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Adaptive Neuro-Fuzzy Inference System integrated with solar zenith angle for forecasting sub-tropical photosynthetically active radiation

Adaptive Neuro-Fuzzy Inference System integrated with solar zenith angle for forecasting sub-tropical photosynthetically active radiation

Satellite (and reanalysis) data sources can fill potential gaps in analysis of PAR availability for sites where insuffi- cient locally measured atmospheric parameters are available (Deo & Sahin, 2017; Ghimire, Deo, Downs, & Raj, 2018; Rubio, Lopez, Tovar, Pozo, & Batlles, 2005). However, satel- lite swaths at daily (or longer) timescales do not offer the ben- efit of near real- time (i.e., very short- term) PAR estimations, considered vital for accurately describing a plant’s photosyn- thetic behavior at a micro- level (Escobedo, Gomes, Oliveira, & Soares, 2011; Ge, Smith, Jacovides, Kramer, & Carruthers, 2011; Wang et al., 2015). Data- driven approaches using input datasets (initial conditions and mathematical equations are not required as with empirical and physical models) can be trained and adapted to variable climates for modeling PAR at the local scale. As a result, data- driven models have recently emerged as pertinent tools in energy systems (e.g., (Deo & Sahin, 2017; Deo, Downs, Parisi, Adamowski, & Quilty, 2017; Deo, Wen, & Feng, 2016; Ghimire et al., 2018; Hu, Wang, & Zeng, 2013)). Such models offer added opportunity to fore- cast future PAR on very short- and long- term scales, without needing extensive atmospheric model initialization condi- tions. Yet, even though much research has been performed for solar, wind, and atmospheric modeling applications (e.g., (Deo & Sahin, 2017; Deo et al., 2016; Dokur, Kurban, & Ceyhan, 2015; Ghorbani, Khatibi, Hosseini, & Bilgili, 2013; Islam, Mohandes, & Rehman, 2016; Mohammadi et al., 2015; Salcedo- Sanz, Deo, Cornejo- Bueno, Camacho- Gómez, & Ghimire, 2018)), modeling of very short- term (i.e., near real- time) PAR in sub- tropical regions remains scarce. These re- gions have less cloud cover than tropical or temperate climate areas and therefore enhance the suitability of sites for solar and bio- energy generation.
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The effect of solar zenith angle on MODIS cloud optical and microphysical retrievals within marine liquid water clouds

The effect of solar zenith angle on MODIS cloud optical and microphysical retrievals within marine liquid water clouds

Figure 17. An example of the effect of 3-D effects on MODIS retrievals at small averaging scales. 3-D effects at high θ 0 are assumed to cause an equal increase and decrease (1R) in the reflectances of both the absorbing band (R ab ) and the non-absorbing band (R nab ). For this demonstration it is assumed that there are an equal number of small-scale cloud elements all with r e = 14 µm and τ = 23.6. Retrievals are then made on the reflectances that have been distorted by the 3-D effects using MODIS lookup tables (LUTs) that are used for converting non-absorbing (0.86 µm) and absorbing reflectance pairs into τ and r e . These are shown for θ 0 = 79 ◦ and a nadir viewing angle: (a) is for the 1.6 µm absorbing band, (b) for 2.1 µm and (c) for 3.7 µm. It can be seen that in all cases the retrieved r e would be greater than the true r e of 14 µm. See Sect. 5.1 for further details.
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Enhanced spectral UV irradiance: a one year preliminary study

Enhanced spectral UV irradiance: a one year preliminary study

The UV spectra on cloudy days were compared to those on cloud free days to determine which part of the UV spectrum has the greatest enhancement due to the cloud compared to both corresponding measured clear-sky spectra as well as other enhanced spectra. In this preliminary study, cloud enhanced UV spectra selected for maximum UVA enhancement compared to a clear-sky UV spectrum at similar solar zenith angle (SZA) and ozone values, showed that the ratio of the two sets of spectral irradiances was approximately wavelength independent (approximately 1.1) above the cut-off wavelength of approximately 306 nm. Similarly, above 306 nm the average ratio of the spectral irradiances of a maximum UVB enhanced UV spectrum compared to a clear-sky spectrum was 1.2 with maximum values generally above this average between 316 and 344 nm and generally below 1.2 above the wavelength of 344 nm. The UVA and UVB enhanced spectra were separated into five SZA ranges and the irradiance at each wavelength averaged for each range and compared to clear-sky spectra in each of the ranges. Above approximately 306 nm, the ratios are wavelength independent for all SZA. However, with the exception of the SZA range centred on 20°, there is an increasing dependency with shorter wavelengths below the 306 nm. Also there appears to be two distinct groupings of the average irradiance ratios, corresponding to the SZA range centred on 20°, 37° and 49° (ratio of 1.2) and 32° and 42° (ratio 1.0), the latter cases suggesting that on average there is no enhancement for these SZA, except for wavelengths less than 306 nm.
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Diffuse solar ultraviolet radiation

Diffuse solar ultraviolet radiation

For a given concentration of atmospheric absorbing and scattering particles and increasing solar zenith angle, the path of the solar UV through the atmosphere is longer. This results in a higher degree of atmospheric scattering and the portion of diffuse UV increases for increasing solar zenith angles. The proportion of diffuse erythemal UV measured in full sun at a sub-tropical site was approximately 26% at noon and 40% in the morning and afternoon. 22 This was averaged for a series of measurements over a season and the maximum proportion of diffuse UV is higher than this.
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On the role of the seawater absorption-to-attenuation ratio in the radiance polarization above the southern Baltic surface

On the role of the seawater absorption-to-attenuation ratio in the radiance polarization above the southern Baltic surface

Abstract. Information about polarization of light leaving the ocean surface has the potential to improve the quality of bio- optical parameter retrieval from ocean color remote sens- ing (OCRS). This improvement can be applied in numerous ways, such as limiting of Sun glints and obtaining informa- tion about atmospheric aerosol properties for atmospheric correction as well as increasing the accuracy of the algo- rithms based on the water-leaving signal. Polarization signals at the top of the atmosphere (ToA) that include the water- leaving signal are strongly influenced by atmospheric molec- ular scattering and by direct Sun and sky reflections from the sea surface. For these reasons, it is necessary to better un- derstand the factors that change the polarization of light in the atmosphere–ocean system, especially in coastal zones af- fected by dynamic changes. In this paper, the influence of seasonal variability of light absorption and scattering coeffi- cients (inherent optical properties; IOPs) of seawater, wind speed and solar zenith angle (SZA) on the polarization of upwelling radiance over the sea surface in the visible light bands is discussed. The results come from a polarized radia- tive transfer model based on the Monte Carlo code and ap- plied to the atmosphere–ocean system using averaged IOPs as input data. The results, presented in the form of polar plots of the total upwelling radiance degree of polarization (DoP), indicate that regardless of the wavelength of light and type of water, the highest value of the above-water DoP is strongly correlated with the absorption-to-attenuation ratio. The cor- relation is a power function that depends on both the SZA and the wind speed. The correlation versatility for different wavelengths of light is very unusual in optics of the sea and is therefore worth emphasizing.
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Annual variation of the angular distribution of the UV beneath public shade structures

Annual variation of the angular distribution of the UV beneath public shade structures

Local governments provide many shade structures at parks and sporting ovals for public use. However, the question remains of how effective are public shade structures at reducing biologically effective UV radiation throughout the year? Broadband measurements of the angular distribution of scattered UV beneath three specific public shade structures was conducted for relatively clear skies and for a solar zenith angle (SZA) ranging from 13 o to 76 o . The ultraviolet protection factors (UPF) for the shade structures ranged from 18.3 to 1.5 for an increasing SZA. Measurements showed that the horizontal plane received the highest SUV levels from the SZA of 28 o to 75 o , 42 o to 76 o , and 50 o to 76 o for the small, medium and large structures respectively. This was due to the angle of the sun causing the shade created by the shade structure to be outside the structure. For the small shade structure, the measurements directed to the west were the highest levels in the shade after approximately 28 o . For the medium and large shade structures, the measurements directed to the west and south were the highest levels in the shade after roughly 42 o and 50 o respectively.
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Radiative budget and cloud radiative effect over the Atlantic from ship-based observations

Radiative budget and cloud radiative effect over the Atlantic from ship-based observations

There is no obvious meridional dependency of the net ra- diative flux within the present latitudinal extent. The nega- tive LW flux mostly depends on cloud cover and cloud base height. The positive SW flux depends on solar zenith angle, cloud cover and cloud type and dominates daily net radiative sums. Thus, smaller flux values south of 35 ◦ S and north of 45 ◦ N are consistent with the smaller solar budget at higher latitudes. However, the data were recorded with lower data density and therefore have a weaker climatological signifi- cance. In addition, the ship tracks do not sufficiently extend into the mid-latitudes to show a clear meridional variability. Furthermore, meridional changes in cloud cover and cloud bottom height may dominate over the purely astronomical conditions.
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Optimizing UV Index determination from broadband irradiances

Optimizing UV Index determination from broadband irradiances

At present, the UV Index determination for the ECCC forecast system relies on a statistically derived weather-based computation of the total column ozone field, adjustments us- ing total column measurements of the Canadian Brewer net- work, and empirical conversions to the UV Index accounting for the solar zenith angle, cloud conditions, surface altitude, and snow cover. A recently undertaken study toward improv- ing the UV Index forecast system makes direct use of ozone data assimilation, ozone model forecasts, and model UV ir- radiance forecasts for both clear-sky and cloudy conditions as carried out in some capacity at other forecast centres (e.g., NCEP/NOAA, KNMI, and ECMWF). A summary of UV In- dex forecasting practices conducted by various governmen- tal organizations worldwide were compiled by Long (2003); a more recently updated overview of UV measurement sta- tions and monitoring networks in Europe was reported by Schmalwieser et al. (2017).
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Accounting for surface reflectance anisotropy in satellite retrievals of tropospheric NO 2

Accounting for surface reflectance anisotropy in satellite retrievals of tropospheric NO 2

temporal resolution (retrieved every 8 days based on all clear- sky observations over a 16-day interval), and an atmospheric correction that accounts for trace gas absorption, molecular and aerosol scattering, and coupling between atmospheric and surface BRDF (Vermote et al., 2002). The operational MODIS BRDF model characterizes the surface anisotropy with a linear combination of pre-set BRDF kernels (see Eq. 1 below), which are derived from detailed modeling of surface reflectance. All the MODIS BRDF/albedo products are pro- vided with quality flags, and these products have been thor- oughly validated against a variety of surface measurements taken at different locations world-wide. The validation stud- ies suggest that the overall accuracy of the MODIS albedo (broadband, integrated from 0.3 to 5 µm) is of the order of 10% with an increasing uncertainty in winter months espe- cially as solar zenith angle increases beyond 70 ◦ –75 ◦ (Jin et al., 2003; Knobelspiesse et al., 2008; Liang et al., 2002; Liu et al., 2009; Salomon et al., 2006). Very little informa- tion is available, however, on the uncertainties of the spectral albedo in different wavelength bands, but it can be larger, es- pecially at the short wavelengths (470 nm) relevant for the present study (Vermote and Kotchenova, 2008).
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Extended and refined multi sensor reanalysis of total ozone for the period 1970–2012

Extended and refined multi sensor reanalysis of total ozone for the period 1970–2012

for this month. The RMS error of the OmF is smaller than the observational error compared to ground-based observa- tions, because representative errors of the satellite observa- tions compared to level 4 data are likely to be smaller than for satellite observations compared to ground-based observa- tions. For high solar zenith angles the RMS value increases, because these measurements are usually associated with the highly variable ozone concentrations in and around the polar vortex. Plots similar to Fig. 6 show that the bias between the forecast and the satellite columns is generally smaller than 1 % after 1979. The bias between analyses and observations is in general even smaller (less than 1 DU), which shows the effect of data assimilation. Compared to the MSR1 results (van der A et al., 2010), the bias is slightly decreased proba- bly as a result of the higher spatial resolution for the MSR2, the improved data assimilation and the improved solar zenith angle correction.
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Effects of solar flares on the ionosphere as shown by the dynamics of ionograms recorded in Europe and South Africa

Effects of solar flares on the ionosphere as shown by the dynamics of ionograms recorded in Europe and South Africa

the solar zenith angle. Furthermore, Nogueira et al. (2015) demonstrated an abrupt increase in the TEC. The observed anomaly seemed larger and remained for a longer time in the crest region of the equatorial ionization anomaly (EIA) than at the subsolar point. We also observed the largest and the longest-lasting perturbation of the ionospheric absorption in the equatorial region (at Ascension Island) in most of the cases. However, our results suggest that the solar zenith angle of the observation site plays an important role. For instance, at the peak time of the X9 flare (5 December 2006) the zenith angle of the ionosonde station at Ascension Island (geomag- netic latitude: − 2.31 ◦ ) was 36.14 ◦ and the duration of the fade-out was 60 min, smaller than that measured at Graham- stown (geomagnetic latitude: − 34.01 ◦ ; see Table 3). Even a larger difference was observed at the two stations during the M5-class flare at 09:27 UTC on 27 October 2003. The so- lar zenith angle of Ascension Island was 47.96 ◦ at the peak time and there was no detected total radio fade-out, while at Grahamstown, with a smaller solar zenith angle (21.77 ◦ ), the duration of the total attenuation of HF waves was 150 min (Table 3). Therefore, our observations confirm the results of Zhang and Xiao (2005), Sripathi et al. (2013) and the D-RAP model that the solar zenith angle plays an important role in the ionospheric response to solar flares.
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Simulation study of near-Earth space disturbances: 2. Auroral substorms

Simulation study of near-Earth space disturbances: 2. Auroral substorms

The global magnetohydrodynamics (MHD) simulation developed by Prof. Takashi Tanaka, called a REPPU (REProduce Plasma Universe) code, solves a set of ideal MHD equations using the finite volume total variation diminishing (TVD) scheme (Tanaka 1994). The inner boundary is located on the sphere at a geocentric dis- tance of ~ 3 Re. Although the MHD equations are not solved in the region between the inner boundary and the ionosphere, the magnetosphere-ionosphere coupling is taken into consideration by exchanging quantities along the dipole magnetic field line. The following calculation is performed at every time step (~ 0.03 s). First, the field-aligned current (FAC) and the plasma pressure at the inner boundary are mapped from the inner boundary of the magnetospheric domain to the ionosphere. Secondly, the ionospheric conductivities (Pedersen and Hall conductivities) are calculated on the basis of the mapped values (the FAC and the plasma pressure), and the solar zenith angle. The ionospheric conductivity is increased where the upward FACs flow and the plasma pressure is high. Thirdly, to satisfy the current continuity conditions in the ionosphere, an elliptic partial differen- tial equation is solved for the given FACs and the iono- spheric conductivity. The conjugate residual method was used to solve the partial differential equation. Fourthly, the electric field is mapped from the ionosphere to the inner boundary of the magnetospheric domain along the dipole magnetic field line. Fifthly, the velocity corre- sponding to the electric field is imposed on the inner boundary as one of the boundary conditions. For detailed explanations concerning this calculation, readers
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High-resolution and Monte Carlo additions to the SASKTRAN radiative transfer model

High-resolution and Monte Carlo additions to the SASKTRAN radiative transfer model

The Monte Carlo model is intended for use as an accu- rate reference model that estimates solutions to the radiative transfer problem without bias. The model is implemented within the SASKTRAN framework and is therefore useful as a tool for error checking other models within the framework. Furthermore, it can been used to prescribe the resolution nec- essary in faster successive-orders discrete-ordinates models to achieve accuracy to within some limit. In this work, con- figurations were found that allow the high-resolution model to agree with the Monte Carlo reference model to within 0.2 % for a wide variety of solar geometries and wavelengths. The two radiative transfer models were used to identify and eliminate a bias in the OSIRIS ozone product. OSIRIS scans were simulated using the Monte Carlo model, and ver- tical profiles of ozone were retrieved from these simulated scans using the high-resolution model. It was shown that calculating the multiply scattered diffuse radiance field at only one solar zenith angle introduces a bias of up to 4 % for typical OSIRIS geometries. The shape and magnitude of the bias is different when the instrument is scanning up or down, and is an artefact of the correlation between scan height and local solar zenith angle, complicated by the use of a high-altitude normalization measurement in the retrieval algorithm. It was found that calculating the diffuse radiance field at five equally spaced solar zenith angles eliminates the effect and is sufficient to reduce biases in the OSIRIS ozone
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Investigation of Aerosol Optical Properties in the Ultraviolet Spectrum

Investigation of Aerosol Optical Properties in the Ultraviolet Spectrum

measurements from the USDA’s Lake Wheeler site near Raleigh, North Carolina. Aerosol single scattering albedo (SSA) was retrieved at the 45-degree morning solar zenith angle for 15 days from March to September of 2004 at the seven operational wavelengths of the UVMFR-SR. The results ranged from 0.680 to 0.990 and varied quadratically with increasing wavelength. This range of SSA was within the range of previous studies. The overall average SSA for this study was 0.867, indicating that most of the UV radiation incident to the particles is scattered, rather than absorbed. This reduces the direct UV irradiance by increasing the diffuse component. In addition, two of these days were selected for hourly retrievals of SSA and it was found that the minimum amount of scattering of UV radiation by aerosols occurred near solar noon. More scattering occurred earlier in the morning and later in the afternoon.
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Fast and simple model for atmospheric radiative transfer

Fast and simple model for atmospheric radiative transfer

Abstract. Radiative transfer models (RTMs) are of utmost importance for quantitative remote sensing, especially for compensating atmospheric perturbation. A persistent trade- off exists between approaches that prefer accuracy at the cost of computational complexity, versus those favouring simplic- ity at the cost of reduced accuracy. We propose an approach in the latter category, using analytical equations, parameter- izations and a correction factor to efficiently estimate the effect of molecular multiple scattering. We discuss the ap- proximations together with an analysis of the resulting per- formance and accuracy. The proposed Simple Model for At- mospheric Radiative Transfer (SMART) decreases the calcu- lation time by a factor of more than 25 in comparison to the benchmark RTM 6S on the same infrastructure. The relative difference between SMART and 6S is about 5% for space- borne and about 10% for airborne computations of the atmo- spheric reflectance function. The combination of a large solar zenith angle (SZA) with high aerosol optical depth (AOD) at low wavelengths lead to relative differences of up to 15%. SMART can be used to simulate the hemispherical conical reflectance factor (HCRF) for spaceborne and airborne sen- sors, as well as for the retrieval of columnar AOD.
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Signature Simulation and Characterization of Mixed Solids in the Visible and Thermal Regimes

Signature Simulation and Characterization of Mixed Solids in the Visible and Thermal Regimes

simulation or a physical imaging system. With radiance in hand, solving for BRDF should be straight forward. However, sensors do not exhibit perfect sensitivity at all wavelengths. This was explained theoretically in Section 4.2.4. Every simulation photon that hits a detector does not necessarily result in a signal electron. Therefore, solving for BRDF requires compensation for device sensitivity. Detectors typically have spectral response functions that describe how efficiently photons are converted to signal over a range of wavelengths. The virtual sensor used in this experiment was characterized by Gaussian shaped response functions centered at 450nm, 550nm, 650nm, 868nm, 1000nm, and 1915nm. Bachmann et al. (2014) also analyzed spectral reflectance at these wavelengths at a shorter observation distance. Half nanometer spectral resolution was used. The virtual sensor was positioned 1.78m from the virtual soil surface. A reduced instantaneous field of view (IFOV) of 0.092m was evaluated in an attempt to maintain a constant view of the scene as the sensor zenith angle was increased. This sensor configuration matches that of the University of Lethbridge goniometer system version 2.5 (ULGS-2.5) (Wang et al., 2010). Prior to simulation, the total scene irradiance, E, is specified by the user. The solar illumination source was initially positioned with a zenith angle of 30 from nadir. Scenes with a solar zenith angle of 20 were also subjected to simulation. DIRSIG will not allow for remotely sensed signal to exceed that of the illumination source.
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Validation of Spectral and Broadband UV B (290   325 nm) Irradiance for Canada

Validation of Spectral and Broadband UV B (290 325 nm) Irradiance for Canada

· The delta-Eddington method produces daily total spectral irradiances for all sky conditions, which are generally 3 - 7% larger than those from the 8-stream DISORT method. The fractional overestimation de- creases as wavelength increases. Irradiances are accept- able for wavelengths ≥ 305 nm. This method is unsuit- able for wavelengths below 305 nm where ozone absorp- tion is high due to the truncation of the scattering phase function to two terms. At longer wavelengths its per- formance varies with solar zenith angle and cloudiness. For clear skies, the method always overestimates irradi- ances at all sun angles with the error increasing as the solar zenith angle increases. For cloudy skies the errors are much smaller.
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Solar Power Output with Optimum Tilt Angle using Matlab

Solar Power Output with Optimum Tilt Angle using Matlab

important parameters for capturing maximum solar radiation falling on the solar panels. This angle is site specific as it depends on the daily, monthly and yearly path of the sun. An accurate determination of optimum tilt angle for the location of interest is essential for maximum energy extraction from the system. A numerous methods are being used for determining the tilt angle at different locations worldwide. Keeping in view the relevance of the optimum tilt angle in energy production and reducing the cost of solar energy systems, the present study has been undertaken. The study shows that for maximum energy gain, the optimum tilt angle for solar system must be determined accurately for each location. This review will be useful for designers and researchers to select suitable methodology for determining optimum tilt angle for solar systems at any site.
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KM3NeT/ORCA status and plans

KM3NeT/ORCA status and plans

The background from the abundant down-going muons is suppressed at first with basic cuts on the reconstructed zenith angle and vertex position. Only up-going events are selected and the vertex position is constrained to reside approximately in the instrumented volume. This decreases the amount of atmospheric muons by three orders of magnitude. Further suppression, by two orders of magnitude, is achieved by using a boosted decision tree (BDT) for the identification of these events. Only a few percent of misreconstructed muon events remain in the final sample of reconstructed events.
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Smartphone based Android app for determining UVA aerosol optical depth and direct solar irradiances

Smartphone based Android app for determining UVA aerosol optical depth and direct solar irradiances

The most common ground based methods to measure direct solar irradiance and aerosol optical depth involve the use of specialised equipment including sunphotometers and sky radiometers [1][2]. The costs of and accessibility of this equipment often mean that its use, hence the spatial resolution of aerosol data collected is limited. Portable means of ground based measurement, such as the Microtops sunphotometer, while easy to use, are expensive, hence largely inaccessible to the wider community [3].

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