Introduction

IRAS90 is a package of applications which provides facilities for the reduction and analysis of IRAS Survey and Pointed Observation (PO) data (also known as ``Additional Observation'', or ``AO'' data). It does not provide facilities for handling Low Resolution Spectrometer (LRS) data, or catalogue data.

Specifically, IRAS90 provides the following facilities:

• Creation of surface brightness images by the co-addition of Calibrated Reconstructed Detector Data (CRDD) samples. This includes destriping, background removal, and mapping of the CRDD.
• Graphical inspection of individual CRDD files.
• Creation of simulated CRDD from a trial sky image, using individual detector Point Spread Functions (PSFs).
• Preparation of IRAS FITS images prior to use by other IRAS90 applications, or other ADAM packages such as KAPPA, CCDPACK, PISA, etc.
• Creation of colour temperature maps, optical depth maps and colour corrected surface brightness maps, based on optically thin greybody source spectra.
• Various astrometric operations such as returning celestial coordinates at given image pixels, aligning a group of images, annotating a displayed image with a celestial coordinates grid, etc.
• Routines for assigning nominated ``qualities'' to selected elements of an image or CRDD file.

IRAS90 runs under the Starlink ADAM environment, on either VMS or UNIX operating systems, and uses the ``Extensible N-dimensional data format'' (NDF) for storing data in HDS files. IRAS90 uses an NDF ``extension'' named `` IRAS'' to store package-specific information within each data file. SG/4 gives an overview of ADAM, NDF and HDS concepts.