This data-set is recorded with an ARIS Explorer sonar:
http://www.soundmetrics.com/Products/ARIS-Sonars/ARIS-Explorer-3000

It shows different objects in form of 
(1) three paving tiles with different amounts of cracks (the cracks are most of the time not visible in the sonar data)
(2) a construction brick with holes
[pic's of the objects from an underwater camera are also provided]

In addition, there is a video from the shore of the river Weser, which can be used for classification/recognition methods to test whether the absence of the objects is correctly detected:
  2016-08-24-15-03-56-aris-CUT02.avi

The data was recorded in the context of the FloodEvac project; see, e.g.:

Christian A. Mueller, Tobias Fromm, Heiko Buelow, Andreas Birk, Maximilian Garsch, Norbert Gebbeken.Robotic Bridge Inspection Within Strategic Flood Evacuation Planning. IEEE Oceans. Aberdeen, UK, IEEE Press, 2017

Maik Benndorf, Maximilian Garsch, Christian Atanas Mueller, Tobias Fromm, Thomas Haenselmann, Norbert Gebbeken, Tomasz Luczynski, Andreas Birk. Robotic Bridge Statics Assessment Within Strategic Flood Evacuation Planning Using Low-Cost Sensors. IEEE Symposium on Safety, Security and Rescue Robotics (SSRR). Shanghai, China. 2017