I am working on Hyperion hyperspectral imagery and I cannot figure out whether L1GST level does do show DN values, radiance or reflectance.
The values are scaled to limit the amount of saturation and storage space. Undoing the scaling with simple band math will convert the scaled values to absolute radiance. The Hyperion documentation recommends using FLAASH or ACORN to convert radiance to reflectance.
Detailed instructions on how to rescale the data are available in the EO-1 User Guide v. 2.3 on pp. 18 - 21. Instructions on converting radiance to reflectance start on p. 22.