Why are laser footprint shape parameters not available for low energy campaigns?

Several parameters help quantify the shape of the GLAS laser footprint, which changes slightly for each campaign.  These parameters are:

GLAS Binary Products

i_tpintensity_avg Transmit pulse intensity - frame average
i_tpazimuth_avg Transmit pulse azimuth - frame average
i_tpeccentricity_avg Transmit pulse eccentricity - frame average
i_tpmajoraxis_avg Transmit pulse major axis - frame average

GLAS HDF5 Products

d_tpintensity_avg Transmit pulse intensity - frame average
d_tpazimuth_avg Transmit pulse azimuth - frame average
d_tpeccentricity_avg Transmit pulse eccentricity - frame average
d_tpmajoraxis_avg Transmit pulse major axis - frame average

These parameters are fine on most campaigns, but in the later campaigns (after Laser 2D), the laser energy was too weak to be able to compute the pulse shape, so these parameters show values of 0.