Magnification bias describes the fact that observed galaxies are magnified by the lensing effect. This leads to three consequences:
However, even from a very massive cluster, the expected signal-to-noise ratio (S/N) is very small. One way to enhance the S/N is to stack many similar samples. If we stack several dozens of annulus areas of massive clusters, the signal turn out to be measurable.
Magnification bias can be estimated by analyzing the deficit of the source number density in clusters' neighborhood. I am working on measuring this effect, and the aim is to provide a forecast for the Euclid mission, a upcoming space-based lensing survey expected to be launched in 2020.