L. Da Silva

Ground-Based Ultraviolet-Radiation Measurements during Springtime in the Southern Hemisphere

We report the first measurements obtained by a network of UV-B detectors established through Argentina and Chile, at locations covering latitudes extending from 53? S to 18? S. Evidence that UV-B increases are detected at these latitudes during the Austral spring 1993 is presented.

The extent of the ozone hole over South America during the spring of 1993, 1994 and 1995

The evolution of the total ozone measured by a network of ground stations located in Argentina and Chile between latitudes 53S and 33S during the spring of 1993, 1994 and 1995 is given. Ozone data obtained from the ground stations are compared with total ozone values supplied by the satellite showing a very good agreement. Ground station data were taken with a very low cost detection system based on differential optical absorption techniques under specific conditions. Several ozone depletion events were detected in the south of Argentina and Chile during those time intervals, even at latitudes as low as 33S. Potential vorticity maps obtained for those events indicate that the ozone depletions observed have an Antarctic origin.

Structure in the temperature dependence of the lifetime of the excited F-center in KCl

Abstract Evidence of a temperature-dependent structure in the lifetime of excited F-centers in KCl is reported. The sharp features are revealed when the temperature control of the sample is better than a few hundreth of a degree. For less accurate temperature control, as currently used in lifetime measurements, sharp variations of the lifetime with temperature are averaged, and the structure is not detectable. A theoretical explanation is suggested.

Spectral UV radiance measured at a coastal site: a case study

We have sampled the spatial distribution of the UV radiation (i.e. the UV radiance) at a station located on the southern pacific coastline (Valparaiso, Chile, 33.03°S-71.58°W). The site is characterized by the partial horizon obstruction (due to the surrounding topography). Our spectral measurements were carried out over the period January-March 2012 and were meant to weigh up the effects of the local cloudiness, the heterogeneous albedo, and the horizon obscuration. We found that a nearly translucent overcast sky affects the radiance distribution such that from its maximum (measured close to the solar zenith angle) the radiance is monotonically decreasing towards the horizon. Under cloudless conditions, the radiance distribution becomes less isotropic with the wavelength; we detected spatial variations in the distribution of radiation up to a factor of 5 at 320 nm, and up to a factor of 9 at 400 nm. We also observed that radiances measured at points over the sea are greater than those measured at the corresponding point over the land; we partially attributed this effect to the spatial variations in the albedo. Moreover, we found that the horizon obscuration leads to significant reductions in the radiance at points on the blocked horizon; these reductions range from 60% (at 400 nm) to 80% (at 300 nm). Methodological details are provided below.

Numerical modeling of solar irradiance on earth's surface

Modeling studies and estimation of solar radiation in base area, touch from the problems of estimating equation of time, distance equation solar space, solar declination, calculation of surface irradiance, considering that there are a lot of studies you reported the inability of these theoretical equations to be accurate estimates of radiation, many authors have proceeded to make corrections through calibrations with Pyranometers field (solarimeters) or the use of satellites, this being very poor technique last because there a differentiation between radiation and radiant kinetic effects. Because of the above and considering that there is a weather station properly calibrated ground in the Susques Salar in the Jujuy Province, Republic of Argentina, proceeded to make the following modeling of the variable in question, it proceeded to perform the following process: 1. Theoretical Modeling, 2. graphic study of the theoretical and actual data, 3. Adjust primary calibration data through data segmentation on an hourly basis, through horizontal and adding asymptotic constant, 4. Analysis of scatter plot and contrast series. Based on the above steps, the modeling data obtained: Step One: Theoretical data were generated, Step Two: The theoretical data moved 5 hours, Step Three: an asymptote of all negative emissivity values applied, Solve Excel algorithm was applied to least squares minimization between actual and modeled values, obtaining new values of asymptotes with the corresponding theoretical reformulation of data. Add a constant value by month, over time range set (4:00 pm to 6:00 pm). Step Four: The modeling equation coefficients had monthly correlation between actual and theoretical data ranging from 0.7 to 0.9.

Characteristic variogram for land use in Multispectral Images

In remote sensing is the concept of spectral signature in multispectral imagery to recognize different land uses in the area; This study proposes the existence of a characteristic variogram for land use in multispectral images. To test this idea we proceeded to work with a sector of a scene image of multispectral Landsat 7 ETM +, in 6 of their bands (1- 450nm to 520nm, 2 - 520nm to 600nm, 3 - 630nm to 690nm, 4 - 760nm to 900nm 5 - over 1550nm to 1.750nm and 7 - 2.080nm to 2.350nm), corresponding to two uses of urban land and agricultural, the omnidirectional variogram for each band was analyzed and modal variogram for each land use was established in the stripe set. Of the analyzed claims data for each land use is a model characteristic and modal cross variogram how their wavelengths.

Electronic processes of f-centers in KCl crystals by L1-light excitation

Abstract F-centers in an additively colored KCl crystals were excited by light of the L1-band (3371 A). The emission spectrum of the main bands were measured at several temperatures ranging from 47 to 171 K. At least three bands were clearly identified, the F*-band, the K-band, and the M-band. A mechanism for the electron decay which leads to an interpretation of the data is proposed. In addition, the experiment suggests that under L1-light excitation, the luminiscence lifetime may contain at least three lifetimes: the lifetime of F* (∼600 ns), the lifetime for the K-band (335 ns) (Da Silva, Phy. Stat. Sol. (b) 169 (1992) K119–122) and the one corresponding to the M-center (30 ns).