1000x shadow-free mirror-based Köhler concentrator

A new design for a photovoltaic concentrator, the most recent advance based on the Kohler concept, is presented. The system is mirror-based, and with geometry that guaranties a maximum sunlight collection area (without shadows, like those caused by secondary stages or receivers and heat-sinks in other mirror-based systems). Designed for a concentration of 1000x, this off axis system combines both good acceptance angle and good irradiance uniformity on the solar cell. The advanced performance features (concentration-acceptance products ?CAP- about 0.73 and affordable peak and average irradiances) are achieved through the combination of four reflective folds combined with four refractive surfaces, all of them free-form, performing Köhler integration 2 . In Köhler devices, the irradiance uniformity is not achieved through additional optical stages (TIR prisms), thus no complex/expensive elements to manufacture are required. The rim angle and geometry are such that the secondary stage and receivers are hidden below the primary mirrors, so maximum collection is assured. The entire system was designed to allow loose assembly/alignment tolerances (through high acceptance angle) and to be manufactured using already well-developed methods for mass production, with high potential for low cost. The optical surfaces for Köhler integration, although with a quite different optical behavior, have approximately the same dimensions and can be manufactured with the same techniques as the more traditional secondary optical elements used for concentration (typically plastic injection molding or glass molding).

Aplicaciones de interés forestal de las imágenes obtenidas con el sensor Multi-angle Imaging SpectroRadiometer (MISR)

Las aplicaciones de la teledetección al seguimiento de lo que ocurre en la superficie terrestre se han ido multiplicando y afinando con el lanzamiento de nuevos sensores por parte de las diferentes agencias espaciales. La necesidad de tener información actualizada cada poco tiempo y espacialmente homogénea, ha provocado el desarrollo de nuevos programas como el Earth Observing System (EOS) de la National Aeronautics and Space Administration (NASA). Uno de los sensores que incorpora el buque insignia de ese programa, el satélite TERRA, es el Multi-angle Imaging SpectroRadiometer (MISR), diseñado para capturar información multiangular de la superficie terrestre. Ya desde los años 1970, se conocía que la reflectancia de las diversas ocupaciones y usos del suelo variaba en función del ángulo de observación y de iluminación, es decir, que eran anisotrópicas. Tal variación estaba además relacionada con la estructura tridimensional de tales ocupaciones, por lo que se podía aprovechar tal relación para obtener información de esa estructura, más allá de la que pudiera proporcionar la información meramente espectral. El sensor MISR incorpora 9 cámaras a diferentes ángulos para capturar 9 imágenes casi simultáneas del mismo punto, lo que permite estimar con relativa fiabilidad la respuesta anisotrópica de la superficie terrestre. Varios trabajos han demostrado que se pueden estimar variables relacionadas con la estructura de la vegetación con la información que proporciona MISR. En esta Tesis se ha realizado una primera aplicación a la Península Ibérica, para comprobar su utilidad a la hora de estimar variables de interés forestal. En un primer paso se ha analizado la variabilidad temporal que se produce en los datos, debido a los cambios en la geometría de captación, es decir, debido a la posición relativa de sensores y fuente de iluminación, que en este caso es el Sol. Se ha comprobado cómo la anisotropía es mayor desde finales de otoño hasta principios de primavera debido a que la posición del Sol es más cercana al plano de los sensores. También se ha comprobado que los valores máximo y mínimo se van desplazando temporalmente entre el centro y el extremo angular. En la caracterización multiangular de ocupaciones del suelo de CORINE Land Cover que se ha realizado, se puede observar cómo la forma predominante en las imágenes con el Sol más alto es convexa con un máximo en la cámara más cercana a la fuente de iluminación. Sin embargo, cuando el Sol se encuentra mucho más bajo, ese máximo es muy externo. Por otra parte, los datos obtenidos en verano son mucho más variables para cada ocupación que los de noviembre, posiblemente debido al aumento proporcional de las zonas en sombra. Para comprobar si la información multiangular tiene algún efecto en la obtención de imágenes clasificadas según ocupación y usos del suelo, se han realizado una serie de clasificaciones variando la información utilizada, desde sólo multiespectral, a multiangular y multiespectral. Los resultados muestran que, mientras para las clasificaciones más genéricas la información multiangular proporciona los peores resultados, a medida que se amplían el número de clases a obtener tal información mejora a lo obtenido únicamente con información multiespectral. Por otra parte, se ha realizado una estimación de variables cuantitativas como la fracción de cabida cubierta (Fcc) y la altura de la vegetación a partir de información proporcionada por MISR a diferentes resoluciones. En el valle de Alcudia (Ciudad Real) se ha estimado la fracción de cabida cubierta del arbolado para un píxel de 275 m utilizando redes neuronales. Los resultados muestran que utilizar información multiespectral y multiangular puede mejorar casi un 20% las estimaciones realizadas sólo con datos multiespectrales. Además, las relaciones obtenidas llegan al 0,7 de R con errores inferiores a un 10% en Fcc, siendo éstos mucho mejores que los obtenidos con el producto elaborado a partir de datos multiespectrales del sensor Moderate Resolution Imaging Spectroradiometer (MODIS), también a bordo de Terra, para la misma variable. Por último, se ha estimado la fracción de cabida cubierta y la altura efectiva de la vegetación para 700.000 ha de la provincia de Murcia, con una resolución de 1.100 m. Los resultados muestran la relación existente entre los datos espectrales y los multiangulares, obteniéndose coeficientes de Spearman del orden de 0,8 en el caso de la fracción de cabida cubierta de la vegetación, y de 0,4 en el caso de la altura efectiva. Las estimaciones de ambas variables con redes neuronales y diversas combinaciones de datos, arrojan resultados con R superiores a 0,85 para el caso del grado de cubierta vegetal, y 0,6 para la altura efectiva. Los parámetros multiangulares proporcionados en los productos elaborados con MISR a 1.100 m, no obtienen buenos resultados por sí mismos pero producen cierta mejora al incorporarlos a la información espectral. Los errores cuadráticos medios obtenidos son inferiores a 0,016 para la Fcc de la vegetación en tanto por uno, y 0,7 m para la altura efectiva de la misma. Regresiones geográficamente ponderadas muestran además que localmente se pueden obtener mejores resultados aún mejores, especialmente cuando hay una mayor variabilidad espacial de las variables estimadas. En resumen, la utilización de los datos proporcionados por MISR ofrece una prometedora vía de mejora de resultados en la media-baja resolución, tanto para la clasificación de imágenes como para la obtención de variables cuantitativas de la estructura de la vegetación. ABSTRACT Applications of remote sensing for monitoring what is happening on the land surface have been multiplied and refined with the launch of new sensors by different Space Agencies. The need of having up to date and spatially homogeneous data, has led to the development of new programs such as the Earth Observing System (EOS) of the National Aeronautics and Space Administration (NASA). One of the sensors incorporating the flagship of that program, the TERRA satellite, is Multi-angle Imaging Spectroradiometer (MISR), designed to capture the multi-angle information of the Earth's surface. Since the 1970s, it was known that the reflectance of various land covers and land uses varied depending on the viewing and ilumination angles, so they are anisotropic. Such variation was also related to the three dimensional structure of such covers, so that one could take advantage of such a relationship to obtain information from that structure, beyond which spectral information could provide. The MISR sensor incorporates 9 cameras at different angles to capture 9 almost simultaneous images of the same point, allowing relatively reliable estimates of the anisotropic response of the Earth's surface. Several studies have shown that we can estimate variables related to the vegetation structure with the information provided by this sensor, so this thesis has made an initial application to the Iberian Peninsula, to check their usefulness in estimating forest variables of interest. In a first step we analyzed the temporal variability that occurs in the data, due to the changes in the acquisition geometry, i.e. the relative position of sensor and light source, which in this case is the Sun. It has been found that the anisotropy is greater from late fall through early spring due to the Sun's position closer to the plane of the sensors. It was also found that the maximum and minimum values are displaced temporarily between the center and the ends. In characterizing CORINE Land Covers that has been done, one could see how the predominant form in the images with the highest sun is convex with a maximum in the camera closer to the light source. However, when the sun is much lower, the maximum is external. Moreover, the data obtained for each land cover are much more variable in summer that in November, possibly due to the proportional increase in shadow areas. To check whether the information has any effect on multi-angle imaging classification of land cover and land use, a series of classifications have been produced changing the data used, from only multispectrally, to multi-angle and multispectral. The results show that while for the most generic classifications multi-angle information is the worst, as there are extended the number of classes to obtain such information it improves the results. On the other hand, an estimate was made of quantitative variables such as canopy cover and vegetation height using information provided by MISR at different resolutions. In the valley of Alcudia (Ciudad Real), we estimated the canopy cover of trees for a pixel of 275 m by using neural networks. The results showed that using multispectral and multiangle information can improve by almost 20% the estimates that only used multispectral data. Furthermore, the relationships obtained reached an R coefficient of 0.7 with errors below 10% in canopy cover, which is much better result than the one obtained using data from the Moderate Resolution Imaging Spectroradiometer (MODIS), also onboard Terra, for the same variable. Finally we estimated the canopy cover and the effective height of the vegetation for 700,000 hectares in the province of Murcia, with a spatial resolution of 1,100 m. The results show a relationship between the spectral and the multi-angle data, and provide estimates of the canopy cover with a Spearman’s coefficient of 0.8 in the case of the vegetation canopy cover, and 0.4 in the case of the effective height. The estimates of both variables using neural networks and various combinations of data, yield results with an R coefficient greater than 0.85 for the case of the canopy cover, and 0.6 for the effective height. Multi-angle parameters provided in the products made from MISR at 1,100 m pixel size, did not produce good results from themselves but improved the results when included to the spectral information. The mean square errors were less than 0.016 for the canopy cover, and 0.7 m for the effective height. Geographically weighted regressions also showed that locally we can have even better results, especially when there is high spatial variability of estimated variables. In summary, the use of the data provided by MISR offers a promising way of improving remote sensing performance in the low-medium spatial resolution, both for image classification and for the estimation of quantitative variables of the vegetation structure.

Shadow Analysis of Soil Surface Roughness Compared to the Chain Set Method and Direct Measurement of Micro-relief.

Erosion potential and the effects of tillage can be evaluated from quantitative descriptions of soil surface roughness. The present study therefore aimed to fill the need for a reliable, low-cost and convenient method to measure that parameter. Based on the interpretation of micro-topographic shadows, this new procedure is primarily designed for use in the field after tillage. The principle underlying shadow analysis is the direct relationship between soil surface roughness and the shadows cast by soil structures under fixed sunlight conditions. The results obtained with this method were compared to the statistical indexes used to interpret field readings recorded by a pin meter. The tests were conducted on 4-m2 sandy loam and sandy clay loam plots divided into 1-m2 subplots tilled with three different tools: chisel, tiller and roller. The highly significant correlation between the statistical indexes and shadow analysis results obtained in the laboratory as well as in the field for all the soil?tool combinations proved that both variability (CV) and dispersion (SD) are accommodated by the new method. This procedure simplifies the interpretation of soil surface roughness and shortens the time involved in field operations by a factor ranging from 12 to 20.

Modelling Structural Flexure Effects in CPV Sun Trackers

Nowadays CPV trends mostly based in lens parqueted flat modules, enable the separate design of the sun tracker. To enable this possibility a set of specifications is to be prescribed for the tracker design team, which take into account fundamental requisites such as the maximum service loads both permanent and variable, the sun tracking accuracy and the tracker structural stiffness required to maintain the CPV array acceptance angle loss below a certain threshold. In its first part this paper outlines the author’s approach to confront these issues. Next, a method is introduced to estimate the acceptance angle losses due to the tracker’s structural flexure, which in last instance relies in the computation of the minimum enclosing circle of a set of points in the plane. This method is also useful to simulate the drifts in the tracker’s pointing vector due to structural deformation as a function of the aperture orientation angle. Results of this method when applied to the design of a two axis CPV pedestal tracker are presented.

Utzon and the sun path as an organizing element of life in a house

The present text intends to analyze the hypothesis stating that the path of the sun can be an organizing element for how you live in the houses designed by Jørn Utzon. To do so, I have selected twenty houses and building complexes designed by him between the years 1950-94, in Denmark, Sweden, The United Kingdom and Spain. In these projects I will look for elements which are repeated and their possible meaning. The aim is to reach practical conclusions that could help us decide how to orientate a house.

Where is photonics going? Reflections under the sun

After a short personal view of the first years of the photonics in Spain, some references about its present situation are given. As a possible future, the first steps towards a Photonics based on the study of the employed mechanisms in the visual system of the living beings are presented.

Change factors that may influence sun and beach destinations in a low-growth scenario

Análisis de los principales factores de cambio que previsiblemente incidirán en los destinos turísticos de sol y playa en un escenario de bajo crecimiento.

EL AIRE SE SERENA Y VISTE DE HERMOSURA Y LUZ NO USADA. De cómo el espacio arquitectónico es como el instrumento musical. Dedicado a Luis Suñén.

Se intenta en este texto establecer un paralelismo entre el instrumento musical y el espacio arquitectónico. El instrumento musical mediante el aire produce el regalo de la música. El espacio arquitectónico mediante la luz produce ese algo inefable que es la arquitectura.

Foresight in designing sun-beach destinations

Planteamiento de un Nuevo enfoque metodológico para incorporar la prospectiva en la planificación de destinos turísticos de sol y playa.

Reseña. Architecture of the Sun: Los Angeles Modernism 1900-1970

Reseña bibliográfica de Architecture of the Sun: Los Angeles Modernism 1900-1970

Magnetic Attitude Control for Satellites in Polar or Sun-Synchronous Orbits

In this work, a new law for magnetic control of satellites in near-polar orbits is presented. This law has been developed for the UMPSat-2 microsatellite, which has been designed and manufactured by Universidad Politécnica de Madrid, Madrid. The control law is a modification of the B-dot strategy that enables the satellite to control the rotation rate. Besides, the satellite?s equilibrium state is characterized by having the rotation axis perpendicular to the orbit?s plane. The control law described in the present work only needs magnetometers and magnetorquers, as sensors and actuators, respectively, to carry out a successful attitude control on the spacecraft. A description of the analysis is included. Performance and applicability of the proposed method have been demonstrated by control dynamics together with Monte Carlo techniques and by implementing the control law in the UPMSat-2 mission simulator. Results show good performance in terms of acquisition and stability of the satellite rotation rate and orientation with respect to its orbit?s plane.

Outreach Testing of Ancient Astronomy

This work is an outreach approach to an ubiquitous recent problem in secondary-school education: how to face back the decreasing interest in natural sciences shown by students under ‘pressure’ of convenient resources in digital devices/applications. The approach rests on two features. First, empowering of teen-age students to understand regular natural events around, as very few educated people they meet could do. Secondly, an understanding that rests on personal capability to test and verify experimental results from the oldest science, astronomy, with simple instruments as used from antiquity down to the Renaissance (a capability restricted to just solar and lunar motions). Because lengths in astronomy and daily life are so disparate, astronomy basically involved observing and registering values of angles (along with times), measurements being of two types, of angles on the ground and of angles in space, from the ground. First, the gnomon, a simple vertical stick introduced in Babylonia and Egypt, and then in Greece, is used to understand solar motion. The gnomon shadow turns around during any given day, varying in length and thus angle between solar ray and vertical as it turns, going through a minimum (noon time, at a meridian direction) while sweeping some angular range from sunrise to sunset. Further, the shadow minimum length varies through the year, with times when shortest and sun closest to vertical, at summer solstice, and times when longest, at winter solstice six months later. The extreme directions at sunset and sunrise correspond to the solstices, swept angular range greatest at summer, over 180 degrees, and the opposite at winter, with less daytime hours; in between, spring and fall equinoxes occur, marked by collinear shadow directions at sunrise and sunset. The gnomon allows students to determine, in addition to latitude (about 40.4° North at Madrid, say), the inclination of earth equator to plane of its orbit around the sun (ecliptic), this fundamental quantity being given by half the difference between solar distances to vertical at winter and summer solstices, with value about 23.5°. Day and year periods greatly differing by about 2 ½ orders of magnitude, 1 day against 365 days, helps students to correctly visualize and interpret the experimental measurements. Since the gnomon serves to observe at night the moon shadow too, students can also determine the inclination of the lunar orbital plane, as about 5 degrees away from the ecliptic, thus explaining why eclipses are infrequent. Independently, earth taking longer between spring and fall equinoxes than from fall to spring (the solar anomaly), as again verified by the students, was explained in ancient Greek science, which posited orbits universally as circles or their combination, by introducing the eccentric circle, with earth placed some distance away from the orbital centre when considering the relative motion of the sun, which would be closer to the earth in winter. In a sense, this can be seen as hint and approximation of the elliptic orbit proposed by Kepler many centuries later.

Proyecto y lugar en la arquitectura doméstica de Jørn Utzon

En medio de un bosque danés, de altos arboles que se mueven al fuerte viento nórdico bajo el débil sol de las latitudes altas, y cargado de unos cuantos tableros de madera que consiguió de una exposición ya terminada, realizó Utzon su maqueta a escala real de su primera casa familiar en Hellebæk (1950-52) a la edad de treinta y dos años. De la misma manera que el pintor William Turner necesitó atarse a lo alto de un mástil de un barco, para vivir en directo una de las muchas tormentas que tantas y tantas veces había pintado en sus cuadros, el joven Utzon consideró indispensable introducirse dentro de la maqueta de su propia casa antes de construirla, para valorar in situ las potencialidades de aquel proyecto en relación al lugar. La obra de Jørn Utzon (1918-2008) es una arquitectura expectante y atenta del lugar donde se ubica. Jørn Utzon es un arquitecto de origen nórdico, que descubre su verdadera idiosincrasia en la cultura mediterránea, cultura en la que reside durante casi la mitad de toda su vida. Esta tesis se ha centrado en analizar exhaustivamente la relación de su arquitectura doméstica con el lugar donde se halla. Aspecto tan citado en la bibliografía existente de su obra, aunque nunca desarrollado de manera exhaustiva. El objetivo del análisis ha sido intentar encontrar invariantes o patrones que pudieran subyacer en su obra residencial en relación a ese tema. Para dicho análisis, se ha tomado una muestra suficientemente amplia de veinte viviendas o conjuntos residenciales (entre ellas sus cuatro viviendas familiares proyectadas), repartidas por cinco países (Suecia, Dinamarca, Reino Unido, España y Nueva Gales del Sur), que constituyen la tercera parte de su obra doméstica y la mitad de su obra construida residencial, así como las citas explícitas del autor sobre este tema en su obra escrita, y los planos o croquis de su obra gráfica. Como metodología de trabajo se ha recurrido a la consulta de las fuentes primarias: viajando y conociendo in-situ las casas seleccionadas en Dinamarca, Suecia, España y Australia; viviendo un mes en una de las casas (Can Lis) gracias a una beca del Gobierno danés y la Utzon Foundation; y realizando entrevistas a las personas que más cerca estuvieron del arquitecto en su entorno familiar y profesional. Asimismo, también se ha publicado parte de su contenido en medios internacionales: 4th International Utzon Symposium (7/3/2013-9/3/2014) y la página web oficial de Can Lis dependiente de la Utzon Foundation (www.canlis.dk). Las doce invariantes encontradas en relación al proyecto y lugar en los proyectos seleccionados, han sido agrupadas en torno a tres grandes elementos sobre los que Utzon constantemente reflexiona en sus escritos propios: horizonte, sol y material autóctono. Elementos que tienen su origen en la influencia que la navegación tuvo en su vida, y en su carácter espiritual y austero en lo material. La historia de Utzon es la de un nórdico, de vocación navegante, que encuentra su lugar en la cultura mediterránea, rodeado entre piedras de Marés, mientras divisa en silencio el horizonte marino en el umbral entre luz y sombra. ABSTRACT In the middle of a Danish forest, with high trees which move with the Nordic wind under the weak sun of high latitudes, and with the help of some wooden canvases acquired from an already completed exhibition, Jørn Utzon built a real-scale model of his first family house in Hellebæk (1950-52) at the age of thirty-two. In the same way that William Turner needed to be tied up on the top of a boat flagpole in order to have a first-hand experience of one of the many storms that he had depicted in his paintings so many times before, the young Utzon thought it was crucial to go into the model of his own house before building it, to evaluate in situ the potential of that project in relation to the place. Utzon’s work is architecture interested in and attentive of the place where it is situated. Jørn Utzon (1918-2008) is an architect of Nordic origin who discovered his own idiosyncrasy in the Mediterranean culture, in which he resided for half of his live. This thesis has focused on an exhaustive analysis of the relation between his domestic architecture and the place where it is located. This issue has been often cited in the existing bibliography, although it has never been exhaustively developed. The analysis objective has been to attempt to find invariants and patterns that could exist in his domestic work in relation to this subject. For this analysis, a sufficiently large sample has been selected: twenty houses or housing complexes (among others his own four family houses), distributed in five countries (Sweden, Denmark, United Kingdom, Spain and New South Wales), which constitute the third part of his domestic work, and half of his residential constructed projects, as well as Utzon’s written texts about this theme, and the drawings and sketches of his graphic work. The methodology used was based on consultation of primary sources: travelling and examining in situ the selected houses in Denmark, Sweden, Spain and Australia; living for a month in one of the houses (Can Lis) thanks to a research grant from the Danish Government and the Utzon Foundation; and interviewing people from his closest family and professional circles. Furthermore, part of the thesis has been published in international media: 4th International Utzon Symposium (7/3/2013-9/3/2014) and on the official web site of Can Lis, an Utzon Foundation subsidiary(www.canlis.dk). The twelve invariants discovered in relation to the project and the location of the selected projects, have been grouped according to three elements which Utzon continuously reflects upon in his own writings: the horizon, the sun and autochthonous material. Elements which originate from the influence that navigation had in his life, and from his spiritual and austere character. The story of Utzon is that of a Nordic person, with the vocation of a navigator, who found his place in the Mediterranean culture, surrounded with Marés stones, while silently making out the sea horizon on the threshold between light and shadow.