[CF-metadata] COARDS name for a time offset

[Ed Armstrong]

Hi CF folks,

I would like some advice from your group on a name for a COARDS 
metadata atttribute to describe a time offset for a field.

First off, I  represent the data management side  of GHRSST: 
http://www.ghrsst-pp.org,  which has adopted netCDF and the CF format 
for all our sea surface temperature satellite products.

The problem is straightforward.  In all files we represent time of 
the satellite observations of SST as the following field:

int time(time) ;
                 time:long_name = "reference time of sst file" ;
                 time:units = "seconds since 1981-01-01 00:00:00" ;

however, within our files we have many other observations or model 
predictions of other fields (observed or predicted at different 
times) and we would like to propose something like a 
"offset_from_time" field that represents the time difference in 
seconds from "time" above.  An example might be :


  byte wind_speed(time, nj, ni) ;
                 wind_speed:long_name = "wind speed" ;
                 wind_speed:units = "m s-1" ;
                 wind_speed:_FillValue = -128b ;
                 wind_speed:add_offset = 0.f ;
                 wind_speed:scale_factor = 1.f ;
                 wind_speed:valid_min = -127b ;
                 wind_speed:valid_max = 127b ;
                 wind_speed:coordinates = "lon lat" ;
                 wind_speed: offset_from_time = 3600s
                 wind_speed:offset_from_time_units: "seconds"

Looking over the COARDS/CF documentation I found on the web, I could 
not find anything that describes what I would like to do. What I have 
proposed..... does it sound reasonable or have I overlooked existing 
COARDS metadata attributes that would fufill our needs ???

Any advice appreciated



-- 

    ~ed

Edward M. Armstrong
Physical Oceanography DAAC		Tel: 818 393-6710
Jet Propulsion Laboratory		Fax: 818 393-2710
	edward.armstrong at jpl.nasa.gov