Information on how our Data Products are generated can be found in the Data Product Specifications and Data Product Algorithms. You can find those through the OOI website here: Data Products – Ocean Observatories Initiative
(Note that the current Echo Intensity (ECHOINT) DPS should be version 2-00 from 2020; it should be updated on the website shortly.)
The bin_depth parameter is the calculated center of the bins. There is the depth of the instrument, and then there is a blanking distance before the bins start, and then the bins have a defined length.
The ADCPs are configured for a particular range which may be greater than the depth at which they are deployed. This is particularly important for ADCPs on the Flanking Moorings as they may get “blown down” to deeper depths, but we still want them to be able to measure to the sea surface. So the negative depths are are essentially “in air” and can be excluded.
You may want to also look at this ticket: ADCP range bins contaminated by sea surface - a robust QC option?
I hope that helps to clarify the data.
Thanks and stay safe,
Sheri
OOI Data Team