  Details are presented of the HI Jodrell All Sky Survey (HIJASS). HIJASS is a
blind neutral hydrogen (HI) survey of the northern sky, being conducted using
the multibeam receiver on the Lovell Telescope at Jodrell Bank. HIJASS covers
the velocity range -3500 km/s to 10000 km/s with a velocity resolution of 18.1
km/s and a spatial positional accuracy of ~2.5 arcmin. Thus far about 1115 sq
deg have been surveyed. We describe the methods of detecting galaxies within
the HIJASS data and of measuring their HI parameters. The properties of the
resulting HI-selected sample of galaxies are described. Of the 222 sources so
far confirmed, 170 (77 per cent) are clearly associated with a previously
catalogued galaxy. A further 23 sources (10 percent) lie close (within 6
arcmin) to a previously catalogued galaxy for which no previous redshift
exists. A further 29 sources (13 per cent) do not appear to be associated with
any previously catalogued galaxy. The distributions of peak flux, integrated
flux, HI mass and cz are discussed. We show, using the HIJASS data, that HI
self-absorption is a significant, but often overlooked, effect in galaxies with
large inclination angles to the line of sight. Properly accounting for it could
increase the derived HI mass density of the local Universe by at least 25 per
cent. The effect this will have on the shape of the HI Mass Function will
depend on how self-absorption affects galaxies of different morphological types
and HI masses. We also show that galaxies with small inclinations to the line
of sight may also be excluded from HI-selected samples, since many such
galaxies will have observed linewidths which are too narrow for them to be
distinguished from narrow-band radio frequency interference.
