8160eae2____GeoServer_2_7_x_User_Manual__Description
[Parameter] Levels [Mandatory] Y [Description] 
Represents the resolutions for the various levels of the granules of this mosaic. Please remember that we are currently assuming that the number of levels and the resolutions for such levels are the same across alll the granules.
Using the ImageMosaic plugin — GeoServer 2.7.x User Manual