We describe the measurement of the beam profiles and window functions for the Atacama Cosmology Telescope ( ACT ) , which operated from 2007 to 2010 with kilo-pixel bolometer arrays centered at 148 , 218 , and 277 GHz .
Maps of Saturn are used to measure the beam shape in each array and for each season of observations .
Radial profiles are transformed to Fourier space in a way that preserves the spatial correlations in the beam uncertainty , to derive window functions relevant for angular power spectrum analysis .
Several corrections are applied to the resulting beam transforms , including an empirical correction measured from the final CMB survey maps to account for the effects of mild pointing variation and alignment errors .
Observations of Uranus made regularly throughout each observing season are used to measure the effects of atmospheric opacity and to monitor deviations in telescope focus over the season .
Using the WMAP-based calibration of the ACT maps to the CMB blackbody , we obtain precise measurements of the brightness temperatures of the Uranus and Saturn disks at effective frequencies of 149 and 219 GHz .
For Uranus we obtain thermodynamic brightness temperatures T _ { U } ^ { 149 } = 106.7 \pm 2.2 K and T _ { U } ^ { 219 } = 100.1 \pm 3.1 K. For Saturn , we model the effects of the ring opacity and emission using a simple model and obtain resulting ( unobscured ) disk temperatures of T _ { S } ^ { 149 } = 137.3 \pm 3.2 K and T _ { S } ^ { 219 } = 137.3 \pm 4.7 K .