Estimated value of φ_D averaged over the first and second surveys. The central frequencies of the radiometers are 70 GHz for 18M...23S, 44 GHz for 24M...26S, and 30 GHz for 27M...28M. In order to reduce the amount of data to consider, the time-dependent quantity φ_D was projected on a Healpix map (with NSIDE equal to 64) and binned. The error bars represent the first and third quartiles of the values of the 49 152 pixels in the map, while the middle point is the median.