The HI Parkes All Sky Survey: southern observations, calibration and robust imaging

The acquisition of HI Parkes All Shy Survey (HIPASS) southern sky data comm enced at the Australia Telescope National Facility's Parkes 64-m telescope in 1997 February, and was completed in 2000 March. HIPASS is the deepest HI survey yet of the sky south of declination +2 degrees, and is sensitive to emission out to 170 h(75)(-1) Mpc. The characteristic root mean square noi se in the survey images is 13.3 mJy. This paper describes the survey observ ations, which comprise 23 020 eight-degree scans of 9-min duration, and det ails the techniques used to calibrate and image the data. The processing al gorithms are successfully designed to be statistically robust to the presen ce of interference signals, and are particular to imaging point (or nearly point) sources. Specifically, a major improvement in image quality is obtai ned by designing a median-gridding algorithm which uses the median estimato r in place of the mean estimator.