TWP/SKYRAD/C2 - Reprocess: Incorrect datalogger program affecting PIR1 and PIR2 
downwelling longwave

The excitation delays using in measuring the PIR1 case thermistor commonly named "Case1" 
and the PIR2 dome thermistor called "Dome2" were discovered to have been incorrectly set 
to 0 in the Skyrad datalogger program when the new CR23X based Skyrad loggers were 
installed.  The result of no delay in these measurements results in an error in the measured 
resistance of the thermistors, Case1 and Dome2, and thus the calculated PIR1 and PIR2 
irradiances.  The absolute value of the errors are inversely proportial to temperature.

Users can apply the temperature dependent irradiance corrections shown in the table below. 
 Recall that the reported uncertainty of PIRs is typically +-.25% to +-.5% or 1 to 2 
W/m2. The error corrections become the same order of magnitude or larger than the instrument 
uncertainties at or below 260K or 9F.
 
Irradiance Correction Table for Skyrad (TWP and NSA) DIR1 and DIR2 Irradiance
		DIR1	DIR1	DIR2	DIR2
	T[F]	Tcase[K]	Correction[W/m2]	Tdome[K]       
		Correction[W/m2]
	109.4	316.13	0.00	316.13	0.00
	100.5	311.20	-0.15	311.20	0.12
	93.2	307.14	-0.12	307.14	0.10
	87.0	303.70	-0.10	303.70	0.08
	81.6	300.70	-0.17	300.70	0.14
	77.0	298.15	-0.22	298.15	0.18
	59.4	288.35	-0.34	288.35	0.27
	47.4	281.72	-0.23	281.72	0.18
	38.5	276.74	-0.42	276.74	0.34
	31.3	272.77	-0.48	272.77	0.38
	25.4	269.48	-0.61	269.48	0.49
	20.3	266.67	-0.67	266.67	0.54
	16.0	264.25	-0.82	264.25	0.66
	12.1	262.11	-0.98	262.11	0.79
	8.7	260.19	-0.97	260.19	0.78
	5.6	258.46	-1.07	258.46	0.86
	2.7	256.89	-1.17	256.89	0.94
	0.1	255.44	-1.33	255.44	1.07
	-2.3	254.11	-1.41	254.11	1.13
	-4.5	252.87	-1.43	252.87	1.15
	-6.6	251.71	-1.52	251.71	1.22
	-8.5	250.63	-1.63	250.63	1.31
	-10.4	249.62	-1.73	249.62	1.39
	-12.2	248.58	-1.79	248.58	1.44
	-15.4	246.82	-1.93	246.82	1.55
	-18.3	245.23	-2.05	245.23	1.65
	-20.9	243.78	-2.22	243.78	1.78
	-23.3	242.44	-2.36	242.44	1.89
	-25.5	241.21	-2.58	241.21	2.07
	-27.5	240.07	-2.65	240.07	2.13
	-29.5	239.01	-2.75	239.01	2.21
	-31.3	238.00	-3.02	238.00	2.42

• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer1(down_long_hemisp_shaded1)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer2, Minima(down_long_hemisp_shaded2_min)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer2, Standard
  Deviation(down_long_hemisp_shaded2_std)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer2(down_long_hemisp_shaded2)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer1, Standard
  Deviation(down_long_hemisp_shaded1_std)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer2, Maxima(down_long_hemisp_shaded2_max)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer1, Maxima(down_long_hemisp_shaded1_max)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer1, Minima(down_long_hemisp_shaded1_min)

• Instantaneous Downwelling Pyrgeometer Dome Thermistor Resistance, Shaded
  Pyrgeometer2(inst_down_long_shaded2_dome_resist)
• Instantaneous Downwelling Pyrgeometer Thermopile, Shaded Pyrgeometer2(inst_down_long_hemisp_shaded2_tp)
• Instantaneous Downwelling Pyrgeometer Thermopile, Shaded Pyrgeometer1(inst_down_long_hemisp_shaded1_tp)
• Instantaneous Downwelling Pyrgeometer Case Thermistor Resistance, Shaded
  Pyrgeometer2(inst_down_long_shaded2_case_resist)
• Instantaneous Downwelling Pyrgeometer Case Thermistor Resistance, Shaded
  Pyrgeometer1(inst_down_long_shaded1_case_resist)
• Instantaneous Downwelling Pyrgeometer Dome Thermistor Resistance, Shaded
  Pyrgeometer1(inst_down_long_shaded1_dome_resist)

TWP/SKYRAD/C2 - Reprocess: Longwave Calibration error

Modified pyrgeometer calibration procedures were implemented beginning in December 2003.  
These modified procedures introduced a calibration bias in the longwave data.  The 
previous procedures were re-implemented at all sites between December 2005 and February 2006 to 
restore proper calibrations.                                                             
                The data collected while the incorrect procedures were in place are 
being reprocessing to remove the calibration bias.  Note, this also affected standard 
deviation, maximum and minimum data fields.

• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer1(down_long_hemisp_shaded1)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer2(down_long_hemisp_shaded2)

TWP/SKYRAD/C2 - IRT signal loss

There was a significant drop in logger voltage that corresponds with a loss of the IR 
temperature. This was possibly due to a loose connection.

• Sky/Cloud Infra-Red Temperature Minima(sky_ir_temp_min)
• Sky/Cloud Infra-Red Temperature Maxima(sky_ir_temp_max)
• Sky/Cloud Infra-Red Temperature(sky_ir_temp)
• Sky/Cloud Infra-Red Temperature Standard Deviation(sky_ir_temp_std)

TWP/SKYRAD/C2 - IRT signal

The IRT exhibited a bias of the analog voltage output that caused problems with the 
signals from the other SKYRAD radiometers. The bias was due to corrosion between the power and 
signal connections in the IRT cable. The IRT was disconnected on 10/18/2006 at 01:20 and 
replaced on 11/6/2006 at 23:00 but it too appeared to have grounding problems due to 
internal corrosion and was disconnected on 11/11/2006 at 11:42 and then intermittently 
reconnected for testing. A second spare was installed on 12/4/2006 which did not cause problems 
with the signals from the other instruments.

• Sky/Cloud Infra-Red Temperature Minima(sky_ir_temp_min)
• Sky/Cloud Infra-Red Temperature Maxima(sky_ir_temp_max)
• Sky/Cloud Infra-Red Temperature(sky_ir_temp)
• Sky/Cloud Infra-Red Temperature Standard Deviation(sky_ir_temp_std)

TWP/SKYRAD/C2 - Short direct normal

The short_direct_normal (NIP) data are missing or incorrect due to instrument cable 
failure.  The cable was replaced.

The short_direct_normal can be calculated using the following relationship for shortwave 
radiometers:
global hemispheric = diffuse hemispheric + direct normal *cos (zenith angle)

• Shortwave Direct Normal Irradiance, Pyrheliometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer(short_direct_normal)

• Instantaneous Direct Normal Shortwave Irradiance, Pyrheliometer Thermopile
  Voltage(inst_direct_normal)

TWP/SKYRAD/C2 - IRT calibration

The IRT was not properly calibrated and was able to measure sky temperatures below 273.2 
K. (This instrument was the same one damaged by lightning in November 2005 in Darwin. It 
was returned for repair and received a new lens but was calibrated only down to 0 deg C, 
so the problem was neither detected nor repaired.) The IRT was replaced on 2/22/2007.

• Sky/Cloud Infra-Red Temperature Minima(sky_ir_temp_min)
• Sky/Cloud Infra-Red Temperature Maxima(sky_ir_temp_max)
• Sky/Cloud Infra-Red Temperature(sky_ir_temp)
• Sky/Cloud Infra-Red Temperature Standard Deviation(sky_ir_temp_std)