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New AREA Format InformationCopyright 1996 Space Science and Engineering Center (SSEC)
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Storing Satellite Imagery
in McIDAS Data Structures
February 1997
Space Science and Engineering Center
University of Wisconsin - Madison
1225 West Dayton Street
Madison, WI 53706
Additional signal transmission reference materials:
METEOSAT High Resolution Image Dissemination,
1992, EUMETSAT.
Operations Ground Equipment, Internal
Specification, DRL 504-02-1 Part 1, Specification No
E007020, released February 9, 1994, Space
Systems/Loral, 3825 Fabian Way, Palo Alto, CA,
94303-4604.
Introduction
Satellite imagery is collected by instruments on
geostationary or earth orbiting satellites. These
instruments make a series of parallel scans over a section
of the earth. Ingestors collect and store the scanned data
in area files. In addition to the image data, area files
include information about the image's geography and
physical characteristics, and modifications to the data.
This document describes the structure of McIDAS area
files and how image data is stored and accessed. Since
this is a only a reference document, no information is
provided about how to manipulate data in the structures
described. If you plan to build area structures, it is
important that you are familiar with the data structure
formats described here and the signal transmission
formats described in the reference documents on page 2.
Currently, this document contains information about
METEOSAT PDUS, GVAR and GOES-7 data structure
formats only. Future revisions will include other
satellites.
This document includes the following information:
a description of McIDAS area file components
including the Area Directory and image data
descriptions of area file characteristics specific to
METEOSAT, GVAR and GOES-7 satellites
Area File Description
In McIDAS, satellite imagery data and supplemental
information are stored on disk in data structures called
areas. Each area is a binary file containing all the
information necessary to display and navigate the image.
Area files are named AREAnnnn, where nnnn is a four-
digit number between 0000 and 9999. This number is
referred to as the area file number. For example,
AREA0013 is the name of the file that contains area 13.
Complete images are often too large to be stored
completely in an area file. An area may be a geographic
portion of the image or a subset produced by sampling or
averaging the image data. Any point in the area can be
described with image coordinates, its position in the full
satellite image, or with area coordinates, its position in
the area or subset of the image.
Area files consists of six sections, or blocks:
The Area Directory block describes the area data
and the image from which the area was created. It
also contains pointers used for locating other blocks
and data in the file.
The Auxiliary (AUX) block contains information
created by the user such as histograms or long
comments.
The Navigation (NAV) block contains information
used to associate earth coordinates with the image
pixels.
The Calibration (CAL) block contains information
that relates sensor data to meaningful physical units
such as temperature, albedo or visible brightness.
The Digital Data (DATA) block contains the actual
data values for the image.
The Comment Records (AUDIT) block documents
modifications to the file data.
Area Directory Block
The first 256 bytes of every area file are the Area
Directory block for the image. The Area Directory
describes the kind of data in the area and contains
pointers used for locating the remaining blocks and other
subsets of data in the file. It also contains information
about the image from which the area was created.
The data in the Area Directory is stored as 32-bit (4-byte)
twos complement binary integers or as ASCII character
data. The directory is divided in 64 words. Each word is
described below. Some words are satellite specific. See
the next section for specific satellites. All byte offsets are
zero-based.
Word
Description
W1
contains zeros if the record is valid
W2
area format: always 4 (as of June 1985)
W3
sensor source number; see Appendix A
W4
nominal start date; scheduled date for image
data collection; YYDDD
W5
nominal start time; scheduled time for image
data collection; HHMMSS UTC
W6
image line coordinate of area line 0, element 0
W7
image element coordinate of area line 0,
element 0
W8
not used
W9
number of lines in the area
W10
number of elements in each line
W11
number of bytes per element (1, 2 or 4)
W12
line resolution; number of image lines between
consecutive area lines
W13
element resolution; number of image elements
between consecutive area elements
W14
maximum number of bands per line of the area
W15
length of the DATA block line prefix, in bytes;
sum of W49, W50, W51 (+ 4 if W36 validity
code is present)
W16
McIDAS user project number under which the
area was created
W17
actual ingest date; date the area was created;
provided by the ingesting computer; YYDDD
W18
actual ingest time; time the area was created;
provided by the ingesting computer; HHMMSS
W19
32-bit filter band map for multichannel
images; if a bit is set, data exists for the band;
band 1 is the least significant byte (rightmost)
W20-24
satellite specific information
W25-32
memo; 32 ASCII characters available for
comments
W33
area file number; last four digits of the file
name
W34
byte offset to the start of the area file's DATA
block
W35
byte offset to the start of the area file's NAV
block
W36
validity code; contains zeros if this area does
not have validity codes; if these bytes are non-
zero, they must match the first four bytes of
each DATA block line prefix or the line's data
is ignored; this word is usually constructed
from the date and time of the Area Directory
creation; DDDHHMMSS
W37-45
satellite specific
W46
actual image start date; date the ingestor
begins receiving image data; YYDDD
W47
actual image start time; time the ingestor
begins receiving image data; HHMMSS
W48
actual starting scan line; the first scan line
received by the ingestor
W49
length of the DATA block line prefix
documentation region, in bytes
W50
length of the DATA block line prefix
calibration region, in bytes
W51
length of the DATA block line prefix level map
region, in bytes
W52
image source type; for example, VISR, VAS,
AAA, ERBE, AVHR
W53
calibration type; units in which the digital data
is stored; for example, RAW, TEMP, BRIT
W54-59
internal use only; initialized to 0
W60
byte offset to the beginning of the area file's
AUX block
W61
length of the area file's AUX block, in bytes
W62
not used
W63
byte offset to the beginning of the area file's
CAL block
W64
number of comment records in the area file's
AUDIT block
Auxiliary (AUX) Block
This block contains information like histograms or long
comments created by the user to describe or explain the
area data. Word 60 of the Area Directory contains the
number of bytes from the beginning of the area file to the
beginning of the AUX block. Word 61 contains the total
number of bytes in the block. If the area file does not
contain an AUX block, Words 60 and 61 are both zero.
Ordinarily, when an image is first ingested there is no
AUX block in the area file.
Navigation (NAV) Block
This block contains the navigation data for the image.
This information is used to associate earth coordinates,
usually latitude and longitude, with the pixels of the
image. Word 35 of the Area Directory contains the
number of bytes from the beginning of the area file to the
beginning of the NAV block. If there is no navigation for
the image, Word 35 is zero. The NAV block's last byte is
the byte before the CAL block, pointed to in Area
Directory Word 63. If Word 63 is zero, the NAV block's
last byte is the byte before the DATA block, pointed to in
Word 34. The navigation block format varies with each
satellite. See the next section for specific satellites.
Calibration (CAL) Block
This block contains the calibration data for the image. It
is present in the area file if the data must be calibrated
before it can be displayed. Calibration data is used to
relate the sensor data to meaningful physical units such
as temperature, albedo and visible brightness. Word 63 of
the Area Directory contains the number of bytes from the
beginning of the area file to the beginning of the CAL
block. If the area file does not contain a CAL block, Word
63 is zero. The CAL block's last byte is the byte before the
DATA block, pointed to in Area Directory Word 34. The
calibration block format varies with each satellite. See
the next section for specific satellites.
Digital Data (DATA) Block
This block contains the actual data values for the image.
These values are stored in the area file in a series of lines
and elements.
Coordinate Systems
Any point in an area can be described with image
coordinates, its position in the full satellite image, or
with area coordinates, its position in the area or subset of
the image.
Regardless of the source, a satellite image is a sequence
of lines numbered from top to bottom. Each line is a
sequence of elements numbered across the line from left
to right. This line/element numbering scheme determines
the coordinates for each element, called the image
coordinates. The top line and leftmost element have
image coordinates (1,1). This coordinate system is defined
only by the satellite/camera combination and is
independent of how the data is stored.
The data stored in an area file is also arranged in a
sequence of lines and elements, like the image from
which it was created. The line/element pair determines
the coordinates for the elements in the area, called the
area coordinates. The top line and leftmost element have
area coordinates (0,0).
If entire satellite images could be stored in a single area,
there would be no point in distinguishing between image
and area coordinates. However, images are usually too
large to process efficiently in their entirety. For example,
a GOES VISSR image in the visible-light band contains
14568 lines with 15288 elements per line. This image
requires over 200 megabytes of storage. The data
actually stored in an area file is a subset of the image. An
area may be a geographic portion of an image, the USA
taken from a global image for example.
Resolution
An area file may be produced from an image by sampling
or averaging the data. In the case of multiband images,
an area may include only a portion of the measured
spectral bands, so that each element contains fewer data
values than are contained in the original image.
To map an area back to the original image the following
formulas are used:
Image Line = UpperLeftLine + (Area Line *
LineResolution)
Image Element = UpperLeftEle + (Area Element
* ElementResolution)
UpperLeftLine is the image line coordinate of the first
area line. UpperLeftEle is the image element coordinate
of the first area element.
When LineResolution and ElementResolution are both 1,
the area is said to be at Resolution 1 or Full Visible
Resolution. If the area is at Resolution 4, every fourth
line and element of an image originally at Resolution 1
are included in the area. Resolutions are relative to full
resolution. The coverage of a pixel at full resolution will
vary with each satellite.
Data Structure
The DATA block may be viewed as a continuous stream
of bytes numbered from zero. The area data is arranged
line after line, first to last. If a line of data is missing, the
corresponding place in the data file must be either filled
with zeros or flagged using non-matching validity codes.
line prefix 1 line data 1 line prefix 2 line data 2 etc
|_____________|___________|_____________|___________|___...
0 byte numbers increase >>
Figure 1. Area File DATA Block Structure
Each line is divided into two parts: the line prefix and the
actual line data (image elements). See Figure 1 below.
The line prefix contains documentation about the image
and the particular line.
Although the size and content of the line prefix depend
on the image source type defined in Area Directory Word
52, each line in an area has the same prefix length. Area
Directory Word 15 contains the length of the prefix, in
bytes. If no line prefix exists, Word 15 is zero.
The line prefix may contain any of the following regions.
The lengths of these regions, when present, are multiples
of four bytes.
validity code
documentation
calibration
level map
If present, the validity code is the first four bytes of the
line prefix. When this code is present, Area Directory
Word 36 contains a non-zero value. If the line prefix's
validity code does not match the value in Word 36, the
line is invalid and is ignored.
The documentation region contains information specific
to a particular satellite line (such as the VISSR IR
documentation). Area Directory Word 49 contains the
region's length, in bytes.
The calibration region contains a set of calibration
coefficients for each band in the line. For example, AAA
Sounder images contain 13 bands per line, each with 8
bytes of calibration information. With an additional 12
bytes of information, an AAA Sounder calibration region
has 116 bytes. Calibration regions in a line prefix are
useful when coefficients change for individual bands
during the course of a transmission. Area Directory Word
50 contains the region's length, in bytes.
The level map region contains a 1-byte entry for each
band/channel in the line. These are only meaningful if
they are greater than zero. For an image containing a
single band, the level map region is optional; for
multiband areas, it must be present. Area Directory
Word 51 contains the region's length, in bytes.
validity code documentation calibration level map
|______________|_______________|_____________|___________|
0 byte numbers increase >>
Figure 2. Area Line Prefix Structure
Calculating Prefix, Line, and DATA Block Sizes
Area Directory Word 34 contains the number of bytes
from the beginning of the area file to the beginning of the
DATA block. Each line in an area has the same length.
This length is a multiple of four bytes. The length of a
line prefix, line data section, or the entire DATA block
can be determined from information in the Area
Directory. Use the information and the formulas that
follow to calculate the sizes.
Area Directory Information
Word
validity code length (valcode)
4 bytes if W36 is not 0,
0 otherwise
documentation length (doc)
W49
calibration length (cal)
W50
level map length (level)
W51
number of bands per line (nbands)
W14
number of elements per line (nele)
W10
number of bytes per element (nbytes)
W11
number of lines in the area (nlines)
W9
line prefix length = valcode (0 or 4) + doc + cal + level
line data section length = nbands*nele*nbytes
line length = line prefix length + line data section length
DATA block length = nlines * line length
Comment Records (AUDIT) Block
Comment records may be included in an area file. These
records are usually used to keep an audit trail of
modifications made to data in the file. Each comment
record is 80 ASCII characters. Area Directory Word 64
contains the number of comment records. Ordinarily,
when an image is first ingested there is no AUDIT block
in the area file.
Satellite Specific Characteristics
of McIDAS Area Files
Some aspects of McIDAS area files are satellite specific.
This section describes characteristics specific to the
following satellites:
METEOSAT PDUS
GVAR IMAGER
GVAR BLOCK 11
GVAR SOUNDER
GVAR VISSR
GOES-7
Future revisions of this document will include other
satellites.
METEOSAT PDUS
Because METEOSAT PDUS images are remapped and
calibrated at the ground station before the stretched
signal is disseminated, the navigation and calibration
data sections are simpler. This data is eight bits and each
band is stored in a separate area file.
For more information on METEOSAT labels and headers,
see the EUMETSAT document METEOSAT High
Resolution Image Dissemination.
PDUS Area Directory Block
Word
Value and Description
W14
1; each band is stored separately
W19
band filter map values:
0 for visible image
128 (eighth bit from right) for IR
512 (tenth bit from right) for WV
W22
MIEC absolute calibration band value (IR or
WV) from the calibration section of the
METEOSAT header; stored as scaled integer
xxxxx, value is .xxxxx
W23
space count corresponding to calibration value
from the calibration section of the METEOSAT
header; stored as scaled integer xxx, value is
xx.x
W24
1 or 2; physical sensor number from the
METEOSAT header
W37
line offset of the southeast corner of the area in
image coordinates; 16-bit value from the
METEOSAT header, right justified plus 1
W38
element offset of the southeast corner of the
area in image coordinates; 16-bit value from
the METEOSAT header, right justified plus 1
W39
satellite center longitude of rectification; 16-bit
value from the METEOSAT header and right
justified
W44
0
W49
24; length of the DATA block line prefix
documentation, in bytes
W50
0; length of the DATA block line prefix
calibration, in bytes
W51
0; length of the DATA block line prefix level
map, in bytes
W52
MSAT; image source type
W53
RAW; calibration type
W54
0 if data was ingested as sent (full resolution);
1 if data was sampled down (every other pixel);
VIS is sent as Resolution 1 in some images and
Resolution 2 in others
W55
bitmap indicating types of data included in the
original image; bits are numbered right to left
(least significant to most significant bit)
bit 0: 1 if VIS was included in
transmission, 0 if not
bit 1: 1 if IR was included in transmission,
0 if not
bit 2: 1 if WV included in transmission, 0 if
not
all other bits = 0
PDUS DATA Block
Line Prefix
Validity code: Optional but recommended to flag
missing data. Missing data cannot be simply omitted;
it must have zeros as placeholder data or a validity
code that does not match the value in Area Directory
Word 36.
Documentation: 24 bytes. This is a copy of the label
that arrives with every subframe.
Calibration: 0 bytes. Not used.
Level map: 0 bytes. Not used. Each METEOSAT
band is stored in a separate area.
Line Data
Each value is transmitted as eight bits and is stored west
to east and north to south in the area, the opposite of
how it is transmitted.
PDUS NAV Block
A PDUS navigation block is divided into 256 words:
Word
Value and Description
W1
MSAT; navigation type
W2
Julian day of this navigation, YYDDD
W3
time of this navigation, HHMMSS
W4
0; reference position for the telescope
W5
0; line number corresponding to the telescope
reference position
W6
1250; center scan line
W7
center longitude of rectification (west positive),
DDMMSS
W8
0; not used
W9
0; not used
W10
Julian day of this navigation, YYDDD
W11-256
0; not used
PDUS CAL Block
No calibration information is needed for PDUS.
GVAR IMAGER
The tables mentioned in the line prefix, line data,
calibration and navigation descriptions in this section are
from Operations Ground Equipment, Internal
Specification, DRL 504-02-1 Part 1, Specification No
E007020. This document describes data formatted by the
ground station and then retransmitted. It is referred to
in this document as the OGE.
Imager Documentation (Block 0)
The GVAR Imager documentation, Block 0, is
supplemental control information about an image, not
image data. Some of the information is also contained in
Imager sensor data. For each line of GVAR Imager
sensor data transmitted, one line of Block 0
documentation is transmitted and stored in a separate
area.
Area Directory Block
Word
Value and Description
W12
8; line resolution
W13
1; element resolution
W14
1; number of bands
W19
1; band number
W25-32
ordinarily contains the ASCII string RT IMGR DOC
W49
44; length of the DATA block line prefix
documentation region, in bytes
W50
0; length of the DATA block line prefix
calibration region, in bytes
W51
0; length of the DATA block line prefix level
map region, in bytes
W52
GVAR; image source type
W53
RAW; calibration type
Line Prefix
Validity Code: 4 bytes
Documentation: 44 bytes. The documentation region
consists of the following:
- Block Header CRC: 2 bytes (OGE Table 3-5)
- Scan Status: 4 bytes (OGE Table 3-6)
- Year, Day, Time from Block 0: 8 bytes (OGE
Table 3-6)
- Block Header: 30 bytes (OGE Table 3-5)
Bytes 17-24 now contain the time the block was disseminated
from the ground station.
The rest of the line is made up of 8040 bytes of 8-bit data.
(OGE Table 3-6)
Imager Area DIRECTORY Block (For blocks 1-10, bands 1-5)
Word
Value and Description
W5
1; size of the z-dimension
W14
1; number of bands requested
W19
band filter map; 1 for VIS; 2, 4, 8 or 16 for IR
bands; only one bit should be set
W25-32
RT IMGR IR; (ASCII string)
RT IMGR VIS if the band is visible
W49
76; length of the DATA block line prefix
documentation region, in bytes
W50
0; length of the DATA block line prefix
calibration region, in bytes
W51
0; length of the DATA block line prefix level
map region, in bytes
W52
GVAR; image source type
W53
RAW; calibration type
W55
1
Imager area DATA Block
GOES Variable Imager data is transmitted in five
spectral bands: VISIBLE (VIS) and four INFRARED (IR)
bands. An area contains only one of these five bands.
Area Directory Word 19 contains a band filter map
indicating the area file's band.
The highest resolution (lowest values of line and element
resolution in the Area Directory) possible for a visible
area is 1. The highest resolution for an IR area is 4
because longer wavelengths inherently have less
resolution. For a GVAR satellite, Resolution 1 means
approximately 1 km resolution at the satellite subpoint.
Every element in a GOES-8 area contains one 10-bit
pixel representing raw data from the instrument. Each
pixel is stored as two bytes in the McIDAS area file. The
hardware shifts the data so that the 10 bits are formatted
as follows:
| 0 | x | x | x | x | x | x | x | x | x | x | 0 | 0 | 0 | 0 | 0 |
The x represents a data bit and the rest is 0-filled after
shifting.
Line Prefix
Validity Code: 4 bytes
Documentation: 76 bytes. The documentation region
consists of the following:
- Block Header CRC: 2 bytes. Last three bits only;
bit is set if Block Header copy is good. This data
is usually 00,07.
- Scan Status: 4 bytes (OGE Table 3-6)
- Year, Day, Time from Block 0: 8 bytes
- Block Header: 30 bytes (OGE Table 3-5)
Bytes 17-24 now contain the time the block was disseminated from
the ground station.
- Additional Line Documentation: 32 bytes. 16 10-
bit fields, right-justified. (OGE Table 3-7)
The 6 bit field on the left hand side is not zero filled.
To get the 10 bit field a logical AND against 03FF (hex) must be used.
Data
The rest of the line consists of up to 41920 bytes of data.
Because it is 2-byte data, half that many pixels are
represented.
Imager NAV Block
Navigation blocks are divided into 640 words. Unless
otherwise noted, words are twos complement binary
integers.
This navigation information comes from Block 0 records.
Bytes designated R*4 in OGE Tables are in Gould
format. They must be scaled and then converted to
integers; or converted to Real on the machine doing the
decoding, scaled as designated below, and then converted
to integer.
Word
Value and Description
W1
GVAR; navigation type
W2
ASCII string; usually a letter followed by three
integers, for example, U001
W3
imager scan status; bits 0-15 are right justified, bit
15 is the least significant bit; IMC active flag is bit
8, counting from the least significant bit; 1=active;
see OGE Table 3-6, bytes 3-6
W4-5
0; not used
W6-62
see OGE Table 3-6, bytes 295-522
W6
reference longitude, rad * 10000000
W7
reference distance from nominal, km * 10000000
W8
reference latitude, rad * 10000000
W9
reference yaw, rad * 10000000
W10
reference attitude roll, rad * 10000000
W11
reference attitude pitch, rad * 10000000
W12
reference attitude yaw, rad * 10000000
W13-14
epoch date/time, BCD format
W15
delta from epoch time, minutes * 100
W16
image motion compensation roll, rad * 10000000
W17
image motion compensation pitch, rad * 10000000
W18
image motion compensation yaw, rad * 10000000
W19-31
longitude delta from reference values, rad *
10000000
W32-42
radial distance delta from reference values, rad *
10000000
W43-51
geocentric latitude delta values, no units *
10000000
W52-60
orbit yaw delta values, no units * 10000000
W61
daily solar rate, rad/min * 10000000
W62
exponential start time from epoch, minutes * 100
W63-117
roll attitude angle information;
see OGE Table 3-6, bytes 523-742
W63
exponential magnitude, rad * 10000000
W64
exponential time constant, minutes * 100
W65
mean attitude angle, rad * 10000000
W66
number of sinusoids/angles, no units
W67
magnitude of first order sinusoid, rad * 10000000
W68
phase angle of first order sinusoid, rad * 10000000
:
W95
magnitude of fifteenth sinusoid, rad * 10000000
W96
phase angle of fifteenth sinusoid, rad * 10000000
W97
number of monomial sinusoid, no units
W98
order of applicable sinusoid, no units
W99
order of first monomial sinusoid, no units
W100
magnitude of monomial sinusoid, rad * 10000000
W101
phase angle of monomial sinusoid, rad * 10000000
W102
angle from epoch at daily solar rate, rad * 10000000
W103-107
repeat of Words 98-102 for second monomial
W108-112
repeat of Words 98-102 for third monomial
W113-117
repeat of Words 98-102 for fourth monomial
W118-127
reserved
W128
MORE; 4-byte ASCII
W129
GVAR; 4-byte ASCII
W130-239
attitude angles
W130-184
repeat of Words 63-117 for pitch attitude angle;
see OGE Table 3-6, bytes 743-962
W185-239
repeat of Words 63-117 for yaw attitude angle;
see OGE Table 3-6, bytes 963-1182
W240-255
reserved
W256
MORE; 4-byte ASCII
W257
GVAR; 4-byte ASCII
W258-367
misalignment angles
W258-312
repeat of Words 63-117 for roll misalignment angle;
see OGE Table 3-6, bytes 1183-1402
W313-367
repeat of Words 63-117 for pitch misalignment
angle; see OGE Table 3-6, bytes 1403-1622
W368
year and Julian day, YYDDD
W369
nominal start time of image, HHMMSS
W370
1; Imager/Sounder instrument flag; 1 = Imager,
2 = Sounder
W371-379
reserved
W380
instrument nadir, north/south cycles;
see OGE Table 3-6, byte 6305
W381
instrument nadir, east/west cycles;
see OGE Table 3-6, byte 6306
W382
instrument nadir, north/south increments;
see OGE Table 3-6, byte 6307-6308
W383
instrument nadir, east/west increments;
see OGE Table 3-6, byte 6309-6310
W384
MORE; 4-byte ASCII
W385
GVAR; 4-byte ASCII
W386-511
reserved
W512
MORE; 4-byte ASCII
W513
GVAR; 4-byte ASCII
W514-640
reserved
Imager CAL Block
There are two instruments on the GOES-8 through
GOES-12 series of satellites: the Sounder and the
Imager. Even sensor source numbers represent Imager
data and odd sensor source numbers represent Sounder
data. Area Directory Word 52 contains the image source
type:
GVAR for GVAR data as it is ingested (2 byte)
VISR for 1-byte visible or infrared imagery
VISR data cannot be ingested; GVAR data can be
transformed to VISR with a McIDAS utility such as AA
or SENAA.
Area Directory Word 53 contains the units in which the
data is stored:
RAW for 2-byte raw GVAR data
BRIT for 1-byte visible or infrared values
Area Directory Word 14 contains the number of spectral
bands present in an Imager area. The filter band map in
Area Directory Word 19 describes the bands in an area. A
bit is set for each band appearing in the area. The
number of bands must match the value in Word 14.
The Imager calibration block is made up of 128 words
(512 bytes). The data is in the Gould format.
Word
Value and Description
W1-W8
visible bias coefficients; one per detector (OGE Table
3-6, bytes 6399-6430)
W9-W16
visible first order gain coefficients; one per detector
(OGE Table 3-6, bytes 6431-6462)
W17-W24
visible second order gain coefficients; one per detector
(OGE Table 3-6, bytes 6463-6494)
W25
visible radiance to albedo conversion factor (OGE
Table 3-6, bytes 6495-6498)
W26-W29
det side 1 IR bias scaling factors; one per IR channel
(OGE Table 3-6: bytes 6667-6670 Ch 4, Side 1; bytes
6675-6679 Ch 5, Side 1; bytes 6683-6686 Ch 2, Side 1;
bytes 6691-6694 Ch 3, Side 1)
W30-W33
det side 2 IR bias scaling factors; one per IR channel
(OGE Table 3-6: bytes 6695-6698 Ch 4, Side 2; bytes
6703-6706 Ch 5, Side 2; bytes 6711-6714 Ch 2, Side 2;
bytes 6719-6722 Ch 3, Side 2)
W34-W37
det side 1 IR gain scaling factors; one per IR channel
(OGE Table 3-6: bytes 6723-6726 Ch 4, Side 1; bytes
6731-6734 Ch 5, Side 1; bytes 6739-6742 Ch 2, Side 1;
bytes 6747-6750 Ch 3, Side 1)
W38-W41
det side 2 IR gain scaling factors; one per IR channel
(OGE Table 3-6: bytes 6751-6753 Ch 4, Side 2; bytes
6759-6762 Ch 5, Side 2;bytes 6767-6770 Ch 2, Side 2;
bytes 6775-6778 Ch 3, Side 2)
W42-W128
0
BLOCK 11
Block 11 Holding areas contain data for Sounder images.
This data cannot be easily accessed. A decoder must
reformat the raw Block 11 data and place it in Sounder
image areas, where it is available for analysis and
display.
Block 11 Holding Area DIRECTORY Block
Word
Value and Description
W11
number of bytes per element; 1 or 2 depending
on the element size of the desired band; a
holding area cannot contain both 1- and 2-byte
data
W14
1; number of bands in the image
W19
block type filter; positions of set bits
correspond to the block types requested; the
least significant bit is the right hand bit; a
value of 787968 translates to 0c0600 hex with
bits set in positions 20, 19, 11 and 10
W25-32
ordinarily contains the ASCII string RT BK11 BYT1
W49
40; length of the DATA block line prefix
documentation region, in bytes
W50
0; length of the DATA block line prefix
calibration region, in bytes
W51
0; length of the DATA block line prefix level
map region, in bytes
W52
BK11; image source type
W53
RAW; calibration type
Block 11 Holding Area DATA Block
GVAR transmits 22 types of Block 11 data. This can be
6-, 8-, or 10-bit data. The user can specify any type to be
stored in a single holding area. Control fields in the line
prefix or the first portion of the data (called the SAD ID)
are used by post-processes, such as the Sounder decoder,
to determine the block type. Each DATA block line
consists of a single Block 11 sector (or block). All blocks
are 8040 bytes. Refer to the OGE, sections 3.3.7 - 3.3.7.14
for a detailed breakdown of the contents of each block
type.
The 10-bit data is formatted as follows:
| 0 | x | x | x | x | x | x | x | x | x | x | 0 | 0 | 0 | 0 | 0 |
The x represents a data bit and the rest is zero-filled
after shifting.
The 8-bit data is formatted as follows:
| x | x | x | x | x | x | x | x |
The 6-bit data is formatted as follows:
| 0 | 0 | x | x | x | x | x | x |
Line Prefix
Validity Code: 4 bytes
Documentation: 40 bytes. The documentation region
consists of the following:
- Block Header CRC: 2 bytes (OGE Table 3-5)
- Current Year, Day and Time from Block 0: 8
bytes (OGE Table 3-6)
- Block Header: 30 bytes (OGE Table 3-5)
Bytes 17-24 now contain the time the block was disseminated from
the ground station.
The rest of the line consists of up to 8040 bytes of data,
depending on block type.
WARNING: The Block Header CRC field is overwritten
in the mainframe by a 2-byte counter. This is used to
check sequencing of the data flow.
GVAR SOUNDER
Sounder areas are decoded from Block 11 holding area
data.
Block 11 Decoded Sounder Area DIRECTORY Block
Word
Value and Description
W12
line resolution; 10 is the base resolution; if
lines are sampled or averaged, the resolution
is in multiples of 10.
W13
element resolution; 10 is the base resolution;
if pixels are sampled or averaged, the
resolution is in multiples of 10.
W14
19; number of bands
W19
54287; band filter map; translates to 0007ffff
hex; bits set for bands 1-19
W25-32
ordinarily contains the ASCII string PRIORITY
COMPLETED
W49
36; length of the DATA block line prefix
documentation region, in bytes
W50
0; length of the DATA block line prefix
calibration region, in bytes
W51
24; length of the DATA block line prefix level
map region, in bytes
W52
GVAR; image source type
W53
RAW; calibration type
Block 11 Decoded Sounder Area DATA Block
The GVAR Sounder Decoder reads Block 11 Holding
areas, which contain blocks of type 32 (20hex) and type
35 (23hex) as well as others. These blocks are
documented in OGE, section 3.3.7.2 and section 3.3.7.3.
Navigation and calibration data is read from type 32
blocks (Sounder documentation blocks). Sensor data is
read from type 35 blocks (Sounder scan data blocks) and
then reformatted and placed in the Sounder image area.
All Sounder data fields are 13 bits and are placed in 2-
byte (16-bit) fields. There are 23 bands of data for each
pixel in a Sounder scan data block. The pixels correspond
to a geographic area 11 pixels west-east and 4 pixels
north-south. For each image line, the decoder produces
11 sets of 23 interleaved fields of data.
Bands 20-23 of this data are not displayable; they hold
the latitude and longitude of the first 19 bands. The
latitude and longitudes are 32-bit values. Since the
actual Sounder data is 16 bits, the latitude and longitude
values must be split in half to store them in the area
structure. Band 20 holds the two most significant bytes
and band 21 holds the two least significant bytes of the
latitude. Band 22 holds the two most significant bytes
and band 23 holds the two least significant bytes of the
longitude.
These latitude and longitude values are in the Gould
floating point format. See OGE, section 3.5.4. For
example, if the latitude of a pixel is 100.1640625, the hex
representation is 42642A00; band 20 holds 4264, and
band 21 holds 2A00.
No code is provided in this package to use these latitudes
and longitudes; they are included only for reference
purposes.
There are four Sounder sensors: A through D. Each
DATA block line contains information from only one
sensor. The first line contains sensor A information, the
second line, sensor B, etc. This pattern is repeated for the
entire DATA block.
Line Prefix
Validity Code: 4 bytes
Documentation: 36 bytes. The documentation region
consists of the following:
- First 9 words of SAD Block ID: 9 bytes
(OGE Table 3-8)
- Year, Day, Time of scan line start: 8 bytes
(OGE Table 3-11)
- Sounder scan status: 2 bytes (OGE Table 3-11)
- Number of Block 11 blocks in the scan: 2 bytes
(OGE Table 3-11)
- O&A Location: 2 bytes. No longer used.
- Detector status: 10 bytes (OGE Table 3-11)
- Detector used in this area line: 1 byte
- padding: 2 bytes
Level map; indicates band order for this line: 24 bytes
The rest of the line is made up of the interleaved Sounder
data.
Block 11 Decoded Sounder Area NAV Block
Navigation blocks are divided into 640 words. Unless
otherwise noted, words are twos complement binary
integers.
This navigation information comes from Block 11 records,
type 32. Bytes designated R*4 in the OGE Tables are in
Gould format in the holding areas. They must be scaled
and then converted to integers; or converted to Real on
the machine doing the decoding, scaled as designated
below, and then converted to integer.
Word
Value and Description
W1
GVAR; navigation type
W2
ASCII string; usually a letter followed by three
integers, for example, U001
W3
imager scan status; bits 0-15 are right justified, bit
15 is the least significant bit; IMC active flag is bit
8, counting from the least significant bit; 1=active;
see OGE Table 3-11, bytes 3-6
W4-5
0; not used
W6-62
see OGE Table 3-11, bytes 323-550
W6
reference longitude, rad * 10000000
W7
reference distance from nominal, km * 10000000
W8
reference latitude, rad * 10000000
W9
reference yaw, rad * 10000000
W10
reference attitude roll, rad * 10000000
W11
reference attitude pitch, rad * 10000000
W12
reference attitude yaw, rad * 10000000
W13-14
epoch date/time, BCD format
W15
delta from epoch time, minutes * 100
W16
image motion compensation roll, rad * 10000000
W17
image motion compensation pitch, rad * 10000000
W18
image motion compensation yaw, rad * 10000000
W19-31
longitude delta from reference values, rad *
10000000
W32-42
radial distance delta from reference values, rad *
10000000
W43-51
geocentric latitude delta values, no units *
10000000
W52-60
orbit yaw delta values, no units * 10000000
W61
daily solar rate, rad/min * 10000000
W62
exponential start time from epoch, minutes * 100
W63-117
roll attitude angle information;
see OGE Table 3-11, bytes 551-770
W63
exponential magnitude, rad * 10000000
W64
exponential time constant, minutes * 100
W65
mean attitude angle, rad * 10000000
W66
number of sinusoids/angles, no units
W67
magnitude of first order sinusoid, rad * 10000000
W68
phase angle of first order sinusoid, rad * 10000000
:
W95
magnitude of fifteenth sinusoid, rad * 10000000
W96
phase angle of fifteenth sinusoid, rad * 10000000
W97
number of monomial sinusoid, no units
W98
order of applicable sinusoid, no units
W99
order of first monomial sinusoid, no units
W100
magnitude of monomial sinusoid, rad * 10000000
W101
phase angle of monomial sinusoid, rad * 10000000
W102
angle from epoch at daily solar rate, rad * 10000000
W103-107
repeat of Words 98-102 for second monomial
W108-112
repeat of Words 98-102 for third monomial
W113-117
repeat of Words 98-102 for fourth monomial
W118-127
reserved
W128
MORE; 4-byte ASCII
W129
GVAR; 4-byte ASCII
W130-239
attitude angles see OGE Table 3-11, bytes 771-1210
W130-184
repeat of Words 63-117 for pitch attitude angle;
see OGE Table 3-11, bytes 771-990
W185-239
repeat of Words 63-117 for yaw attitude angle;
see OGE Table 3-11, bytes 991-1210
W240-255
reserved
W256
MORE; 4-byte ASCII
W257
GVAR; 4-byte ASCII
W258-367
misalignment angles
W258-312
repeat of Words 63-117 for roll misalignment angle;
see OGE Table 3-11; bytes 1211-1430
W313-367
repeat of Words 63-117 for pitch misalignment
angle; see OGE Table 3-11; bytes 1431-1650
W368
year and Julian day, YYDDD
W369
nominal start time of the image, HHMMSS
W370
2; Imager/Sounder instrument flag; 1 = Imager,
2 = Sounder
W371-379
reserved
W380
instrument nadir, north/south cycles;
see OGE Table 3-6, byte 3005
W381
instrument nadir, east/west cycles;
see OGE Table 3-6, byte 3006
W382
instrument nadir, north/south increments;
see OGE Table 3-6, byte 3007-3008
W383
instrument nadir, east/west increments;
see OGE Table 3-6, byte 3009-3010
W384
MORE; 4-byte ASCII
W385
GVAR; 4-byte ASCII
W386-511
reserved
W512
MORE; 4-byte ASCII
W513
GVAR; 4-byte ASCII
W514-640
reserved
Block 11 Decoded Sounder Area CAL Block
Sounder calibration blocks are made up of 128 words
(512 bytes):
Word
Value and Description
W1-W4
visible bias coefficients; one per detector
(OGE Table 3-11, bytes 3075-3090)
W5-W8
visible first order gain coefficients; one per detector
(OGE Table 3-11, bytes 3091-3106)
W9-W12
visible second order gain coefficients; one per
detector (OGE Table 3-11, bytes 3107-3122)
W13
visible radiance to albedo conversion factor (OGE
Table 3-11, bytes 3123-3126)
W14-W31
IR bias scaling factors; one per IR channel (OGE
Table 3-11, bytes 3127-3414)
W32-W49
IR gain scaling factors; one per IR channel (OGE
Table 3-11, bytes 3415-3702)
W50-W128
0
GVAR VISSR
Brightness to Temperature Conversion Algorithm
The following description is for image source type VISR
from Area Directory Word 52. GVAR VISSR areas can be
made with the McIDAS commands AA and ARAGET.
Every element in a VISSR area contains one 8-bit pixel,
representing raw data from the instrument. If the area
contains IR data, the observed temperature may be
calculated from the pixel value using the following
formulas:
T = 418 - B (B>176 OR B=176)
T = 330 - (B / 2) (B<176 OR B=176)
T is the brightness temperature (degrees K). B is the
pixel value (0 to 255). For IR data, the highest pixel
values correspond to the coldest temperatures (space is
white).
The line prefix in a VISSR area may be absent or it may
contain only the 4-byte validity code. The highest
resolution, lowest values of line and element resolution in
the Area Directory, possible for a visible area is 1. The
highest resolution for an IR area is 4 because longer
wavelengths inherently have less resolution. For a GOES
satellite, resolution 1 means approximately 1 km
resolution at the satellite subpoint.
GOES-7
GOES-7 Area NAV Block
Unless otherwise noted, the words in the navigation
block are twos complement binary integers.
Word
Value and Description
W1
GOES; navigation type
W2
satellite ID, year, and Julian day,
SSYYDDD
W3
nominal start time of image, HHMMSS
Orbit parameters
W4
1; orbit type
W5
epoch date (ETIMY), YYMMDD
W6
epoch time (ETIMH), HHMMSS
W7
semimajor axis (SEMIMA), Km * 100
W8
orbital eccentricity (ECCEN) * 100000
W9
orbital inclination (ORBINC), Deg * 1000
W10
mean anomaly (MEANA), Deg * 1000
W11
argument of perigee (PERIGEE), Deg *
1000
W12
right ascension of ascending node
(ASNODE), Deg * 1000
Attitude parameters
W13
declination of satellite axis (DECLIN),
DDDMMSS (+ = NORTH)
W14
right ascension of satellite axis (RASCEN),
DDDMMSS
W15
picture center line number (PICLIN)
Spin
W16
spin period (SPINP); the satellite period, in
microseconds, or the spin rate in
revolutions/minute.
Frame geometry
W17
total sweep angle, line direction (DEGLIN),
DDDMMSS
W18
number of scan lines (LINTOT), NNLLLLL
where NN is number of sensors, LLLLL is
number of scans; total number of actual
lines is NN * LLLLL
W19
total sweep angle, element direction
(DEGELE), DDDMMSS
W20
number of elements in a scan line
(ELETOT)
Camera geometry
W21
forward-leaning (PITCH), DDDMMSS
W22
sideways-leaning (YAW), DDDMMSS
W23
rotation (ROLL), DDDMMSS
W24
reserved
W25
east-west adjustment value (IAJUST), in
visible elements (+ or -)
W26
time computed by IAJUST from the first
valid landmark of the day (IAJTIM),
HHMMSS
W27
reserved
W28
angle between the VISSR and sun sensor
(ISEANG), DDDMMSS
W29
0; reserved for later implementation of
*SKEW*
W30
reserved
Betas for this area
W31
scan line of first the beta
W32
time of first beta's scan line (beginning),
HHMMSS
W33
time of first beta's scan line (continued),
milliseconds * 10
W34
beta count 1
W35
scan line of second beta
W36
time of second beta's scan line (beginning),
HHMMSS
W37
time of second beta's scan line (continued),
milliseconds * 10
W38
beta count 2
Gammas for this area
W39
gamma, element offset * 100; this is the
nominal offset at time zero of this day
W40
gamma-dot, element drift per hour * 100
W41-120
reserved
W121-128
memo; up to 32 ASCII characters of
comments
Appendix A
Sensor Source Numbers
Use this table to find the number used by McIDAS
software to identify sensors.
Number Sensor Source
0 Non-Image Derived Data
2 Graphics
3 MDR Radar
4 PDUS METEOSAT Visible
5 PDUS METEOSAT Infrared
6 PDUS METEOSAT Water Vapor
7 Radar
8 Miscellaneous Aircraft Data (MAMS)
9 Raw METEOSAT
12 GMS Visible prior to GMS-5
13 GMS Infrared prior to GMS-5
14 ATS 6 Visible
15 ATS 6 Infrared
16 SMS-1 Visible
17 SMS-1 Infrared
18 SMS-2 Visible
19 SMS-2 Infrared
20 GOES-1 Visible
21 GOES-1 Infrared
22 GOES-2 Visible
23 GOES-2 Infrared
24 GOES-3 Visible
25 GOES-3 Infrared
26 GOES-4 Visible (VAS)
27 GOES-4 Infrared and Water Vapor (VAS)
28 GOES-5 Visible
29 GOES-5 Infrared and Water Vapor (VAS)
30 GOES-6 Visible
31 GOES-6 Infrared
32 GOES-7 Visible
33 GOES-7 Infrared
41 TIROS-N (POES)
42 NOAA-6
43 NOAA-7
44 NOAA-8
45 NOAA-9
46-49 MARINER X Spacecraft
50 Hubble Space Telescope
54 METEOSAT-3
55 METEOSAT-4
56 METEOSAT-5
57 METEOSAT-6
60 NOAA-10
61 NOAA-11
62 NOAA-12
63 NOAA-13
64 NOAA-14
70 GOES-8 (Imager)
71 GOES-8 (Sounder)
72 GOES-9 (Imager)
73 GOES-9 (Sounder)
74 GOES-10 (Imager)
75 GOES-10 (Sounder)
76 GOES-11 (Imager)
77 GOES-11 (Sounder)
78 GOES-12 (Imager)
79 GOES-12 (Sounder)
80 ERBE
82 GMS-4
83 GMS-5
84 GMS-6
85 GMS-7
87 DMSP F-8
88 DMSP F-9
89 DMSP F-10
90 DMSP F-11
91 DMSP F-12
95 FY-1b
96 FY-1c
97 FY-1d
Appendix B
GVAR Calibration Tables
Imager Sensor Characteristics
The IMAGER produces observation data for a given
spatial location in four different IR spectral bands and a
visible band. The characteristics of the Imager bands are
given below:
Band No.
Wavelength Range (um)
Range of Measurement
Meteorological Objective
And Maximum Temp. Range
1
00.55 00.75
1.6 to 100 % albedo
Cloud Cover
2
03.80 04.00
4 to 320 K
Night clouds (space - 340 K)
3
06.50 07.00
4 to 320 K
Water vapor (space - 290 K)
4
10.20 11.20
4 to 320 K
Surf Temp (space - 340 K)
5
11.50 12.50
4 to 320 K
Sea surface temp and water
vapor (space - 335 K)
Sounder Detector Characteristics
The Sounder produces data for a given spatial location in
18 IR spectral bands and a visible band. The
characteristics of the Sounder bands are listed below:
Band No.
Central Wavelength (um)
Wave No. (cm -1)
Meteorological Objective And
Maximum Temp. Range
Longwave
1
14.71
680
Temperature (space - 280 K)
2
14.37
696
Sounding (space - 280 K)
3
14.06
711
Sounding (space - 290 K)
4
13.64
733
Sounding (space - 310 K)
5
13.37
748
Sounding (space - 320 K)
6
12.66
790
Sounding (space - 330 K)
7
12.02
832
Surface temp. (space - 340 K)
Midwave
8
11.03
907
Surface temp (space - 345 K)
9
9.71
1030
Total ozone (space - 330 K)
10
7.43
1345
Water vapor (space - 310 K)
11
7.02
1425
Sounding (space - 295 K)
12
6.51
1535
Sounding (space - 290 K)
Shortwave
13
4.57
2188
Temperature (space - 320 K)
14
4.52
2210
Sounding (space - 310 K)
15
4.45
2248
Sounding (space - 295 K)
16
4.13
2420
Sounding (space - 240 K)
17
3.98
2513
Surface temp (space - 345 K)
18
3.74
2671
Temperature (space - 345 K)
Visible
19
0.70
14367
Cloud cover
The number of spectral bands present in Imager and
Sounder areas is contained in Area Directory Word 14.
The filter map in Word 19 describes the bands in an area.
A bit is set for each band in the area. The number of
bands must match the value in Word 14.
Storing Satellite Imagery in McIDAS Data Structures
Preliminary Issue 12/95
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