Home >> Forums >> Spatial resolution of OSMOSE model

Spatial resolution of OSMOSE model

Dear Sir/Ma'am,
We have come across a technical document (http://www.meece.eu/library/OSMOSE/OSMOSE_descrip_shin.pdf) that states the spatial resolution of  OSMOSE model is 0.15 degrees. We have the following queries regarding the same.
Query 1
Why was 0.15 degrees chosen as the spatial resolution for the model? 
Query 2
Does the end-user have the freedom to alter the spatial resolution in order to make it coarser (for eg: 0.50 degrees) or finer (for eg: 0.10 degrees)?
Query 3
Is there any criteria which the end-user should be aware of while deciding what the spatial resolution of the model ought to be?
We look forward to your responses at the earliest.
Kind regards,
Tarun Joseph 

Hello Tarun,
Hope my reply could help you.
The technical document which you mentioned is an older file which was written by OSMOSE team. The spatial resolution is set to 0.15°*0.15° in Southern Benguela project, and it does not mean that your project must set the same value. Furthermore, you could make your grid be a rectangle with different spatial resolution such as 0.1°*0.2°.
As far as I know, there were no criteria about setting this parameter. In my view, this parameter should be set an optim value which is up to your study, and if you make it coarser or coarser, it will influence your results. Meanwhile, you should also make your HTL’s grids be same as LTL and keep them in a suitable number. 
The web site document (http://www.osmose-model.org/documentation) could help you learn more about OSMOSE’s parameters, and papers would make you understand the model better.
Lei Xing
Ocean University of China

Thank you Lei Xing for your input.
Kind regards,
Tarun Joseph

Dear Tarun,

Here is an excerpt of the yet-to-be-released Osmose book:

Geographical extension
Osmose is a spatial model and as a consequence you must carefully define the geographical extension of the simulated domain, taking into account biological considerations and technical constraints. The domain should encompass all the natural habitats of the focus species (species explicitly modelled in Osmose) to ensure that their full life cycle occurs within the boundaries. Osmose provides a few processes to account for migration (inward and outward the domain) but it should be avoided since what happens outside the simulated domain is sort of a black box. Details about migration processes is provided further down in section #.
Another consideration that may influence the geographical extension of you domain is the existence of a biogeochemical model (BGC model) for inputting low trophic levels compartiments into Osmose. If you do have such model outputs then Osmose domain should either match the BGC spatial extension or fall within the boundaries.
Spatial resolution
Once you have delimited the geographical extension of the domain, you must define the spatial resolution of the grid, i.e. what will be the size of the cells. The area of the cell should be of the same order of magnitude than the smallest foraging range of the focus species within one time step. The foraging amplitude in Osmose is expressed in number of cells per time steps (for details refer to parameter description movement.randomwalk.range.sp# in section #). As a consequence the size of the cell is tightly linked to the time step of the model.
Another practical consideration for determining the spatial resolution is how precisely will you be able or willing to build the spatial distribution maps ?

Let me know if you need clarification.