  A set of co-aligned high resolution images from the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO) is used to
investigate propagating disturbances (PDs) in warm fan loops at the periphery
of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple
coronal temperatures, a new data analysis methodology is proposed enabling
quantitative description of subvisual coronal motions with low signal-to-noise
ratios of the order of 0.1 %. The technique operates with a set of
one-dimensional "surfing" signals extracted from position-time plots of several
AIA channels through a modified version of Radon transform. The signals are
used to evaluate a two-dimensional power spectral density distribution in the
frequency - velocity space which exhibits a resonance in the presence of
quasi-periodic PDs. By applying this analysis to the same fan loop structures
observed in several AIA channels, we found that the traveling velocity of PDs
increases with the temperature of the coronal plasma following the square root
dependence predicted for the slow mode magneto-acoustic wave which seems to be
the dominating wave mode in the studied loop structures. This result extends
recent observations by Kiddie et al. (Solar Phys., 2012) to a more general
class of fan loop systems not associated with sunspots and demonstrating
consistent slow mode activity in up to four AIA channels.
