Juan Carlos Ceballos

Solar Ultraviolet Radiation Measurements in One of the Most Populous Cities of the World: Aspects Related to Skin Cancer Cases and Vitamin D Availability

A number of studies published in the scientific literature have shown the relationship between sun exposure and nonmelanoma skin cancer (NMSC) and vitamin D synthesis. However, the paucity of medical data, particularly in developing countries, hampers a global assessment of the impact of sun exposure on NMSC and vitamin D. To improve knowledge on this subject, this paper presents UV index (UVI) measurements performed in São Paulo City (SPC) in the period 2005–2008. It was found that 65% of the UVI measured 2 h around local noon during the summer show very high (8 < UVI < 10) and extreme (UVI > 11) levels according to the World Health Organization (WHO) classification. During the winter, 40% of the measurements around noontime show high or very high levels. In spite of worrisome recent statistics from SPC, showing that NMSCs make up about 28% of over a million of new cases of cancer in 2008, sun protection is not considered a real problem in these urban areas. UV measurements also show that every month of the year UV levels are high enough to ensure vitamin D production in human skin from incidental sun exposure.

Uvb surface albedo measurements using biometers

This work describes ultraviolet-B albedo measurements performed over several surfaces and different atmospheric conditions. These results provide a complement to previous studies as Blumthaler & Ambach (1988), widely used as albedo reference for the main UV radiative transfer models. A custom-built albedometer composed of apair of Solarlight UVB501 biometer was used to measure the albedo over the following surfaces: green and yellowish grass, sand, wood (natural and painted), formica (synthetic plate), and iron. Influence of clouds and the sensors response to temperature variations are also discussed. Presence of clouds on surface albedo measurement seems negligible, but athermo-regulated instrument is indispensable to an accurate analysis. Comparison with previous works shows the need for studies on the detailed characterization of the type of surface.

Estimativa da radiação solar global à superfície usando um modelo estocástico: caso sem nuvens

A radiative transfer model was implemented for a 16-layer stratified atmosphere. The scheme is of a stochastic structure, with a random walk of diffuse photons between transition states until arriving to absorption states within layers, sky or ground. The formalism is associated a first order Markov process. The model exhibits a simple but powerful structure, when compared with other models used for multiple-layered atmospheres. The structure of the model allows the calculation of the planetary reflectance, global radiance in the surface and the absorption in the atmosphere. Transition parameters for each layer are calculated using a delta-SS two-flux approximation. Comparisons with surface measurements and with SBDART code (Santa Barbara DISORT Atmospheric Radiative Transfer), show a good performance of the model when assessing global radiation at ground level for Rayleigh atmospheres as well as for high-loaded aerosol atmospheres during burning season. The precision of the model, in the atmosphere transmittance estimation, makes it important for researchers that act in the area of remote sensing. Main advantages of the model are: simple structure, good accuracy and easy adaptation to an atmosphere composed of an even number of layers.

Daytime cloud classification over South American region using multispectral GOES-8 imagery

Information about a minimal set of characteristic variables and types of scene was searched for Geostationary Operational Environmental Satellite (GOES)-8 Imager multispectral imagery over an extended area of South America, September 2002, 1600 UTC (near local noon over most parts of the area). Thirteen variables were considered for each pixel: five of them described reflectance and brightness temperature in four channels, three variables assessed temperature difference related to channel 4; finally, five variables assessed local homogeneity (texture) in each channel. Thirty-two clusters were determined by a classification scheme (‘dynamic cluster’) based on minimal Euclidean distance. Factor analysis in principal components (PCs) applied to cluster centroids shows that only five variables might be taken as non-redundant, namely reflectance in channel 1 and brightness temperature in channel 4 as well as their textures, together with difference between channels 5 and 4. Although factor analysis suggests defining about seven clusters (which in turn are consistent with image nephanalysis), PC analysis makes it evident that an objective minimal number of scenes is actually loosely defined but provides some useful criteria for definition of proper centroids, depending on the user’s convenience.

A Successful Practical Experience with Dedicated Geostationary Operational Environmental Satellites GOES-10 and -12 Supporting Brazil

AbstractThis paper summarizes the successful use of Geostationary Operational Environmental Satellite-10 (GOES-10) and -12 (GOES-12), mainly beyond their retirement as operational satellites in the United States, in support of meteorological activities in South America (SA). These satellites were maneuvered by the National Oceanic and Atmospheric Administration (NOAA) to approximately 60°W, enabling other countries in Central and South America to benefit from their ongoing measurements. The extended usefulness of GOES-10 and -12 was only possible as a result of a new image geolocalization system developed by NOAA for correcting image distortions and evaluated in collaboration with the Brazilian National Institute for Space Research. The extension allowed GOES-10 and -12 to monitor SA for an additional 7 years proving the efficiency of this navigation capability implemented for the first time in the GOES series well beyond the expected satellites’ lifetime. Such successful capability is incorporated in the...

Surface Albedo Assessment in Clear Sky and Dense Smoke Atmospheres Using a Shortwave Radiation Stochastic Model and MODIS 1B Image

The surface albedo, which is a fundamental parameter in the estimation of the radiation balance, corresponds to the reflectance integrated in the solar spectrum. It can be obtained through satellite images that have great spatial coverage. A stochastic model of two‐flux, presented by Ceballos [1] and developed by Souza and Ceballos [2], is used to establish a direct relationship between the reflectance of the surface and the radiance measured by MODIS‐Terra/Aqua sensor. The propagation of radiation, in the solar spectrum from 0.3 to 3.0 μm, is described by an scheme of 16 layers. In such scheme, it is obtained the necessary parameters to establish the radiation balance in the top of the atmosphere. The optical properties of the atmospheric layers are defined by aerosol, ozone and water vapor. In this way, to determine the surface albedo, it is considered that the radiance originated from the system earth‐atmosphere, measured by the satellite, is isotropic. A simple adjustment factor is introduced to compe...

Solar Radiation Assessed by CPTEC Model GL: A Comparison between Results with GOES and MSG over Northeastern Brazil

Distribution of solar radiation over South America is daily assessed by the CPTEC’s GL1.2 model using GOES satellite imagery (VIS channel). Meteosat Second Generation full‐resolution imagery is also being ingested from 2007 on. VIS MSG images used for estimating solar radiation with essentially the same code GL show similar results over Northeastern Brazil (where lines‐of‐sight of both satellites have similar zenith angles, helping comparisons). This result encourages the integrated use of both satellites for monitoring of solar radiation over a large area including South America and Africa.

Time Series of Daily Mean Solar Irradiance over South America: Some Results of 11 Years of CPTEC GL Model Using GOES Imagery

Distribution of solar radiation over South America is daily assessed by the CPTEC’s GL1.2 model using GOES satellite imagery (VIS channel). A time series of 11 years, January 1996 to Dezember 2006 is now available and may be used for climatological, agricultural and energy‐source studies in the scale of 1 day, 0.04°. A compact version (averages over 0.4° and five‐day intervals) is available for download. Comparison with values provided by several solarimetric stations exhibits fair fitting (about 7% or less for monthly averages). This resolution allows for an acceptable detail of geographical distribution. Comparison of annual cycles for 5 and 11 years suggest that both periods have similar behavior within one standard deviation expected for each average pentad, so that the 11‐year series can be used for preliminary climatic studies.

Stochastic Model for Shortwave Radiation Transfer in a Multiple‐Layered Atmosphere: Surface Global Radiation in Cloudless Conditions

A two‐flux method is presented, which describes propagation of solar radiation in the atmosphere as a random walk of diffuse photons among several atmospheric layers. Results are obtained in terms of absorption probabilities in each layer, at ground and within sky, allowing to easily introduce and to analyze influence of profiles of the main atmospheric absorbers (ozone, aerosols and water vapor). Global radiation is obtained by integration of monochromatic irradiances. Application of this model to cloudless situations in the extreme cases of rural environment and high aerosol load by burning biomass shows good results when compared with SBDART code (they have a systematic deviation of +10 W⋅m−2), and both differ from ground measurements of global radiation within 30 to 50 W⋅m−2. This difference could be lowered having a better definition of aerosol load during daytime. It is observed that the stochastic model performance is five times faster than SBDART.