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[Datastream #SXB-674928]: GOES East West imagery...

Hi Gilles,

re:
> I tired as you mentioned by loading West, then East (before that I loaded
> the composite, disabled the Auto-set Projection...)
> 
> Please find attached the images captured from 1) only West IR, 2) West and
> East IR, and 3) the East/West IR composite
> 
> It seems the last one give a nicer result, at least more usable for the
> region of interest.
> 
> What do you think?

Something looks wrong to me, or, if not wrong, not as good as it should be.
I say this be cause the pixel resolution in the individual GOES-East
and GOES-West IR sectors that we distribute in the IDD UNIWISC datastream
are higher in resolution than the East/West IR composite we distribute
in the same datastream.  Here is the IMGLIST output from McIDAS-X that 
illustrates
the difference in resolutions for the East and West images used in creation
of the East/West composite for 21:45 UTC today

IMGLIST RTIMAGES/GE-IR FORM=ALL TIME=21:30 21:59

Image file directory listing for:RTIMAGES/GE-IR
 Pos Satellite/         Date       Time      Center      Res (km)   Image_Size
     sensor                                 Lat  Lon    Lat   Lon
 --- -------------  ------------  --------  ---- ----  ----- ----- ------------
  95  G-13 IMG       4 FEB 15035  21:45:00     0   72
   Band: 4    10.7 um IR Surface/Cloud-top Temp         4.03  4.59  2726 x 1732
     proj:    0 created: 2015035 220047  memo: RT GVAR
     type:VISR     cal type:BRIT
     offsets:  data=    2816 navigation=  256 calibration=    0 auxiliary=    0
     doc length:   0   cal length:   0   lev length:   0 PREFIX=   0
     valcod:          0 zcor:  0 avg-smp: N
     start yyddd: 2015035  start time:214519  start scan:  356
     lcor: 2605  ecor:  9017  bytes per pixel: 1  ss:180
     Resolution Factors (base=1):   Line=    4.0   Element=    8.0
IMGLIST: done
 
IMGLIST RTIMAGES/GW-IR FORM=ALL TIME=21:30 21:59

Image file directory listing for:RTIMAGES/GW-IR
 Pos Satellite/         Date       Time      Center      Res (km)   Image_Size
     sensor                                 Lat  Lon    Lat   Lon
 --- -------------  ------------  --------  ---- ----  ----- ----- ------------
  95  G-15 IMG       4 FEB 15035  21:30:00    24  137
   Band: 4    10.7 um IR Surface/Cloud-top Temp         4.64  4.66  1400 x 1740
     proj:    0 created: 2015035 213801  memo: RT GVAR
     type:VISR     cal type:BRIT
     offsets:  data=    2816 navigation=  256 calibration=    0 auxiliary=    0
     doc length:   0   cal length:   0   lev length:   0 PREFIX=   0
     valcod:          0 zcor:  0 avg-smp: N
     start yyddd: 2015035  start time:213019  start scan:  306
     lcor: 2553  ecor:  8101  bytes per pixel: 1  ss:184
     Resolution Factors (base=1):   Line=    4.0   Element=    8.0
IMGLIST: done
 
IMGLIST RTIMAGES/GEW-IR FORM=ALL TIME=21:30 21:59

Image file directory listing for:RTIMAGES/GEW-IR
 Pos Satellite/         Date       Time      Center      Res (km)   Image_Size
     sensor                                 Lat  Lon    Lat   Lon
 --- -------------  ------------  --------  ---- ----  ----- ----- ------------
  95  G-13 IMG       4 FEB 15035  21:45:00    26  100
   Band: 4    10.7 um IR Surface/Cloud-top Temp        10.72  9.14   592 x 1204
     proj:    0 created: 2015035 220117  memo: GOES East-West Composite
     type:VISR     cal type:BRIT
     offsets:  data=    1280 navigation=  256 calibration=  768 auxiliary=    0
     doc length:   0   cal length:   0   lev length:   0 PREFIX=   0
     valcod:          0 zcor:  1 avg-smp: A
     pdl:  0  0  0  1  0  0  0  1  0  0  0  0  0  0  0  0
           0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
     start yyddd: 1996019  start time:160000  start scan: 2500
     lcor:   91  ecor:    89  bytes per pixel: 1  ss:180
     Resolution Factors (base=1):   Line=    4.0   Element=    4.0
IMGLIST: done

The listings show that the resolution of the East and West images is nominally
4 km while the resolution of the composite is nominally 10 km.   The size of
individual pixels in the attached West_IR_Only and W_and_E_IR are much larger
(meaning lower resolution) than for the EW_IR_Comp image captures you attached.
This strongly suggests that progressive resolution was in effect when you
displayed the West_IR_Only and W_and_E_IR images.

Please try experiment again, but this time:

- turn off adaptive resolution (from Dashboard -> Edit -> Preferences -> View)
  and restart the IDV to make sure the preference change is active

- make sure to set the Magnification factors in the Advanced tab of the
  Field Selector tab to 1 for all three of the image displays

You should observe the following for your area of interest:

1) the pixels shown will be from the last image loaded when loading both
   GOES-East and GOES-West IR images

   I.e., if you loaded GOES-West IR first and then GOES-East IR, then
   the pixels shown will be the ones from GOES-East IR image; if you
   loaded GOES-East first and then GOES-West, the pixels would be from
   the GOES-West image.

   It is up to you to choose which satellite's IR image is most representative
   for the phenomena you are investigating.  This may be a hard decision
   depending on how widespread the phenomena you are investigating are
   since your area of interest (which appears to be around 103W longitude)
   is close to being as far from GOES-East as it is from GOES-West (GOES-East
   is located at 75W and GOES-West is at 135W)

2) the size of the pixels in the display of first GOES-West then GOES-East
   (or visa versa) will be much smaller (meaning higher resolution) than
   the pixels from the East/West composite (~4 km vs ~10 km)

   Higher resolution imagery should be better for the type of investigation
   you (your student) is conducting.

In case you didn't already know, the East/West composite images are created
using pixels from GOES-East for longitudes <= 97:30W and from GOES-West for
longitudes >= 102:30W and a blend of the two for longitudes between 97:30W
and 102:30W. Since the scan time for the East sector is 15 minutes later
the scan time for the West sector (see the times indicated in the IMGLIST
listings above) used in the composite, the use of pixels from one satellite
on one side of the composite and from the satellite on the other side of the
composite can result in feature disconnections.  This is the reason that I
chose to blend East and West pixel values in the 97:30W to 102:30 middle of
the composite (the composite's center is 100W).

** I hope that this description is not too confusing; please let me know if
it was !! **

Cheers,

Tom
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Ticket Details
===================
Ticket ID: SXB-674928
Department: Support Datastream
Priority: Normal
Status: Closed