Skynoise subtraction

Even in a sparsely sampled array like MAMBO and SCUBA, skynoise is highly correlated between neighbouring pixels. It is therefore unlikely that filled arrays will allow a significantly better sky noise subtraction. They would perform better for pointed observations under conditions of anomalous refraction. However, such conditions should be generally avoided for sensitive bolometer observations. Deep on-off integrations with the 37-element MAMBO have shown no limit yet to the noise level that can be reached. The deepest on-off integration detected a $z=$5.5 QSO at 0.87$\pm$0.20 mJy, and in maps rms noise levels of 0.5 mJy were reached. Currently, the average per pixel sensitivity of the 37-element MAMBO is ca. $25 e^{\tau_{los}}$ mJy s$^{1/2}$.