Scielo RSS http://www.scielo.org.bo/rss.php?pid=1562-382320120004&lang=en vol. 20 num. 20 lang. en http://www.scielo.org.bo/img/en/fbpelogp.gif http://www.scielo.org.bo http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400001&lng=en&nrm=iso&tlng=en One year of Cloud Optical Depth (COD) measurements obtained with the radiometer (sunphotometer Cimel CE - 318) are presented. As the first step a validation method is proposed in order to confirm the cloud in the measurement. This method is based in the cloud information derived from the actinometrical observations and radar data. In the second step of the work, the statistical results from the one year of the COD measurements in Camagüey are analyzed. The results show the high quality of COD measurements at Camagüey. The analysis of the COD frequency shows one peak close to 15. Similar behavior occurs each month. The mean COD average value for the entire period is 27.2, with a standard deviation of 17.3. The mean monthly minimum and maximum value of COD occur in December and May, respectively. The diurnal cycle of the mean hourly COD values shows an increase in the afternoon hours. In the afternoon the number of cases measured decrease. The preliminary results shown in this paper constitute the first report of such measurements in the country. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400002&lng=en&nrm=iso&tlng=en In atmospheric LIDAR (Light Detection and Ranging) remote sensing, the dynamic range of the return power signals can span up to five orders of magnitude. Modern acquisition systems such as those based on LicelTM transient recorders combine a dual acquisition mode in which the return signal is recorded simultaneously in both analog (analog-to-digital (AD) conversion) and photon-counting (PC) modes. Although both data records can be analyzed separately, their combination obtained through gluing gives the advantage of the high linearity of the AD conversion for high light-level signals (especially in the near range) and the high sensitivity of the PC mode for low light-level signals (in the far range). Recently, eruptions of volcanoes such as Eyjafjalla (Iceland) in 2010, Grímsvötn (Iceland Puyehue (Argentina) Nabro (Eritrea) and Mount Lokon (Indonesia) in 2011 have yielded emergency situations with a strong economical cost due to human evacuation and/or air traffic interruption. Volcanic aerosols are first injected in the troposphere and often reach the stratosphere where they can reside for several years. The mixed analog/photo-counting acquisition approach is particularly suitable for the detection of volcanic aerosols in both the troposphere (near/mid range) and the stratosphere (far range). In this line, a case study showing volcanic aerosols from the Nabro volcano (Eritrea, 2011) in the stratosphere and simultaneously Saharan dust in the troposphere over the multi-spectral Barcelona lidar station during the period 27 June - 1 July 2011 is presented. The benefits of the proposed gluing technique will be shown through the comparison of analog, PC, and glued backscatter-coefficient time series. Existing gluing algorithms solve the fitting coefficients by matching both analog and PC data over a predefined spatial range (or equivalently, over a predefined upper and lower counting rate) depending on which kind of photodetector (usually a photomultiplier) is being used. In this work, an enhanced data-gluing formulation is presented. The method automatically finds the spatial range where both analog and PC signals are more similar based on Euclidian distance minimization over piece-wise range intervals along the whole acquisition spatial range. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400003&lng=en&nrm=iso&tlng=en La contaminación atmosférica es un problema delicado de importancia a nivel mundial, especialmente en México D.F. y sus principales metrópolis. Actualmente, factores tales como sobrepoblación, industrias, medios de transporte, quema de combustibles la han incrementado de manera alarmante, provocando una gran concentración de gases invernadero (dióxido de carbono, metano, óxido nitroso y clorofluorocarbonos) en la atmósfera, de tal manera que se han creado planes de contingencia ambiental; como un ejemplo el programa de hoy no circulan automóviles cuyas placas tengan una particular terminación numérica. Debido a esto se ha tenido la necesidad de un constante monitoreo de la calidad del aire de diferentes ciudades. Lamentablemente en México no se ha desarrollado y/o explotado técnicas de monitoreo a través de luz, en especial de luz laser (Lidar). En este trabajo se muestran las características principales de la construcción de un Lidar de retrodispersión elástica, con una fuente Laser pulsada de Nd:YAG en 1064 y 532nm. El rango de repetición de los pulsos es de 1-10 Hz con energías de 100 a 350mJ y duraciones de hasta 20ns en el modo de operación de Q-conmutada. El sistema de recolección de energía es un telescopio Newtoniano con una longitud focal de 121cm y un espejo primario de 20cm. El telescopio está montado sobre una base Dobsoniana que le permite girar en el plano horizontal (azimut) y en el plano vertical (zenit) para cambiar de altitud. El detector es un fotomultiplicador de la marca Hamamatsu con un rango espectral que va desde 400 a 1200nm. Para evitar el fenómeno de la compresión; es decir, regiones en donde no hay un perfecto traslape de las áreas del campo de visión del telescopio y la del haz laser, se decidió construir una configuración monoestática coaxial. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400004&lng=en&nrm=iso&tlng=en En este trabajo se muestran los resultados de las mediciones en laboratorio de los perfiles de intensidad, la razón de depolarización; así como el ensanchamiento de cinco diferentes líneas de un laser de Argón y una a 632nm de un laser de HeNe; al pasar a través de una cámara de neblina de gotas de agua con diferentes densidades. Los resultados obtenidos están en gran concordancia con los obtenidos Ryan y Carswell en [1]. Con la construcción de esta cámara de neblina, se pudo medir el ancho angular del lóbulo de dispersión frontal. Además con la ayuda de un arreglo interferómetrico y un microscopio con un desplazamiento mínimo de una diezmilésima de pulgada, se pudo medir el tamaño de las gotas de agua; se observó que el mejor ajuste para la distribución del tamaño de las gotas, fue con la función gamma generalizada, del tipo propuesta por Deirmendjian [2]. Una vez que se obtuvieron el valor de las constantes, de la función gamma, que mejor ajustaron el histograma de frecuencia se obtuvo el número de densidad de gotas por unidad de volumen. Aunque la mayoría de los estudios realizados, se han centrado en la retrodispersión de la luz por diferentes medios, principalmente nubes; sin embargo, el estudio del lóbulo de dispersión frontal se han podido estudiar con extrema precisión muchos factores, tales como la existencia de simple o múltiple dispersión y la cantidad en que se llevó a cabo. Esto es de gran importancia en la estimación de retornos lidar pues con esta fundamentaciones se puede conocer datos importantes como los coeficientes de extinción y retrodispersión, de partículas contaminantes en la atmosfera y entender el modelo de funcionamiento de la naturaleza. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400005&lng=en&nrm=iso&tlng=en The depletion of the polar ozone layer is one of the strongest anthropogenic signals in the Earth system. Subpolar regions in the southern part of South America are affected by this phenomenon, covered sometimes by air masses with less ozone than normal with the corresponding UV enhancements at ground surface. Motivated by these atmospheric events, Argentina and Chile with the financial support of JICA has joined scientific efforts to develop UVO3 Patagonia project. It has as main objectives monitoring ozone and UV radiation in Southern Patagonia. The Ozone and RUV laboratory (Chile) and the Lidar Division of CEILAP (Argentina) are the execute laboratories of this project. The Observatorio Atmosférico de la Patagonia Austral (Atmospheric Observatory of Southern Patagonia) is located in South Patagonia (51º 55’S, 69º 14’W), in subpolar region and it is a convenient monitoring site of the atmosphere in the Southern Hemisphere. In this experimental site is operative a differential absorption lidar instrument (DIAL) for the measurement of ozone vertical distribution. This instrument belongs of Network Data for Atmospheric Composition Change (NDACC). The altitude range of the ozone measurement is 14-45 km, which provides the opportunity to monitor the perturbations due to the passage of stratospheric polar air over Río Gallegos. Systematic stratospheric ozone profile measurement has been carried on in this experimental site since 2005. We identified three mayor perturbation of ozone hole over the stratospheric ozone profile in Río Gallegos. Approach of polar vortex during late winter, overpass of ozone hole in middle spring and dilution process during late spring change the shape and content of stratospheric ozone profile and by consequences the solar UV. Solar surface irradiance and total ozone content were measured with a Brewer spectraphotometer and moderate narrow band radiometer GUV-541 deployed in the Río Gallegos experimental site. Depleted ozone columns were measured during ozone hole overpass, and the analysis of unique extreme ozone depletion event in November 2009 is reported and compared with Multisensor Data Reanalysis of TOMS/OMI satellite data. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400006&lng=en&nrm=iso&tlng=en Understanding the effect of aerosols upon radiative forcing requires information about vertical profiles. Lidar techniques represent a powerful tool for studies of the vertical structure of the aerosol field. During the SPAin Lidar Intercomparison 2010 (SPALI10) campaign, several multiwavelength Raman lidar systems measured simultaneously in order to assess their performances. Multiwavelength lidars can provide relevant vertically-resolved information on aerosol optical properties because the wavelength dependence of the backscatter and extinction coefficients allows for a more detailed discrimination of aerosol types. Several lidar stations belonging to SPALINET, the Spanish and Portuguese Lidar NETwork and also EARLINET, the European Aerosol Research Lidar NETwork, intercompared during a campaign that took place in Madrid from 18 October to 5 November 2010. The products provided by the lidar systems were compared with ancillary data. At ground level, aerosol size distribution was continuously monitored. Additionally, the column-integrated characterization of the atmospheric aerosol was performed by means of a sun photometer. The extensive dataset obtained during SPALI10 field campaign enables to compare ground-level in-situ measurements with remote sensing techniques to determine vertically-resolved optical and microphysical properties of aerosols. Several relevant features shown in the comparison of the results obtained by the different instruments are discussed in this work. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400007&lng=en&nrm=iso&tlng=en The DIAL system belonging to Observatorio Atmosférico de la Patagonia Austral, Río Gallegos, Argentina has been included in the NDACC since December 2008. One caveat of large networks such as NDACC is the difficulty to report information of similar nature consistently from one research group (or instrument) to another. The inversion algorithm used in the stratospheric ozone DIAL measurements involves different source of systematic and statistic errors. Due to the rapid decrease of the signal-to- noise ratio in the high stratosphere, it is necessary to degrade the vertical resolution of the measurement in order to limit the statistical error at this altitude range, to reasonable values. The final statistical error on the measurement is the result of a compromise between the experimental system characteristics such as the duration of the measurement and the final vertical resolution. The aim of this study is test the DIAL algorithm resolution used to retrieve the ozone profile comparing with the synthetic ozone profile. This synthetic ozone profile is calculated by mean of lidar equation using an ECC sonde profile as input parameter. This ozone profile was measured with an ozonesonde launched in Río Gallegos in March 2011 as part of intercomparison campaign. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400008&lng=en&nrm=iso&tlng=en Aerosols in the atmosphere directly and indirectly influence the climate of a region. However, studies related to the effects of aerosols in some areas are scarce. The southern region of Brazil is located next to major known sources of particulate matter (Brazilian savanna, Amazonia and southeastern Brazil). Thus, it has the peculiarity of having the contribution of the transport of aerosols from other sources with optical characteristics very different from each other, also with the influence of regional aerosols. This paper aims to present a project to analyze the impact of aerosols in the atmosphere over the Southern region using satellite data from Terra/Aqua (MODIS) and CALIPSO (CALIOP sensor) in the period from 2007 to 2010. With the measurements of aerosol optical depth, the atmosphere in the region will be classified into different groups. We also intend to analyze the vertical profile of aerosols and transport patterns of particulate matter from sources close to the study area, the latter with FNL data from NCEP with 1.0 ° of space resolution and time resolution of 6h. Through the preliminary results it is clear that the optical depth of aerosols in the years 2009 and 2010 reached a maximum during the winter period, probably due to fires that occur in a large part of South America http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400009&lng=en&nrm=iso&tlng=en Ourinhos is situated in one of the major sugar cane producing regions in the State of São Paulo, where the manual harvesting is generally preceded by burning the foliage, resulting in large quantities of aerosols being emitted into the atmosphere. A one- month pilot study was executed during August 2010, to characterize the effects of those emissions on the atmosphere, considering the local circulation and the consequences for the region. The plumes were tracked by IPMet´s two S-band Doppler radars, also deploying a large range of meteorological, physical and chemistry instrumentation: a mobile Lidar with Raman channel to observe elevated layers and the type of aerosols, a medium-sized Sodar, as well as 6 Automatic Weather Stations spread through town. Various gases and particulates were also sampled, providing the atmospheric chemistry data base and thus documenting the impact on the region. This paper highlights a case study on 26 August, when a plume was tracked by TITAN Radar Software from the start of the fire, moving southwards at 14-17 km.h-1 with the winds at about 3,5 km above ground level, until it reached Ourinhos 2h15min later, where it was observed by the Raman Lidar and also detected by the aerosol and gas samplers. The high aerosol load of the atmosphere was confirmed by hourly mean values of AOD varying between 0,265 and 0,288 until 07:00 LT, after which they increased to 0,433 by 09:00 LT, as well as hourly mean backscatter profiles. Hourly values of the Lidar Ratio identified the aerosols as biomass burning products, also confirmed through the analysis of gas and aerosol samples simultaneously collected at the Lidar site. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400010&lng=en&nrm=iso&tlng=en The SKIRON model AOD forecasts for Saharan dust clouds arriving to Camagüey, Cuba, during July 2009 were evaluated. For such a goal AOD measurements from a surface sunphotometer were used. Additional information from MODIS was also available for the comparison. The results demonstrate the capabilities for developing an alert and tracking system for Saharan dust events across the Atlantic. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400011&lng=en&nrm=iso&tlng=en At CEILAP (CITEDEF-CONICET), a multiangle Raman lidar is under development to monitor aerosol extinction in the frame of the CTA (Cherenkov Telescope Array) Project. This is an initiative to build the next generation of ground-based instruments to collect very high energy gamma-ray radiation. It will serve as an open observatory for a wide astrophysics community and will explore the Universe in depth in Very High Energy (> 10 GeV) gamma-rays. The atmospheric conditions are is a major interest for CTA, and this instrument plays a major role measuring the atmospheric optical depth. The reception system is made by six 40 cm in diameter Newtonian telescopes, totally exposed to the hard environmental condition during the shifts. These working conditions could produce misalignments between laser and telescopes, losing the required overlap. To avoid that, a telescope controlled by a self-alignment system is under development to solve this problem. This is performed by PC software running from the acquisition module which is connected via ethernet to a microcontroller. This paper, describes the self-alignment method and hardware work in progress. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400012&lng=en&nrm=iso&tlng=en The determination of temperature measurements from the Rayleigh scattering is an important remote sensing technique for obtaining stratospheric profiles. This technique is applied to signals acquired by a Rayleigh lidar (Light Detection and Ranging). Currently the Observatorio Atmosférico de la Patagonia Austral (51° 55’S, 69° 14’W) in Río Gallegos, Argentina is part of the UVO3Patagonia project in collaboration with the laboratory of Ozone and UV Radiation in the city of Punta Arenas, Chile distant 200 km, for more information www.uvo3patagonia.com. In this paper we showed the technique to measure temperature profiles in the stratosphere between 15-60 km altitude. We compared the temperature profiles obtained of the second ozone sounding campaign called OZITOS (OZone profile aT RíO GallegOS) carried out in March 2011 in Río Gallegos with the temperature profile retrieved by the Rayleigh lidar using the line of 355 nm, in the same period. The results presented in this paper are validated through intercomparisons with measurements made by MLS instrument (Microwave Limb Sounder) onboard the NASA AURA satellite platform and NCEP data. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400013&lng=en&nrm=iso&tlng=en The present paper reports on the development of a simulation and modeling tool which allows to estimate the propagation effects on a laser beam passing through a laser-diode-pumped Nd:YAG slab amplifier. This in-house research work is motivated by current ESA spaceborne LIDAR programs (ADM, Earth Care) as a mean to provide understanding of the LIDAR beam pointing stability as results of thermal and mechanical stresses. A dynamic model has been generated that can simulate the optical characteristics of the laser beam propagation, as a result of the various thermal and mechanical processes occurring inside the laser Pumping Unit and the thermal lensing occurring along the crystal slab. The simulation results and their comparison with actual laboratory tests are being presented and discussed. The model developed is based on the Finite Element Model (FEM) methodology, where the slab as an active element is "broken" down into interdependent segments, each simulated as being heated by an individual LD source. The light beam is propagated along the slab using dynamically varying boundary conditions, to the next so to account for the cumulated thermal and mechanical loads. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400014&lng=en&nrm=iso&tlng=en LIDARS involved in space applications are mainly used as atmospheric monitoring sensors or as altimeters (i.e. ALADIN, ATLID, LOLA, MOLA or BELA). In future exploration missions, like the Mars Sample Return mission, LIDARs shall be implemented as imaging and ranging devices for different applications: in the support of the autonomous landing of a spacecraft on a planetary surface; during the deployment of rovers provided with autonomous navigation and hazard avoidance capabilities; and for the support of rendezvous and docking operations between spacecrafts in orbit. The ability to rapidly derive 3-D topographic information is vital for the realization of these missions. We present a recently developed Imaging LIDAR (IL) performance model, which was created in order to simulate and optimize Imaging LIDAR instruments, under various scenarios and applications. The IL performance model is based primarily on the LIDAR equation and takes into account all basic parameters of a LIDAR device, which apparently affect the overall instrument performance, such as the laser power, telescope aperture, detection method, background illumination, range gating etc. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400015&lng=en&nrm=iso&tlng=en The importance of particulate matter transport over the Andean glaciers has recently grown because new studies have suggested that at least part of the local warming at the Himalayas might be due to transport of particles to this region. In the Andean region the rapid retreat of glaciers and a moderate increase in temperature suggest that particulate matter product of biomass burning could also be playing a role in the observed glacier recession. Satellite imagery from MODIS, measurements from photometers as well as in-situ measurements were used to try to characterize some optical and chemical properties of particulate matter arriving to the Andean region. Backward trajectories and electronic microscopy were also used for this purpose. Preliminary results are reported here. In addition, the implementation of a new GAW station at Chacaltaya (5200 masl; 16°21’S, 68°07’W) is discussed in this context. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400016&lng=en&nrm=iso&tlng=en Stratospheric ozone (O3) plays a critical role in the atmosphere by absorbing most of the biologically damaging solar UV radiation before it reaches the Earth’s surface. Nitrogen dioxide (NO2) is a key trace gas in the ozone photochemical. The systematic sensing of NO2 and other minority gases is essential in order to understand the stratospheric O3 destruction and formation processes. We present the study carried out on the seasonal variation of the O3 and NO2 vertical column density (VCD), using a zenith-sky DOAS (Differential Optical Absorption Spectroscopy). This system is composed of a spectral analyzer (portable spectrometer HR4000, Ocean Optics), two optical fibers (400 µm of core, 25 cm and 6 m of longitude) and an automatic mechanical shutter. NO2 and O3 VCD are derived from solar spectra acquired during twilights (87° - 91° zenithal angles). The data retrieved by our instrument are compared with those coming from the SAOZ spectrometer (Systeme d'Analyse par Observation Zenithale, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), France). Both systems are located in Rio Gallegos, Santa Cruz province, Argentine (51° 36’ S; 69° 19’ W, 15 m asl), in the CEILAP-RG remote sensing station. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400017&lng=en&nrm=iso&tlng=en An important contemporary problem is the identification of aerosols from space. Ground based lidar systems can use correlative measurements to determine aerosol types but spaceborne lidar systems (such as CALIPSO) rely on models for this identification. Most spaceborne systems (including CALIPSO, MODIS, and OMI) use models based on observations by AERONET, a world- wide network of ground based sun photometers. The aerosol parameters determined by AERONET include the real and imaginary refractive indices, the single scattering albedo and the extinction and absorption Angstrom coefficients. We compare the predictions of the satellite models with AERONET measurements by evaluating the Mahalonibis distances from the model prediction to clusters of aerosols of specific types (such as Urban-Industrial, Biomass Burning, and Dust). We show that some regions do not fit any of the traditional categories; consequently, aerosol identification is problematic. We discuss some of the difficulties associated with aerosol identification from space, specifically considering the CALIPSO system http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400018&lng=en&nrm=iso&tlng=en Aerosol Optical Depth (AOD) measurements, carried out with a sun photometer CIMEL CE-318, installed in Camagüey, Cuba, are reported. More than 700 days of measurements are analyzed, of them 400 days corresponds to level 2.0 of Aerosol Robotic Network (AERONET) dataset. These data cover from October 7, 2008 to April 22, 2010. To the level 1.5 corresponds more than 300 days from June 3, 2010 to June 17, 2011. The average value of AOD for the first period (level 2.0) is ta(500 nm) = 0.14, while for the second ta(500 nm) = 0.17, both cases with relatively high values. These AOD values confirm preliminary results about the Maritime Mixed characteristic for the Camagüey site. Several Saharan dust events are reported during the analyzed period. http://www.scielo.org.bo/scielo.php?script=sci_arttext&pid=S1562-38232012000400019&lng=en&nrm=iso&tlng=en As part of the R&D effort conducted within the Laser Laboratory of the European Space Agency, various simulation tools are being developed to understand and correct the thermal effects of side pumping an Nd:YAG slab with multiple individual High Power Laser Diodes. The scope of the present activity, which complements the work reported elsewhere at this workshop, is to emulate the thermal effects of a real amplifier and study the effects of various combinations of laser diode stacks with different characteristics, such as operational wavelength, temperature of operation, transmitted energy and pumping efficiency on the dynamic temperature distribution inside the slab. The motivation of this analysis is to work towards a simplification of the phenomena of heat generation and convection inside the crystal which account for the thermal lensing effect. Transient analysis is performed at different pump intensities under variable boundary conditions and the results are compared with experimental data as well as other software such as Zemax and LASCAD. Also the effects of laser diode stack failures are investigated and reported. The algorithm developed is based on the finite element method using tetrahedral elements for the adjustable meshing.