Browsing by Author "Kouahla, M. N."

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    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, Oscar
    A 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.
    Palabras clave:Gravity wavesStereoscopy3D Imaging
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    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, Oscar
    The 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.
    Palabras clave:Airglow layerGravity wavesStereoscopy