Data Units

 IRAS90 recognises several different system of data units, which may be specified using the following strings:

pW/(M**2)

- Flux values in Pico-Watts per square metre. (1pW = 10^-12W)

(pW/M**2)/sr

- Surface brightness values in Pico-Watts per square metre, per steradian.

Jy

- Flux density values in Janskys.

Jy/sr

- Surface brightness values in Janskys per steradian.

MJy/sr

- Surface brightness values in Mega-Janskys per steradian.

Jy/PIXEL

- Surface brightness values in Janskys per pixel

(pW/M**2)/PIXEL

- Surface brightness values in Pico-Watts per square metre, per pixel.

Note, the possible effects of varying pixel size should be borne in mind when using either of the last two systems of units, especially if dealing with very large areas of the sky. If this may be a problem, then an equal area projection should be used (see section ) when creating the pixel values.

Some of these units are only available when dealing with CRDD files (eg ``Jy''), and some when dealing with images (eg Jy/PIXEL).

Conversions between flux and flux density values use the detector bandwidths described in section . Conversions between flux density and surface brightness values use the effective detector solid angles described in section .