[ferret_users] Problem with @AVE gridding on intermitent time series data

["McCann, Mike" <mccann@xxxxxxxxx>]

Hello,
 
I'm use the @AVE regridding transform to take in situ mooring data and create regular hourly gridded data sets.

I've encountered a problem which I think might be a bug, namely because the @AVE and @MAX transforms behave differently.  Here is an example using an actual data set:

! An original Conductivity Temperature Depth data "10-minute" time series
USE "http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/m1/200610/m1_ctd0000_20070405_original.nc";

! Define an hourly axis
DEFINE AXIS/T="12-Oct-2006 18:00:00":"15-Oct-2007 18:00:00":3600/T0="01-JAN-1970 00:00:00"/UNITS=seconds HR_TIME

! Set region for when telemetry was lost for 15 hours
SET REGION/T="4-JUL-2007 20:00":"5-JUL-2007 14:00"

! Show the data to see the gap
LIST TEMPERATURE				


! Grid the data with the @MAX gridding transform  This does the appropriate thing:
! finds max from input and puts in missing values for the time period of the gap.
LIST TEMPERATURE[gt=HR_TIME@MAX]	

yes? LIST TEMPERATURE[gt=HR_TIME@MAX]
             VARIABLE : Water Temperature (deg C)
                        regrid: 3600 sec on T@MAX
             DATA SET : Mooring M1 CTD data from MBARI at original sampling intervals
             FILENAME : m1_ctd0000_20070405_original.nc
             FILEPATH : http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/m1/200610/
             SUBSET   : 19 points (TIME)
             LONGITUDE: 122W(-122)
             LATITUDE : 36.8N
             DEPTH (m): 0
                            122W
                              1
 04-JUL-2007 20:00 / 6363:  11.30
 04-JUL-2007 21:00 / 6364:  11.37
 04-JUL-2007 22:00 / 6365:   ....
 04-JUL-2007 23:00 / 6366:   ....
 05-JUL-2007 00:00 / 6367:   ....
 05-JUL-2007 01:00 / 6368:   ....
 05-JUL-2007 02:00 / 6369:   ....
 05-JUL-2007 03:00 / 6370:   ....
 05-JUL-2007 04:00 / 6371:   ....
 05-JUL-2007 05:00 / 6372:   ....
 05-JUL-2007 06:00 / 6373:   ....
 05-JUL-2007 07:00 / 6374:   ....
 05-JUL-2007 08:00 / 6375:   ....
 05-JUL-2007 09:00 / 6376:   ....
 05-JUL-2007 10:00 / 6377:   ....
 05-JUL-2007 11:00 / 6378:   ....
 05-JUL-2007 12:00 / 6379:  11.96
 05-JUL-2007 13:00 / 6380:  12.08
 05-JUL-2007 14:00 / 6381:  12.13

 
! Grid the data with the @AVE gridding transform.  This does an unexpected thing:
! fills the time period of the gap with numbers that are extrapolations of bounding 
! good points except for the center point which is an average of those two points.
LIST TEMPERATURE[gt=HR_TIME@AVE]	

yes? LIST TEMPERATURE[gt=HR_TIME@AVE]
             VARIABLE : Water Temperature (deg C)
                        regrid: 3600 sec on T@AVE
             DATA SET : Mooring M1 CTD data from MBARI at original sampling intervals
             FILENAME : m1_ctd0000_20070405_original.nc
             FILEPATH : http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/m1/200610/
             SUBSET   : 19 points (TIME)
             LONGITUDE: 122W(-122)
             LATITUDE : 36.8N
             DEPTH (m): 0
                            122W
                              1
 04-JUL-2007 20:00 / 6363:  11.13
 04-JUL-2007 21:00 / 6364:  11.33
 04-JUL-2007 22:00 / 6365:  11.32
 04-JUL-2007 23:00 / 6366:  11.32
 05-JUL-2007 00:00 / 6367:  11.32
 05-JUL-2007 01:00 / 6368:  11.32
 05-JUL-2007 02:00 / 6369:  11.32
 05-JUL-2007 03:00 / 6370:  11.32
 05-JUL-2007 04:00 / 6371:  11.32
 05-JUL-2007 05:00 / 6372:  11.79
 05-JUL-2007 06:00 / 6373:  11.96
 05-JUL-2007 07:00 / 6374:  11.96
 05-JUL-2007 08:00 / 6375:  11.96
 05-JUL-2007 09:00 / 6376:  11.96
 05-JUL-2007 10:00 / 6377:  11.96
 05-JUL-2007 11:00 / 6378:  11.96
 05-JUL-2007 12:00 / 6379:  11.96
 05-JUL-2007 13:00 / 6380:  12.04
 05-JUL-2007 14:00 / 6381:  12.12


Am I interpreting these transforms properly?  Should @AVE have a behavior similar to @MAX (and @MIN)?  I'd think that if there were no data for a time period then that should be reflected with missing data values for whatever gridding transform is used.

Thanks,
Mike

--
Mike McCann
Software Engineer
Monterey Bay Aquarium Research Institute
7700 Sandholdt Road
Moss Landing, CA 95039-9644
Voice: 831.775.1769  Fax: 831.775.1736 http://www.mbari.org <http://www.mbari.org/>