Acknowledgements

I would like to thank Summer Li, Qian Xie, Shuwei Gan, Wei Liu, Zixiang Cheng, Tingting Liu for helpful discussions, and Bob Hardage for making the Boonsville dataset publicly available. I also thank associate editor Hongliu Zeng, Victor Aarre, and two anonymous reviewers for constructive suggestions that improved the manuscript greatly. Finally, thanks to Dmytro Iatsenko for sharing the SSWT code online:

http://www.physics.lancs.ac.uk/research/nbmphysics/diats/tfr/.