Gaps and @AVE regridding transform

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

Hello ferret users,

I've encountered a little problem in re-gridding a 10-minute gappy time series to a 1-hour axis using the @AVE transform.  Here's a ferret script that shows the problem:

USE "http://dods.mbari.org/cgi-bin/nph-nc/data/OASISdata/deployments/m1/199705/m1/netcdf/m1_metsys_19970731.nc";
DEFINE SYMBOL DMIN = "31-JUL-1997 18:00"
DEFINE SYMBOL DMAX = "24-SEP-1998 21:00"
LET BAR = y[gy=LATITUDE]   	! Scalar for below
LET FOO = x[gx=LONGITUDE]  	! Scalar for below
DEFINE SYMBOL TOUT = TIME_HR
DEFINE SYMBOL YOUT = LATITUDE_MET_HR
DEFINE SYMBOL XOUT = LONGITUDE_MET_HR
DEFINE AXIS/T=($DMIN):($DMAX):3600/T0="01-JAN-1970 00:00:00"/UNITS=seconds ($TOUT)
DEFINE AXIS/Y/UNITS=deg ($YOUT)=BAR
DEFINE AXIS/X/UNITS=deg ($XOUT)=`FOO+360`
SET AXIS/MODULO LONGITUDE LONGITUDE[L=1]

! Change missing data flag so that it's not 1
LET WIND_SPEED_1 = missing(WIND_SPEED_FLAG, -9999)

!
! Catch all flags.  Good data set to 1
!
LET WIND_SPEED_1F = IF WIND_SPEED_1 EQ 0 THEN 1
LET WIND_SPEED_2 = WIND_SPEED * WIND_SPEED_1F

!
! Regrid WIND_SPEED to new time grid
!
LET WIND_SPEED_AVG = WIND_SPEED_2[gt=($TOUT)@AVE,gy=($YOUT),gx=($XOUT)]

LET WIND_SPEED_LIN = WIND_SPEED_2[gt=($TOUT)@LIN,gy=($YOUT),gx=($XOUT)]

SET REGION/T=22-sep-1997:24-sep-1997
PLOT WIND_SPEED_2
PLOT/OV WIND_SPEED_AVG, WIND_SPEED_LIN



WIND_SPEED_AVG has a value of 120.7 after the 7 hour gap that begins at 1800 on Sep 22.  There also appears to be "invented" values at the beginning of the gap.  Perhaps I don't understand the use of the @AVE transform for doing this re-gridding.  Is there something better I should be using?

Thanks in advance for any help.

-Mike

--
Mike McCann (mccann@mbari.org)
Monterey Bay Aquarium Research Institute
7700 Sandholdt Road
Moss Landing, CA 95039-9644
Voice: (831) 775-1769 Fax: (831) 775-1646 http://www.mbari.org/rd/iag.htm