Data are provided as daily SIR files and associated GIF images, and 4-day average SIR files and associated GIF images.
Each SIR file consists of one 512-byte header containing all the information required to read the remainder of the file and the map projection information required to map pixels to latitude and longitude points on the Earth's surface. Pixel values are stored as 2-byte integers in big-endian format. Scale factors to convert the pixel values to native floating point units are stored in the file header.
The SIR file dimensions are 191 columns by 267 rows. SIR images are stored in row-scanned (left to right) order from the lower left corner up through the upper right corner. The origin of pixel 1,1 is the lower left corner of the image. The array index n of the i,j pixel where i is horizontal and j is vertical is given by using the following formula: n=(j-1)*Nx+i where Nx is the horizontal dimension of the image.
Image files are provided in GIF format for quick views. The grayscale for each GIF is -30 to 0 dB, black to white. Values less than -32 dB indicate no data. The text in the lower-left corner of the image shows the year and day range of the data. The bright spots are urban areas.