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Atmospheric extinction in solar tower plants: the Absorption and Broadband Correction for MOR measurements

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Atmos. Meas. Tech. Discuss., 8, 4737–4768, 2015 www.atmos-meas-tech-discuss.net/8/4737/2015/ doi:10.5194/amtd-8-4737-2015 © Author(s) 2015. CC Attribution 3.0 License. This discussion paper is/has been under review for the journal Atmospheric Measurement Techniques (AMT). Please refer to the corresponding final paper in AMT if available. Atmospheric extinction in solar tower plants: the Absorption and Broadband Correction for MOR measurements N. Hanrieder1, S. Wilbert1, R. Pitz-Paal2, C. Emde3, J. Gasteiger3, B. Mayer3,4, and J. Polo5 1German Aerospace Center (DLR), Institute of Solar Research, Plataforma Solar de Almería, Ctra. de Senés s/n km 4, Apartado 39, 04200 Tabernas, Spain 2German Aerospace Center (DLR), Institute of Solar Research, Linder Höhe, 51147 Cologne, Germany 3Meteorological Institute Munich (MIM), Ludwig-Maximilian-University Munich, Theresienstr. 37, 80333 Munich, Germany 4German Aerospace Center (DLR), Institute for Atmospheric Physics, Münchner Str. 20, 82234 Weßling, Germany 5Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Energy Department, Renewable Energy Division, Avda. Complutense 40, 28040 Madrid, Spain 4737 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Received: 22 January 2015 – Accepted: 8 April 2015 – Published: 7 May 2015 Correspondence to: N. Hanrieder (natalie.hanrieder@dlr.de) Published by Copernicus Publications on behalf of the European Geosciences Union. 4738 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Abstract Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrating solar tower plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a solar tower plant 5 are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in raytracing or plant optimization tools. Information about on-site atmospheric extinction is only rarely 10 available. To measure these radiation losses, two different commercially available instruments were tested and more than 19 months of measurements were collected at the Plataforma Solar de Almería and compared. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the 15 strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband solar attenuation is of interest for solar resource assessment for Concentrating Solar Power 20 (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the actual, timedependent by the collector reflected solar spectrum. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the Absorption and 25 Broadband Correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from one year measurements at the Plataforma 4739 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Solar de Almería, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.6 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile 5 for continental regions instead of additional sun photometer input results in a mean difference of 0.81 %. Therefore, applying this new correction method, both instruments can now be utilized to determine the solar broadband extinction in tower plants sufficiently accurate. 1 Introduction 10 One promising point-focusing solar-thermal technology is the solar tower plant technology. In contrary to linear-focusing systems, e.g. parabolic trough plants, a concentrator (in the case of tower plants called heliostat) is focusing the reflected solar irradiance onto a receiver on the top of a tower. A heliostat field consisting of many heliostats can therefore achieve high temperatures at the surface of the receiver due to the high re- 15 sulting concentration factor. The direct normal irradiance (DNI) which is the important parameter for Concentrating Solar Power (CSP) plants is one part of the incoming solar radiation reaching the Earth’s surface. It is known that the “sun belt” region is displaying high potential for CSP plant technologies due to the high DNI resources available. Large parts of this area are in semi-arid or arid conditions, like the largest desert of 20 the world, the African Sahara. It is the primary source for mineral dust aerosol particles (Washington et al., 2003) and next to sea salt particles, mineral dust has a considerable contribution to atmospheric aerosol (D’Almeida and Schütz, 1983). Atmospheric aerosol extinction can lower the DNI reaching the surface by up to 30 % (Gueymard, 2003). Especially in the lowest hundreds of meters of the Earth’s atmosphere higher 25 loads of aerosol particles like mineral dust or e.g. sea salt can be expected. This might be a crucial factor for solar tower plants. The solar radiation which is reflected by the heliostats to the receiver at the top of the tower has to travel a second time through the 4740 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion lowest atmospheric layers and this distance might be up to a few kilometers (depending on the solar field size). Therefore, the extinction has to be accounted for in solar resource assessment as well as plant optimization. State of the art in tower plant models (which are both used for plant yield assess5 ment and plant optimization) is that atmospheric extinction is modeled for standard atmospheric conditions. Some tools provide a choice of different attenuation conditions (Schwarzbözl et al., 2009; Belhomme et al., 2009; Buck, 2011; Kistler, 1986). For example in the DELSOL software by Kistler (1986) the default clear day with low aerosol and humidity load results in 10 % DNI attenuation for a slant range (distance between 10 heliostat and receiver) of 1 km (further denoted with T1 km) and 25 % on a hazy day. Even if some tools recently allow user-defined extinction input to provide eventually more accurate power output calculation, usually missing information about on-site extinction conditions is the main problem and the challenge plant operators are facing. There are several models developed to determine DNI attenuation and atmospheric 15 extinction in the lowest layer of the atmosphere. The model of Sengupta and Wagner (2012) is based on on-site DNI ground measurements to estimate the AOD (aerosol optical depth) in the lowest atmospheric layers. Attenuation between a heliostat and a receiver is estimated only from these measurements. This approach is already implemented in the simulation tool named SoFiA (Solar Field Assessment for Central Re20 ceiver Systems) presented by Gertig et al. (2013). Tahboub et al. (2012) presented the “Swaihan Experiment” consisting of pyrheliometers in different distances to a heliostat and also the “Jebel Hafeet Experiment” in UAE (United Arab Emirates) which utilizes pyrheliometers located at different altitudes at the Jebel Hafeet mountain. The Pitman and Vant-Hull transmittance model (Pitman and Vant-Hull, 1982) was developed on the 25 basis of a dataset by Vittitoe and Biggs (1978). The software tool for layout and optimization of heliostat fields HFLCAL (Schwarzbözl et al., 2009) also provides in addition to the different attenuation levels the utilization of the Pitman and Vant-Hull model. It determines the atmospheric extinction in solar tower plants including 12 different specific atmospheric conditions, using standard atmospheres and assuming exponential 4741 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion decrease of air and aerosol density with height. For these reasons the model might not be representative for other atmospheric situations (e.g. low level haze). Nevertheless, additional input of meteorological optical range (MOR) and water vapor measurements in the Pitman and Vant-Hull model might improve the performance of raytracing tools 5 significantly (Hanrieder et al., 2012). Due to the limited knowledge about suitable sensors to measure the atmospheric extinction, Hanrieder et al. (2012) investigated different commercially available instruments and proposed one scatterometer of Vaisala (FS11) and one long-path visibility transmissometer of Optec (LPV4). To measure the MOR and therefore indirectly the 10 transmittance (see Sect. 2.1), the scatterometer and the transmissometer have been chosen to perform continuous measurement at the Plataforma Solar de Almería (PSA) for more than 19 months. A dataset of one complete year (May 2013 to May 2014) is intercompared and analysed. Both instruments are measuring the MOR at one wavelength and are suitable for usage for on-site ground measurements. In both instruments 15 the MOR is derived from extinction or scattering of monochromatic light. As the current reflected solar spectral transmittance (broadband transmittance) is the relevant parameter for CSP and the solar spectrum shows a considerable diurnal cycle and is also dependent on current aerosol conditions, a narrowband-to-broadband conversion has to be applied on the raw measurements of both sensors (Sect. 2.3.4). The instruments 20 are further not equally considering the absorption (e.g. by water vapor) and scatter effects (Sect. 2.3.3). This has to be kept in mind if e.g. MOR measurements are feed into the Pitman and Vant-Hull model and therefore it also has to be corrected to receive a satisfying corrected measurement result. After applying the here presented correction procedure, both sensor measurements provide valuable input to CSP tools 25 to significantly improve solar resource assessment. 4742 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 2 Methodology 2.1 Measurements Atmospheric extinction is caused by absorption and scattering. Aerosol particles and water vapor have an important influence on the extinction. A beam of incident light 5 is partly attenuated while travelling through an atmospheric layer and parts are transmitted. The Beer-Lambert-Bouguer law describes the monochromatic transmittance introducing the spectral extinction coefficient βext,λ: T (λ, x) = DNI (λ, x) = e−βext,λx DNI (λ, 0) (1) where DNI (λ, 0) is the incoming spectral DNI at wavelength λ and DNI (λ, x) the spec10 tral DNI after transmittance through a medium after a distance of x. Atmospheric extinction is lowering the “visibility” which is often reported for traffic or aviation purposes. An exact knowledge about visibility is of importance for safety reasons. There are several definitions to describe the visibility in a distinct atmospheric condition (Gueymard, 2001). Usually visibility is referred to the definition by a human 15 observer and therefore only a rough estimate. Another option to define the visibility is the MOR. The MOR is defined as the length of the path in the atmosphere which is required to reduce the luminous flux in a collimated beam from an incandescent lamp, at a color temperature of 2700 K, to 5 % of its original value (Griggs et al., 1989). Visual range (VR), another parameter to describe visibility, is defined similar but with 20 a 2 % threshold. Following the Koschmieder approximation (Koschmieder, 1924) which is connecting the VR with βext at 550 nm (βext,550) neglecting the spectral variation of the extinction coefficient, MOR can be approximated as follows: MOR ≈ − ln(0.05) βext,550 ≈ 3 βext,550 (2) 4743 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 2.1.1 FS11 Vaisala scatterometer The Vaisala FS11 scatterometer is a commercially available instrument to measure the MOR (Vaisala, 2010). It consists of a transmitter which transmits via a LED a pulsed near-infrared light beam with a peak wavelength of 875 nm (see Fig. 1, left). A lens is 5 concentrating the beam at a small volume of air and a receiver is detecting the scattered photons in a distinct scatter angle (42 ). Both optics are orientated downwards. The MOR measurement range includes 5 m to 75 km. This corresponds to a measurable transmittance for 1 km light path of 0 to 0.961 (see upper limit in Fig. 5). The accuracy in MOR measurement is claimed by the manufacturer to be 10 % up to 10 km 10 and 25 % above. The accuracy in transmittance is claimed to be 3 % for a path length of 1 km. A dirt compensation algorithm is implemented which promises the correction of systematic errors of dust deposition on the instrument: additional infrared LEDs and photodiodes measure the reflectance of the sensor windows from the inside of the sensor housing so that contamination can be detected. After several months of mea15 surements the FS11 scatterometer has been characterized as a robust and compact instrument (Hanrieder et al., 2012). Low maintenance demand due to a small required cleaning frequency (about all 2 to 3 months at PSA), as well as low temperature and wind-sensitivity and low power consumption led to the conclusion that this instrument is suitable to be mounted at remote sites for solar resource assessment. The instru20 ment is measuring the beam attenuation due to scatter processes and is not physically taking absorption e.g. by water vapour into account. Nevertheless, the response of the scatterometer resembles a (visible light band) transmissometer response in the typical range of weather conditions (Vaisala, personal communication per email, 2014). The manufacturer claims that the response of the FS11 has been tested, evaluated and 25 verified with a transmissometer including a visible light band emitter at different locations around the world. Therefore is the absorption effect covered to a certain extent, according to the manufacturer, but strongly absorbing phenomena have not been evaluated. Following the WMO standard (Griggs et al., 1989) and the according MOR def- 4744 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | AMTD 8, 4737–4768, 2015 Atmospheric extinction in solar tower plants N. Hanrieder et al. Title Page Abstract Introduction Conclusions References Tables Figures ◭◮ ◭◮ Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion inition, the transmissometer lamp should correspond to a white light beam source with a center wavelength of about 1070 nm. We assume that the scatterometer is therefore calibrated to measurements based on a center wavelength of about 1070 nm. 2.1.2 Optec LPV4 transmissometer 5 The long-path visibility transmissometer LPV4 of Optec (see Fig. 1, center) consists of a transmitter and a receiver unit. Both units can be mounted separately in a distance of up to 20 km. At PSA the transmitter unit was located 485 m south-eastwards to the receiver. The transmitter consists of a equilibrium value of MeCpG steps (,+14 deg.) [31,44]. In comparison, methylation has a significantly lower stability cost when happening at major groove positions, such as 211 and 21 base pair from dyad (mutations 9 and 12), where the roll of the nucleosome bound conformation (+10 deg.) is more compatible with the equilibrium geometry of MeCpG steps. The nucleosome destabilizing effect of cytosine methylation increases with the number of methylated cytosines, following the same position dependence as the single methylations. The multiple-methylation case reveals that each major groove meth- PLOS Computational Biology | www.ploscompbiol.org 3 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning ylation destabilizes the nucleosome by around 1 kJ/mol (close to the average estimate of 2 kJ/mol obtained for from individual methylation studies), while each minor groove methylation destabilizes it by up to 5 kJ/mol (average free energy as single mutation is around 6 kJ/mol). This energetic position-dependence is the reverse of what was observed in a recent FRET/SAXS study [30]. The differences can be attributed to the use of different ionic conditions and different sequences: a modified Widom-601 sequence of 157 bp, which already contains multiple CpG steps in mixed orientations, and which could assume different positioning due to the introduction of new CpG steps and by effect of the methylation. The analysis of our trajectories reveals a larger root mean square deviation (RMSD) and fluctuation (RMSF; see Figures S2– S3 in Text S1) for the methylated nucleosomes, but failed to detect any systematic change in DNA geometry or in intermolecular DNA-histone energy related to methylation (Fig. S1B, S1C, S4–S6 in Text S1). The hydrophobic effect should favor orientation of the methyl group out from the solvent but this effect alone is not likely to justify the positional dependent stability changes in Figure 2, as the differential solvation of the methyl groups in the bound and unbound states is only in the order of a fraction of a water molecule (Figure S5 in Text S1). We find however, a reasonable correlation between methylation-induced changes in hydrogen bond and stacking interactions of the bases and the change in nucleosome stability (see Figure S6 in Text S1). This finding suggests that methylation-induced nucleosome destabilization is related to the poorer ability of methylated DNA to fit into the required conformation for DNA in a nucleosome. Changes in the elastic deformation energy between methylated and un-methylated DNA correlate with nucleosomal differential binding free energies To further analyze the idea that methylation-induced nucleosome destabilization is connected to a worse fit of methylated DNA into the required nucleosome-bound conformation, we computed the elastic energy of the nucleosomal DNA using a harmonic deformation method [36,37,44]. This method provides a rough estimate of the energy required to deform a DNA fiber to adopt the super helical conformation in the nucleosome (full details in Suppl. Information Text S1). As shown in Figure 2, there is an evident correlation between the increase that methylation produces in the elastic deformation energy (DDE def.) and the free energy variation (DDG bind.) computed from MD/TI calculations. Clearly, methylation increases the stiffness of the CpG step [31], raising the energy cost required to wrap DNA around the histone octamers. This extra energy cost will be smaller in regions of high positive roll (naked DNA MeCpG steps have a higher roll than CpG steps [31]) than in regions of high negative roll. Thus, simple elastic considerations explain why methylation is better tolerated when the DNA faces the histones through the major groove (where positive roll is required) that when it faces histones through the minor groove (where negative roll is required). Nucleosome methylation can give rise to nucleosome repositioning We have established that methylation affects the wrapping of DNA in nucleosomes, but how does this translate into chromatin structure? As noted above, accumulation of minor groove methylations strongly destabilizes the nucleosome, and could trigger nucleosome unfolding, or notable changes in positioning or phasing of DNA around the histone core. While accumulation of methylations might be well tolerated if placed in favorable positions, accumulation in unfavorable positions would destabilize the nucleosome, which might trigger changes in chromatin structure. Chromatin could in fact react in two different ways in response to significant levels of methylation in unfavorable positions: i) the DNA could either detach from the histone core, leading to nucleosome eviction or nucleosome repositioning, or ii) the DNA could rotate around the histone core, changing its phase to place MeCpG steps in favorable positions. Both effects are anticipated to alter DNA accessibility and impact gene expression regulation. The sub-microsecond time scale of our MD trajectories of methylated DNAs bound to nucleosomes is not large enough to capture these effects, but clear trends are visible in cases of multiple mutations occurring in unfavorable positions, where unmethylated and methylated DNA sequences are out of phase by around 28 degrees (Figure S7 in Text S1). Due to this repositioning, large or small, DNA could move and the nucleosome structure could assume a more compact and distorted conformation, as detected by Lee and Lee [29], or a slightly open conformation as found in Jimenez-Useche et al. [30]. Using the harmonic deformation method, we additionally predicted the change in stability induced by cytosine methylation for millions of different nucleosomal DNA sequences. Consistently with our calculations, we used two extreme scenarios to prepare our DNA sequences (see Fig. 3): i) all positions where the minor grooves contact the histone core are occupied by CpG steps, and ii) all positions where the major grooves contact the histone core are occupied by CpG steps. We then computed the elastic energy required to wrap the DNA around the histone proteins in unmethylated and methylated states, and, as expected, observed that methylation disfavors DNA wrapping (Figure 3A). We have rescaled the elastic energy differences with a factor of 0.23 to match the DDG prediction in figure 2B. In agreement with the rest of our results, our analysis confirms that the effect of methylation is position-dependent. In fact, the overall difference between the two extreme methylation scenarios (all-in-minor vs all-in-major) is larger than 60 kJ/mol, the average difference being around 15 kJ/ mol. We have also computed the elastic energy differences for a million sequences with CpG/MeCpG steps positioned at all possible intermediate locations with respect to the position (figure 3B). The large differences between the extreme cases can induce rotations of DNA around the histone core, shifting its phase to allow the placement of the methylated CpG steps facing the histones through the major groove. It is illustrative to compare the magnitude of CpG methylation penalty with sequence dependent differences. Since there are roughly 1.5e88 possible 147 base pairs long sequence combinations (i.e., (4n+4(n/2))/2, n = 147), it is unfeasible to calculate all the possible sequence effects. However, using our elastic model we can provide a range of values based on a reasonably large number of samples. If we consider all possible nucleosomal sequences in the yeast genome (around 12 Mbp), the energy difference between the best and the worst sequence that could form a nucleosome is 0.7 kj/mol per base (a minimum of 1 kJ/mol and maximum of around 1.7 kJ/mol per base, the first best and the last worst sequences are displayed in Table S3 in Text S1). We repeated the same calculation for one million random sequences and we obtained equivalent results. Placing one CpG step every helical turn gives an average energetic difference between minor groove and major groove methylation of 15 kJ/ mol, which translates into ,0.5 kJ/mol per methyl group, 2 kJ/ mol per base for the largest effects. Considering that not all nucleosome base pair steps are likely to be CpG steps, we can conclude that the balance between the destabilization due to CpG methylation and sequence repositioning will depend on the PLOS Computational Biology | www.ploscompbiol.org 4 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning Figure 3. Methylated and non-methylated DNA elastic deformation energies. (A) Distribution of deformation energies for 147 bplong random DNA sequences with CpG steps positioned every 10 base steps (one helical turn) in minor (red and dark red) and major (light and dark blue) grooves respectively. The energy values were rescaled by the slope of a best-fit straight line of figure 2, which is 0.23, to por la lectura a través de la lectura de la prensa. La educación en los medios las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio adquiere pleno derecho y entidad en la sección sexta titulada «competencias sociales y cívi- técnico de los aparatos. cas» que indica que «los alum- nos deberán ser capaces de juz- gar y tendrán espíritu crítico, lo que supone ser educados en los las programaciones oficiales, ya que, a lo largo de un medios y tener conciencia de su lugar y de su influencia estudio de los textos, los documentalistas del CLEMI en la sociedad». han podido señalar más de una centena de referencias a la educación de los medios en el seno de disciplinas 4. Un entorno positivo como el francés, la historia, la geografía, las lenguas, Si nos atenemos a las cifras, el panorama de la las artes plásticas : trabajos sobre las portadas de educación en medios es muy positivo. Una gran ope- prensa, reflexiones sobre temas mediáticos, análisis de ración de visibilidad como la «Semana de la prensa y publicidad, análisis de imágenes desde todos los ángu- de los medios en la escuela», coordinada por el CLE- los, reflexión sobre las noticias en los países europeos, MI, confirma año tras año, después de 17 convocato- información y opinión rias, el atractivo que ejerce sobre los profesores y los Esta presencia se constata desde la escuela mater- alumnos. Concebida como una gran operación de nal (2 a 6 años) donde, por ejemplo, se le pregunta a complementariedad entre la escuela y los profesiona- los niños más pequeños si saben diferenciar entre un les de los medios, alrededor del aprendizaje ciudada- periódico, un libro, un catálogo, a través de activida- no de la comunicación mediática, este evento moviliza des sensoriales, si saben para qué sirve un cartel, un durante toda una semana un porcentaje elevado de periódico, un cuaderno, un ordenador si son capa- centros escolares que representan un potencial de 4,3 ces de reconocer y distinguir imágenes de origen y de millones de alumnos (cifras de 2006). Basada en el naturaleza distintas. Podríamos continuar con más voluntariado, la semana permite desarrollar activida- ejemplos en todos los niveles de enseñanza y práctica- des más o menos ambiciosas centradas en la introduc- Páginas 43-48 ción de los medios en la vida de la escuela a través de la instalación de kioscos, organización de debates con profesionales y la confección por parte de los alumnos de documentos difundidos en los medios profesionales. Es la ocasión de dar un empujón a la educación en medios y de disfrutarlos. Los medios –un millar en 2006– se asocian de maneras diversas ofreciendo ejemplares de periódicos, acceso a noticias o a imágenes, proponiendo encuentros, permitiendo intervenir a los jóvenes en sus ondas o en sus columnas Esta operación da luz al trabajo de la educación en medios y moviliza a los diferentes participantes en el proyecto. 5. La formación de los docentes La formación es uno de los pilares principales de la educación en los medios. Su función es indispensable ya que no se trata de una disciplina, sino de una enseñanza que se hace sobre la base del voluntariado y del compromiso personal. Se trata de convencer, de mostrar, de interactuar. En primer lugar es necesario incluirla en la formación continua de los docentes, cuyo volumen se ha incrementado desde 1981 con la aparición de una verdadera política de formación continua de personal. Es difícil dar una imagen completa del volumen y del público, pero si nos atenemos a las cifras del CLEMI, hay más de 24.000 profesores que han asistido y se han involucrado durante 2004-05. 5.1. La formación continua En la mayoría de los casos, los profesores reciben su formación en contextos cercanos a su centro de trabajo, o incluso en este mismo. Después de una política centrada en la oferta que hacían los formadores, se valora más positivamente la demanda por parte del profesorado, ya que sólo así será verdaderamente fructífera. Los cursos de formación se repartieron en varias categorías: desde los formatos más tradicionales (cursos, debates, animaciones), hasta actividades de asesoramiento y de acompañamiento, y por supuesto los coloquios que permiten un trabajo en profundidad ya que van acompañados de expertos investigadores y profesionales. Citemos, por ejemplo en 2005, los coloquios del CLEMI-Toulouse sobre el cine documental o el del CLEMI-Dijon sobre «Políticos y medios: ¿connivencia?». Estos coloquios, que forman parte de un trabajo pedagógico regular, reagrupan a los diferentes participantes regionales y nacionales alrededor de grandes temas de la educación en medios y permiten generar nuevos conocimientos de aproximación y una profundización. Páginas 43-48 Hay otro tipo de formación original que se viene desarrollando desde hace menos tiempo, a través de cursos profesionales, como por ejemplo, en el Festival Internacional de Foto-periodismo «Visa para la imagen», en Perpignan. La formación se consolida en el curso, da acceso a las exposiciones, a las conferencias de profesionales y a los grandes debates, pero añade además propuestas pedagógicas y reflexiones didácticas destinadas a los docentes. Estas nuevas modalidades de formación son también consecuencia del agotamiento de la formación tradicional en las regiones. Los contenidos más frecuentes en formación continua conciernen tanto a los temas más clásicos como a los cambios que se están llevando a cabo en las prácticas mediáticas. Así encontramos distintas tendencias para 2004-05: La imagen desde el ángulo de la producción de imágenes animadas, el análisis de la imagen de la información o las imágenes del J.T. La prensa escrita y el periódico escolar. Internet y la información en línea. Medios y educación de los medios. 5.2 La formación inicial La formación inicial está aun en un grado muy ini- cial. El hecho de que la educación en medios no sea una disciplina impide su presencia en los IUFM (Institutos Universitarios de Formación de Maestros) que dan una prioridad absoluta a la didáctica de las disciplinas. En 2003, alrededor de 1.400 cursillistas sobre un total de 30.000 participaron en un momento u otro de un módulo de educación en medios. Estos módulos se ofrecen en función del interés que ese formador encuentra puntualmente y forman parte a menudo de varias disciplinas: documentación, letras, historia-geografía Estamos aún lejos de una política concertada en este dominio. La optativa «Cine-audiovisual» ha entrado desde hace muy poco tiempo en algunos IUFM destinada a obtener un certificado de enseñanza de la opción audiovisual y cine. Internet tiene cabida también en los cursos de formación inicial, recientemente con la aparición de un certificado informático y de Internet para los docentes, dirigido más a constatar competencias personales que a valorar una aptitud para enseñarlos. 6. ¿Y el futuro? El problema del futuro se plantea una vez más por la irrupción de nuevas técnicas y nuevos soportes. La difusión acelerada de lo digital replantea hoy muchas cuestiones relativas a prácticas mediáticas. Muchos Comunicar, 28, 2007 47 Comunicar, 28, 2007 Enrique Martínez-Salanova '2007 para Comunicar 48 trabajos que llevan el rótulo de la educación en medios solicitan una revisión ya que los conceptos cambian. La metodología elaborada en el marco de la educación en medios parece incluso permitir la inclinación de la sociedad de la información hacia una sociedad del conocimiento, como defiende la UNESCO. En Francia, se necesitaría unir las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio técnico de los aparatos. Los avances recientes en el reconocimiento de estos contenidos y las competencias que supondrían podrían permitirlo. Referencias CLEMI/ACADEMIE DE BORDEAUX (Ed.) (2003): Parcours médias au collège: approches disciplinaires et transdisciplinaires. Aquitaine, Sceren-CRDP. GONNET, J. (2001): Education aux médias. Les controverses fécondes. Paris, Hachette Education/CNDP. SAVINO, J.; MARMIESSE, C. et BENSA, F. (2005): L’éducation aux médias de la maternelle au lycée. Direction de l’Enseignement Scolaire. Paris, Ministère de l’Education Nationale, Sceren/CNDP, Témoigner. BEVORT, E. et FREMONT, P. (2001): Médias, violence et education. Paris, CNDP, Actes et rapports pour l’éducation. – www.clemi.org: fiches pédagogiques, rapports et liens avec les pages régionales/académiques. – www.ac-nancy-metz.fr/cinemav/quai.html: Le site «Quai des images» est dédié à l’enseignement du cinéma et de l’audiovisuel. – www.france5.fr/education: la rubrique «Côté profs» a une entrée «education aux médias». – www.educaunet.org: Programme européen d’éducation aux risques liés à Internet. dResedfeleexliobnuetsacón Páginas 43-48
Atmospheric extinction in solar tower plants: the Absorption and Broadband Correction for MOR measurements
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Atmospheric extinction in solar tower plants: the Absorption and Broadband Correction for MOR measurements

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