Ground Reflected Research Articles

Incorporating theoretical and practical approaches to assess the amount of sunlight captured by a tilted surface in a tropical climate

Global solar radiation can theoretically be approximated in terms of tilt and azimuth of the surface regarding the impossibility of simultaneous measurement of solar radiation at various surface tilt and azimuth angles. Moreover, the random and anisotropic nature of diffuse radiation in a tropical climate makes it extremely difficult to estimate global solar radiation accurately as a function of surface tilt and azimuth angles. This study aims to develop a novel experimental and theoretical approach in the form of a computational network in order to determine a precise combined model integrated with global horizontal solar radiation to evaluate global tilted solar radiation in a tropical climate. Obtained results revealed that precisely estimation of the global tilted solar radiation was possible, by combining geometric factors for the tilted beam solar radiation, a combination of Gueymard and Louche models for the tilted diffuse solar radiation, and isotropic ground reflectance model for the ground reflected radiation, along with global horizontal solar radiation. It was observed that the accuracy of the model developed was higher for the partly sunny sky compared to the cloudy and rainy sky, estimates were more accurate on south-facing surfaces, and the model's accuracy declined with the increasing tilt angle of the surface. The statistical analysis exhibited excellent agreement between the measured data and simulation results, considering the value of normalized mean absolute error (nMAE %), normalized root mean squared error (nRMSE %), and mean absolute percentage error (MAPE %), which were in the ranges 0.22–0.94, 0.27–1.11, and 0.23–1.02, respectively for estimating global tilted solar radiation in various regions of Peninsular Malaysia, and they were respectively found in the range of 10.2–27.5%, 16.1–38.9%, and 6.0–17.8%, for evaluating the monthly optimum tilt angle towards the south, that leads to a loss of solar energy from 1.3 to 5.4 kWh/m2/year in Peninsular Malaysia. This search revealed that the experimental and theoretical approach employed in this study can be extended to more climatic regions.

Assessing effect of ground reflections on gunshot noise exposure

Investigation of weapons noise exposure outdoors necessitates including the impact of ground reflections. When analyzing the reflections’ impact on A-weighted equivalent level (LAeq), the contribution of the reflected waveform to the total level can often be acceptably modeled using a Friedlander equation-based source model and an ideal reflection based on the measurement geometry. However, the Friedlander model does not adequately model the negative phase of a gunshot waveform, making it inaccurate for locations where the waveform of the direct blast and the waveform of the reflection begin to overlap temporally. This merging of the waveforms for locations where the direct and ground-reflected path length difference is relatively small also makes it difficult to separate the waveforms and calculate the reflected wave’s contribution to noise exposure. As such, this paper investigates different approaches to estimating the contribution of the ground reflected wave to the LAeq, using direct and reflected waveforms in regions where they are well separated and then adjusting timing and amplitude for different geometries where merging takes place. Results reveal regions where the ground reflection contributes negligibly or even negatively to the total LAeq, which is not predicted by the Friedlander model nor by simple energy-addition approaches. [Work supported by Air Force Research Laboratory through Ball Aerospace Technology Corporation.]

A model for predicting the solar reflectivity of the ground that considers the effects of accumulating and melting snow

ABSTRACTSimulation tools for predicting building thermal performance and solar system performance must accurately calculate solar irradiance to surfaces of arbitrary orientation. This is imperative to correctly predict passive solar gains to buildings and to accurately estimate thermal and electrical production of solar collectors. In cold climates, where snow covers the ground for long periods of time, ground reflected radiation can represent a substantial fraction of the total incident irradiance to highly tilted and vertical surfaces (e.g. windows). A new model has been developed to improve the calculation of ground-reflected radiation in simulation tools. The model is based upon empirical observations taken at a measurement site in Ottawa (Canada), and has been validated using disjunct data from the measurement site, and with published data from two other sites in the USA. The model was found to increase the accuracy of ground reflectivity predictions for cold and humid climates.

Ground albedo impacts on higher-order scattering spectral radiances of night sky

The contribution from ground reflected light to the night sky radiance is of increased interest because of constant modernization of street lighting systems that now efficiently eliminate light emissions above the horizontal plane, so the appreciable fraction of artificial light directed upwards is from ground reflection. Diffuse light of a night sky shows a positive correlation with ground albedo (α), but it seems there is no linear trend between α and the night sky brightness (NSB), at least not for all sky elements, and, the mechanism of this relationship becomes even more complicated due to multiple scattering effects. The extent to which the ground reflectance influences the higher-order scattering radiance of night sky, and, the factors that initiate the crossover from single- to multiple-scattering dominance of the sky glow has been virtually unexplored until now.We demonstrate here that albedo-induced effects in NSB exhibit an angular dependence, with amplitudes enhanced towards shorter wavelengths. For low values of ground reflectance and at short distances from a light source, the second-scattering radiance is found to be only a few percent of the first-order scattering radiance. However, the ratio of a higher- to the first-order scattering radiance gradually increases near horizon, specifically at the side opposite to the azimuthal position of the light source. Also the NSB in blue band has decreasing gradation tendency when increasing the altitude above sea level. The findings in this paper are significant in a proper incorporation of higher-order scattering in modeling the NSB under elevated reflectance conditions, and may be critical for saving computational time.

Enhancement of Albedo for Solar Energy Gain with Particular Emphasis on Overcast Skies

In the absence of ground reflected radiation measured data, an average albedo value of 0.2, which describes the reflective properties of the bare ground is generally used. The variation of albedo based on different foreground surfaces and under different atmospheric conditions is an area which is under research. This paper presents an experimental investigation of albedos of different foreground materials that can be used for photovoltaic (PV) applications. Overcast skies are predominant in northerly locations and will have a high frequency of low solar altitudes, and thus ground reflection is an important contributor towards total solar energy gain. The foreground surfaces include common materials: Grass, sand, and cement slabs, and some non-conventional materials: White pebbles, white boards, white tiles, and aluminium foil. The impact of factors, such as ageing, solar elevation, rain, and cloud cover (sky conditions) is analysed to determine the changes in albedos of these materials. Each material was observed to have individual performance characteristics under these factors. It was found that the non-conventional materials were least prone to weather-related changes and have higher albedo values as compared to the conventional materials, and also have good potential to replace the conventional materials for any given PV application.

Directional monitoring terminal for aircraft noise

This paper presents a concept of an aircraft noise monitoring terminal (NMT) that reduces background noise and the influence of ground reflection, in comparison with a single microphone. Also, it automatically identifies aircraft sound events based on the direction of arrival of the sound rather than on the sound pressure level (or radar data). And moreover, it provides an indicator of the quality of the sound pressure level measurement, i.e. if it is possibly disturbed by extraneous sources. The performance of this NMT is experimentally tested under real conditions in a measurement site close to Zurich airport. The results show that the NMT unambiguously identifies the noise events generated by the target aircraft, correctly detects those aircraft noise events that may be disturbed by the presence of other sources, and offers a substantial reduction in background and ground reflected sound.

Ground Reflection with Turbulence Induced Coherence Loss in Flyover Auralization

A method to include the effect of coherence loss due to turbulence is proposed for real-time auralization of aircraft noise. By modifying the direct ray contribution relative to the ground reflected ray, using filters, the coherence loss effect can be included in a propagation scheme. The results of this approach match with the theoretical predictions thereby verifying the ability of the method. Furthermore, the modulation of aircraft tonal components, due to changing ground interference during a flyover, is diminished as a result of the proposed method. Application to an auralization and comparing to a measurement shows that auralizations can benefit from this method. Therefore the current method forms an essential addition to the techniques currently used in the auralization of aircraft noise.

Simulation of Energy Production by Bifacial Modules with Revision of Ground Reflection

Bifacial solar modules are becoming increasingly more attractive stimulated by the development of new solar cell structures enabling to capture solar insolation on both front and rear surfaces. The possibilities to be installed in the conventional south facing orientation or even vertically are further advantages. Although the potential of bifacial modules have been already shown in specific time intervals and for various ground albedos there is a lack in simulation studies up to now. In this study, we simulated the annual energy yield (AEY) of south facing bifacial modules using a rigorous calculation method of the ground reflected radiation reaching the rear module surface. The necessary tilt angle optimization is done incorporating the influence of module elevation and considering the inherent albedo coefficient. These simulations are able to reproduce measurement observations and show that at optimum tilt angles produced annual energy can be increased by 30% compared to a standard module simply by positioning modules two meters above ground instead of a close to ground installation. Furthermore, a linear relationship between albedo coefficient and AEY is demonstrated.

On combating deep fades due to ground reflection in point-to-point WiMAX communications

In point-to-point wireless communications, the re- ceived signal may experience deep fading due to different propa- gation phenomena. In this paper, we deal specifically with ground reflection and show how it affects the system communication. As application, we consider the example of point-to-point WiMAX communications between base stations (BSs) and trains. The fading problem is mainly due to the fact that both direct and reflected rays are located in the main lobe of the base station antenna and then the correspondant fields have almost the same amplitude. In this paper, we propose several efficient solutions in order to overcome the fading problem. These solutions perform different techniques based, first, on modifying the shape of the main lobe of the BS antenna in order to decrease the magnitude of the ground reflected field, and second, on modifying the antennas polarization. In order to support our propositions, a large set of simulation results is reported and discussed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26063

A computer simulation of XPD degradation due to multipath propagation

A computer program has been constructed to study degradation inXpd(cross-polarization discrimination) due to multipath propagation. The geometric optics limit is used. The program will accept any analytic index of refraction including those with discontinuities in n or ∇n. Antenna effects are included and all reflected, refracted, direct and ground reflected rays can be considered. Using a realistic index of refraction and realistic discontinuity, we have found that, after the antenna pattern, the major influence onXpdis interference between the ground-reflected wave and the direct wave. There is also significant interference due to the waves reflected from the refractive index discontinuity which may arrive without ground reflection or may be reflected once or twice from the ground.

Ground reflection and standard procedures for measuring noise

The effect of interference between direct and ground reflected rays is examined for standard methods of measurement of the noise emitted by road vehicles, snowmobiles, and other devices powered by internal combustion engines, such as chainsaws and lawn mowers. It is shown that cancellation leads to particularly erratic measurements for accelerating large trucks where the propagation is over asphalt, and for all devices where the propagation is over a porous surface, such as grass or snow. For propagation over asphalt, placing the microphone on the asphalt surface eliminates these effects, best considered as transmission artifacts. No such simple cure is available over porous surfaces. Good agreement is achieved between experiment and theory.