Brief description of FIS files


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
satmos2006 Météo-France