring the free‐radical 1,1‐diphenyl‐2‐picrylhydrazyl in homogenates of PL8, decayed drastically under radiation treatment M‐PAR + UVR fed with algae of the D‐PAR + UVR treatment. It is concluded that the bioaccumulation of UV‐absorbing compounds and the highest antioxidant activity in PL could improve the biochemical and photophysiological responses of shrimp under UVR stress.

Hyposaline conditions affect UV susceptibility in the Arctic kelp Alaria esculenta (Phaeophyceae)

:The kelp Alaria esculenta represents a key species in high Arctic marine fjord ecosystems. However, the European Arctic is currently experiencing extensive environmental change. Glacial fjord systems, such as Kongsfjorden (Spitsbergen, Svalbard), are subjected to rising temperature, increased freshwater inflow from glaciers and melting snow and a changing ultraviolet (UV) radiation regime related to stratospheric ozone depletion. Thus, in addition to natural seasonality, sessile organisms require acclimation in order to adapt to an environment in transition. We examined the physiological and ultrastructural responses of A. esculenta to the combined exposure to hyposalinity and UV radiation. Photosynthetic quantum yield slightly decreased during a low-salinity treatment of 7 d. Exposure to UV radiation also lowered quantum yield, but specimens previously treated with hyposalinity were significantly less susceptible to UV than nontreated individuals. Concomitant with a loss of chlorophyll during the hyposaline treatment, phlorotannin and antioxidant contents were maintained, and samples treated with low salinities exhibited higher UV-screening characteristics as demonstrated by significantly higher absorption ratios at 300/680 nm. Ultrastructural analyses revealed a treatment-dependent swelling of cell walls and accumulations of phlorotannin-containing vesicles. Our findings point to a strategy by which kelps apply a fast and cost-efficient redistribution of phlorotannins rather than increased synthesis as a general stress response to different environmental drivers in contrast to stress-specific responses. The notion that acclimation to one stressor (low salinity) reflects increased tolerance towards a second stressor (UV radiation) supports the concept of ‘cross-acclimation’ as established for higher plants but not yet for seaweeds.

Characteristic of radiation and thermal resources in Ukraine for the period up to 2050 under conditions of climate change

The article considers parameters of heat and radiation regime within natural and climatic zones of Ukraine for the period of 1986 - 2005 in comparison with their expected changes calculated with regard to two scenarios of climate change: RCP4,5 and RCP8,5 for the period up to 2050. It is noted that during the period up to 2050 there will be an increase of parameters of radiation and thermal regime observed within all natural and climatic zones of Ukraine based on the calculations related to both scenarios. Increase of values of parameters of radiation regime will be observed mainly in the second half of summer and in early autumn. Due to increased amounts of solar radiation in some regions of Ukraine amount of temperatures during the period in question will increase as well with air temperatures exceeding 5°C. However expected increase of amount of temperatures will not exceed 200°C. Increase of amount of temperatures will promote better heat supply for agricultural crops.

Radiation-and-temperature resources of the steppe zone in Ukraine under the climate change conditions in the period of up to 2050

Indices of the radiation-and-temperature regime in the Steppe zone of Ukraine in the period of 1986 through 2005, as compared to the expected changes in these indices, calculated in accordance with the two climate change scenarios, RCP4.5 and RCP8.5, for the period of up to 2050, are under consideration in the paper. RCP4.5 is a scenario of stabilization of greenhouse gas emissions into the atmosphere, while RCP8.5 is the one of very high greenhouse gas emissions. To characterize the radiation and thermal resources in the Steppe zone of Ukraine in the period of 1986 through 2005 (the basic period), and the change in the period of 2021 through 2050 calculations of average long-term values for the first group of environmental factors were performed: the duration of daytime, the total daily solar radiation, the intensity of photosynthetically active radiation (PAR), the accumulated PAR, the radiation balance of the vegetation cover, and the temperature regime. The following principal agro-climatic characteristics of the temperature regime were considered: dates of stable rise of the air temperature above 0, 5, 10, 15 °C in spring and autumn, duration of the period with air temperatures above 0, 5, 10, 15 °C, the accumulated positive air temperatures for the period with air temperatures above 0, 5, 10, 15 °C, the average air temperature in January and July, and the amplitude.
 It is pointed out that in the period of up to 2050, according to the calculations in both scenarios, increased indices of the radiation-and-temperature regime will be observed. The values of the radiation regime parameters will predominantly increase in late summer and early autumn. As a result of the inflow of increased accumulated solar radiation, the accumulated temperatures in the period with air temperatures above 5 °C will also rise. The expected increase in the accumulated temperatures will nevertheless not exceed 200 °C. A rise in the total temperature will contribute to better heat supply for the crops.

Monitoring the solar energy resources of Ukraine

Amid political and, consequently, economic and environmental problems engulfing Ukraine one of the today's challenges consists in studying the possibility of use of natural potential of renewable energy sources. Resources of solar radiation have no negative impact on the natural environment and human activity. Therefore development of helioenergetics and at the same time climatic substantiation of solar power plants use research become more and more important. The purpose of this article is to evaluate of the solar radiation potential opportunities for implementation of technical innovations within the territory of Ukraine and to identify prospects of helioenergetics development. Special indicators of solar radiation components for 1961-1990 s are showed. Using the method of mathematical statistics we defined a value of direct solar radiation contribution forming a part of the total radiation for the warm season (April-September). During the period of 1991-2015 an increase of solar radiation climatic resources relative to climatological standard norm of 1961-1990 was revealed. Over 2001-2015 annual direct and total solar radiation values increased even more in comparison to 1991-2000. Increase of duration of sunshine was also observed. Due to changes of radiation characteristics special indicators of solar for 1991-2015 were specified. The prospects of solar radiation use in helioenergetics proved their feasibility in Crimea, steppe zone, eastern part of forest-steppe zone and even in some parts of Polissya. Comparing to previous years, in terms of sunshine duration over 2000 hours per annum the territory expanded northward. Restrictions on innovations implementation apply to western forest-steppe zone and mountainous areas of Ukrainian Carpathians. Increase of solar radiation regime components determining the feasibility of solar power energy resources form the basis for their countrywide use.

Impact of radiation technique, radiation fraction dose, and total cisplatin dose on hearing : Retrospective analysis of 29medulloblastoma patients.

To analyze the incidence and degree of sensorineural hearing loss (SNHL) resulting from different radiation techniques, fractionation dose, mean cochlear radiation dose (Dmean), and total cisplatin dose. In all, 29children with medulloblastoma (58ears) with subclinical pretreatment hearing thresholds participated. Radiotherapy (RT) and cisplatin had been applied sequentially according to the HIT MED Guidance. Audiological outcomes up to the latest follow-up (median 2.6years) were compared. Bilateral high-frequency SNHL was observed in 26patients (90%). No significant differences were found in mean hearing threshold between left and right ears at any frequency. Asignificantly better audiological outcome (p< 0.05) was found after tomotherapy at the 6 kHz bone-conduction threshold (BCT) and left-sided 8 kHz air-conduction threshold (ACT) than after acombined radiotherapy technique (CT). Fraction dose was not found to have any impact on the incidence, degree, and time-to-onset of SNHL. Patients treated with CT had agreater risk of SNHL at high frequencies than tomotherapy patients even though Dmean was similar. Increase in severity of SNHL was seen when the total cisplatin dose reached above 210 mg/m2, with the highest abnormal level found 8-12months after RT regardless of radiation technique or fraction dose. The cochlear radiation dose should be kept as low as possible in patients who receive simultaneous cisplatin-based chemotherapy. The risk of clinically relevant HL was shown when Dmean exceeds 45 Gy independent of radiation technique or radiation regime. Cisplatin ototoxicity was shown to have adose-dependent effect on bilateral SNHL, which was more pronounced in higher frequencies.

UV Screening in Native and Non-native Plant Species in the Tropical Alpine: Implications for Climate Change-Driven Migration of Species to Higher Elevations.

Ongoing changes in Earth’s climate are shifting the elevation ranges of many plant species with non-native species often experiencing greater expansion into higher elevations than native species. These climate change-induced shifts in distributions inevitably expose plants to novel biotic and abiotic environments, including altered solar ultraviolet (UV)-B (280–315 nm) radiation regimes. Do the greater migration potentials of non-native species into higher elevations imply that they have more effective UV-protective mechanisms than native species? In this study, we surveyed leaf epidermal UV-A transmittance (TUV A) in a diversity of plant species representing different growth forms to test whether native and non-native species growing above 2800 m elevation on Mauna Kea, Hawaii differed in their UV screening capabilities. We further compared the degree to which TUV A varied along an elevation gradient in the native shrub Vaccinium reticulatum and the introduced forb Verbascum thapsus to evaluate whether these species differed in their abilities to adjust their levels of UV screening in response to elevation changes in UV-B. For plants growing in the Mauna Kea alpine/upper subalpine, we found that adaxial TUV A, measured with a UVA-PAM fluorometer, varied significantly among species but did not differ between native (mean = 6.0%; n = 8) and non-native (mean = 5.8%; n = 11) species. When data were pooled across native and non-native taxa, we also found no significant effect of growth form on TUV A, though woody plants (shrubs and trees) were represented solely by native species whereas herbaceous growth forms (grasses and forbs) were dominated by non-native species. Along an elevation gradient spanning 2600–3800 m, TUV A was variable (mean range = 6.0–11.2%) and strongly correlated with elevation and relative biologically effective UV-B in the exotic V. thapsus; however, TUV A was consistently low (3%) and did not vary with elevation in the native V. reticulatum. Results indicate that high levels of UV protection occur in both native and non-native species in this high UV-B tropical alpine environment, and that flexibility in UV screening is a mechanism employed by some, but not all species to cope with varying solar UV-B exposures along elevation gradients.

Role of Slip Velocity in a Magneto-Micropolar Fluid Flow from a Radiative Surface with Variable Permeability: A Numerical Study

An analysis is presented to describe the hydromagnetic mixed convection flow of an electrically conducting micropolar fluid past a vertical plate through a porous medium with radiation and slip flow regime. A uniform magnetic field has been considered in the study which absorbs the micropolar fluid with a varying suction velocity and acts perpendicular to the porous surface of the above plate. The governing non-linear partial differential equations have been transformed into linear partial differential equations, which are solved numerically by applying the explicit finite difference method. The numerical results are presented graphically in the form of velocity, micro-rotation, concentration and temperature profiles, the skin-friction coefficient, the couple stress coefficient, the rate of heat and mass transfers at the wall for different material parameters.

Aphid orientation and performance in glasshouses under different UV‐A/UV‐B radiation regimes

AbstractVisual cues leading to host selection and landing are of major importance for aphids and evidence suggests that flight activity is very dependent on ultraviolet (UV)‐A radiation in the environment. At the same time research on insect plant hosts suggest that the UV‐B component can deter some pests via changes in secondary metabolite chemistry. Here, we examine the potential of UV (UV‐A/UV‐B) radiation to control insect pests in the glasshouse environment. We first examined artificial exposure to UV‐B and the potential to trigger morphological and biochemical modifications in pepper (Capsicum annuum L., Solanaceae) with implications for the fitness of green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). UV‐B caused accumulation of leaf secondary metabolites and soluble carbohydrates, and stimulated photosynthetic pigments. However, UV‐B did not impact on foliar protein content and aphid performance was unaffected. Next, we studied how altering the UV‐A/UV‐B ratio environment affected aphid orientation and spatial distribution over time, either directly or by exposing plants to supplemental UV before insect introduction. Aphids directly settled and dispersed on their host pepper plants more readily in the presence of supplemental UV‐A and UV‐B. In the control treatment with ambient glasshouse UV‐A and UV‐B, insects remained more aggregated. Furthermore, insects were less attracted to peppers pre‐exposed to supplemental UV‐A and UV‐B radiation. Our results suggest that suppression of UV‐A and UV‐B inside the protected environment reduces aphid colonization and dispersal. Furthermore, application of moderate exposure of young pepper plants to supplemental UV‐B radiation could aid in protection from the colonization by phytophagous insects.

Assessing the consistency of optical properties measured in four integrating spheres

ABSTRACTLeaf optical properties (LOPs) determine the radiation regime of vegetation, thus being key input parameters in leaf and canopy radiative transfer models. It is of great importance to know the uncertainties originating from the LOP measurements. The most common approach to measure LOP uses integrating spheres. They allow measurements of both directional-hemispherical reflectance factor (R) and transmittance factor (T). However, sphere’s design, inner surface coating and measurement protocol differ among the spheres’ models and manufacturers. Our main goal was to evaluate the consistency of optical properties measured in four integrating spheres (Dualsphere, Labspehre, ASD, and Li-cor). Our test samples were three Spectralon® panels, four artificial materials and leaves from six common broadleaf tree species. Results showed that spectra measured in the four integrating spheres were generally similar in the spectral region between 400 and 1600 nm. The average standard deviation computed among the spectra of all samples measured in all spheres was around 0.023 (and varied between 0.005 and 0.044). Statistically significant differences were detected mainly between Dualsphere and Li-cor spheres.

Phenological and ecophysiological responses of Capsicum annuum var. glabriusculum to native arbuscular mycorrhizal fungi and phosphorus availability

Due to climate change, the assessment of environmental variations associated to phenology and ecophysiology of iconic Sonoran Desert plants such as Capsicum annuum var. glabriusculum (Cag), during their interaction with the native arbuscular mycorrhizal fungi (AMF) and soil nutrients availability, is the keystone to understand its biological significance in the extreme conditions of semiarid environments. Seasonal patterns of high solar radiation regimes and extreme daily air temperatures thresholds were reflected in a high accumulation of heat from physiological maturity (2699°D) until the end of reproduction season (4002°D). In treatments without chemical fertilization, low and intermediate P availability, the native AMFCag inoculum significantly increased Cag’s relative growth rates and changed the biomass allometric allocation patterns causing a lower partition to the roots and a higher partition to the growth of shoots and photosynthetic assimilation surface. Depending on the phenological stage, the levels of P availability and the levels of native AMF propagules in the soil, significantly modified the content of C, H, S, P, N, Ca, Fe, Mn or Ni in the shoots. The native AMFCag inoculum significantly increased the functional colonization (Arum-Paris type) of roots except with higher P availability. However, when AMF propagules in the soil are low, P increase and presence of other mineral nutrients is detrimental to symbiotic establishment. Conversely, when AMF propagules in the soil are high, symbiotic traits indicate that the native AMF taxa tested, have different tolerance capabilities to colonize functionally the roots to obtain the carbon for their development even under a high P and other mineral nutrients availability in the soil. In extreme conditions of sunlight and air temperatures, Cag’s phenological and ecophysiological traits were enhanced by the native AMFCag inoculum in different P availability levels, however, the mycorrhizal growth response decreased significantly as the availability of P increases, and the highest level of native AMF propagules in soil was the factor that promoted the increase of reproductive yield of Cag plants, not the increase of nutrients availability. This study provides novel information on AMF-Cag symbiotic interactions during plant development and phenological stages, as well as proposes different insights and hypothesis of research about Cag-AMF ecophysiology.

Light-driven growth in Amazon evergreen forests explained by seasonal variations of vertical canopy structure

Light-regime variability is an important limiting factor constraining tree growth in tropical forests. However, there is considerable debate about whether radiation-induced green-up during the dry season is real, or an apparent artifact of the remote-sensing techniques used to infer seasonal changes in canopy leaf area. Direct and widespread observations of vertical canopy structures that drive radiation regimes have been largely absent. Here we analyze seasonal dynamic patterns between the canopy and understory layers in Amazon evergreen forests using observations of vertical canopy structure from a spaceborne lidar. We discovered that net leaf flushing of the canopy layer mainly occurs in early dry season, and is followed by net abscission in late dry season that coincides with increasing leaf area of the understory layer. Our observations of understory development from lidar either weakly respond to or are not correlated to seasonal variations in precipitation or insolation, but are strongly related to the seasonal structural dynamics of the canopy layer. We hypothesize that understory growth is driven by increased light gaps caused by seasonal variations of the canopy. This light-regime variability that exists in both spatial and temporal domains can better reveal the drought-induced green-up phenomenon, which appears less obvious when treating the Amazon forests as a whole.

Fungal tissue per se is stronger as a UV-B screen than secondary fungal extrolites in Lobaria pulmonaria

Abstract To test the hypotheses that (1) protective mycobiont tissues and/or (2) medullary UV-B-absorbing carbon-based secondary compounds (CBSCs) protect lichen photobionts against UV-B radiation, we quantified cortical UV-transmittance and ran a three-way factorial lab experiment with (1) three UV radiation regimes, (2) photobiont layers with/without a screening cortex, and (3) with natural/reduced CBSC-concentration. We used melanin-deficient Lobaria pulmonaria from shaded forests. Maximum photochemical efficiency of photosystem II ( F v/ F m) in photobionts inside thalli with natural CBSC-concentrations was not affected by any UV-regime, consistent with close to 0% measured cortical transmittance of wavelengths P P P = 0.001), mainly affecting exposed photobiont layers given short-wavelength UV radiation. Based on these findings, we conclude that the primary role of extrolites in L. pulmonaria is not to screen excess solar radiation.

Statistical analysis for the characterization of solar energy utilization and inter-comparison of solar radiation at two sites in Cyprus

A statistical analysis and inter-comparison of the solar radiation at two sites in Cyprus representing two different climate regimes of the island (Athalassa-inland plain vs Larnaca-coastal location) covering the period January 2013–December 2015 is presented. Mean annual and mean monthly daily totals of the global, horizontal beam and diffuse radiation and their frequency distribution at both sites are computed and discussed. The values of skewness and kurtosis coefficients are used to define the frequency distribution type of the above radiation parameters on a monthly basis. The statistical analysis is extended to the daily clearness index (KT), diffuse ratio (KD), and the ratio of horizontal beam to global radiation (KB,G). Furthermore, the influencing factors on the magnitude of the radiation components were examined. The value of KT was used to classify three different types of days such as clear, partially cloudy and cloudy days. Then, a statistical analysis of the solar radiation components was performed. On an average annual basis, more than 80% of the days are classified as either clear or partially cloudy at both stations. Additionally, the influence of the atmospheric absorption and scattering of the solar radiation under clear skies was examined on the basis of the Linke turbidity factor (TL). The results of this analysis are used to characterize and compare the radiation regimes of the two sites. Both sites have relatively high intensity of global and direct horizontal radiation. The annual average daily global radiation intensity is 18.5MJm−2 at Athalassa and 19.9MJm−2 at Larnaca. The horizontal beam radiation is 13.1MJm−2 for Athalassa and 14.2MJm−2 for Larnaca. Therefore, the fraction of the beam component of the global radiation is comparatively high at both sites, as indicated by the annual average daily fraction which is greater than 0.600. Generally, Larnaca has slightly higher rates of global radiation than Athalassa, as indicated by the average yearly cumulative global irradiation which is 6763MJm−2 for Athalassa and 7274MJm−2 for Larnaca.

Retrieving forest canopy extinction coefficient from terrestrial and airborne lidar

Accurately retrieving the extinction coefficient (k) of foliage elements is a key step to spatially mapping the radiation regime within and under a forest canopy. The azimuthal angle of foliage elements (characterized by their normal vectors) is an important factor for improving the retrieval accuracy of k using 3-D voxels derived from lidar data. In this work, we first developed and validated an approach to retrieve k for a forest canopy by considering both inclination and azimuthal angles from terrestrial laser scanning (TLS) data. Then, we explored the feasibility of applying the proposed method to aerial laser scanning (ALS) data through four point thinning experiments for both broadleaf and coniferous trees. Our results showed that: (1) TLS-based foliage orientation could capture 86% (N=209, p<0.001) and 64% (N=78, p<0.001) of the variance in manually measured azimuthal and inclination angles, respectively for an artificial broadleaf tree; (2) the proposed lidar-based k retrieval method can be applied to both ALS- and TLS- based forest lidar data; and (3) the azimuthal angle of foliage elements is an important factor for retrieving k of a forest canopy, and both TLS and ALS platforms have differing effects on the estimates of forest k. Using this new framework, we were able to use lidar data to model the expected spatio-temporal distribution of photosynthetically active radiation within forest canopies.

An analysis of beamed wireless power transfer in the Fresnel zone using a dynamic, metasurface aperture

Wireless power transfer (WPT) has been an active topic of research, with a number of WPT schemes implemented in the near-field (coupling) and far-field (radiation) regimes. Here, we consider a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel region. In this context, the dynamic aperture resembles a reconfigurable lens capable of focusing power to a well-defined spot, whose dimension can be related to a point spread function. The necessary amplitude and phase distribution of the field imposed over the aperture can be determined in a holographic sense, by interfering a hypothetical point source located at the receiver location with a plane wave at the aperture location. While conventional technologies, such as phased arrays, can achieve the required control over phase and amplitude, they typically do so at a high cost; alternatively, metasurface apertures can achieve dynamic focusing with potentially lower cost. We present an initial tradeoff analysis of the Fresnel region WPT concept assuming a metasurface aperture, relating the key parameters such as spot size, aperture size, wavelength, and focal distance, as well as reviewing system considerations such as the availability of sources and power transfer efficiency. We find that approximate design formulas derived from the Gaussian optics approximation provide useful estimates of system performance, including transfer efficiency and coverage volume. The accuracy of these formulas is confirmed through numerical studies.