Backward modelling and buoyancy

[sadie-ds]

Hello,

To give a brief background, I'm using the Oceandrift model to backwards model from washed up objects to potential sources. I'm seeding along a transect with delayed releases even across time to cover spatial and temporal uncertainty. I have a few queries (please excuse if some of these are simple im new to particle modelling). im also seeding about 600m out from the bay due to ROMS coverage. i'm seeding hundreds to thousands of particles and creating a trajectory "envelope,"i.e. there is no endpoint. i just cut it off at about 2 weeks (per particle), but might do some sensitivity analysis and play around with that. coastline action: previous

1. currently, I'm seeding close to the seafloor due to particles having slightly more negative buoyancy than seawater and associated with the seafloor, yet it is currently just acting as a passive tracer. I don't have exact terminal velocity and could probably find a proxy; however, I've read vertical physics can be hard to interpret in reverse time. Does anyone have any advice on this? is it worth doing or is simplicity best? Id also like to do more dense objects at some point (very much negative buoyancy). Would it just be the case of adding a normal terminal velocity and vertical mixing? or do i have to switch the signs (+/-) for reverse time tracking?

2. back and forth -- is there a way i can find out where particles finish to seed forwards for sensitivity analysis (cropped at 14 days; seeding over a period of 14 days would mean those seeded first would be active for 28 days)?

3. i have seabed interaction as previous; is this the best course of action? shall i change this if terminal velocity is appropriate to add

Thank you so much for any and all opinions !