Underwater light characterisation for correction of remotely sensed images

Evanthia Karpouzli, Tim Malthus, Chris Place, Anthony Mitchell Chui, Martha Ines Garcia, James McD Mair

    Research output: Contribution to journalArticle

    Abstract

    Objective measurement of habitat change using remote sensing requires processing of the images to enhance the bottom reflectance signal. This process typically uses correction techniques to remove the influence of the water column on bottom reflectance, and to enable the accurate correction of the imagery for varying bathymetry. Such correction measures depend on reliable estimates of water column light attenuation. An investigation into the spatial variation in attenuation in a typical tropical region was undertaken. Measurements of gross spatial variations in downwelling attenuation around San Andres and Old Providence islands in the western Caribbean were made using a PAR sensor. Measurements of specific attenuation were also made for blue, green and red light using filters fitted to the sensor. High spectral resolution attenuation measurements were also made using a spectroradiometer. Results showed a four-fold variation in light attenuation in shallow littoral regions alone. Spectral attenuation measurements suggested that this variation was largely the result of scattering by particulate matter rather than varying concentrations of dissolved yellow substances. These findings suggest that the results of studies where single measurements of 'average' attenuation have been used to depth-correct remotely sensed imagery should be interpreted with a high degree of caution. The paper goes on to show that simple models can be empirically obtained where attenuation can be spatially predicted with confidence, based on the variables of water depth, distance to and size of mangrove beds, and distance to and size of towns. The models obtained showed high statistical significance, with 89% and 78% of the spatial variation in attenuation explained for San Andres and Old Providence, respectively. It is postulated that the use of such approaches for the estimation of attenuation will lead to more accurate depth correction and hence improved interpretation of remotely sensed imagery for littoral regions.

    Original languageEnglish
    Pages (from-to)2683-2702
    Number of pages20
    JournalInternational Journal of Remote Sensing
    Volume24
    Issue number13
    DOIs
    Publication statusPublished - 10 Jul 2003

    Fingerprint

    light attenuation
    imagery
    spatial variation
    reflectance
    water column
    sensor
    downwelling
    tropical region
    photosynthetically active radiation
    spectral resolution
    bathymetry
    mangrove
    particulate matter
    water depth
    scattering
    fold
    filter
    remote sensing
    habitat
    littoral

    Cite this

    Karpouzli, E., Malthus, T., Place, C., Chui, A. M., Garcia, M. I., & Mair, J. M. (2003). Underwater light characterisation for correction of remotely sensed images. International Journal of Remote Sensing, 24(13), 2683-2702. https://doi.org/10.1080/0143116031000066972
    Karpouzli, Evanthia ; Malthus, Tim ; Place, Chris ; Chui, Anthony Mitchell ; Garcia, Martha Ines ; Mair, James McD. / Underwater light characterisation for correction of remotely sensed images. In: International Journal of Remote Sensing. 2003 ; Vol. 24, No. 13. pp. 2683-2702.
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    Karpouzli, E, Malthus, T, Place, C, Chui, AM, Garcia, MI & Mair, JM 2003, 'Underwater light characterisation for correction of remotely sensed images', International Journal of Remote Sensing, vol. 24, no. 13, pp. 2683-2702. https://doi.org/10.1080/0143116031000066972

    Underwater light characterisation for correction of remotely sensed images. / Karpouzli, Evanthia; Malthus, Tim; Place, Chris; Chui, Anthony Mitchell; Garcia, Martha Ines; Mair, James McD.

    In: International Journal of Remote Sensing, Vol. 24, No. 13, 10.07.2003, p. 2683-2702.

    Research output: Contribution to journalArticle

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    AU - Malthus, Tim

    AU - Place, Chris

    AU - Chui, Anthony Mitchell

    AU - Garcia, Martha Ines

    AU - Mair, James McD

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    AB - Objective measurement of habitat change using remote sensing requires processing of the images to enhance the bottom reflectance signal. This process typically uses correction techniques to remove the influence of the water column on bottom reflectance, and to enable the accurate correction of the imagery for varying bathymetry. Such correction measures depend on reliable estimates of water column light attenuation. An investigation into the spatial variation in attenuation in a typical tropical region was undertaken. Measurements of gross spatial variations in downwelling attenuation around San Andres and Old Providence islands in the western Caribbean were made using a PAR sensor. Measurements of specific attenuation were also made for blue, green and red light using filters fitted to the sensor. High spectral resolution attenuation measurements were also made using a spectroradiometer. Results showed a four-fold variation in light attenuation in shallow littoral regions alone. Spectral attenuation measurements suggested that this variation was largely the result of scattering by particulate matter rather than varying concentrations of dissolved yellow substances. These findings suggest that the results of studies where single measurements of 'average' attenuation have been used to depth-correct remotely sensed imagery should be interpreted with a high degree of caution. The paper goes on to show that simple models can be empirically obtained where attenuation can be spatially predicted with confidence, based on the variables of water depth, distance to and size of mangrove beds, and distance to and size of towns. The models obtained showed high statistical significance, with 89% and 78% of the spatial variation in attenuation explained for San Andres and Old Providence, respectively. It is postulated that the use of such approaches for the estimation of attenuation will lead to more accurate depth correction and hence improved interpretation of remotely sensed imagery for littoral regions.

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