Since this data represents the accumulation of data over years from many different sources, image formats are variable. Often there is the usual README file that explains the format or files have a corresponding .hdr file that may give some indication of the format. The most common formats of this data is raw raster (no header) data or the block format (with header) for using Image Calc or RCDE. We try not to be too choosy on formats and attempt to use data in whatever form it comes in. Data we created years ago was raw raster, data we have created more recently is in the RCDE format.
Image data possibilities: