• DocumentCode
    69239
  • Title

    Synthetic Aperture Radar (SAR) Doppler Anomaly Detected During the 2010 Merapi (Java, Indonesia) Eruption

  • Author

    de Michele, Marcello ; Raucoules, Daniel ; Wegmuller, Urs ; Bignami, Christian

  • Author_Institution
    Bur. de Rech. Geologiques et Minieres, Orleans, France
  • Volume
    10
  • Issue
    6
  • fYear
    2013
  • fDate
    Nov. 2013
  • Firstpage
    1319
  • Lastpage
    1323
  • Abstract
    In this letter, we report the presence of a localized Doppler anomaly occurring during the focusing of a Radarsat-2 data set acquired on the Merapi volcano (Indonesia) during the devastating 2010 eruption. The Doppler anomaly is manifested as ~ 3-km-wide bull´s-eye-shaped azimuth pixel shifts between two subaperture images. The Doppler anomaly is centered on the summit-south flank of the Merapi volcano. The pixel shifts reach up to 11.6 m. Since the Merapi volcano was undergoing a large eruption during the data acquisition, it is possible that there is a volcano-related phenomenon that has delayed the radar signal so much to create measurable pixel offsets within a single synthetic aperture radar (SAR) data set, similar, but more extensive, to the signal generated by targets motions; similar, but less extensive, to the signal generated by ionospheric perturbations. It is known that the SAR signal is delayed as it passes through heterogeneous layers of the atmosphere, but this delay typically affects the SAR signal to a fraction of the phase cycle or few centimeters depending on the radar wavelength employed by the system. We investigate the source of this anomalous metric signal; we review the theoretical basis of SAR image focusing, and we try to provide a consistent physical framework to our observations. Our results are compatible with the SAR signal being perturbed during the actual process of image focusing by the presence of a contrasting medium located approximately between 6- and 12.5-km altitude, which we propose being associated with the presence of volcanic ash plume.
  • Keywords
    ash; data acquisition; geophysical image processing; ionospheric disturbances; radar signal processing; remote sensing by radar; signal detection; synthetic aperture radar; volcanology; AD 2010; Indonesia; Merapi eruption; Merapi volcano; Radarsat-2 data set; SAR image focusing; SAR signal; anomalous metric signal; atmosphere heterogeneous layers; bull-eye-shaped azimuth pixel shifts; data acquisition; ionospheric perturbations; localized Doppler anomaly; phase cycle; physical framework; pixel offsets; radar signal; radar wavelength; subaperture images; summit-south flank; synthetic aperture radar Doppler anomaly; synthetic aperture radar data set; targets motions; volcanic ash plume; volcano-related phenomenon; Azimuth; Delay; Doppler effect; Doppler radar; Synthetic aperture radar; Volcanoes; Doppler measurements; synthetic aperture radar (SAR); volcanic activity;
  • fLanguage
    English
  • Journal_Title
    Geoscience and Remote Sensing Letters, IEEE
  • Publisher
    ieee
  • ISSN
    1545-598X
  • Type

    jour

  • DOI
    10.1109/LGRS.2013.2239602
  • Filename
    6470635