Skip to main content
Microwave Earth Remote Sensing

BYU-MERS SIR Image Format - Documentation and Source

The BYU-MERS "sir" image file format was developed by the Brigham Young University MERS Laboratory in the early 1990's to store images of the Earth along with the information required to earth-locate the image pixels.

A "sir" file consists of one or more 512 byte headers containing all the information required read the remainder of the file and the map projection information required to map pixels to lat/lon on the Earth surface.

Image pixel values are generally stored as 2 byte (high order byte first) integers though can be stored as bytes or IEEE floating point. The latter is not portable to all machines and so is not recommended but is available. Scale factors to convert the integer or byte pixel values to native floating point units are stored in the file header.

The origin of the images is in the lower left corner of the displayed image. The earth location of a pixel is identified with its lower-left corner.

The standard sir format supports a variety of image projections including:

  • Rectangular array (no projection)
  • A rectangular lat/lon array
  • Two different types of Lambert equal-area projections which can be use in both non-polar and polar projections
  • Polar stereographic projections
  • EASE grid polar and global projection with various resolutions
  • EASE2 grid polar and global projections (includes CETB standards)

SIR image file format links:

Note: standard source code in C, Fortran, IDL, PVWAVE, Python, and Matlab to read/write/display SIR image files are available at this location. Sample files and utilities to convert SIR image files to other formats are also available at this location.