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ON-ORBIT SPATIAL RESOLUTION ESTIMATION OF CBERS-1 CCD IMAGING SYSTEM FROM BRIDGE IMAGES

The first China-Brazil Earth Resources Satellite (CBERS) was launched in 1999 and recently was substituted by CBERS-2. CBERS1 and CBERS-2 have the same specifications and carry three sensors which combine features that are specially designed to cover the broad range of space and time scales involved in the monitoring and preservation of the ecosystem: Wide Field Imager (WFI), High Resolution CCD Camera (CCD) and Infrared Multispectral Scanner (IRMSS). In general, the imaging systems cause a blurring due to the cumulative effects of the instrumental optics (diffraction, aberrations, focusing error) and image motion induced by the movement of the satellite during imaging. This blurring can be understood by describing the imaging system in terms of the Point Spread Function (PSF). For a satellite sensor, the knowledge of the point spread function is of fundamental importance since it enables an objective assessment of spatial resolution through the parameter known as EIFOV (Effective Instantaneous Field of View). This paper describes an original approach to estimate the spatial resolution of the CBERS-1 CCD camera. The imaging system point spread function is modeled as a separable gaussian function. The PSF is estimated using images of Rio-Niteroi Bridge in Rio de Janeiro (Brazil) and the Lake Pontchartrain Causeway in Louisiana (United States). The results showed that the spatial resolution in across-track direction is outside the specifications for all bands while the spatial resolution in along-track direction is within the specification for all bands, except the band 4.