Thesis (M.S.)--Naval Postgraduate School, 1977. / Includes bibliographical references (leaves 88-90).

No description available.

Thesis (Ph.D.) -- McMaster University, 2002. / Includes bibliographical references (leaves 145-157). Also available via World Wide Web.

No description available.

This thesis presents the outcome of investigations undertaken in the field of terrestrial spectral solar irradiance characterisation and its impact on photovoltaics. Spectral irradiance has not previously been widely researched in the context of photovoltaic applications. Long-term, natural environment spectral irradiance observations are practically non-existent with availability very limited in terms of covered period, temporal resolution and site location. The work presented concentrates on four major aspects of spectral irradiance: spectroradiometer calibration spectral irradiance calibration transfer standards natural spectral irradiance variability and its impact on photovoltaic device efficiency impact of reference sensor spectral mismatch on accuracy of reference irradiance measurements.

Oxygenic photosynthesis is responsible for virtually all of the biochemical production of organic matter in both marine and terrestrial ecosystems. Despite the large amount of research on phytoplankton, macroalgae have received less attention despite them being, on a per-area basis, one of the most productive ecosystems on earth. Furthermore, there has been a tendency of studies to measure primary production in single thalli, or monospecific stands. The lack of studies examining in situ production of whole assemblages using photorespirometry, as is common practice in soft-sediment systems, may be related to a lack of suitable apparatus. This research aimed to develop unique techniques and an apparatus for measuring primary production of intact macroalgal assemblages in laboratory and field conditions. Photorespirometry chambers were developed and tested on in situ macroalgal assemblages, giving information on the role of species identity, biodiversity, irradiance and community structure on overall primary production. Furthermore, the successful application of these methods was used to model annual primary production over local and regional scales, as well as the potential effects of human disturbance on production. In this study, photosynthesis-irradiance relationships (P-E curves) of intact intertidal algal assemblages showed no signs of saturation at high irradiance levels, as is typically seen in single species curves. Furthermore, diverse macroalgal assemblages showed a two-stage rise in production, with a significant enhancement of production at high irradiance. Evidence from this study suggests that the three-dimensional structure of natural assemblages, functional diversity and their interaction with a complex light environment is responsible for the unique P-E curves. The increased efficiency of light use in complex assemblages suggests an important role of species complmentarity in enhancing production with species diversity. This research also shows the potential consequences of disturbance on macroalgal assemblages, with the loss of several species causing a major decline in net production. The methods developed in this thesis have allowed simple modelling of annual rates of primary production and the parameters driving production of macroalgae over long time-scales. Respiration rates have a particularly large influence on production models and indicate that increasing temperature due to climate change could have significant consequences for net carbon fixation of macroalgae. This research gives valuable insight into the production of marine macroalgae and reinforces the notion that they are amongst the most productive systems on earth. These results revealed the importance of examining natural communities, as opposed to randomised assemblages and suggest a vital role of species diversity and community composition. Although there was no functional redundancy of the canopy forming species there did appear to be significant redundancy within the subcanopy assemblage. The identity of subcanopy species had little effect on production, but over longer temporal scales, as species come and go, they may help buffer the communities in terms of primary production. Furthermore, the relationship between biodiversity and ecosystem function (primary production), although driven by diversity, is moderated by resource levels. The complex relationship between irradiance, diversity and production shows the importance of resource levels in the enhancement of function with increasing biodiversity. Due to fundamental differences in terrestrial and marine systems, I was able to examine the effects of discrete levels of irradiance on production, which indicated an important role of complementary light use. This study represents advancements not only in the understanding of primary production in macroalgal assemblages, but also has implications for how diversity may enhance function in other autotrophic systems. The important role of enhanced efficiency of photon capture in multi-canopy layer communities may prove an essential process in ecosystems as diverse as macroalgal beds and tropical rain-forests.

<p> The effect of clouds on the performance of the McMaster Solar Radiation Model was analyzed using global irradiance data from five Australian stations for the period 1978 to 1982. Ten cloud types were examined. Using values of RMSE and MBE, the model was found to perform well in 15 of the 24 years of analyzed data. The results, on average, parallel those found in previous Canadian studies. The dominance of low layer clouds coincided with all years displaying bad performance but a l so for some years displaying good performance. The analysis of specific cloud effects revealed that the model underestimates in the presence o f low layer clouds, is not well represented with middle layer clouds and overestimates with high layer clouds. These cloud effects can be used to explain some of the error found in the model's performance, much of the error present is random and cannot be explained by the effects of clouds. </p> / Thesis / Bachelor of Arts (BA)

The present work proposes methods to calculate street-level exposures to solar radiation. The methods comprise a combination of different software algorithms, online databases and real-time standard measurements of solar radiation. Firstly, the use of the free access image database “Google Street View” to reconstruct urban geometries is illustrated. Google Street View represents an enormous source of information readily available for its general use in the field of urban atmospheric studies. With the aid of existing software packages, it was possible to reconstruct urban geometries as projected fisheye images of the canyon upper-hemispheric view, and to model total-shortwave solar irradiance within an urban canyon. The models allowed the calculation of relative street-canyon irradiance as a fraction of that received under a full-sky view, depending on the visibility of the solar disc and the reduced sky view factor. The combined use of the ideal models with real-time data allows for the calculation of street-canyon irradiance under any cloud conditions. Validation of these techniques was obtained by comparing the calculations against in situ measurements of irradiance from a local street canyon. The existing software, however, does not allow the calculation of spectral irradiance, required for inferring, for example, the biological effects of solar radiation. The use of spectral radiative transfer software was explored to provide spectral irradiance, but commonly available models do not include the effects of horizon obstructions. The approach presented here followed the same general guidelines used to calculate total-shortwave irradiance. The spectral models required a spectral partitioning of global irradiance into direct and diffuse components, allowing the independent analysis of horizon obstruction effects on these components at each wavelength. To partition global irradiance, two equations were developed for the calculation of the diffuse-to-global irradiance ratio (DGR) under cloudless conditions: one based on simplified radiative transfer theory, and an empirical fit for local conditions. Afterwards, the effects of horizon obstructions were evaluated in combination with real-time measurements of unobstructed global spectral irradiance. A set of simulated obstructions were used to validate the models. Finally, it was observed that neglecting the anisotropic distribution of the diffuse component of solar radiation in these simple models could produce large uncertainties in some situations. A practical solution for including the anisotropy of diffuse radiation was proposed, requiring images from an unobstructed digital sky camera. The combination of tools described here will allow calculation of total and spectral global irradiance upon a flat horizontal surface whatever the local field of view. This is possible at any geographical location were the urban geometries can be described, either by manually obtaining digital photographs, or through the Google Street View database, and where there is a reasonably local standard measurement of radiation.

Cette thèse présente des reconstructions de l'irradiance totale et spectrale durant les 400 dernières années à l'aide des modèles pour l'irradiance totale et l'irradiance spectrale dans l'ultraviolet développés à l'Université de Montréal. Tous deux sont basés sur la simulation de l'émergence, de la fragmentation et de l'érosion des taches solaires, qui permet d'obtenir une distribution de l'aire des taches sombres et des facules brillantes en fonction du temps. Ces deux composantes sont principalement responsables de la variation de l'irradiance sur l'échelle de temps de la décennie, qui peut être calculée en sommant leur émissivité à celle de la photosphère inactive. La version améliorée du modèle d'irradiance solaire spectrale MOCASSIM inclut une extension de son domaine spectral entre 150 et 400 nm ainsi que de son domaine temporel, débutant originalement en 1874 et couvrant maintenant la période débutant en 1610 jusqu'au présent. Cela permet de reconstruire le spectre ultraviolet durant le minimum de Maunder et de le comparer à celui du minimum de 2009. Les conclusions tirées de cette étude spécifient que l'émissivité dans l'ultraviolet était plus élevée en 2009 que durant le minimum de Maunder, que le niveau de base de la photosphère non magnétisée contribuait pour environ les deux tiers de cette différence et que les structures magnétiques restantes étaient responsables pour le tiers restant. Le modèle d'irradiance totale a vu son domaine temporel étendu sur la même période et une composante représentant le réseau magnétique de façon réaliste y a été ajoutée. Il a été démontré que les observations des 30 dernières années ne sont bien reproduites qu'en incluant la composante du Soleil non magnétisé variable à long terme. Le processus d'optimisation des paramètres libres du modèle a été effectué en minimisant le carré de la somme de l'écart journalier entre les résultats des calculs et les données observées. Les trois composites disponibles, soit celui du PMOD (Physikalisch Meteorologisches Observatorium Davos), d'ACRIM (ACtive Radiometer Irradiance Monitor) et du IRMB (Institut Royal Météorologique de Belgique), ne sont pas en accord entre eux, en particulier au niveau des minima du cycle d'activité, et le modèle permet seulement de reproduire celui du PMOD avec exactitude lorsque la composante variable à long terme est proportionnelle au flux radio à 10.7 cm. Toutefois, en utilisant des polynômes de Lagrange pour représenter la variation du Soleil inactif, l'accord est amélioré pour les trois composites durant les minima, bien que les relations entre le niveau minimal de l'irradiance et la longueur du cycle précédent varient d'un cas à l'autre. Les résultats obtenus avec le modèle d'irradiance spectrale ont été utilisés dans une étude d'intercomparaison de la réponse de la photochimie stratosphérique à différentes représentations du spectre solaire. Les simulations en mode transitoire d'une durée de 10 jours ont été effectuées avec un spectre solaire constant correspondant soit à une période d'activité minimale ou à une période d'activité maximale. Ceci a permis d'évaluer la réponse de la concentration d'ozone à la variabilité solaire au cours d'un cycle et la différence entre deux minima. En plus de ceux de MOCASSIM, les spectres produits par deux modèles ont été utilisés (NRLSSI et MGNM) ainsi que les données de SIM et SOLSTICE/SORCE. La variabilité spectrale de chacun a été extraite et multipliée à un spectre de base représentant le minimum d'activité afin de simuler le spectre au maximum d'activité. Cela a été effectué dans le but d'isoler l'effet de la variabilité seule et d'exclure celui de la valeur absolue du spectre. La variabilité spectrale d'amplitude relativement élevée des observations de SORCE n'a pas provoqué l'inversion de la réponse de l'ozone à hautes altitudes obtenues par d'autres études, ce qui peut être expliqué par la nature même du modèle utilisé ainsi que par sa limite supérieure en altitude. Finalement, la réponse de l'ozone semble être à peu près proportionnelle à la variabilité de l'intégrale du flux pour lambda<241 nm. La comparaison des concentrations d'ozone obtenues avec les spectres originaux au minimum d'activité démontre que leur différence est du même ordre de grandeur que la variabilité entre le minimum et le maximum d'un cycle typique. Le problème du choix de la reconstruction de l'irradiance à utiliser pour les simulations climatiques dans le passé demeure non résolu. / This thesis presents reconstructions of the total and spectral solar irradiance for the last 400 years produced with the improved versions of the models for total and spectral solar irradiance in the ultraviolet developed at Université de Montréal. Both are based on the simulation of sunspot emergence, fragmentation and erosion, which produces a time-evolving area distribution of dark spots and bright faculae. These two components are the main drivers of irradiance decadal variations and this quantity can be calculated by summing their emissivity to that of the quiet photosphere. The improved version of the model for spectral irradiance, MOCASSIM, includes an extension of its spectral domain between 150 and 400 nm and of its temporal domain, with reconstructions now starting in 1610 instead of 1874. This allows to reconstruct the UV spectrum during the Maunder minimum and to compare it to the spectrum during the minimum of 2009. The conclusions of this study state that the Sun was slightly brighter during the recent minimum and that the slowly-varying quiet Sun contribution accounts for about two thirds of this difference, whereas remnant magnetic structure decay products account for the other third. The model for total irradiance was also extended further in the past, with reconstructions now starting in 1610. Also, a realistic network component was added. This was expected to help reproduce the observations spanning the last 30 years, especially the varying level of the irradiance during minimum activity. It was shown that the inclusion of a slowly-varying quiet Sun component was necessary to account for the observations. The free parameters of the model were adjusted by minimizing the sum of the daily squared difference between the model's output and the observations. The three available composites, from the PMOD (Physikalisch Meteorologisches Observatorium Davos), ACRIM (ACtive Radiometer Irradiance Monitor) and IRMB (Institut Royal Météorologique de Belgique) teams, do not agree between them, especially considering the minima of the activity cycle. The only composite reproduced in a satisfactory manner by the model when the variable quiet Sun component is proportionnal to the radio flux at 10.7 cm is the PMOD composite. However, using Lagrange polynomials to represent this component helps improve the agreement at minimum activity for all composites, even though the relation between the irradiance during the minima and the length of the preceding cycle varies from one to another. The results obtained with MOCASSIM were used during an intercomparison study of the photochemical response in the stratosphere to different representations of the solar spectrum. Transient simulations of duration 10-days were performed with a constant solar spectrum corresponding to either a maximum or minimum activity period. This allowed to estimate the response in stratospheric ozone to the solar variability over a cycle or between two minima. The spectra obtained with MOCASSIM were used along with those from two other models, NRLSSI and MGNM, and the SIM and SOLSTICE/SORCE data. The spectral variability from each data set was multiplied to a common baseline spectrum to produce the high activity spectrum in order to isolate the effet of the variability only, and to exclude the effect of the absolute spectral calibration. The high spectral variability of the SORCE data in the UV did not induce a negative response in ozone at high altitude, as obtained by various other studies. This is explained by the nature of the model and by its limited vertical extent. Finally, the ozone response is approximately proportional to the integrated UV flux below 241 nm. The comparison of the ozone concentration at minimum activity obtained with the original spectra shows that the difference is of the same magnitude as the response over a solar cycle. The problem of choosing a solar spectral irradiance reconstruction for climatic simulations in the past remains unsolved.

A study of the parameters effecting diffuse irradiance in mountainous terrain was made. Ground/location parameters of site elevation, ground albedo, elevated horizon and surface tilt were examined under the pertinent atmospheric conditions of clear, polluted, overcast , and cloudy. Measured diffuse irradiance data used for comparisons were taken from fall 1977-spring 1979 at four sites located in northern Utah. Diffuse irradiance varied with elevation according to the existing atmospheric conditions. For clear sky, diffuse irradiance decreased with elevation due t o the shorter optical pathlength, thus less scatter of the direct beam. However, with completely overcast sky, diffuse irradiance increased with elevation. The thinner cloud cover associated with higher elevations causes less adsorption of the diffuse irradiance. For partially cloudy conditions a correlation of diffuse irradiance with duration of sunshine showed curved relationships with maximum diffuse irradiance at 70 percent cloud cover. At high elevation, the curves were much steeper than at low elevation , becoming almost linear. Climatic changes in ground albedo were found to modify diffuse irradiance considerably. This occurred mainly through multiple reflection between ground and atmosphere with maximum enhancement for snow covered ground and overcas t sky. Even for clear days snow cover shifted the maximum in the annual cycle of diffuse irradiance day totals towards the spring months. A comparison of March (snow cover) and September (bare ground) diffuse irradiance values for various amounts of cloud cover showed that diffuse enhancement increased steadily with cloud amount to a maximum at overcast conditions. The effects of elevated horizon such as might be found in a mountain valley were examined through validation of a physical model describing a V-shaped valley. Comparisons between calculated and measured diffuse irradiance showed excellent results for clear days during winter, spring, and summer. The ratio of measured diffuse irradiance on a south facing sao tilt to that on the horizontal was plotted against duration of sunshine for different seasons. For clear days the Sao tilt enhanced diffuse irradiance values as much as two times the horizontal values during winter while during summer sao values dropped to .8 of the horizontal values. For overcast days the ratio varied from 1.0-0.3 for winter and summer, respectively. A model predicting diffuse irradiance on a tilted surface for clear day was developed and validated using measured data. A good comparison is shown for spring and fall days using high and low elevation data.