The SuperCOSMOS Sky Survey - II. Image detection, parameterization, 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 similar to1.5 mag of the nominal plate limits. We show that for the B-J survey data, the image classification is externally >99 per cent reliable to B(J)similar to 19.5. Internally, the image classification is reliable at a level of >90 per cent to B(J)similar to 21, R similar to 19. The photometric accuracy of our data is typically similar to0.3 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 similar to5 per cent for wen-exposed stellar images. Colours are externally accurate to sigma (B-R,R-I) similar to 0.07 at B(J)similar to 16.5, rising to sigma (B-RR-I) similar to 0.16 at B(J)similar to 20.