Browsing by Author "Vidal Safor, Erick"
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Item Restricted 3D Imaging of the OH mesospheric emissive layer(Elsevier, 2010-01-15) Kouahla, M. N.; Moreels, G.; Faivre, M.; Clairemidi, J.; Meriwether, J. W.; Lehmacher, G. A.; Vidal Safor, Erick; Veliz, OscarA new and original stereo imaging method is introduced to measure the altitude of the OH nightglow layer and provide a 3D perspective map of the altitude of the layer centroid. Near-IR photographs of the OH layer are taken at two sites separated by a 645 km distance. Each photograph is processed in order to provide a satellite view of the layer. When superposed, the two views present a common diamond-shaped area. Pairs of matched points that correspond to a physical emissive point in the common area are identified in calculating a normalized cross-correlation coefficient (NCC). This method is suitable for obtaining 3D representations in the case of low-contrast objects. An observational campaign was conducted in July 2006 in Peru. The images were taken simultaneously at Cerro Cosmos (12 09 08.2 S, 75 33 49.3 W, altitude 4630 m) close to Huancayo and Cerro Verde Tellolo (16 33 17.6 S, 71 39 59.4 W, altitude 2272 m) close to Arequipa. 3D maps of the layer surface were retrieved and compared with pseudo-relief intensity maps of the same region. The mean altitude of the emission barycenter is located at 86.3 km on July 26. Comparable relief wavy features appear in the 3D and intensity maps. It is shown that the vertical amplitude of the wave system varies as exp (z/2H) within the altitude range z = 83.5–88.0 km, H being the scale height. The oscillatory kinetic energy at the altitude of the OH layer is comprised between 3 × 10−4 and 5.4 × 10−4 J/m3, which is 2–3 times smaller than the values derived from partial radio wave at 52N latitude.Item Open Access Control de sensibilidad de los magnetovariografos mediante observaciones absolutas(Instituto Geofísico del Perú, 2010) Rosales Corilloclla, Domingo; Vidal Safor, Erick; Orihuela Lazo, SilvanoUno de los aspectos más importante en un Observatorio Geomagnético es el control de la calidad de los datos que se registran, para ello a los instrumentos geomagnéticos se les aplica diversas técnicas de control para evaluar su performance. En este caso realizamos un control de calidad a los magnetovariografos como son: Sensibilidad, linealidad y estabilidad. Se aplica una técnica que permite determinar el estado operativo de los magnetovariografos sin la necesidad de tener que parar el registro de datos, evitando de esta manera la pérdida de datos no registrados y tener que manipular los magnetovariografos físicamente para conocer su estado de operatividad.Item Open Access Implementación de registrador digital para variometros tradicionales del tipo Eschenhagen(Instituto Geofísico del Perú, 2010-12) Vidal Safor, Erick; Rosales Corilloclla, DomingoEl área de Geomagnetismo del Observatorio de Huancayo cuenta con variometros tradicionales mecánicos como sensor a imanes suspendidos y equilibrados los cuales perciben los cambios que ocurren en las distintas componentes del campo magnético que por ellos traviesan. Este tipo de magnetómetros utilizan un modo de registro por rebote de luz el cuál es registrado en un papel fotográfico. Los magnetómetros del tipo tradicional han demostrado ser buenos equipos de medición mostrando gran estabilidad en el tiempo, pero su diseño original demanda el uso de papel fotográfico. Hoy en día es escasa la producción de papel fotográfico por lo que la adquisición de este insumo se hace muy costosa. En la actualidad la tecnología ha desarrollado equipos que realizan el mismo trabajo pero de mayor resolución, velocidad de registro entre otros como los magnetómetros tipo FluxGate o de bombeo óptico, llevándolos al desuso a los magnetómetros mecánicos tradicionales del tipo Eschenhagen. De la misma manera que la tecnología ha contribuido con el desarrollo de nuevos equipos de registro, ésta también ha desarrollado los elementos necesarios que en su conjunto son capaces de reproducir el comportamiento del papel fotográfico haciendo posible la continuidad del registro de los magnetómetros tradicionales mediante medios óptico/electrónicos el cuál brinda la oportunidad a que equipos históricos continúen su funcionamiento registrando la variación del campo magnético terrestre y los datos puedan ser observa dos en tiempo real."Item Open Access Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile’s Calbuco volcano(SpringerOpen, 2016-08-31) Aoyama, Tadashi; Iyemori, Toshihiko; Nakanishi, Kunihito; Nishioka, Michi; Rosales Corilloclla, Domingo; Veliz, Oscar; Vidal Safor, ErickThe Calbuco volcano in southern Chile erupted on April 22, 2015. About 2 h after the first eruption, a Swarm satellite passed above the volcano and observed enhancement of small-amplitude (~0.5 nT) magnetic fluctuations with wave-packet structure which extends 15° in latitude. Similar wave packet is seen at the geomagnetic conjugate point of the volcano. Just after the eruption, geomagnetic fluctuations with the spectral peaks around the vertical acoustic resonance periods, 215 and 260 s, were also observed at Huancayo Geomagnetic Observatory located on the magnetic equator. Besides these observations, around 4-min, i.e., 175, 205 and 260 s, oscillations of total electron content (TEC) were observed at global positioning system stations near the volcano. The horizontal propagation velocity and the spatial scale of the TEC oscillation are estimated to be 720 m/s and 1600 km, respectively. These observations strongly suggest that the atmospheric waves induced by explosive volcanic eruption generate TEC variation and electric currents. The Swarm observation may be explained as a manifestation of their magnetic effects observed in the topside ionosphere.Item Restricted Near-infrared sky background fluctuations at mid- and low latitudes(Springer, 2008-10) Moreels, G.; Clairemidi, J.; Faivre, M.; Pautet, D.; Rubio Da Costa, F.; Rousselot, P.; Meriwether, J. W.; Lehmacher, G. A.; Vidal Safor, Erick; Chau Chong Shing, Jorge Luis; Monnet, G.The emission of the upper atmosphere introduces an additional variable component into observations of astronomical objects in the NIR 700–3,000 nm range. The subtraction of this component is not easy because it varies during the night by as much as 100% and it is not homogeneous over the sky. A program aimed at measuring and understanding the main characteristics of the atmospheric NIR emission was undertaken. A 512 × 512 CCD camera equipped with a RG780/2 mm filter is used to obtain images of the sky in a 36° × 36° field of view. The intensities of a given star and of the nearby region devoid of star in a 439 arcmin2 area are monitored during periods of time of several hours. The sky intensity measured in the 754–900 nm bandpass, reduced to zenith and zero airmass is comprised between mag20 and mag18.5 per arcsecond2. A diminution by a factor of two during the night is frequently observed. Intensity fluctuations having an amplitude of 15% and periods of 5–40 min are present in the images with a structure of regularly spaced stripes. The fluctuations of the NIR sky background intensity are due to (1) the chemical evolution of the upper atmosphere composition during the night and (2) dynamical processes such as tides with periods of 3–6 h or gravity waves with periods of several tens of minutes. We suggest that a monitoring of the sky background intensity could be set up when quantitative observations of astronomical objects require exposure times longer than ~10 min. The publication is illustrated with several video films accessible on the web site http://www.obs-besancon.fr/nirsky/. Enter username: nirsky and password: skynir.Item Restricted Stereoscopic imaging of the hydroxyl emissive layer at low latitudes(Elsevier, 2008-05-04) Moreels, G.; Clairemidi, J.; Faivre, M.; Mougin-Sisini, D.; Kouahla, M. N.; Meriwether, J. W.; Lehmacher, G. A.; Vidal Safor, Erick; Veliz, OscarThe hydroxyl nightglow layer is an excellent tracer of the dynamical processes occurring within the mesosphere. A new stereo-imaging method is applied that not only measures the altitude of the airglow layer but also provides a three-dimensional map of the OH-layer centroid heights. A campaign was conducted in July 2006 in Peru to obtain NIR images of the OH nightglow layer which were simultaneously taken for two sites separated by 645 km: Cerro Cosmos (12°09′08.2″S, 75°33′49.3″W, altitude 4630 m) and Cerro Verde Tellolo (16°33′17.6″S, 71°39′59.4″W, altitude 2330 m). Data represented by pairs of images obtained during the nights of July 26–27 and 28–29 are analyzed to yield satellite-type views of the wave field. These are obtained by application of an inversion algorithm. In calculating the normalized cross-correlation parameter for the intensity, three-dimensional maps of the OH nightglow layer surface are retrieved. The mean altitude of the emission profile barycenter is found to be at 87.1 km on July 26 and 89.5 km on July 28. In these two cases the horizontal wavelengths determined are 21.1 and 24.6 km with periods of 18 and 34 min, respectively. A panoramic view of the OH nightglow emission obtained on July 29 at 8 h51–9 h26 UT is presented, in which the overall direction of the waves is found to be N–NW to S–SE, azimuth 150°–330° (counted from South). The wave kinetic energy density at the OH nightglow layer altitude is 3.9×10−4 W/kg, which is comparable to the values derived from partial reflection radiowave data.