After flat fielding, the integrations are combined into observations. If oversampling was not used then an observation results simply from co-adding the relevant integrations. On the other hand, if oversampling was used, the integrations corresponding to the different detector positions are interleaved to produce the observation frame. An observation frame is produced for each OBJECT/SKY command given in the EXEC, i.e. a spectral image at the target source and another at the sky position (see Figure 3.1). Henceforth, a target source observation frame will be called object and a sky position observation frame will be called sky.
Figure 3.1: Top panel - Example of an
object observation peaked-up in row 29. Bottom panel -
Example of a sky observation peaked-up in row 39. The
vertical lines seen towards the left hand side in these images are sky
airglow OH lines.