Background/aim: The angular distribution of solar radiance and its spectral characteristics is required for the determination of vitamin D3 production in humans. Materials and methods: The vitamin D3 weighted exposure can be calculated by... more
Background/aim: The angular distribution of solar radiance and its spectral characteristics is required for the determination of vitamin D3 production in humans. Materials and methods: The vitamin D3 weighted exposure can be calculated by integrating the incident solar spectral radiance over all relevant parts of the human body. A novel instrument allowing simultaneous measurements of spectral radiance from more than 100 directions has been developed. A large solar simulator for controlled experiments is described. Results: In summer it is relatively easy to obtain sufficient vitamin D because sun exposure times are short. In winter solstice vitamin D3 cannot be obtained with realistic clothing even if the exposure were extended to all daylight hours. Conclusion: Improved and controlled experiments to determine vitamin D3 production are required to assess the positive effects of solar UV radiation and to assess its natural variability.
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The estimate of a quantity and its standard uncertainty are commonly associated with the mean and the standard deviation of a set of data obtained from measuring repeatedly the measurand (this procedure is known as 'type A'... more
The estimate of a quantity and its standard uncertainty are commonly associated with the mean and the standard deviation of a set of data obtained from measuring repeatedly the measurand (this procedure is known as 'type A' analysis). Both can be affected by the resolution of the measuring instrument. The resolution is the smallest difference between indications that can be distinguished and it is obviously limited in the case of digital instruments. In this paper, we characterize the effect of the limited resolution on a set of measurements. We realized that, if a certain minimum limit for the standard deviation of the measured data is not achieved, biased estimates and unrealistic uncertainties can be obtained. Beyond this limit, the influence of the resolution on the mean is insignificant and standard deviation includes the effect of resolution such that, in order to carry out the uncertainty evaluation, additional corrections appear to be unnecessary.
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A method for the calibration of multidirectional spectroradiometers (MUDISs) capable of the simultaneous measurement of spectral radiance at different wavelengths is presented. The calibration of the spectroradiometer is challenging and... more
A method for the calibration of multidirectional spectroradiometers (MUDISs) capable of the simultaneous measurement of spectral radiance at different wavelengths is presented. The calibration of the spectroradiometer is challenging and crucial for high quality measurements of the angular dependence of the radiance. The calibration device consists of an integrating sphere (also known as Ulbrichtkugel), with a diameter of 100 cm, equipped with three 100 W lamps positioned in the lower hemisphere, with the input optics of the MUDIS directed towards the upper hemisphere. The MUDIS detects radiation from 113 different directions simultaneously in a wavelength range from 300 nm to 550 nm. Due to multiple reflections within the sphere, the radiance from the upper hemisphere is nearly homogeneous with deviations of less than 3% on average. Disregarding the 3% variability and assuming a homogeneous radiance inside the upper hemisphere of the integrating sphere, the spectral responsivities of all the MUDIS channels were determined based on the measured zenith radiance, which was detected by a pre-calibrated Network for the Detection of Atmospheric Composition Change reference spectroradiometer containing a scanning double monochromator with a unidirectional input optics. The input optics of the MUDIS contains thin fibers that should not be moved to avoid changes in the instrument’s responsivity. The proposed method is therefore suited to determine the absolute responsivity of the MUDIS for all directions.
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The study of ultraviolet effects on the biosphere requires an accurate knowledge of UV-B irradiances reaching the Earth's surface. Here we present the technical specifications and... more
The study of ultraviolet effects on the biosphere requires an accurate knowledge of UV-B irradiances reaching the Earth's surface. Here we present the technical specifications and the performance of a spectroradiometer for the highly accurate determination of actual UV levels. The sensitivity, the spectral resolution and the wavelength accuracy of the instrument, as well as results from a series of
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Research Interests: Mechanical Engineering, Computer Science, Optics, Medical Imaging, Fiber Optics, and 15 moreNonlinear Optics, Photonics, Medicine, Society, Correlation, Optical, Light, Feedback, Applied Optics, Optical physics, Chaotic Systems, Nonlinear system, Electrical And Electronic Engineering, Feedback System, and Chaotic
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... 3, Gunther Seckmeyer2, Darius Pissulla2 and Fernando Labbe1 1 Universidad Técnica Federico Santa Maria, Ave. Espana 1680, Valparaıso, Chile 2 Leibniz Universität Hannover, Herrenhäuser Street 2, 30419 Hannover, Germany 3 Universidad... more
... 3, Gunther Seckmeyer2, Darius Pissulla2 and Fernando Labbe1 1 Universidad Técnica Federico Santa Maria, Ave. Espana 1680, Valparaıso, Chile 2 Leibniz Universität Hannover, Herrenhäuser Street 2, 30419 Hannover, Germany 3 Universidad de Santiago de Chile ...
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ABSTRACT We present a novel non-scanning multidirectional spectroradiometer (MUDIS) measuring the spectral sky radiance as a function of zenith and azimuth angle with a high spectral and temporal resolution. The instrument is based on a... more
ABSTRACT We present a novel non-scanning multidirectional spectroradiometer (MUDIS) measuring the spectral sky radiance as a function of zenith and azimuth angle with a high spectral and temporal resolution. The instrument is based on a hyperspectral imager and measures spectral sky radiance in the wavelength range of 250-600 nm at 113 different directions simultaneously. MUDIS has been intercalibrated with a sky scanning CCD spectroradiometer (SCCD). Sky radiance measurements have been performed with both instruments under cloudless and overcast sky. The spectral actinic irradiance derived from those measurements agrees within 8% for wavelengths higher than 320 nm. The bias between synchronous MUDIS and SCCD sky radiance measurements during cloudless and overcast sky is below 5% for 320 and 500 nm with a 1sigma standard deviation of less than 10%. MUDIS enables us to perform more than 220000 spectral sky radiance measurements instead of approximately 6000 SCCD spectral sky radiance measurements per day and to measure spatial variations of spectral sky radiance simultaneously.
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Nonlinear feedback systems may show a principally different dynamical behavior compared with linear systems: Chaos may appear; in other words, unpredictability in any practical sense. Sometimes, however, cooperative effects can be... more
Nonlinear feedback systems may show a principally different dynamical behavior compared with linear systems: Chaos may appear; in other words, unpredictability in any practical sense. Sometimes, however, cooperative effects can be observed. We use the term cooperative when stable patterns evolve with long-range spatial correlation. With optics, TV, and a computer we can study the dynamics of pictures running through a nonlinear feedback loop. Coupling between different pixels is introduced by convolution. The most interesting features of such pictorial feedback systems are (1) weak coupling of adjacent pixels always leads to chaos, (2) strong coupling with positive point-spread function leads to chaos, (3) strong coupling with bipolar point-spread functions leads to stable patterns with long-range spatial order, (4) stability is not destroyed by a considerable amount of noise.
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Research Interests: Art and Clinical Sciences
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The Andean snowpack is an important source of water for many communities. As other snow-covered regions around the world, the Andes are sensitive to black carbon (BC) deposition from fossil fuel and biomass combustion. BC darkens the snow... more
The Andean snowpack is an important source of water for many communities. As other snow-covered regions around the world, the Andes are sensitive to black carbon (BC) deposition from fossil fuel and biomass combustion. BC darkens the snow surface, reduces the albedo, and accelerates melting. Here, we report on measurements of the BC content conducted by using the meltwater filtration (MF) technique in snow samples collected across a transect of more than 2500 km from the mid-latitude Andes to the southern tip of South America. Addressing some of the key knowledge gaps regarding the effects of the BC deposition on the Andean snow, we identified BC-impacted areas, assessed the BC-related albedo reduction, and estimated the resulting snow losses. We found that BC concentrations in our samples generally ranged from 2 to 15 ng g−1, except for the nearly BC-free Patagonian Icefields and for the BC-impacted sites nearby Santiago (a metropolis of 6 million inhabitants). We estimate that the...
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The continuous negative trend in total ozone column measured in the past 20 years has inspired research on its consequences. It is now very likely that severe depletions of ozone observed especially during 1991–1995 over the northern... more
The continuous negative trend in total ozone column measured in the past 20 years has inspired research on its consequences. It is now very likely that severe depletions of ozone observed especially during 1991–1995 over the northern hemisphere will remain a problem at least until the first decades of the next century. There is overwhelming experimental evidence that, all other atmospheric (and ground) variables being constant, decreases in atmospheric ozone result in UV-B increases at the Earth’s surface, in quantitative agreement with predictions of radiative transfer models. However, it must be noted that stratospheric ozone is not the only component that influences UV-B irradiances at the ground level. Tropospheric ozone and aerosols can reduce global UV-B irradiances appreciably, whereas high albedo can enhance global UV-B irradiances. The variablity of clouds and their influcence on UV-B irradiance further complicate the detection of UV-B changes at the ground level. Only a few studies have monitored UV-B over time scales of decades, and these have yielded conflicting results on the magnitude and even the sign of trends. Some studies may have been affected by problems with instrument instability and calibration, and local pollution trends.
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Spectral sky radiance is a fundamental measurement quantity for the characterization of the atmospheric radiation field. We present results of spectral sky radiance measurements from Hannover (52.23° N, 9.42° E), Germany and the German... more
Spectral sky radiance is a fundamental measurement quantity for the characterization of the atmospheric radiation field. We present results of spectral sky radiance measurements from Hannover (52.23° N, 9.42° E), Germany and the German Antarctic station Neumayer (70.65° S, 8.25° W). The spectral sky radiance is a function of incident and azimuth angle, and it is not uniformly distributed over the sky. A distinct minimum can be found for all wavelengths opposite of the Sun whereas a maximum is to be found around the Sun. For wavelengths shorter than 500 nm the distribution of sky radiance is much more homogeneous and concentrates only around the Sun. For longer wavelengths the distribution of sky radiance becomes more inhomogeneous and concentrates additionally around the Sun also close to the horizon. The reason for the homogenous distribution of sky radiance for short wavelengths (Figure 1) is Rayleigh scattering since it is most effective for short wavelengths (Lenoble, 1993). The...