... Neutral Hydrogen 21cm line emission is widely used to chart the warm and cool diffuse components of the interstellar medium. ... The ongoing Canadian Galactic Plane Survey (CGPS) meets these criteria to an unprecedented degree, permitting the comparison of HI, CO, and dust features at arcminute scales over hundreds of square of degrees of the Milky Way. We will present the first results of an investigation of neutral Hydrogen self-absorption features in the CGPS dataset. ...

... 2.3 Data acquisition Spectra generated by the Multibeam correlator contain the usual structure seen in spectra from other H i instruments: a bandpass spectrum which is the sum of the sky , ground and receiver temperatures multiplied by the product of the filters in the receiver chain; superimposed on this is a noise ... Note also that sources extended much beyond ,40 arcmin can be imaged poorly in HIPASS images because of the bandpass sidelobe effect described in Section 3.3. ...