Documentation: Seabed property units

[JPalmerK]

Hey there,
Thanks for putting this package together. In the documentation it would be great to have some confirmation on the units. Specifically for the density. I believe in the original model they are kg/m^3 but I've noticed the default value is 1600 which is the same as the default sound speed for the bottom. It's unclear whether thats just a carryover or the system is looking for different units. Either way, having all of the units made explicit would be very helpful. Thanks!

[mchitre]

Yes, the unit is kg/m³. Why do you feel that 1600 kg/m³ is not reasonable or confusing?

Happy to take in a documentation update PR, if you'd like to contribute one.

[JPalmerK]

The only real reason is that I don't have a lot of intuition on seabed densities and I'm having trouble finding that written out in the documentation. An older version of the documentation on the HLS website states that bottom density should be given in g/cm3 which is in line (same order of magnitude) with the values used in Zimmer's example (Passive acoustic Monitoring of Cetaceans) where he uses 2.4 (no units). He also lists the densities of common seabeds including limestone at 2400 kgm-3 earlier in the book. Kusel et al. 2016 also use Bellhop and state their bottom density is 1.5 kg/m-3 but that seems rather low given that air is 1.293 kg m-3. So yeah, I think this hasn't been well addressed in either the original Bellhop instructions which is causing headaches for upstream packages.

[mchitre]

Yes, bellhop uses non SI units in some places. In arlpy, I covert SI units to bellhop ones where necessary. So in arlpy, you specify SI units.

[JPalmerK]

That's hugely helpful. Thank you so much. I'll work on making a pull request documenting this as well as the PCHIP modification.