NIM/SKYRAD/M1 - IRTs do not agree with AERI

Since deployment at PYE, and then at NIM, the AMF SKYRAD IRT measured about 10K higher sky 
temperatures than the AERI and the MWRP IRT measureed about 20K higher than the AERI.  
Several actions were taken to diagnose the problem including confirming the correct 
configuration of the IRTs and data logger, cleaning the mirror and lens, and replacing the mirror.

After several days of rain beginning 6/2/2006, the three instruments came into agreement. 
It is unknown whether this was a problem with the AERI, MWRP-IRT or SKYRAD-IRT.

• sky_ir_temp_min
• Temperature, Sky Infra-Red(sky_ir_temp)
• sky_ir_temp_max

NIM/SKYRAD/M1 - Instrument ventilator problem

Data quality office first reported that PIR1 and PIR2 appear to be deviating more than 
typical during the daylight hours.  It was found that the Skyrad PIR ventilator fans were 
building up debris on the intake air filter.  Obstructed air flow results in solar heating 
of the PIR ventilator housing in the later part of the day and biasing the incomming IR 
irradiance values. The slow buildup was insidious and wasn't discovered and corrected 
(i.e. ventilator fans cleaned on a regular and frequent basis) until Feb 23rd. On or around 
December 23rd was when this problem may have first started.  We are unable to quantify the 
extent of the problem in W/m2.  Normal deviation between PIRs is typically 3-5 W/m2.

• inst_down_long_shaded2_dome_temp
• down_long_hemisp_shaded1_std
• down_long_hemisp_shaded1_min
• down_long_hemisp_shaded1_max
• Irradiance, longwave, downwelling, hemispheric, thermopile (Shaded Pyrgeometer2)(inst_down_long_hemisp_shaded2_tp)
• Irradiance, longwave, downwelling, hemispheric, shaded pyrgeometer1(down_long_hemisp_shaded1)
• down_long_hemisp_shaded2_min
• Irradiance, longwave, downwelling, hemispheric, shaded pyrgeometer2(down_long_hemisp_shaded2)
• down_long_hemisp_shaded2_max
• down_long_hemisp_shaded2_std
• inst_down_long_shaded1_dome_temp
• inst_down_long_shaded2_case_temp
• inst_down_long_shaded1_case_temp
• Irradiance, longwave, downwelling, hemispheric, thermopile (Shaded Pyrgeometer1)(inst_down_long_hemisp_shaded1_tp)

NIM/SKYRAD/M1 - Unknown problem with PIR1

Spikes in Shaded 1 occur frequently during this time period, resulting in differences b/t 
shaded1 and shaded2 exceeding 20W/m2.  Instrument connections were checked and a spare 
PIR instrument was tried in the place of PIR1 (shaded1).  After returning the original PIR1 
to its original location data again looked good and very close to PIR2.  Problem appears 
resolved but exact cure is unknown.

• inst_down_long_shaded2_dome_temp
• down_long_hemisp_shaded1_std
• down_long_hemisp_shaded1_min
• down_long_hemisp_shaded1_max
• Irradiance, longwave, downwelling, hemispheric, thermopile (Shaded Pyrgeometer2)(inst_down_long_hemisp_shaded2_tp)
• Irradiance, longwave, downwelling, hemispheric, shaded pyrgeometer1(down_long_hemisp_shaded1)
• down_long_hemisp_shaded2_min
• Irradiance, longwave, downwelling, hemispheric, shaded pyrgeometer2(down_long_hemisp_shaded2)
• down_long_hemisp_shaded2_max
• down_long_hemisp_shaded2_std
• inst_down_long_shaded1_dome_temp
• inst_down_long_shaded2_case_temp
• inst_down_long_shaded1_case_temp
• Irradiance, longwave, downwelling, hemispheric, thermopile (Shaded Pyrgeometer1)(inst_down_long_hemisp_shaded1_tp)

NIM/SKYRAD/M1 - Tracker inoperative

Starting on 9/12 the NIM radiometer tracker drifted enough due to sinking supports and a 
drifting clock that the direct normal measurments (NIP) and the downwelling hemispheric 
diffuse shortwave measurments (8-48) were adversely affected in the afternoon hours.  The 
shortwave hemispheric global instrument (PSP) and downelling hemispheric longwave shaded1 
and shaded2 (PIR) are unaffected by this problem. 

The tracker problem greatly affected direct measurements and affected the diffuse 
measurement to a lesser extent. There are no redundant measurements for these instruments.  
However, during this time range the data collected before local noon (aprox 1140GMT) for all 
shortwave Skyrad instruments appear to be good.

• Irradiance, shortwave, direct normal, pyrheliometer, mifkba(short_direct_normal_min)
• Irradiance, shortwave, downwelling, diffuse, hemispheric, pyranometer(down_short_diffuse_hemisp)
• down_short_diffuse_hemisp_std
• short_direct_normal_std
• Shortwave Direct Normal Irradiance(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Irradiance, shortwave, downwelling, diffuse, hemispheric, pyranometer, minima(down_short_diffuse_hemisp_min)
• Irradiance, shortwave, downwelling, diffuse, hemispheric, pyranometer, maxima(down_short_diffuse_hemisp_max)

NIM/SKYRAD/M1 - IRT bias

Measurements of sky temperature, especially those <250K, were positively biased compared 
with AERI because there was no compensation for the reflectivity of the gold mirror. The 
problem was corrected by changing the IRT emissivity from 1.000 to 0.987.

Use sky temperature measurements less than 230K with caution. Biases as large as 30K have 
been observed when the actual temperature, as measured by AERI, is less than 210 K.

• sky_ir_temp_min
• Temperature, Sky Infra-Red(sky_ir_temp)
• sky_ir_temp_max