What is backbone intensity of bionano optical data and why high this value means chimeric.

Question

[freeheart.steven]

As mentioned in title, I am confused about the concept of backbone intensity of bionano optical data.

Some bionano data analysis tools (like, runBNG) will filtered away data with backbone intensity > 0.6.

Some paper mentioned that the high backbone intensity means likely chimeric. (like, this paper)

Thank you very much for your kind help!