Metadata for "Height" variable field

The metadata defining the variable "Height" is incorrect.  The metadata 
states that "Height" is the altitude of the BOTTOM of the range bins.  
In fact, "Height" is the altitude to the MIDDLE of the range bins.  
This amounts to an interpreted difference of 150 meters, since the range 
bins are 300 meters in width.  The actual data values are unchanged, only 
interpretation of the altitude is different.  This pertains to all existing 
data produces from the MPL02 at the SGP site.

• Laser output energy per pulse(energy_monitor)
• Dummy altitude for Zeb(alt)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Time offset of tweaks from base_time(time_offset)
• base time(base_time)
• Cloud base height, measured by MPL(cloud_base_height)
• Detector Temperature(detector_temp)
• lon(lon)
• Array of heights for the range gates(height)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Binary data quality flag(cloud_base_height_dq_flag)
• Filter Temperature(filter_temp)
• Instrument Temperature(instrument_temp)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Voltage level which operates the thermistor(voltage_10)
• Laser Temperature(laser_temp)
• Number of laser shots recorded(shots_summed)
• Voltage level which operates the energy monitor(voltage_15)
• Background Signal(background_signal)
• lat(lat)