SHEBA/GNDMFR: Drop in signal

Drop in signal, accompanied by changes in detector temperature and voltage, occurred 
intermittently five times during day for as much as half an hour each time. Data was bad 
during these signal drops and these should be filtered out when using the data.

• mfr_temp
• lat
• alt
• time_offset
• raw_file
• base_time
• logger_volt
• up_hemisp_broadband
• up_hemisp_narrowband
• lon

• base_time
• lon
• time_offset
• up_hemisp_narrowband
• callang_flags
• raw_file
• logger_volt
• up_hemisp_broadband
• cosine_solar_zenith_angle
• lat
• mfr_temp
• alt

• lat
• time_offset
• raw_file
• up_hemisp_broadband
• up_hemisp_narrowband
• logger_volt
• alt
• cosine_solar_zenith_angle
• callang_flags
• mfr_temp
• base_time
• lon