Figure 21. Map showing the sidescan-sonar imagery produced from data collected during NOAA survey H11079 of Great Round Shoal Channel, offshore Massachusetts. Light tones are hard returns and generally coarser grained sediments; dark tones are softer returns and generally finer grained sediments. Tonal artifacts caused by inaccurate across-track normalization during processing complicate interpretation of the sidescan-sonar imagery.