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20040817: MODIS DODS dataset problems with IDV version 1.1

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  • Subject: 20040817: MODIS DODS dataset problems with IDV version 1.1
  • Date: Wed, 18 Aug 2004 08:37:13 -0600
>From: "Valentijn Venus" <address@hidden>
>Organization: ITC
>Keywords: 200408171235.i7HCZIaW012100 MODIS data values

Hi Valentijn-

Just to follow up on my comment:

> >mod07.Data Fields.Surface_Temperature[0], -32768, -32768, -32768, -32768, 
> >-327
> > 68, -32768, 14449, 14699, 14654, -32768
> >mod07.Data Fields.Surface_Temperature[1], -32768, -32768, -32768, -32768, 
> >-327
> > 68, -32768, -32768, -32768, 14716, -32768
> >mod07.Data Fields.Surface_Temperature[2], -32768, -32768, -32768, -32768, 
> >-327
> > 68, -32768, -32768, 14622, 14723, -32768
> >mod07.Data Fields.Surface_Temperature[3], -32768, -32768, -32768, -32768, 
> >-327
> > 68, -32768, -32768, 14613, 14673, -32768
> >mod07.Data Fields.Surface_Temperature[4], -32768, -32768, -32768, -32768, 
> >-327
> > 68, -32768, -32768, 14596, 14637, -32768
> >mod07.Data Fields.Surface_Temperature[5], -32768, -32768, -32768, -32768, 
> >-327
> > 68, -32768, -32768, -32768, 14650, -32768
> 
> Since these are scaled values, it doesn't look like the VisAD DODS adapter
> is using that information.  It may be that it doesn't get that info
> when the request is made The output above indicates that they are not
> all missing.  I'll have to look at that further.

For the Surface_Temperature non-missing values, taking into account
the scale/offset values and valid range, they end up being missing.
For this dataset, the attributes are:

valid_range: 0, 20000
_FillValue: -32768
long_name: "Surface Temperature"
units: "K"
scale_factor: 0.01
add_offset: -15000
Parameter_Type: "Non MODIS Input"
Cell_Along_Swath_Sampling: 3, 2028, 5
Cell_Across_Swath_Sampling: 3, 1348, 5
Geolocation_Pointer: "Internal geolocation arrays"

If we take one of the non missing values (e.g., 14637) and apply
the scale/offset and valid range we get:

scale:  14637*.01 = 146.37
add_offset: 146.37 + -15000 = -14853.63

Since the valid range is 0 to 20000, this ends up as a non-valid 
data point, so it is set to missing.

If you think this is in error, let me know.

Don Murray
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