[gradsusr] GDS date-time standard

[Jennifer Adams]

Hi, Jim --
Does the original descriptor file have a 365_day_calendar? 
--Jennifer

On Oct 7, 2013, at 2:36 PM, James T. Potemra wrote:

> Hi all:
> 
> I'm wondering if anyone knows how GDS derives a date-time value from a GrADS style binary file?  For example, a contributed data set     could have a descriptor file with a TDEF defining a start-date of Jan 1, 2013 and increment of 1dy.  If this file were served via GDS, the OPeNDAP date-time becomes "days-since-1-1-1".  In experimenting with some GDS-served files, it seems that this conversion is off by two days.
> 
> Here's an example.  The following is daily measurements from QUIKSCAT:
> http://apdrc.soest.hawaii.edu:80/dods/public_data/satellite_product/QSCAT/qscat_daily
> 
> The data descriptor file has the following:
> TDEF 3776  linear  20JUL1999  1DY
> 
> and the DDS page seems to have the correct values for time:
> time:	Array of 64 bit Reals [time = 0..3775]             
> grads_dim: "t" 
> grads_mapping: "linear" 
> grads_size: "3776" 
> grads_min: "00z20jul1999" 
> grads_step: "1dy" 
> units: "days since 1-1-1 00:00:0.0" 
> long_name: "time" 
> minimum: "00z20jul1999" 
> maximum: "00z19nov2009" 
> resolution: 1.0
> However, the OPeNDAP supplied first time-step is 729956 (obtained either through python call or ncdump).  I think that this corresponds to July 22, 1999 rather than the actual July 20, 1999 as defined in the descriptor file.
> 
> Can anyone comment on what's going on here?  I found the same behavior with two other daily files, same apparent 2-day off-set.  Thanks,
> 
> Jim
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--
Jennifer M. Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
111 Research Hall, Mail Stop 2B3
George Mason University
4400 University Drive
Fairfax, VA 22030 





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