The strongest returned energy for each elevation angle in a volume scan is compiled into one image called, simply, composite reflectivity. Whereas the base reflectivity image is the first image available during a volume scan, the composite reflectivity image is one of the last views necessitated by the need for all elevation scans to be completed before this image can be produced.
US National Weather Service JetStream - Online School for Weather
2010-01-05
<a rel="nofollow" class="external text" href="http://www.srh.noaa.gov/jetstream/doppler/comprefl.htm">Composite Reflectivity</a>