University of Twente Student Theses


Assessing spatial variation and reflectance of ground calibration targets

Botchway, Kwame (2011) Assessing spatial variation and reflectance of ground calibration targets.

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Abstract:Ground calibration targets (GCTs) are useful in characterizing the radiometric quality of satellite sensors via vicarious calibration (VC) campaigns. However, these targets are always assumed to be spatially homogeneous. A well-characterized GCT with regards to its spatial homogeneity and temporal stability properties is crucial to the quantification of errors/uncertainties associated with satellite sensors postlaunch. Radiometric calibration errors are transferrable throughout the lifespan of a sensor and can generate uncertainties in the sensor’s derived products, compromising the evidence base for decision making. This study sought to identify and investigate “spatial homogeneity” property of GCTs for a thorough understanding of their spatial structure. The study further aims at characterising the influence of scale (pixel size and window size) measurements on spatial homogeneity property of GCTs assessment. This study developed and tested a framework to characterize homogeneity property of GCTs based on Spatial Homogeneity Criteria (SHC) which combines Gi* > 0 and CV< 3% within a localised 3×3 window and variogram/correlogram to characterize the spatial structure of Tuz Gölü test site. These were geared towards establishing best practice guidelines for VC campaigns. Local variation in HDRF across the VNIR and SWIR bands were evaluated for a proposed VC site in Tuz Gölü, Turkey from fine to coarse resolutions using Landsat TM, MODIS multi-temporal imagery and one ASTER image. An area that was spatially homogeneous, temporally stable and exhibited normal distribution in the Landsat TM VNIR spectra (approximately 1400 m × 800 m) was identified as a proposed VC site in Tuz Gölü, Turkey. Identification of such an area across the Landsat TM SWIR bands was not possible due to high variation in the observed CV computation attributable to the geomorphologic properties of the site. It was found that the SHC identified areas within a localised 3×3 window tends to decrease from fine to coarse resolution across the VNIR and SWIR bands, possibly due to the observed increment in CV computation from fine to coarse resolution. This study provides knowledge on the characterization of the spatial variation and reflectance (HDRF) of GCTs respecting their spatial homogeneity property and has implication on the use GCTs for VC and more widely, for their use in atmospheric correction (Bannari et al., 2005; Kneubühler et al., 2006). Keywords: Uncertainty, Hemispherical Directional Reflectance Factor (HDRF), Ground Calibration Targets (GCTs).
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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