Standard Image Files (FIS) are files designed for direct access on disk, the record lengths are constant. FIS is a file structure that can store satellite data, and is why it can support multichannel images.
The FIS is broken down into 3 areas:

1. Header Description (DE): date, satellite, orbit, number of points, lines, channels,
2. Image Data (DI): data specific to the satellite or programme result,
3. Auxiliary Data (DA): location, calibration, missing lines, etc.

Header Description (DE)

1. The DE zone is in ASCII and composed of 2 records (see list attached).
   Only the first record is effective for a limited use. In particular, it contains the length of the records in NOR bytes (bytes 359 to 363).
   The second record is used to address the DA zone for direct access. For each type of auxiliary data, one determines whether the data is present and the number of corresponding records.

Image Data (DI)

1. The DI zone is a succession of satellite data words or programme results such as a vegetation index or a land/sea mask. These words can be 1, 2 or 4 bytes long depending on the TYP field of the DE (bytes 45-48) which will have the value I1, I2 or I4. The DI can be considered as a 3-dimensional table: pixel, line, channel.
   However, the organisation of these 3 dimensions can be one of 6 combinations, p, l, c. This organisation is encoded according to the ORG field of the DE (bytes 41-44).
   In general, and in particular for projection images, the DIs are encoded in 1 or 2 bytes and organised in PLC with a record for all the points of a channel line.

Auxiliary Data (DA)

1. The content of this zone is described in the FIS reference document.

Size of physical records

1. The size of the physical records can be determined as follows, depending on the organisation and size in bytes of the image pixels:
   
   PLC organisation (e.g. cartographic projection file)
   recphys = number of pixels x pixel size
   
   PCL organisation (e.g. AVHRR file) or CPL (e.g. LUX file)
   recphys = number of pixels x number of channels x pixel size.

Calculation of header data length

1. The length of the header data logical records is at least 512 bytes.
   
   There are therefore two possibilities:
   
2. The physical record length is greater than or equal to 512 bytes:
   the header data uses 2 physical records with bytes of 513 at the end that are meaningless.
3. The physical record length is less than or equal to 512 bytes:
   each header data item uses a physical record number equal to:
   if modulo (512, physical record) = 0 nbrecde = 512/recphys
   otherwise nbrecde = 512/recphys + 1.
4. 
   Proposal for a simple method for reading the FIS
   
   

   1- Decode the strictly necessary fields of the DE (Typ, Org, MxP, MxL, MxC, NOR)
   or
   skip the header records, as the record sizes are known by the documentation or the mail accompanying the files.
   nbrecde = 2 or nbrecde = 512/recphys + 1 or nbrecde = 512/recphys
   
   2- Read the image data according to the organisation set:
   E.g. For a cartographic projection image = PLC
   do 100 ican = 1, nbcan
   do 100 lin = 1, nblin
   irec = nbrecde + (ican - 1) * nblin + lin
   read(lu,rec=irec) (tab(ipix,lin,ican),ipix=1,nbpix)
   100 continue
   
   Example:
   For a Master Plus band AVHRR mage= CPL
   do 100 lin = 1, nblin
   irec = nbrecde + lin
   read(lu,rec=irec) (tab(ican,ipix,lin),ican=1,nbcan,ipix=1,nbpix)
   100 continue
   
   3- It is assumed that the problem of geographic location is resolved easily by documentation on the image supplied and that the client requested a particular projection that he knew.

Description of the FIS header data

1. Field number	Field name	Row	Format	Description
   01	FIL	001	a40	FIS name
   FIS characteristics
   02	ORG	041	a4	Organisation
   03	TYP	045	a4	Type
   04	MXP	049	i5	Maximum number of points
   05	MXL	054	i5	Maximum number of lines
   06	MXC	059	i5	Maximum number of channels
   Identification of the FIS creation
   07	AUC	064	a20	Author and programme
   08	DJC	084	i5	Julian date
   09	SER	089	a20	Service
   10	TIT	109	a80	Title
   Identification of an FIS update
   11	AUM	189	a20	Author and programme
   12	DJM	209	i5	Julian date
   Parameters of the mission and the IMAGE DATA instrument
   13	MIS	214	i2	Mission numerical code
   14	NIM	216	i2	Mission order number
   15	INS	218	i2	Instrument numerical code
   16	OSS	220	i5	Orbit, slot or station number
   17	IJR	225	f14.8	Julian time (HNA, slot or observation)
   18	LLP	239	f7.2	LNA, LSP or physical parameters of the station
   19	CSC	246	a4	instrument scan direction: "SN" South to North, "NS" North to South "EW" East to West, "WE" West to East
   IMAGE DATA satellite positions (in angle decrees)
   20	ANW	250	f7.2	NW corner latitude
   21	ONW	257	f7.2	NW corner longitude
   22	ANE	264	f7.2	NE corner latitude
   23	ONE	271	f7.2	NE corner longitude
   24	ASE	278	f7.2	SE corner latitude
   25	OSE	285	f7.2	SE corner longitude
   26	ASW	292	f7.2	SW corner latitude
   27	OSW	299	f7.2	SW corner longitude
   IMAGE DATA positions with respect to the mission
   28	NPP	306	i5	Number of first point
   29	NPL	311	i5	Number of first line
   30	NDP	316	i5	Number of last point
   31	NDL	321	i5	Number of last line
   IMAGE DATA temporal positions
   32	IJD	326	f14.8	Start Julian time
   33	IJF	340	f14.8	End Julian time
   IMAGE DATA missing lines
   34	NLM	354	i5	Number of missing lines
   Other FIS parameters
   35	NOR	359	i5	Number of bytes per record
   36	NRI	364	i6	Number of IMAGE DATA records
   37	NVE	370	a12	Number of the "FIS Package" version used
   38	NMI	382	i6	Number of IMAGE DATA missions
   39	NBR	388	i6	Total number of FIS records
   Free space
   40	---	394	---	Free space of 119 bytes