Measurement of multispectral BRF effects of the megacity Cairo, Egypt, using CHRIS/PROBA data

In this analysis, a series of images from the ESA imaging spectrometer CHRIS on the technology demonstration satellite PROBA, taken in a row over Cairo on 17th  February 2007 and 24th  March 2008 at each five different viewing zenith and azimuth angles are analyzed to find the BRF (bidirectional reflection function) which is typical for urban areas in a developing Arab  country.  The  results  are  only  valid  for  these  sun-sensor  constellations,  since  only  two scenes were analyzed. CHRIS/PROBA features 18 bands in the shortwave range. All bands were first destriped and then corrected for atmospheric influences using the radiative transfer model MODTRAN. Furthermore the images were geo-referenced using manually set pass points. The accuracy of the geolocation varies across the image. Generally pixels match well; however, in some areas there is a shift of one or two pixels. There is a clear dependency in the reflectances on  the  viewing  geometry  of  the  sensor.  The  regression  coefficients  r2   from  the  regression between the reflectance and the viewing geometry are high for all bands in all urban areas. No distinct difference was found for high or medium dense housing.