University of Twente Student Theses
Uncertainty in reflectance factors measured in the field: Implications for the use of ground targets in remote sensing
Odongo, Vincent Omondi (2010) Uncertainty in reflectance factors measured in the field: Implications for the use of ground targets in remote sensing.
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| Abstract: | Ground calibration targets (GCTs) play a significant role in vicarious calibration (VC) and atmospheric correction (AC). However, assumptions are always made that these targets are dynamically stable and have flat spectra at the time of measurements in the field. Consequently, sources of uncertainty introduced in the data acquisition and methods used are in turn transferred on board the earth observation sensors. Errors from VC and AC campaigns can seriously impact upon the uncertainty associated with products derived from the sensors, compromising the evidence base for decision making. This study developed and tested a framework to characterize the reflectance factor of GCTs to establish best practice guidelines for VC and AC. This entailed evaluating sources of uncertainty arising from method of measurement, changes in archetype GCTs of 100cm x 50cm, effect of sky conditions to dynamic changes on a proposed real test site at a spatial domain. The uncertainty of the method was reported to less than 0.27% across all bands (430nm~949nm) of the spectro-radiometer used. The technique provided a means of disassociating uncertainty due to the instrument and its method of use from that due to changes in the target surface and the environment. Effect of sky conditions on HCRF measurements revealed that sky conditions affected hemispherical conical reflectance (HCRF) measurements variably depending on surface archetype and that solar zenith angle (SZA) and solar azimuth angle (SAA) were significant for smooth and rough surfaces even over the ±2 hour measurements around solar noon. It was also realized that both smooth and rough archetype surfaces were highly anisotropic under clear sky during the period of normal measurements.This emphasized the need to measure field spectra synchronously with sensor overpass and minimizing the measurements to within a time when SZA and SAA changes are not significant. Local variation in HCRF was evaluated for a proposed VC site in Tuz Gölü, Turkey at a spatial domain using multi-temporal imagery. It was found that variation in HCRF was dependent on spatial uniformity and temporal stability of the surface. Retrieved HCRF from this surface showed uncertainty in the range of 0.01% to 4.05% for Landsat TM bands 1, 2, 3 and 4. These results were in agreement within the range of reported uncertainties of other calibration test sites in the world. This study provides knowledge on the characterization of HCRF in the field and has wider implication on the use GCTs for VC and AC. Keywords: Uncertainty, Hemispherical Conical Reflectance Factor (HCRF), 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) |
| Link to this item: | https://purl.utwente.nl/essays/92485 |
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