DSG trajectory of drifters measuring parameters at different depth

[ludo-ifr]

Dear cf-convention

I would like to know how to manage drifters that are measuring different parameters at different depth.

Example : We provide the drifter trajectory with:

• wind (from model) at depth = 0m,
• sea temperature measured at -0.5 m,
• and current measured at -15m

First: Do you think it is a trajectoryProfile or a trajectory ?
As you explain that a profile is a series of connected observations along a vertical line, I would say that this is a trajectory

If it is a trajectory, could I used this representation:

dimensions:
      obs = 1000 ;
      level = 3 ;

   variables:
      string trajectory ;
        trajectory:cf_role = "trajectory_id";
        trajectory:long_name = "trajectory name" ;
      float depth(obs, level) ;
           depth:axis = "Z" ;
      float temp(obs,level) ;
           temp:coordinates = "time lon lat depth" ;
      float current(obs,level) ;
           current:coordinates = "time lon lat depth" ;
      float wind(obs,level) ;
           wind:coordinates = "time lon lat depth" ;

The problem of such representation (incomplete multidimensional array representation) is the sacrifice of storage (but it is acceptable)

I was also thinking that it could be 3 trajectories (in the same file) :

• One for the wind
• one for the temperature,
• one for the current

I have some others questions about the depth depending on level:
Is it possible to have a missing value for depth (I think it is acceptable as it is an auxialiary coordinate) ?
Should the depth be ordered monotonically ?

Currently we could have in our files:
temp=
_, 10.0 , _,
11.0, _, _

and the associated depth:
depth=
0, -0.5, 15,
-0.5, 15, _

This is correct as the temperature is always at -0.5m but it is difficult to use for user.

Thanks for your help