3.8 Polarimetry

Polarimetric observations were possible in one PHT-P (at 25$\mu$m) and one PHT-C filter (at 170$\mu$m). Measurements were always made for all three polarisers together with (1) a non-polarised measurement to determine the total intensity and (2) an FCS measurement for photometric calibration. At least two cycles of measurements in the three polarisers were collected in order to obtain sufficient redundancy for signal assessment. The PHT-C polarimetry was usually performed on a $2{\times}2$ raster with step size of one array pixel, so that the central map pixel of the resulting $3{\times}3$ map was seen by all 4 pixels.