Products:NSIDC SSMI NRT SEAICE

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Revision as of 12:15, 19 April 2013

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.

Table 1. File Header Description

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.