Products:NSIDC SSMI NRT SEAICE
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Format
Data are scaled, unsigned flat binary with one byte per pixel, and therefore have no byte order, or endianness. Data are stored as one-byte integers representing scaled sea ice concentration values. Range section for more information. For each data file, a corresponding browse image file in PNG format is also provided.
The file format consists of a 300-byte descriptive header followed by a two-dimensional array of one-byte values containing the data. The file header is composed of:
- a 21-element array of 6-byte character strings that contain information such as polar stereographic grid characteristics
- a 24-byte character string containing the file name
- a 80-character string containing an optional image title
- a 70-byte character string containing ancillary information such as data origin, data set creation date, etc.
For compatibility with ANSI C, IDL, and other languages, character strings are terminated with a NULL byte.
The file header can be accessed in a variety of ways. For example, it can be treated as a simple sequence of bytes containing ASCII character strings or as a complex data structure of arrays. Table 1 describes the file header.
| Bytes | Description |
|---|---|
| 1-6 | Missing data integer value |
| 7-12 | Number of columns in polar stereographic grid |
| 13-18 | Number of rows in polar stereographic grid |
| 19-24 | Unused/internal |
| 25-30 | Latitude enclosed by polar stereographic grid |
| 31-36 | Greenwich orientation of polar stereographic grid |
| 37-42 | Unused/internal |
| 43-48 | J-coordinate of the grid intersection at the pole |
| 49-54 | I-coordinate of the grid intersection at the pole |
| 55-60 | Five-character instrument descriptor (SMMR, SSM/I) |
| 61-66 | Two descriptors of two characters each that describe the data; (for example, 07 cn = Nimbus-7 ice concentration) |
| 67-72 | Starting Julian day of grid data |
| 73-78 | Starting hour of grid data (if available) |
| 79-84 | Starting minute of grid data (if available) |
| 85-90 | Ending Julian day of grid data |
| 91-96 | Ending hour of grid data (if available) |
| 97-102 | Ending minute of grid data (if available) |
| 103-108 | Year of grid data |
| 109-114 | Julian day of grid data |
| 115-120 | Three-digit channel descriptor (000 for ice concentrations) |
| 121-126 | Integer scaling factor |
| 127-150 | 24-character file name (without file-name extension) |
| 151-230 | 80-character image title |
| 231-300 | 70-character data information (creation date, data source, etc.) |
The data can be read with image processing software by specifying a 300-byte header, with an image size of 304 columns x 448 rows for Arctic data and 316 columns x 332 rows for Antarctic data. In a high-level programming language or image processing software, declare a 300-byte array for the header and an array (for example, 304 x 448 for Arctic) for the image. Read the 300-byte array first, then read the image array.
