AREA resolutio

------- Forwarded Message

To: address@hidden (mcidas users-forum)
Date: Mon, 30 Oct 2000 22:04:42 +0000 (GMT)
Subject: area resolution

Hi,
I have a few questions about the pixel resolution of a given mcidas area.
When doing the following commands for a given area I get: 

LA 97                                                                  
  area  ss  yyddd hhmmss  lcor  ecor lr er zr  lsiz  esiz z    bands   
  ---- ---- ----- ------ ----- ----- -- -- -- ----- ----- -    -----   
    97  70  98231   1500  2785  9141  4  8  1  1400  1728 1 ...4......>


IMGLIST MYDATA/IMAGES.97 FORM=EXP                                      
Image file directory listing for:MYDATA/IMAGES                         
 Pos Satellite/         Date       Time      Center      Res (km)   Im>
     sensor                                 Lat  Lon    Lat   Lon      
 --- -------------  ------------  --------  ---- ----  ----- ----- --->
  97  G-8 IMG       19 AUG 98231  00:15:00    23   71                  
    Band: 4  10.7 um Surface temp; longwave window       4.0   8.0  14>
     proj:    0 created: 1998231   3742  memo: RT GVAR                 
     type:VISR     cal type:BRIT                                       
     offsets:  data= 2816 navigation=  256 calibration=    0 auxillary>
     doc length:   0   cal length:   0   lev length:   0 PREFIX=   0   
     valcod:          0 zcor:  0 avg-smp: N                            
     start yyddd: 1998231  start time:  1515  start scan:  351         
     lcor: 2785  ecor:  9141  bytes per pixel: 1  ss: 70               
     Image Center Point Res (derived)  Lat:   4.59 (km)  Lon:   4.67 (>


The way I understand the image information given in these commands is
as follows:  The highest available resolution for a GOES IR image is
4km.  From the learning guide, the resolution for a given area is the
sampling rate(lr,er) times the sensor resolution.  Therefore the pixel
resolution for the above image is 4km*4=16km in the ydir and 4km*8=32km
in the xdir.  However, if I look at the range of entire area(after
blowing down the image sufficiently), I find  the image lat/lon range
is about 30-110 at ~2N.  If there is 1728 elements along this range,
the resolution is around 5km per element in the xdir.  Which, if any,
is the correct resolution contained in the area?


Lastly, what does the last line of the IMGLIST response indicate?

Image Center Point Res (derived)  Lat:   4.59 (km)  Lon:   4.67 

Thanks,

dave
======================================================================
| Dave Vollaro                           address@hidden        |
| SUNYA Atmospheric Science              Phone: (518) 442-4273       |
| Earth Science Bldg Rm 226                                          |
| 1400 Washington Ave                                                |
| Albany, NY 12222                                                   |
======================================================================

------- End of Forwarded Message
From:    "=?ISO-8859-1?Q?Marianne=20K=F6nig?=" <address@hidden>
Subject: Re: area resolution

Dave,
the resolution refers to the approximate value at nadir (subsatellite
point). Re solution will decrease by cosine of viewing angle the
further you move away from
 the point.

Hope this answers your question,

Marianne

From: "M.A. Martinez" <address@hidden>
Date: Tue, 31 Oct 2000 10:56:29 +0000
Organization: inm.es
To: address@hidden
Subject: Re: area resolution

Dear Dave;

The resolution refers to the highest available resolution not for a
GOES IR image that is 4km.; but the highest available resolution for a
GOES image sensor (in this case VISIBLE) that is 1km. In the case of
METEOSAT lr=2 is 5km. at nadir, because the VIS channel has a 2.5 km. at
nadir.

-- 
Dr. Miguel A. Martinez Rubio 
  Instituto Nacional de Meteorologia (I.N.M.). Servicio de
Teledeteccion.
  Madrid. SPAIN.  
  e-mail: address@hidden  Tfno: +34 91 5819 662

From: Russ Dengel <address@hidden>
Date: Tue, 31 Oct 2000 08:17:26 -0600
Organization: SSEC
Subject: Re: area resolution

Image resolution, as defined by SSEC, is the highest resolution
possible for a given instrument (as opposed to sensor). The GOES-8 GVAR
instrument can resolve 1 x 2 KM pixels with its Visible (BRIT) sensor.
This is the base resolution for this instrument. The 10.7um channel
resolution is 4 times less than the base resolution, giving the sensor
a 4 X 8 KM  resolution listed above. Of coarse, this resolution is only
possible at the satellite sub-point. All other pixels within the image
are effectively larger due to curvature.

The "Image Center Point Res (derived)"  is the estimated size of a pixel
at the center of the image which may or may not be the satellite
sub-point. This computation is performed by determining the latitude
and longitude of the image center pixel and the lat/lon of the pixels
to the top, left, right and bottom of the center. The distance from the
surrounding pixels to the center pixel is computed (in spherical
coordinates) and averaged to get the derived image center pixel
resolution.

Russ

From: Tim Schmit <address@hidden>
Date: Tue, 31 Oct 2000 12:14:32 -0600
Subject: Re: area resolution
Cc: address@hidden

It looks like others have answered your question, but allow me to state a few
features in relation to the resolution of the GOES Imager:

- Most infrared (IR) bands (3.9, 11 and 12 um) of the GOES Imager have a
field-of-view of  112 uradians (square). This corresponds to 4 x 4 km at the
sub-satellite point (SSP). 

- These detectors are then over-sampled while scanning in the east-west (and
west-east) directions. This means the detector observes some of the same area,
the over-sampling factor is approx. 1.7. This gives an effective resolution of
2.3 km in the E-W direction, still with 4 km in the North-South direction. See
table 2 of Menzel and Purdom ('94) in BAMS for more details.

- On GOES-8 thru -11, the 6.7 um has a SSP FOV nominal resolution of 4 x 8 km
(E-W x N-S). On GOES-12 (launch of July 2001) it will become 4 x 4 km. And 2.3
km x 4 km with the over-sampling.

- When discussing resolution, we should also remember that with most all IR
systems, most, though not all, of the energy of a given pixel emanates from
that area.

- As far as the visible channel on the GOES Imager, it's nominal SSP resolution
is 1 x 1 km (or 28 uradians--square), with the over-sampling this equates to
0.57 x 1 km.

I hope this e-mail makes sense and doesn't just confuse. 

Tim

From: "David J. Vollaro" <address@hidden>
Date: Tue, 31 Oct 2000 20:55:14 +0000 (GMT)
Subject: IMGREMAP question

Hi,

Thanks for all of the help concerning my question about pixel 
resolution.  I have another question to ask....  I will be using 
IMGREMAP(AAMAP) to transform an image region to a MERCATER projection 
with a uniform resolution.

Exactly how does this routine work?  I am guessing that from the
command parameters(projection,clat,clon and resolution of the
destination image) , IMGREMAP calculates the lat/lon of each point for
the destination image.  Then for each of these points, the brightness
values are calculated from the 4 surrounding points on the source
image using a bilinear or cubic spline interpolation...Does this sound
correct?  Thanks

dave

From: Dave Santek <address@hidden>
Date: Tue, 31 Oct 2000 15:28:05 -0600
Organization: Space Science & Engineering Center
Subject: Re: IMGREMAP question

"David J. Vollaro" wrote:

> ...
> values are calculated from the 4 surrounding points on the source
> image using a bilinear or cubic spline interpolation...Does this sound
> correct?  Thanks

Not quite.

IMGREMAP calculates the lat/lon at the spline box corners...so if the
spline is set to 20, then every 20 elements and 20 lines the nav transform
is computed (line/elem to lat/lon) in the destination file and then a nav
transform from  lat/lon to line/elem is computed for the source file. For
intermediate points in the spline box, a bi-linear interpolation is used.
So for a spline of 20, only 4 navigation transformations are needed for
the 400 pixel box (the bilinear interpolation is much faster than a nav
transform). Therefore, each pixel in the destination file has an
associated pixel from the source file....so there are no holes in the
image. If the destination is lower resolution than the source, the data
are sampled. If the destination is higher resolution, the pixel values are
replicated. Also, only the 8-bit grayscale values are stored in the
destination file. And, by default, there is no interpolation of the 8-bit
values.

There is a keyword to interpolate the 8-bit values, SMOOTH= X YES  for
smoothing the data. This is a 2/3   1/3  weighting of the 2 closest
pixels.

dave