### OTFMAP

In OTFMAP (on-the-fly) observations, the antenna moves relative to the source while recording its position and taking data a high rate, thus performing “scans” in the strict sense of the word. This is a very fast mode for mapping.

The basic parameters of the command are the position offsets of the start and end of the first OTF subscan; the basic parameters of the options are: the number of OTF subscans, the offsets of an off-source reference position, the step (shift) in x- and y-offsets between subsequent OTF subscans, the time per OTF subscan in [s], and the time per off-source reference subscan [s].

This observing mode is normally used either with:

(i) TOTAL POWER with an off-source reference for spectral line observations, or

(ii) FREQUENCY SWITCHING without off-source reference for spectral line observations (see below), or

(iii) WOBBLER SWITCHING and TRUE (ANGLE) HORIZON offsets for continuum mapping with the bolometer.

After you enter an OTF-map setup manually, we recommend to “save” it, optionally to a named file:

SAVE OTFMAP [/FILE otfmap-1]

It can then at any later time be reloaded with @ otfmap[-1], see HELP SAVE.

You may want to save the switching mode seperately or with OTFMAP into the same file:

    SAVE SWITCHING /FILE otfmap-2
    SAVE OTFMAP    /FILE otfmap-2 /APPEND