NSA/VCEIL/C1 - Gaps in data

When the CT25K ceilometer was replaced with a new CL31, checksum errors began occurring at 
regular 6-min intervals and several things were done to diagnose the problem, including 
changing the serial cable and trying different computer types. It was finally corrected 
by replacing the computer with one in which hyperthreading was disabled by default in the 
BIOS.

• Warning, alarm, and internal status information(status_string)
• Millivolts at internal ADC input (0 to 2500)(background_light)
• Percentage of nominal factory setting (0 to 999%)(receiver_sensitivity)
• Sum of detected and normalized backscatter(sum_backscatter)
• Percentage of nominal factory setting (0 to 999%)(laser_pulse_energy)
• Window contamination(window_contamination)
• Vertical visibility(vertical_visibility)
• Distance to the center of the corresponding range bin(range)
• Flag indicating aeri retrieval status(status_flag)
• 6 character string describing instrument measurement parameters(measurement_parameters)
• Detection status.(detection_status)
• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• Degrees from vertical (-15 to +90)(tilt_angle)
• Lowest cloud base height detected(first_cbh)
• Time offset from base_time(time_offset)
• base time in epoch(base_time)
• Third cloud base height(third_cbh)
• Second lowest cloud base height(second_cbh)
• Laser temperature(laser_temperature)
• Altitude of highest signal(alt_highest_signal)