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[McIDAS #MOI-385613]: ADDE



Hi again Ioan,

re:
> Well, the image size is correct inside the directory. But the resolution
> does not seem to be, at least to me.
> 
> For example the directory for band 2 says it has 1 km resolution and a size
> of 21696x21696
> 
> If you look inside any netcdf file  for channel 2 for Rad variable yu can
> see
> 
> Rad:resolution = "y: 0.000014 rad x: 0.000014 rad" ;
> 
> These value for microradians corresponds to the resolution of 0.5 KM.
> McIDASX reports this correctly as you showed.
> 
> So both the NetCDF and McIDASX show the correct resolution but the
> directory shows 1 KM form band 2 as well as for the other bands (5,7,13,15)
> 
> Then again the definition of the directory struct from
> 
> https://www.ssec.wisc.edu/mcidas/doc/prog_man/2015/formats-1.html
> 
> says
> 
> The data in the directory is stored as 32-bit (4-byte) twos- complement
> binary integers or as ASCII characters.
> 
> so there is no way to write 0.5 into the header. This is why I suspected
> they multiplied the resolution by 2 :)))
> 
> This actually checks out as the real resolution in KM for bands is:
> 
> 2:0.5
> 5:1
> 7:2
> 13:2
> 15:2
> 
> while the directory reports
> 
> 2:1
> 5:2
> 7:4
> 13:4
> 15:4
> 
> As you pointed out, there is no 4 km data.
> 
> Maybe this helps a bit

Ah Ha!  I see the problem, and it is with poor wording for the meaning
of AREA directory words (1-based) 12 and 13.  A little better explanation
for the meaning of these words is:

    W12.  LINERES:  Line Resolution; spacing in image-lines between
                    consecutive area lines
    W13.  ELERES:   Element Resolution; spacing in image-elements
                    between consecutive area elements

Even this is phrased in a misleading manner.  The correct interpretation
is that words 12 and 13 are multiplicative factors for the base
resolution of the instrument, and the base resolution for GOES-16
imagery is defined in the McIDAS SATBAND file (BRes):

Sat 186
Cal ABIN 
BRes 0.5 0.5
1 DESC='0.47 um VIS aerosol-over-land' WN=21266 cm-1 WL=0.47 um
2 DESC='0.64 um VIS clouds fog, insol, winds' WN=15712 cm-1 WL=0.64 um
3 DESC='0.86 um Near IR veg/burn scar,aerosol, wind' WN=11575 cm-1 WL=0.86 um
4 DESC='1.37 um Near IR cirrus cloud' WN=7282 cm-1 WL=1.37 um
5 DESC='1.61 um Near IR cloud phase, snow' WN=6215 cm-1 WL=1.61 um
6 DESC='2.24 um Near IR land/cloud, vege, snow' WN=4459 cm-1 WL=2.24 um
7 DESC='3.89 um IR Sfc, cloud, fog, fire, winds' WN=2570 cm-1 WL=3.89 um
8 DESC='6.17 um IR High-level WV, winds, rainfall' WN=1621 cm-1 WL=6.17 um
9 DESC='6.93 um IR Mid-level WV, winds, rainfall' WN=1444 cm-1 WL=6.93 um
10 DESC='7.34 um IR Lower-level WV, winds & SO2' WN=1363 cm-1 WL=7.34 um
11 DESC='8.44 um IR Total WV cloud phase, dust' WN=1184 cm-1 WL=8.44 um
12 DESC='9.61 um IR Total ozone,turbulence,wind' WN=1041 cm-1 WL=9.61 um
13 DESC='10.3 um IR Surface & cloud' WN=968 cm-1 WL=10.3 um
14 DESC='11.2 um IR Imagery,SST,clouds,rainfall' WN=894 cm-1 WL=11.2 um
15 DESC='12.3 um IR Total water, ash, and SST' WN=815 cm-1 WL=12.3 um
16 DESC='13.3 um IR Air temp, cloud hgt and amt' WN=754 cm-1 WL=13.3 um

So, the actual resolutions for the bands are:
Band     BRes  Resolution
---------+----+----------
2  - 1 x 0.5 = 0.5
5  - 2 x 0.5 = 1
7  - 4 x 0.5 = 2
13 - 4 x 0.5 = 2
15 - 4 x 0.5 = 2

This used to trip me up all of the time!  And, as you surmised, this
was done because there is no way to represent a fractional number with
an integer ** without including/assuming a scale and offset **.  So,
in this case, words 12 and 13 must be interpreted as scale factors and
the offsets are zero.

It is interesting that you brought this up.  I am facing the exact
same issue when dealing with the SCMI format GOES-16 imagery that
is being delivered in NOAAPort.  There, all Full Disk images have
been sampled down to 6 km resolution, but there is no reference to
the base resolution of the instrument (ABI that is).

I hope that this helps!

Cheers,

Tom
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Ticket Details
===================
Ticket ID: MOI-385613
Department: Support McIDAS
Priority: Normal
Status: Closed
===================
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