We seem to be short on documentation for the fields in these files.
For 2000, at least, the data fields are:
1) X (state plane)
2) Y (state plane feet)
3) Z (orthometric NAVD88 feet)
4) Z (ellipsoid)
5) GPS time of the week (in seconds)
6) return #
7) scan angle
8) off-nadir angle
9) GPS week
Sound right?