The background swath fitting process is considered to fail a particular Pass 1 swath if any of the following conditions apply.
When a solution for a Pass 1 swath fails any of these tests, the background solution is set to zero for the entire swath. If this occurs for an isolated swath, an interpolated solution based on the two neighboring Pass 1 swaths is substituted for the original solution. If two consecutive Pass 1 swaths, or a total of five, have null values based on these conditions, the background arrays for the entire image are set to zero, and BCKGRD has ``given up" on the image. This occurs for an exceedingly small number of images (e.g., about 13 out of 12,898 images in the GSFC high-dispersion archives), usually as a consequence of a major portion of the image being missing. This condition is documented in the processing history log.