Chapters 4 & 5 discussed the detection and evolution of oscillations in NBPs in three dimensions - two spatial and one temporal. The importance of separating the NBP contribution from that of the internetwork and other non-solar sources is addressed using a contour and contrast method. The contour ensures only NBP pixels are studied, whereas the contrast ensures that only intensity oscillations above that of the background are included. A study of oscillatory power against radial distance showed that oscillations in the 1-4 mHz range are much stronger in the centre of NBPs.
The need for high-cadence, two-dimensional images for this type of study shows the importance of using narrow-band optical filters on ground-based telescopes. Space-based telescopes suffer from the fact that high-cadence imaging will be necessarily combined with short duration sequences and a problem of telemetry rate in transferring the data. Ground-based are also cheaper to run, and easier to upgrade. Recent post-acquisition software also makes it possible to remove a lot of seeing effects from the data.