Format of the Mapped AMSU Data Files

The mapped files are in McIDAS format. Each file consists of three blocks, the Area Block, the Navigation Block, and the Data Block. If you don't have McIDAS, you can still use the data--just follow the shortcut below.

Projections

The AMSU data are mapped into one of three projections:

Parameter Mercator8 Mercator16 North Polar Stereographic South Polar Stereographic
Lines x Elements 2875 x 5000 1437 x 2500 2000 x 2000 2000 x 2000
Map Center Equator, 160°W Equator, 160°W North Pole South Pole
Central Meridian 160°W 160°W 150°W
(at bottom of map) Prime Meridian
(at top of map)
Resolution 8 km @ Equator 16 km @ Equator 8 km @ 60°N 8 km @ 60°S
Top Left Corner 71.271°N, 20.380°E ~71.271°N, ~20.380°E 2.933°N, 75.000°E 2.933°S, 45.000°W
Bottom Right Corner 71.271°S, 19.620°E ~71.271°S, ~19.620°E 2.933°N, 105.000°W 2.933°S, 135.000°E
Areas so mapped 1-8 and 22 25 and 26 9, 10, 16-19, 21, and 24 11 and 20

Parameter	Mercator8	Mercator16	North Polar Stereographic	South Polar Stereographic
Lines x Elements	2875 x 5000	1437 x 2500	2000 x 2000	2000 x 2000
Map Center	Equator, 160°W	Equator, 160°W	North Pole	South Pole
Central Meridian	160°W	160°W	150°W (at bottom of map)	Prime Meridian (at top of map)
Resolution	8 km @ Equator	16 km @ Equator	8 km @ 60°N	8 km @ 60°S
Top Left Corner	71.271°N, 20.380°E	~71.271°N, ~20.380°E	2.933°N, 75.000°E	2.933°S, 45.000°W
Bottom Right Corner	71.271°S, 19.620°E	~71.271°S, ~19.620°E	2.933°N, 105.000°W	2.933°S, 135.000°E
Areas so mapped	1-8 and 22	25 and 26	9, 10, 16-19, 21, and 24	11 and 20

Area Block

The Area Block consists of 256 bytes of intermixed 4-byte integers (words) and ASCII characters. Depending on what kind of machine you have, you may have to swap the byte order of the integers. (But don't swap the order of the characters!) It's easy to tell if you need to swap the order by looking at the second word, which is always 4. Here's the format of the Area Block:

NOTE: Mercator16 will be added soon

Word Contents Mercator8 NP Stereo SP Stereo
1 contains zeros if the record is valid 0 0 0
2 area format: always 4 4 4 4
3 sensor source number 10 (composite) 10 (composite) 10 (composite)
4 end date; YYYDDD
(date of last line in last orbit)
Year = 1900 + YYY
5 end time; HHMMSS UTC
(time of last line in last orbit)
6 starting line number 3563 -7992 -7992
7 starting element number 2501 -7992 -7992
8 not used 0 0 0
9 number of lines in the area 2875 2000 2000
10 number of elements in each line 5000 2000 2000
11 number of bytes per element (1, 2 or 4) 1 1 1
12 line resolution; number of image lines between consecutive area lines 1 8 8
13 element resolution; number of image elements between consecutive area elements 1 8 8
14 maximum number of bands per line of the area 1 1 1
15 length of the DATA block line prefix, in bytes 0 0 0
16 McIDAS user project number under which the area was created 0 0 0
17 ingest date; date the area was created; provided by the ingesting computer; YYDDD 0 (not used) 0 (not used) 0 (not used)
18 ingest time; time the area was created; provided by the ingesting computer; HHMMSS 0 (not used) 0 (not used) 0 (not used)
19 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) 2**(channel -1)
(some products don't have channel numbers) 2**(channel -1)
(some products don't have channel numbers) 2**(channel -1)
(some products don't have channel numbers)
20-24 satellite specific information 0 (not used) 0 (not used) 0 (not used)
25-32 memo; 32 ASCII characters available for comments a brief description of what parameter is in the data field a brief description of what parameter is in the data field a brief description of what parameter is in the data field
33 area file number 0 last four digits of the filename last four digits of the filename
34 byte offset to the start of the area file's DATA block 768 768 768
35 byte offset to the start of the area file's NAV block 256 256 256
36 validity code 0 (not used) 0 (not used) 0 (not used)
37-45 satellite specific 0 0 0
46 actual image start date; date the ingestor begins receiving image data; YYYDDD 0 (not used) 0 (not used) 0 (not used)
47 actual image start time; time the ingestor begins receiving image data; HHMMSS 0 (not used) 0 (not used) 0 (not used)
48 actual starting scan line; the first scan line received by the ingestor 1 (not used) 1 (not used) 1 (not used)
49 length of the DATA block line prefix documentation region, in bytes 0 0 0
50 length of the DATA block line prefix calibration region, in bytes 0 0 0
51 length of the DATA block line prefix level map region, in bytes 0 0 0
52 image source type; for example, VISR, VAS, AAA, ERBE, AVHR VISR VISR VISR
53 calibration type; units in which the digital data is stored; for example, RAW, TEMP, BRIT BRIT BRIT BRIT
54-59 internal use only; initialized to 0 0 0 0
60 byte offset to the beginning of the area file's AUX block 0 0 0
61 length of the area file's AUX block, in bytes 0 0 0
62 not used 0 0 0
63 byte offset to the beginning of the area file's CAL block 0 0 0
64 number of comment records in the area file's AUDIT block 0 0 0

Word	Contents	Mercator8	NP Stereo	SP Stereo
1	contains zeros if the record is valid	0	0	0
2	area format: always 4	4	4	4
3	sensor source number	10 (composite)	10 (composite)	10 (composite)
4	end date; YYYDDD (date of *last* line in *last* orbit) Year = 1900 + YYY
5	end time; HHMMSS UTC (time of *last* line in *last* orbit)
6	starting line number	3563	-7992	-7992
7	starting element number	2501	-7992	-7992
8	not used	0	0	0
9	number of lines in the area	2875	2000	2000
10	number of elements in each line	5000	2000	2000
11	number of bytes per element (1, 2 or 4)	1	1	1
12	line resolution; number of image lines between consecutive area lines	1	8	8
13	element resolution; number of image elements between consecutive area elements	1	8	8
14	maximum number of bands per line of the area	1	1	1
15	length of the DATA block line prefix, in bytes	0	0	0
16	McIDAS user project number under which the area was created	0	0	0
17	ingest date; date the area was created; provided by the ingesting computer; YYDDD	0 (not used)	0 (not used)	0 (not used)
18	ingest time; time the area was created; provided by the ingesting computer; HHMMSS	0 (not used)	0 (not used)	0 (not used)
19	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)	2**(channel -1) (some products don't have channel numbers)	2**(channel -1) (some products don't have channel numbers)	2**(channel -1) (some products don't have channel numbers)
20-24	satellite specific information	0 (not used)	0 (not used)	0 (not used)
25-32	memo; 32 ASCII characters available for comments	a brief description of what parameter is in the data field	a brief description of what parameter is in the data field	a brief description of what parameter is in the data field
33	area file number	0	last four digits of the filename	last four digits of the filename
34	byte offset to the start of the area file's DATA block	768	768	768
35	byte offset to the start of the area file's NAV block	256	256	256
36	validity code	0 (not used)	0 (not used)	0 (not used)
37-45	satellite specific	0	0	0
46	actual image start date; date the ingestor begins receiving image data; YYYDDD	0 (not used)	0 (not used)	0 (not used)
47	actual image start time; time the ingestor begins receiving image data; HHMMSS	0 (not used)	0 (not used)	0 (not used)
48	actual starting scan line; the first scan line received by the ingestor	1 (not used)	1 (not used)	1 (not used)
49	length of the DATA block line prefix documentation region, in bytes	0	0	0
50	length of the DATA block line prefix calibration region, in bytes	0	0	0
51	length of the DATA block line prefix level map region, in bytes	0	0	0
52	image source type; for example, VISR, VAS, AAA, ERBE, AVHR	VISR	VISR	VISR
53	calibration type; units in which the digital data is stored; for example, RAW, TEMP, BRIT	BRIT	BRIT	BRIT
54-59	internal use only; initialized to 0	0	0	0
60	byte offset to the beginning of the area file's AUX block	0	0	0
61	length of the area file's AUX block, in bytes	0	0	0
62	not used	0	0	0
63	byte offset to the beginning of the area file's CAL block	0	0	0
64	number of comment records in the area file's AUDIT block	0	0	0

Navigation Block

The Navigation Block consists of 512 bytes of intermixed 4-byte integers (words) and ASCII characters. The parameters are as follows:

NOTE: Mercator16 will be added soon

Word Contents Mercator8 NP Stereo SP Stereo
1 Navigation type; 4 ASCII characters MERC PS PS
2 Image line of equator/north pole/south pole 5000 0 0
3 Image element of equator/north pole/south pole 5000 0 0
4 Standard latitude (DDDMMSS) 0 600000 -600000
5 Grid spacing at standard latitude (meters; see Words 12 & 13 in Area Block.) 8000 1000 1000
6 Normal longitude (DDDMMSS) 1600000 1500000 0
7 Equatorial radius of planet (meters) 6378388 6378388 6378388
8 Eccentricity of planet (x1000000) 81992 81992 81992
9 Coordinate type 0 (planetodetic) 0 (planetodetic) 0 (planetodetic)
10 Longitude convention 0 (west positive) 0 (west positive) 0 (west positive)
11 Latitude of pole (DDDMMSS) 0 (not used) 0 (North Pole assumed) -900000
12-120 Reserved 0 0 0
121-128 Memo; 32 ASCII characters NULL (not used) NULL (not used) NULL (not used)

Word	Contents	Mercator8	NP Stereo	SP Stereo
1	Navigation type; 4 ASCII characters	MERC	PS	PS
2	Image line of equator/north pole/south pole	5000	0	0
3	Image element of equator/north pole/south pole	5000	0	0
4	Standard latitude (DDDMMSS)	0	600000	-600000
5	Grid spacing at standard latitude (meters; see Words 12 & 13 in Area Block.)	8000	1000	1000
6	Normal longitude (DDDMMSS)	1600000	1500000	0
7	Equatorial radius of planet (meters)	6378388	6378388	6378388
8	Eccentricity of planet (x1000000)	81992	81992	81992
9	Coordinate type	0 (planetodetic)	0 (planetodetic)	0 (planetodetic)
10	Longitude convention	0 (west positive)	0 (west positive)	0 (west positive)
11	Latitude of pole (DDDMMSS)	0 (not used)	0 (North Pole assumed)	-900000
12-120	Reserved	0	0	0
121-128	Memo; 32 ASCII characters	NULL (not used)	NULL (not used)	NULL (not used)

Data Block

The last thing in the file is the Data Block. (The mapped AMSU data files do not have an AUX block, a CAL block, or an AUDIT block.) Each datum (scan spot, pixel, element) is represented by one byte (0-255) as explained in the second table of the Mapped Data page. The total number of bytes in the Data Block is the product of Area Block Words 9 and 10.

Shortcut

To process the mapped AMSU files without using McIDAS, follow these steps:

Find the file which contains the parameter you want.
Read the first 768 bytes of each file. Extract, if you wish, the date and time information in words 4 and 5 as described in the Area Block.
Read the mapped data (in the Data Block, one byte per pixel).
Grid the map using the corner information in the projections table (above).

Questions?

If you have questions about any of this, contact me, Stan Kidder, at kidder@cira.colostate.edu.