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During the science verification run in May 2007, the mean point-source sensitivity of LABOCA has been determined from on-sky integrations. By filtering the low frequencies (hence large scale emission) to reject residual sky noise, can be reached a sensitivity per channel of 75 mJy·sqrt(s) (rms weighted average of all 250 functional bolometers). Without low frequency filtering the mean array sensitivity is 120 mJy·sqrt(s).

In typical  observing conditions of 1 mm of precipitable water vapour (which corresponds to a zenith opacity t = 0.3) this translates into a mapping speed of 1 square degree per hour down to a noise level of 40 mJy/beam. An online time estimator for LABOCA is available here.

The sensitivity distribution across the array is shown in the figure below.



There are significant variations of the sensitivity from pixel to pixel. For detection experiments of compact sources with known position, LABOCA can be centred on the most sensitive part of the array insted of the geometric centre, with an improvement of the sensitivity in compact mapping patterns (like spirals) to ~ 50 mJy·sqrt(s).

The noise behavior for deep integrations has been studied up to an integration time of 4 hours by stacking different observations on faint sources obtained with the raster-spiral observing mode (see the figure below). The noise level reached for the full integration is 2.5 mJy/beam. The central 100 square arcminutes of the map have a noise level within a factor of 2 relative to the deepest part of the map. The noise integrates down with sqrt(t), as expected.