Case Study: IKONOS Multispectral Imagery

IKONOS was launched in September of 1999 in a 680 km high sun-synchronous orbit with a descending node crossing at approximately 10h15 local solar time. The IKONOS satellite simultaneously collects imagery in four multispectral bands and a single panchromatic band with 11-bit radiometric resolution. Data used in this project were collected by the IKONOS sensor on September 23, 2006. Rational polynomial coefficients (RPCs) were included to aid in the geo-rectification of the imagery. Orthorectification was undertaken using ENVI 4.3. RPCs were used in conjunction with a digital elevation model provided by industry partners. The recti­fication of the data was undertaken using 20 ground control points collected using a Leica GS 20 DGPS; the resulting root mean square error was less than half a pixel (<2 m). IKONOS radiometric correction began with converting the 11 bit digital numbers to top-of-atmosphere (TOA) radiance (Pagnutti et al. 2003). Following this the data were radiometrically corrected and converted to unitless reflectance using the Fast Line-of-Sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) correction model (Alder-Golden et al. 1999; Matthew et al. 2000). Conversion to reflectance generally results in temporally independent imagery, since the majority of atmospheric influences are corrected for. This theoretically enables extrapolation of results to other seasons and years, as opposed to the temporally restricted use of radiance imagery.