The SuperCOSMOS Sky Survey – II. Image detection, parametrization, classification and photometry

In this, the second in a series of three papers concerning the SuperCOSMOS Sky Survey, we describe the methods for image detection, parametrization, classification and photometry. We demonstrate the internal and external accuracy of our object parameters. Using examples from the first release of data, the South Galactic Cap survey, we show that our image detection completeness is close to 100 per cent to within ∼1.5 mag of the nominal plate limits. We show that for the BJ survey data, the image classification is externally > 99 per cent reliable to BJ∼19.5. Internally, the image classification is reliable at a level of > 90 per cent to BJ∼21, R∼19. The photometric accuracy of our data is typically ∼0.3 mag with respect to external data for m>15. Internally, the relative photometric accuracy in restricted position and magnitude ranges can be as accurate as ∼5 per cent for well-exposed stellar images. Colours are externally accurate to σB−R,R−I∼0.07 at BJ∼16.5, rising to σB−R,R−I∼0.16 at BJ∼20.