ARM TR-025

> Solar Infrared Radiation Station (SIRS) Handbook
>
> November 2004
>
> T. Stoffel
>
> Work supported by the U.S. Department of Energy,
>
> Office of Science, Office of Biological and Environmental Research

# Contents {#contents .Heading-Front}

[1. General Overview 1](#general-overview)

[2. Contacts 1](#contacts)

[3. Deployment Locations and History
1](#deployment-locations-and-history)

[4. Near-Real-Time Data Plots 2](#near-real-time-data-plots)

[5. Data Description and Examples 2](#data-description-and-examples)

[6. Data Quality 11](#data-quality)

[7. Instrument Details 11](#instrument-details)

**Figures**

[1. 2](#__RefHeading___Toc87419572)

[2. 3](#__RefHeading___Toc87419573)

[3. 4](#__RefHeading___Toc87419574)

[4. 7](#__RefHeading___Toc87419575)

[5. Plan View of SIRS Instrument Locations
13](#__RefHeading___Toc87419576)

[6. Component Summation Calibration 21](#__RefHeading___Toc87419577)

[7. Shade/Unshade Calibration 21](#__RefHeading___Toc87419578)

[8. Photo of PIR BB Production 0809Unit Blackbody Unit in Enclosure
front view 22](#__RefHeading___Toc87419579)

**Tables**

[1. 5](#__RefHeading___Toc87419580)

[2. Flagging Convention for SERI_QC 7](#__RefHeading___Toc87419581)

[3. SIRS Upgrade: Model 8-48 Pyranometer Installation for Diffuse
Irradiance, 4-19-01, Tom Stoffel^1^. 9](#__RefHeading___Toc87419582)

[4. 12](#__RefHeading___Toc87419583)

[5. 17](#__RefHeading___Toc87419584)

# General Overview

The Solar Infrared Radiation Station (SIRS) provides continuous
measurements of broadband shortwave (solar) and longwave (atmospheric or
infrared) irradiances for downwelling and upwelling components. These
1-minute data are collected from a network of stations to help determine
the total energy exchange within the Southern Great Plains CART Site.

\*The current SIRS instrument suite was preceeded as the ARM Operational
broadband instrument suite by the Solar and Infrared Radiation
Observation Station (SIROS) instrument suite which included the MFRSR.
The change to SIRS occurred in 1997-1998 as described in the text below.

# Contacts

## Mentor

### Tom Stoffel National Renewable Energy Laboratory 1617 Cole Blvd. Golden, CO 80401-3393 Phone: 303-384-6395 {#tom-stoffel-national-renewable-energy-laboratory-1617-cole-blvd.-golden-co-80401-3393-phone-303-384-6395 .unnumbered}

### Fax: 303-384-6391 [**Tom_Stoffel@nrel.gov**](mailto:Tom_Stoffel@nrel.gov)  {#fax-303-384-6391-tom_stoffelnrel.gov .unnumbered}

Peter Gotseff (Associate)\
National Renewable Energy Laboratory\
Phone: 303-384-6327\
<peter_gotseff@nrel.gov>

## Instrument Developer

The Eppley Laboratory, Inc.\
12 Sheffield Ave.\
Newport, RI 02840\
Phone: 401-847-1020\
[http://www.eppleylab.com](http://www.eppleylab.com/)

# Deployment Locations and History 

Currently, there are two SIRS located at the Southern Great Plains site:
One at Extended Facility 13 and one at Central Facility 1. Figure 1
shows the location of these two SIRS at SGP:

![](media/image1.jpeg){width="3.1819444444444445in"
height="2.4006944444444445in"}

![](media/image2.jpeg){width="3.1819444444444445in"
height="2.386111111111111in"}

[]{#__RefHeading___Toc87419572 .anchor}Figure 1.

# Near-Real-Time Data Plots

[Daily Plots,](http://r1.sgp.arm.gov/quicklook/sirs/) from SGP
Development System

[SGP Site Scientist Data Quality
Assessment](http://r1.sgp.arm.gov/sst/dq_monitor/sirs.html)

[General Quick
Looks](http://www.nsdl.arm.gov/Visualization/sirs/frame.htm)

# Data Description and Examples

**Typical SIRS Data Time-Series Plots**

Measured data from the suite of six radiometers forming each SIRS is
greatly influenced by the atmospheric conditions and ground cover. The
examples given here represent the common range of shortwave (solar) and
longwave (atmospheric) measurements.

![](media/image3.jpeg){width="5.677777777777778in"
height="4.030555555555556in"}

[]{#__RefHeading___Toc87419573 .anchor}Figure 2.

Data in Figure 2 are typical of the clear-sky conditions at the SGP
during the fall. Near solar noon, when the sun is highest in the sky and
there is the least amount of atmosphere in the photons path to the
surface, the direct normal shortwave (beam) irradiance approaches 1000
Wm^-2^ , the global (total hemispheric) irradiance nears 800 Wm^-2^, the
diffuse (sky) irradiance remains nearly constant at about 50 Wm^-2^, and
the reflected shortwave reaches a peak of 155 Wm^-^2 (or an albedo of
about 19% which is typical for a vegetated surface). Heating of the
surface and the atmosphere is evident from the increasing longwave
(infrared) irradiance measurements. The peak longwave irradiances occur
after solar noon, demonstrating the "thermal lag" of the
earth-atmosphere system response to solar heating. The peak upwelling
longwave irradiance on this day was 488 Wm^-2^ at 19:41 GMT (1:41 PM
local standard time). The peak downwelling (atmospheric) longwave
irradiance was 355 Wm^-2^ at about the same time, producing a net
radiation of 133 Wm^-2^ . The effect of cleaning the pyrheliometer
window is evident from the change in direct normal irradiance prior to
local solar noon. Maintenance records show the pyrheliometer window was
dry, but had light dust removed from the surface at 17:10 GMT. Comparing
the direct normal data before and after the cleaning, 947.81 Wm^-2^ and
963.25 Wm^-2^ respectively, it suggests a decreased irradiance
measurement of 1.6% due to the window contamination.

![](media/image4.jpeg){width="5.722222222222222in"
height="4.054861111111111in"}

[]{#__RefHeading___Toc87419574 .anchor}Figure 3.

Data in Figure 3 are typical of cloudy sky conditions at the SGP during
the fall. With completely overcast conditions, the direct normal
shortwave (beam) irradiance remains near zero all day. Variable cloud
thickness during the day allow the global (total hemispheric) and the
diffuse (sky) irradiance to peak at about 256 Wm^-2^ at 18:20 GMT and a
few hours later. The reflected shortwave reaches a peak of 45 Wm^-^2
(albedo of about 18%). The exchange of infrared radiation is nearly
constant under these conditions, suggesting low clouds. The two SIRS
pyrgeometers indicate 415 W^-2^ of longwave irradiance was consistently
measured at the Central Facility on 23 September 1997.

## Data File Contents

### Primary Variables and Expected Uncertainty

The following *broadband* irradiance measurements are available from the
SIRS platform:

DOWNWELLING SHORTWAVE (0.3 to 3.0 micrometers)

1.  Direct Normal (beam) irradiance measured by a pyrheliometer with a
    5.7 degree field of view.

2.  Diffuse Horizontal (sky) irradiance measured by a shaded and
    ventilated pyranometer with a hemispherical field of view, but
    blocked from the direct normal irradiance by a tracking ball.

3.  Total Hemispheric (global) irradiance measured by an unshaded and
    ventilated pyranometer.

    DOWNWELLING LONGWAVE (4.0 to 50 micrometers)

4.  Total Hemispheric (atmospheric) irradiance measured by a shaded and
    ventilated pyrgeometer with a hemispheric field of view.

    UPWELLING SHORTWAVE (0.3 to 3.0 micrometers)

5.  Reflected irradiance measured by an inverted pyranometer with a
    hemispheric field of view.

    UPWELLING LONGWAVE (4.0 to 50 micrometers)

6.  Irradiance measured by an inverted pyrgeometer with a hemispheric
    field of view.

#### Definition of Uncertainty

Estimating radiometer measurement uncertainties continues to be a topic
for additional research. Based on experiences with these and similar
instruments for renewable energy applications, the following estimated
measurement uncertainties conservatively apply to SIRS measurements.

[]{#__RefHeading___Toc87419580 .anchor}Table 1.

  ----------------- ------------------ -------------- --------------- -------------------
  **Measurement**   **Abbreviation**   **Radiometer   **Typical       **Estimated
                                       Model**        Responsivity\   Measurement
                                                      (μV/Wm^-2^)**   Uncertainty^\*^**

  Direct Normal\    DNI                NIP            8.0             ±3.0% or\
  (beam)                                                              4 Wm^-2^

  Diffuse           DD                 PSP            9.0             ±6.0% or\
  Horizontal\                                                         20 Wm^-2^
  (sky)                                                               

  Downwelling       DS                 PSP            9.0             ±6.0% or\
  Shortwave\                                                          10 Wm^-2^
  (global)                                                            

  Downwelling       DIR                PIR            4.0             ±2.5% or\
  Longwave\                                                           4 Wm^-2^
  (atmospheric)                                                       

  Upwelling         US                 PSP            9.0             ±6.0% or\
  Shortwave\                                                          15 Wm^-2^
  (reflected)                                                         

  Upwelling         UIR                PIR            4.0             ±2.5% or\
  Longwave\                                                           4 Wm^-2^
  (terrestrial)                                                       

  **^\*^**Field                                                       
  measurement                                                         
  uncertainties                                                       
  include the                                                         
  uncertainties                                                       
  associated with                                                     
  instrument                                                          
  calibration,                                                        
  installation,                                                       
  operation and                                                       
  maintenance.                                                        
  ----------------- ------------------ -------------- --------------- -------------------

### Secondary/Underlying Variables

This section is not applicable to this instrument.

### Diagnostic Variables

This section is not applicable to this instrument.

### Data Quality Flags

The SIRS data quality assessments are based on the methods developed by
the National Renewable Energy Laboratory (formerly the Solar Energy
Research Institute - SERI). A description of the SERI-QC approach to
automated quality assessment of broadband radiometric data can be found
at the [NREL Renewable Resource Data
Center](http://rredc.nrel.gov/solar/pubs/seri_qc).

The ARM Program has incorporated the SERI-QC concepts and upgraded the
automated capabilities for SIRS data quality assessment. Information
about the new Data Quality Management System (DQMS) can be found at
<http://www.dqms.com/dqmspart.htm>.

As part of the effort to produce the National Solar Radiation Data Base
(1961-1990), NREL (at that time called the *Solar Energy Research
Institute*) developed an automated quality assessment tool, *SERI-QC*
for evaluating hourly measurements and model estimates of broadband
shortwave irradiance data for 239 locations in the U.S. The ARM Program
has since supported the development of the *Data Quality Management
System Version 3.0 (DQMS-3)* which incorporates the *SERI_QC* methods.
Additional elements of *DQMS-3* are used for assessing SIRS data quality
and providing the means for correcting known instrumentation responses:

1.  SERI_QC converts 1-minute broadband shortwave irradiance data from
    flux densities in Watts per square meter to non-dimensional units
    normalized to the coincident extraterrestrial (exoatmospheric)
    values:

    K~T~ = Total Hemispheric / Extraterrestrial = DS / ETR

    K~N~ = Direct Normal / Extraterrestrial Normal = DNI / ETRN

    K~D~ = Downwelling Diffuse / Extraterrestrial = DD / ETR

    Resulting in the relationship among the three measured shortwave
    components:

    K~T~ = K~N~ + K~D~

    Failing the above "3-component" test, pairs of irradiance data can
    be evaluated using the transformation.

    When presented in K-Space, the data can be evaluated based on
    acceptable limits determined by physical limits, internal
    consistency, and careful inspection of historical data.

![](media/image5.png){width="2.6958333333333333in"
height="2.290277777777778in"}

[]{#__RefHeading___Toc87419575 .anchor}Figure 4.

SERI_QC assigns a two-digit quality flag to each irradiance data element
based on the location in the appropriate K-Space coordinates.

[]{#__RefHeading___Toc87419581 .anchor}Table 2. Flagging Convention for
SERI_QC

+-------+--------------------------------------------------------------+
| **F   | **Description**                                              |
| lag** |                                                              |
+-------+--------------------------------------------------------------+
| 00    | Untested (raw data)                                          |
+-------+--------------------------------------------------------------+
| 01    | Passed one-component test; data fall within max-min limits   |
|       | of Kt, Kn, or Kd                                             |
+-------+--------------------------------------------------------------+
| 02    | Passed two-component test; data fall within 0.03 of the      |
|       | Gompertz boundaries                                          |
+-------+--------------------------------------------------------------+
| 03    | Passed three-component test; data come within ±0.03 of       |
|       | satisfying Kt=Kn+Kd                                          |
+-------+--------------------------------------------------------------+
| 04    | Passed visual inspection; *not used* by SERI_QC              |
+-------+--------------------------------------------------------------+
| 05    | Failed visual inspection; *not used* by SERI_QC              |
+-------+--------------------------------------------------------------+
| 06    | Value estimated; passes all pertinent SERI_QC tests          |
+-------+--------------------------------------------------------------+
| 07    | Failed one-component test; lower than allowed minimum        |
+-------+--------------------------------------------------------------+
| 08    | Failed one-component test; higher than allowed maximum       |
+-------+--------------------------------------------------------------+
| 09    | Passed three-component test but failed two-component test by |
|       | \> 0.05 (K-units)                                            |
+-------+--------------------------------------------------------------+
| 10-93 | Failed two- or three-component tests in one of four ways.    |
|       |                                                              |
|       | To determine the test failed and the manner of failure (high |
|       | or low), examine the remainder of the calculation (flag + 2) |
|       | / 4.                                                         |
|       |                                                              |
|       | Rem Failure:                                                 |
|       |                                                              |
|       | 0            Parameter too low by three-component test (Kt = |
|       | Kn + Kd)                                                     |
|       |                                                              |
|       | 1            Parameter too high by three-component test (Kt  |
|       | = Kn + Kd)                                                   |
|       |                                                              |
|       | 2            Parameter too low by two-component test         |
|       | (Gompertz boundary)                                          |
|       |                                                              |
|       | 3            Parameter too high by two component test        |
|       | (Gompertz boundary)                                          |
|       |                                                              |
|       | The magnitude of the test failure (distance in K-units) is   |
|       | determined from:                                             |
|       |                                                              |
|       | D = INT ( ( flag + 2) / 4) / 100.                            |
+-------+--------------------------------------------------------------+
| 94-97 | Data fall into a physically impossible region where Kn \> Kt |
|       | by K-space distances of 0.05 to 0.10 (94), 0.10 to 0.15      |
|       | (95), 0.15 to 0.20 (96), and ≥0.20 (97)                      |
+-------+--------------------------------------------------------------+
| 98    | Not used                                                     |
+-------+--------------------------------------------------------------+
| 99    | Missing data                                                 |
+-------+--------------------------------------------------------------+

More detailed information about SERI-QC is available from the Renewable
Resource Data Center: [http://rredc.nrel.gov](http://rredc.nrel.gov/).

Additional information may also be found at [SIRS Data Object Design
Changes](http://science.arm.gov/tool/dod/showdod.php?Inst=sirs) for ARM
netCDF file header descriptions.

### Dimension Variables

This section is not applicable to this instrument.

## Annotated Examples

This section is not applicable to this instrument.

## User Notes and Known Problems

### Incorrect Metadata {#incorrect-metadata .unnumbered}

When SIRS radiometers are changed for recalibration or other reasons,
the site operators immediately enter the new serial numbers and
calibrations in to the Campbell Scientific, Inc., dataloggers (CDLs)
dedicated to the SIRS. If this is done properly, the values for the
observed geophysical parameters immediately have the correct calibration
coefficients applied. These values are ingested in the 60-s data and no
further processing is necessary to produce the estimates in geophysical
units with correct calibrations. The 20-s data consist of raw values and
are not affected by the choice of calibration coefficients or serial
numbers. However, the metadata for the 60-s data are not updated with
the new calibration coefficients and serial numbers until a special file
produced daily near midnight GMT by the CDL are read at that time by the
site data system. Hence, it is possible that up to nearly 24 hours of
partially incorrect metadata will be generated. This problem could be
overcome by a procedure of turning off the data ingest and correcting it
whenever the sensors are replaced. All SIRS data collected to date have
this problem, because such a procedure has not been implemented. The
amount of time and effort to take such actions does not seem to be
justified for this fairly minor source of misinformation.

### On Time Formats and Values of Downward Shortwave Hemispheric Radiation (P011004.2) {#on-time-formats-and-values-of-downward-shortwave-hemispheric-radiation-p011004.2 .unnumbered}

All SIRS data are recorded in UTC. This means local sunset will occur
after 24:00 UTC in the summer as can be found, for example, in the data
file sgpsirsC1.a1.20000601.000000.cdf. The large positive values are
valid for the afternoon period. The negative values after sunset (and
throughout the night, depending on the cloud cover) are typical of
single-black thermopile detectors used in the SIRS network (see Dutton,
E.G, et al, \'Measurement of Broadband Diffuse Solar Irradiance Using
Current Commercial Instrumentation with a Correction for Thermal Offset
Errors.\' Journal of Atmospheric and Oceanic Technology, Vol 18, March
2001, pages 297-306.) Prior to the use of Eppley Laboratory, Inc. Model
8-48 in February 2001, the diffuse shortwave and, to a lesser extent,
the global irradiance can be corrected for thermal offsets. In any
event, I would treat the small (\<15 Watts per sq meter) nighttime
shortwave irradiances as \'0.0\' when computing the daily total
irradiation values. We have programmed the Campbell Scientific, Inc.
Model CR10X data loggers to output the measurements using the convention
where midnight is recorded as 00:00:00 and the date reflects the start
of a new 24 hour day. In Campbell-ese, the 4-digit code for \'Time
Options\' is 1110 for the SIRS program. SIRS 1-minute data for a
particular date is then recorded from 00:00 to 23:59. For example, the
data recorded for 10:05 are the averages, minima, maxima, and standard
deviations of the 2-second samples beginning 10:04:02 and ending
10:05:00.

### Pyranometer Thermal Offsets {#pyranometer-thermal-offsets .unnumbered}

Broadband downwelling shortwave diffuse (sky) irradiance measurements
available from SIRS prior to February 22, 2001 may require adjustment
for thermal offsets. After this date, all SIRS were providing diffuse
irradiance data as measured with an Eppley Laboratory, Inc., Model 8-48
(black and white) pyranometer. The operational date of each SIRS in
1997/98 and the date and time of Model 8-48 installation in February
2001 can be found in Table 3.

As described in the above Description of Observational Specifications,
these thermal, or "zero" offsets refer to the generally reduced output
signals from a shaded pyranometer due to the exchange of longwave
(infrared) irradiance between the single black thermopile detector, the
protective glass domes surrounding the detector, and the atmosphere.
Originally considered an acceptable nighttime response of
thermopile-type pyranometers, the generally negative bias is now
recognized to significantly effect the accuracy of SIRS diffuse
irradiance data during daylight periods.

Studies of the Eppley Laboratory, Inc. Model PSP (Precision Spectral
Pyranometer), used for the SIRS measurements of diffuse irradiance,
suggest the thermal offset correction can range from near 0, to as much
as 30 Watts per square meter, depending on the coincident net longwave,
or infrared irradiance \[1, 2\]. Under very clear-sky conditions, the
diffuse irradiance from a shaded PSP can be less than the minimum
physical limit defined by radiative transfer model estimates based only
on Rayleigh scattering effects.

A correction method has been developed for adjusting SIRS diffuse
irradiance data \[3\]. The resulting Value Added Product (VAP) will be
applied to SIRS data for the period of this DQR. The VAP will not be
applied to SIROS data collected before the instrument platform was
converted to SIRS.

Additionally, the Model PSP radiometer has been replaced by a Model 8-48
which uses a black and white thermopile detector known to reduce the
thermal offset errors to less than 2 Watts per square meter \[3\]. The
radiometer replacement at this SIRS location was completed on the date
shown in Table 3.

###  {#section .unnumbered}

[]{#__RefHeading___Toc87419582 .anchor}Table 3. SIRS Upgrade: Model 8-48
Pyranometer Installation for Diffuse Irradiance, 4-19-01, Tom
Stoffel^1^.

  ---------- --------------- ---------------- ---------------- ----------------
  **Site**   **SIROS to      **Model 8-48     **Data Logger    **Returned to
             SIRS^2^**       Installation**   "OFF" (GMT)^3^** Service
                                                               (GMT)^4^**

  C1         01-15-97        02-22-01         20:50            21:00

  E1         11-20-97        02-13-01         20:15            20:25

  E2         11-06-97        02-15-01         15:47            16:02

  E3         11-04-97        02-14-01         19:30            19:50

  E4         11-07-97        02-14-01         15:10            16:06

  E5         11-06-97        02-14-01         19:45            20:03

  E6         11-05-97        02-15-01         15:30            15:50

  E7         10-31-97        02-13-01         19:25            19:45
  ---------- --------------- ---------------- ---------------- ----------------

**Table 3**. (cont'd)

+-------+--------------+--------------+---------------+---------------+
| E8    | 08-19-97     | 02-13-01     | 18:15         | 18:41         |
+-------+--------------+--------------+---------------+---------------+
| E9    | 02-06-98     | 02-13-01     | 15:40         | 16:00         |
+-------+--------------+--------------+---------------+---------------+
| E10   | 10-30-97     | 02-14-01     | 15:00         | 15:10         |
+-------+--------------+--------------+---------------+---------------+
| E11   | 08-20-97     | 02-20-01     | 20:40         | 21:05         |
+-------+--------------+--------------+---------------+---------------+
| E12   | 10-29-97     | 02-20-01     | 16:55         | 17:15         |
+-------+--------------+--------------+---------------+---------------+
| E13   | 08-25-97     | 02-22-01     | 20:21         | 20:35         |
+-------+--------------+--------------+---------------+---------------+
| E15   | 08-23-97     | 02-20-01     | 17:30         | 17:40         |
+-------+--------------+--------------+---------------+---------------+
| E16   | 08-21-97     | 02-21-01     | 16:20         | 16:50         |
+-------+--------------+--------------+---------------+---------------+
| E18   | 09-30-97     | 02-20-01     | 22:20         | 22:40         |
+-------+--------------+--------------+---------------+---------------+
| E19   | 06-16-98     | 02-22-01     | 15:35         | 15:48         |
+-------+--------------+--------------+---------------+---------------+
| E20   | 02-11-98     | 02-20-01     | 18:50         | 19:10         |
+-------+--------------+--------------+---------------+---------------+
| E21   | 07/22/99     | 02-20-01     | 21:00         | 21:35         |
+-------+--------------+--------------+---------------+---------------+
| E22   | 11-24-97     | 02-21-01     | 20:00         | 20:20         |
+-------+--------------+--------------+---------------+---------------+
| E24   | 11-25-97     | 02-22-01     | 16:15         | 16:35         |
+-------+--------------+--------------+---------------+---------------+
| E25   | 10-01-97     | 02-21-01     | 16:00         | 16:15         |
+-------+--------------+--------------+---------------+---------------+
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| D.,   |              |              |               |               |
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| Jing, |              |              |               |               |
| T.    |              |              |               |               |
| Qian, |              |              |               |               |
| and   |              |              |               |               |
| M.    |              |              |               |               |
| Sun.  |              |              |               |               |
| 1999. |              |              |               |               |
| Valid |              |              |               |               |
| ation |              |              |               |               |
| Strat |              |              |               |               |
| egies |              |              |               |               |
| Ap    |              |              |               |               |
| plied |              |              |               |               |
| to    |              |              |               |               |
| the   |              |              |               |               |
| M     |              |              |               |               |
| easur |              |              |               |               |
| ement |              |              |               |               |
| of    |              |              |               |               |
| T     |              |              |               |               |
| otal, |              |              |               |               |
| D     |              |              |               |               |
| irect |              |              |               |               |
| and   |              |              |               |               |
| Di    |              |              |               |               |
| ffuse |              |              |               |               |
| Shor  |              |              |               |               |
| twave |              |              |               |               |
| Radi  |              |              |               |               |
| ation |              |              |               |               |
| at    |              |              |               |               |
| the   |              |              |               |               |
| Sur   |              |              |               |               |
| face. |              |              |               |               |
| *J.   |              |              |               |               |
| Geo   |              |              |               |               |
| phys. |              |              |               |               |
| Res*. |              |              |               |               |
|       |              |              |               |               |
| Du    |              |              |               |               |
| tton, |              |              |               |               |
| E.G., |              |              |               |               |
| J.J.  |              |              |               |               |
| Micha |              |              |               |               |
| lsky, |              |              |               |               |
| T.    |              |              |               |               |
| Sto   |              |              |               |               |
| ffel, |              |              |               |               |
| B.W.  |              |              |               |               |
| Fo    |              |              |               |               |
| rgan, |              |              |               |               |
| J.    |              |              |               |               |
| Hi    |              |              |               |               |
| ckey, |              |              |               |               |
| D.W.  |              |              |               |               |
| Ne    |              |              |               |               |
| lson, |              |              |               |               |
| T.L.  |              |              |               |               |
| Alb   |              |              |               |               |
| erta, |              |              |               |               |
| and   |              |              |               |               |
| I.    |              |              |               |               |
| Reda. |              |              |               |               |
| 2001. |              |              |               |               |
| M     |              |              |               |               |
| easur |              |              |               |               |
| ement |              |              |               |               |
| of    |              |              |               |               |
| Broa  |              |              |               |               |
| dband |              |              |               |               |
| Di    |              |              |               |               |
| ffuse |              |              |               |               |
| Solar |              |              |               |               |
| Irrad |              |              |               |               |
| iance |              |              |               |               |
| Using |              |              |               |               |
| Cu    |              |              |               |               |
| rrent |              |              |               |               |
| Comme |              |              |               |               |
| rcial |              |              |               |               |
| Instr |              |              |               |               |
| ument |              |              |               |               |
| ation |              |              |               |               |
| with  |              |              |               |               |
| a     |              |              |               |               |
| Corre |              |              |               |               |
| ction |              |              |               |               |
| for   |              |              |               |               |
| Th    |              |              |               |               |
| ermal |              |              |               |               |
| O     |              |              |               |               |
| ffset |              |              |               |               |
| Er    |              |              |               |               |
| rors. |              |              |               |               |
| *J.   |              |              |               |               |
| A     |              |              |               |               |
| tmosp |              |              |               |               |
| heric |              |              |               |               |
| &     |              |              |               |               |
| Oc    |              |              |               |               |
| eanic |              |              |               |               |
| Te    |              |              |               |               |
| chnol |              |              |               |               |
| ogy*, |              |              |               |               |
| Vol.  |              |              |               |               |
| 18,   |              |              |               |               |
| No.   |              |              |               |               |
| 3,    |              |              |               |               |
| pp.   |              |              |               |               |
| 297   |              |              |               |               |
| -314. |              |              |               |               |
|       |              |              |               |               |
| Gu    |              |              |               |               |
| lbran |              |              |               |               |
| dsen, |              |              |               |               |
| A.    |              |              |               |               |
| 1978. |              |              |               |               |
| On    |              |              |               |               |
| the   |              |              |               |               |
| Use   |              |              |               |               |
| of    |              |              |               |               |
| Py    |              |              |               |               |
| ranom |              |              |               |               |
| eters |              |              |               |               |
| in    |              |              |               |               |
| the   |              |              |               |               |
| Study |              |              |               |               |
| of    |              |              |               |               |
| Spe   |              |              |               |               |
| ctral |              |              |               |               |
| Solar |              |              |               |               |
| Radi  |              |              |               |               |
| ation |              |              |               |               |
| and   |              |              |               |               |
| A     |              |              |               |               |
| tmosp |              |              |               |               |
| heric |              |              |               |               |
| Aero  |              |              |               |               |
| sols. |              |              |               |               |
| *J.   |              |              |               |               |
| Appl. |              |              |               |               |
| M     |              |              |               |               |
| eteor |              |              |               |               |
| ol*., |              |              |               |               |
| 17,   |              |              |               |               |
| 899   |              |              |               |               |
| -904. |              |              |               |               |
+-------+--------------+--------------+---------------+---------------+

## Frequently Asked Questions

This section is not applicable to this instrument.

# Data Quality

## Data Quality Health and Status

The following links go to current data quality health and status results

### [**DQ HandS**](http://dq.arm.gov/) (Data Quality Health and Status) 

### [**NCVweb**](http://dq.arm.gov/ncvweb/ncvweb.cgi) for interactive data plotting using. 

The tables and graphs shown contain the techniques used by ARM\'s data
quality analysts, instrument mentors, and site scientists to monitor and
diagnose data quality.

## Data Reviews by Instrument Mentor

This section is not applicable to this instrument.

## Data Assessments by Site Scientist/Data Quality Office

All DQ Office and most Site Scientist techniques for checking have been
incorporated within [DQ HandS](http://dq.arm.gov/) and can be viewed
there.

## Value-Added Procedures and Quality Measurement Experiments

Many of the scientific needs of the ARM Program are met through the
analysis and processing of existing data products into \"value-added\"
products or VAPs. Despite extensive instrumentation deployed at the ARM
CART sites, there will always be quantities of interest that are either
impractical or impossible to measure directly or routinely. Physical
models using ARM instrument data as inputs are implemented as VAPs and
can help fill some of the unmet measurement needs of the program.
Conversely, ARM produces some VAPs not in order to fill unmet
measurement needs, but instead to improve the quality of existing
measurements. In addition, when more than one measurement is available,
ARM also produces \"best estimate\" VAPs. A special class of VAP called
a Quality Measurement Experiment (QME) does not output geophysical
parameters of scientific interest. Rather, a QME adds value to the input
datastreams by providing for continuous assessment of the quality of the
input data based on internal consistency checks, comparisons between
independent similar measurements, or comparisons between measurement
with modeled results, and so forth. For more information, see the [VAPs
and QMEs](http://www.arm.gov/data/vaps.stm) web page.

# Instrument Details

## Detailed Description

### List of Components

### The following radiometers manufactured by The Eppley Laboratory, Inc., in Table 4 re used at each SIRS.  {#the-following-radiometers-manufactured-by-the-eppley-laboratory-inc.-in-table-4-re-used-at-each-sirs. .unnumbered}

[]{#__RefHeading___Toc87419583 .anchor}Table 4.

  ----------------- -------------- --------------- --------------- -------------------
  **Measurement**   **Radiometer   **Mounting      **Typical       **Typical
                    Model**        Arrangement**   Responsivity\   Calibration
                                                   (μV/Wm^-2^)**   Uncertainty^\*^**

  Direct Normal     NIP            Solar Tracker   8.0             ±2.5% or\
                                                                   2 Wm^-2^

  Diffuse           PSP            Shaded &        9.0             ±3.0% or\
  Horizontal                       Ventilated                      10 Wm^-2^

  Downwelling       PSP            Unshaded &      9.0             ±3.0% or\
  Shortwave                        Ventilated                      10 Wm^-2^

  Downwelling       PIR            Shaded &        4.0             ±2% or\
  Longwave                         Ventilated                      2 Wm^-2^

  Upwelling         PSP            Inverted w/o    9.0             ±3.0% or\
  Shortwave                        ventilation                     10 Wm^-2^

  Upwelling         PIR            Inverted w/o    4.0             ±2% or\
  Longwave                         ventilation                     2 Wm^-2^

  ^\*^Field                                                        
  measurement                                                      
  uncertainties are                                                
  larger and                                                       
  include the                                                      
  uncertainties                                                    
  associated with                                                  
  instrument                                                       
  calibration,                                                     
  installation,                                                    
  operation and                                                    
  maintenance.                                                     
  ----------------- -------------- --------------- --------------- -------------------

Additional information is available from
[http://www.nrel.gov/srrl/.](http://www.nrel.gov/srrl/)

### System Configuration and Measurement Methods

Depending on the irradiance measurement, SIRS radiometers are mounted on
either an automatic solar tracker or a stationary surface. The following
abbreviations are used to describe the SIRS instrumentation and their
relative locations shown in Figure 5:

DNI = Direct Normal (beam) Shortwave Irradiance\
DD = Downwelling Diffuse (sky) Shortwave Irradiance\
DS = Downwelling Total Hemispheric (global) Shortwave Irradiance\
DIR = Downwelling Infrared (atmospheric) Irradiance\
US = Upwelling Shortwave (reflected) Irradiance\
UIR = Upwelling Infrared (terrestrial) Irradiance.

The data acquisition system is a Campbell Scientific, Inc. Model
CR10X-1M with AM416 Multiplexer, 4 Mb memory card, and modem. These
components are inside a weather-resistant enclosure mounted above
ground. The system is designed to operate over the full range of
environmental conditions anticipated for the network of SIRS stations
(see [http://www.campbellsci.com](http://www.campbellsci.com/) for
detailed measurement and environmental specifications).

### ![](media/image6.png){width="2.0756944444444443in" height="3.3631944444444444in"}  {#section-1 .unnumbered}

[]{#__RefHeading___Toc87419576 .anchor}Figure 5. Plan View of SIRS
Instrument Locations

The system is programmed to sample ten inputs listed below every
2-seconds and output the average, standard deviation, minimum, and
maximum values of the six geophysical elements, described above, at the
end of each minute. Appended to each 1-minute data output record are the
instantaneous values sampled at 20 seconds, 40 seconds, and 60 seconds
within the 1-minute interval. These \"instantaneous\" data actually
require 0.272 milliseconds to complete the analog to digital conversion
of each measurement. Additionally, at 23:59:02 each day, the instrument
serial numbers and calibration factors used by the data logger program
are appended to the last record of the day. The system is designed to
store up to two weeks of measured data and statistics, but the data are
generally collected by telephone modem every 3-hours. Data stored on the
4 Mb memory card at each station are physically removed as part of the
routine SIRS maintenance every two weeks and made available to the SGP
Data System.

Measurements collected by the CR10X-1M logger are listed below with a
sample data record for reference. All data files are reformatted in
NETcdf for distribution.

**Measurement Dictionary**

### DSTp = DS unshaded pyranometer thermopile output voltage (mV) 

### USTp = US inverted pyranometer thermopile output voltage (mV) 

### DDTp = DD shaded pyranometer thermopile output voltage (mV) 

### DNITp = DNI pyrheliometer thermopile output voltage (mV) 

### DIRTp = DIR pyrgeometer thermopile output voltage (mV) 

### DIRCr = DIR pyrgeometer case thermistor resistance (Kohm) 

### DIRDr = DIR pyrgeometer dome thermistor resistance (Kohm) 

### UIRTp = UIR pyrgeometer thermopile output voltage (mV) 

### UIRCr = UIR pyrgeometer case thermistor resistance (Kohm) 

### UIRDr = UIR pyrgeometer dome thermistor resistance (Kohm) 

**Excerpts from SIRS data file for 28 April 1997**

[Typical 60-sec output record]{.underline}:

Note: For improved readability, a space has been added after each comma
in the original CSV Campbell data logger output file.

199, 1997, 108, 1831, 459.01, 344.61, 204.24, 186.11, 738.7, 839.92,
1.363, .74, .755, 1.302, 10.25, 9.06, 462.3, 345.6, 205.9, 189.1, 758,
857, 456.8, 342.4, 203.2, 184.5, 722, 825, 9.8011, 9.9781, 9.0405,
8.7893, .08167, -.52838, 1.9969, 1.7249, 6.3005, 7.1103, 9.8011, 9.9781,
9.0599, 8.7893, .08034, -.52738, 1.9874, 1.7117, 6.2098, 7.059, 9.8012,
9.9585, 9.0212, 8.7894, .09334, -.51988, 1.9829, 1.7183, 6.3546, 7.1512,
13.14

[Penultimate 60-sec output record of the day has **last valid irradiance
data**]{.underline}:

199, 1997, 108, 2359, 423.04, 330.79, 77.44, 61.688, 541.83, 181.26,
.661, .626, .525, 2.231, 25.03, 5.988, 424, 332.2, 78.3, 64.46, 569.2,
188.3, 421.9, 329.9, 76.5, 57.16, 488.7, 169.1, 10.492, 10.592, 9.5264,
9.2535, -.04884, -.54438, .75906, .58593, 4.773, 1.5735, 10.492, 10.592,
9.5068, 9.2535, -.05017, -.54472, .75307, .56289, 4.5574, 1.5175,
10.492, 10.592, 9.5068, 9.2535, -.0505, -.54305, .74609, .52833, 4.1591,
1.4303, 13.16

[Last 60-sec output record of the day has instrument serial numbers and
calibration factors]{.underline}:

(Note: All measurement elements are invalid due to timing restriction.)

199, 1997, 108, 2359, 397.49, 315.72, 72.17, 65.84, 321.97, 272.75,
40.17, 19.63, 95.1, 76.1, 352.5, 335.9, 471.3, 393.9, 400.8, 215.2, 948,
980, 350.3, 291.2, -7.88, -1.427, -4.451, -6.624, 10.492, 10.592,
9.5264, 9.2535, -.04884, -.54438, .75906, .58593, 4.773, 1.5735, 10.492,
10.592, 9.5068, 9.2535, -.05017, -.54472, .75307, .56289, 4.5574,
1.5175, 10.492, 10.592, 9.5068, 9.2535, -.0505, -.54305, .74609, .52833,
4.1591, 1.4303, 13.16, 30783, 245.7, 30696, 268.82, 29618, 102.5, 30802,
108.19, 29737, 117.51, 30891, 118.2

+---+-----------------------+----------+---------------+-----+------+
| * | **Element**           | > *      | **Units**     | **R |      |
| * |                       | *Value** |               | ang |      |
| P |                       |          |               | e** |      |
| o |                       |          |               |     |      |
| s |                       |          |               |     |      |
| * |                       |          |               |     |      |
| * |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
|   |                       |          |               | *   | >    |
|   |                       |          |               | *Mi |  **M |
|   |                       |          |               | n** | ax** |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > Site Identifier     | > 199    | > n/a         | 1   | >    |
| 1 |                       |          |               |     |  511 |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > Year                | > 1997   | > Years       | 1   | >    |
| 2 |                       |          |               | 997 | 2052 |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > Day of Year         | > 145    | > n/a         | 1   | >    |
| 3 |                       |          |               |     |  366 |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > Time (hh:mm)        | > 1345   | > UTC         | 0   | >    |
| 4 |                       |          |               |     | 2359 |
+---+-----------------------+----------+---------------+-----+------+
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
| B |                       |          |               |     |      |
| e |                       |          |               |     |      |
| g |                       |          |               |     |      |
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|   |                       |          |               |     |      |
| 6 |                       |          |               |     |      |
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|   |                       |          |               |     |      |
| A |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| r |                       |          |               |     |      |
| a |                       |          |               |     |      |
| g |                       |          |               |     |      |
| e |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| o |                       |          |               |     |      |
| f |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 2 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
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| s |                       |          |               |     |      |
| a |                       |          |               |     |      |
| m |                       |          |               |     |      |
| p |                       |          |               |     |      |
| l |                       |          |               |     |      |
| e |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| f |                       |          |               |     |      |
| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| h |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| e |                       |          |               |     |      |
| n |                       |          |               |     |      |
| d |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| g |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| a |                       |          |               |     |      |
| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > UIR                 | > 459.01 | > W/sq m      | 100 | >    |
| 5 |                       |          |               |     |  800 |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > DIR                 | > 344.61 | > W/sq m      | 50  | >    |
| 6 |                       |          |               |     |  800 |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > DD                  | > 204.24 | > W/sq m      | -10 | >    |
| 7 |                       |          |               |     |  600 |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > US                  | > 186.11 | > W/sq m      | -10 | >    |
| 8 |                       |          |               |     | 1100 |
+---+-----------------------+----------+---------------+-----+------+
| 0 | > DNI                 | > 738.7  | > W/sq m      | -10 | >    |
| 9 |                       |          |               |     | 1100 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > DS                  | > 839.92 | > W/sq m      | -10 | >    |
| 0 |                       |          |               |     | 1400 |
+---+-----------------------+----------+---------------+-----+------+
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
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| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| h |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| e |                       |          |               |     |      |
| n |                       |          |               |     |      |
| d |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| g |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| a |                       |          |               |     |      |
| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > UIR                 | > 1.363  | > W/sq m      | 0   | >    |
| 1 |                       |          |               |     |  600 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > DIR                 | > 0.74   | > W/sq m      | 0   | >    |
| 2 |                       |          |               |     |  600 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > DD                  | > 0.755  | > W/sq m      | 0   | >    |
| 3 |                       |          |               |     |  500 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > US                  | > 1.302  | > W/sq m      | 0   | >    |
| 4 |                       |          |               |     |  400 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > DNI                 | > 10.25  | > W/sq m      | 0   | >    |
| 5 |                       |          |               |     | 1000 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > DS                  | > 9.06   | > W/sq m      | 0   | >    |
| 6 |                       |          |               |     | 1000 |
+---+-----------------------+----------+---------------+-----+------+
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
| B |                       |          |               |     |      |
| e |                       |          |               |     |      |
| g |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 6 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| M |                       |          |               |     |      |
| a |                       |          |               |     |      |
| x |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| a |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| o |                       |          |               |     |      |
| f |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 2 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| s |                       |          |               |     |      |
| a |                       |          |               |     |      |
| m |                       |          |               |     |      |
| p |                       |          |               |     |      |
| l |                       |          |               |     |      |
| e |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| f |                       |          |               |     |      |
| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| h |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| e |                       |          |               |     |      |
| n |                       |          |               |     |      |
| d |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| g |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| a |                       |          |               |     |      |
| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > UIR                 | > 462.3  | > W/sq m      | 100 | >    |
| 7 |                       |          |               |     |  800 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > DIR                 | > 345.6  | > W/sq m      | 50  | >    |
| 8 |                       |          |               |     |  800 |
+---+-----------------------+----------+---------------+-----+------+
| 1 | > DD                  | > 205.9  | > W/sq m      | -10 | >    |
| 9 |                       |          |               |     |  600 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > US                  | > 189.1  | > W/sq m      | -10 | >    |
| 0 |                       |          |               |     | 1100 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > DNI                 | > 758    | > W/sq m      | -10 | >    |
| 1 |                       |          |               |     | 1100 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > DS                  | > 857    | > W/sq m      | -10 | >    |
| 2 |                       |          |               |     | 1400 |
+---+-----------------------+----------+---------------+-----+------+
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
| B |                       |          |               |     |      |
| e |                       |          |               |     |      |
| g |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 6 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| M |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| a |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| o |                       |          |               |     |      |
| f |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 2 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| s |                       |          |               |     |      |
| a |                       |          |               |     |      |
| m |                       |          |               |     |      |
| p |                       |          |               |     |      |
| l |                       |          |               |     |      |
| e |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| f |                       |          |               |     |      |
| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| h |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| e |                       |          |               |     |      |
| n |                       |          |               |     |      |
| d |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| g |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| a |                       |          |               |     |      |
| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > DIR                 | > 456.8  | > W/sq m      | 100 | >    |
| 3 |                       |          |               |     |  800 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > UIR                 | > 342.4  | > W/sq m      | 50  | >    |
| 4 |                       |          |               |     |  800 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > DD                  | > 203.2  | > W/sq m      | -10 | >    |
| 5 |                       |          |               |     |  600 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > US                  | > 184.5  | > W/sq m      | -10 | >    |
| 6 |                       |          |               |     | 1100 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > DNI                 | > 722    | > W/sq m      | -10 | >    |
| 7 |                       |          |               |     | 1100 |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > DS                  | > 825    | > W/sq m      | -10 | >    |
| 8 |                       |          |               |     | 1400 |
+---+-----------------------+----------+---------------+-----+------+
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
| B |                       |          |               |     |      |
| e |                       |          |               |     |      |
| g |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 2 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| I |                       |          |               |     |      |
| n |                       |          |               |     |      |
| s |                       |          |               |     |      |
| t |                       |          |               |     |      |
| a |                       |          |               |     |      |
| n |                       |          |               |     |      |
| t |                       |          |               |     |      |
| a |                       |          |               |     |      |
| n |                       |          |               |     |      |
| e |                       |          |               |     |      |
| o |                       |          |               |     |      |
| u |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| s |                       |          |               |     |      |
| a |                       |          |               |     |      |
| m |                       |          |               |     |      |
| p |                       |          |               |     |      |
| l |                       |          |               |     |      |
| e |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| f |                       |          |               |     |      |
| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 2 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| t |                       |          |               |     |      |
| o |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| h |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| e |                       |          |               |     |      |
| n |                       |          |               |     |      |
| d |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| g |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| a |                       |          |               |     |      |
| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 2 | > UIRDr               | > 9.8011 | > KOhms       |     |      |
| 9 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > UIRCr               | > 9.9781 | > KOhms       |     |      |
| 0 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > DIRDr               | > 9.0405 | > KOhms       |     |      |
| 1 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > DIRCr               | > 8.7893 | > KOhms       |     |      |
| 2 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > UIRTp               | > .08167 | > mv          | -   | >    |
| 3 |                       |          |               | 0.2 |  7.5 |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > DIRTp               | >        | > mv          | -   | >    |
| 4 |                       |  -.52838 |               | 0.2 |  7.5 |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > DDTp                | > 1.9969 | > mv          | -   | >    |
| 5 |                       |          |               | 0.2 | 15.0 |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > USTp                | > 1.7249 | > mv          | -   | >    |
| 6 |                       |          |               | 0.2 | 15.0 |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > DNITp               | > 6.3005 | > mv          | -   | >    |
| 7 |                       |          |               | 0.2 | 15.0 |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > DSTp                | > 7.1103 | > mv          | -   | >    |
| 8 |                       |          |               | 0.2 | 15.0 |
+---+-----------------------+----------+---------------+-----+------+
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
| B |                       |          |               |     |      |
| e |                       |          |               |     |      |
| g |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 2 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| I |                       |          |               |     |      |
| n |                       |          |               |     |      |
| s |                       |          |               |     |      |
| t |                       |          |               |     |      |
| a |                       |          |               |     |      |
| n |                       |          |               |     |      |
| t |                       |          |               |     |      |
| a |                       |          |               |     |      |
| n |                       |          |               |     |      |
| e |                       |          |               |     |      |
| o |                       |          |               |     |      |
| u |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| s |                       |          |               |     |      |
| a |                       |          |               |     |      |
| m |                       |          |               |     |      |
| p |                       |          |               |     |      |
| l |                       |          |               |     |      |
| e |                       |          |               |     |      |
| s |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| f |                       |          |               |     |      |
| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 4 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| s |                       |          |               |     |      |
| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| t |                       |          |               |     |      |
| o |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| h |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| e |                       |          |               |     |      |
| n |                       |          |               |     |      |
| d |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| g |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| a |                       |          |               |     |      |
| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 3 | > UIRDr               | > 9.8011 | :             |     |      |
| 9 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > UIRCr               | > 9.9781 | :             |     |      |
| 0 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > DIRDr               | >        | : \<\< as     |     |      |
| 1 |                       |  9.0599  | above for     |     |      |
|   |                       |          | 20-sec        |     |      |
|   |                       |          | interval \>\> |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > DIRCr               | > 8.7893 | :             |     |      |
| 2 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > UIRTp               | > .08340 | :             |     |      |
| 3 |                       |          |               |     |      |
|   |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > DIRTp               | >        | :             |     |      |
| 4 |                       |  -.52738 |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > DDTp                | > 1.9874 | :             |     |      |
| 5 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > USTp                | > 1.7117 | :             |     |      |
| 6 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > DNITp               | > 6.2098 | :             |     |      |
| 7 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > DSTp                | > 7.059  | :             |     |      |
| 8 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
| B |                       |          |               |     |      |
| e |                       |          |               |     |      |
| g |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 2 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
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| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| 6 |                       |          |               |     |      |
| 0 |                       |          |               |     |      |
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| e |                       |          |               |     |      |
| c |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| t |                       |          |               |     |      |
| o |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| h |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| m |                       |          |               |     |      |
| e |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| e |                       |          |               |     |      |
| n |                       |          |               |     |      |
| d |                       |          |               |     |      |
| i |                       |          |               |     |      |
| n |                       |          |               |     |      |
| g |                       |          |               |     |      |
| > |                       |          |               |     |      |
|   |                       |          |               |     |      |
| a |                       |          |               |     |      |
| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
| v |                       |          |               |     |      |
| e |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| \ |                       |          |               |     |      |
| - |                       |          |               |     |      |
| - |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 4 | > UIRDr               | > 9.8012 | :             |     |      |
| 9 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > UIRCr               | > 9.9585 | :             |     |      |
| 0 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > DIRDr               | > 9.0212 | :             |     |      |
| 1 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > DIRCr               | > 8.7894 | : \<\<as      |     |      |
| 2 |                       |          | above for     |     |      |
|   |                       |          | 40-sec        |     |      |
|   |                       |          | interval\>\>  |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > UIRTp               | >        | :             |     |      |
| 3 |                       |  0.09334 |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > DIRTp               | >        | :             |     |      |
| 4 |                       |  -.51988 |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > DDTp                | > 1.9829 | :             |     |      |
| 5 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > USTp                | > 1.7183 | :             |     |      |
| 6 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > DNITp               | > 6.3546 | :             |     |      |
| 7 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > DSTp                | > 7.1512 | :             |     |      |
| 8 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 5 | > BATT                | > 13.14  | > V           | 9.2 | >    |
| 9 |                       |          |               |     | 14.0 |
+---+-----------------------+----------+---------------+-----+------+
| O |                       |          |               |     |      |
| n |                       |          |               |     |      |
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| A |                       |          |               |     |      |
| F |                       |          |               |     |      |
| T |                       |          |               |     |      |
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| b |                       |          |               |     |      |
| o |                       |          |               |     |      |
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| e |                       |          |               |     |      |
| f |                       |          |               |     |      |
| o |                       |          |               |     |      |
| r |                       |          |               |     |      |
| p |                       |          |               |     |      |
| o |                       |          |               |     |      |
| s |                       |          |               |     |      |
| i |                       |          |               |     |      |
| t |                       |          |               |     |      |
| i |                       |          |               |     |      |
| o |                       |          |               |     |      |
| n |                       |          |               |     |      |
| s |                       |          |               |     |      |
| 1 |                       |          |               |     |      |
| - |                       |          |               |     |      |
| 5 |                       |          |               |     |      |
| 9 |                       |          |               |     |      |
| . |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > UIR Serial No.      | > 30783  | "F3" implied  |     |      |
| 0 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > UIR Calibration     | > 245.7  | W/sq m per mv |     |      |
| 1 | > Factor              |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > DIR Serial No.      | > 30696  | "F3" implied  |     |      |
| 2 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > DIR Calibration     | > 268.82 | W/sq m per mv |     |      |
| 3 | > Factor              |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > DD Serial No.       | > 29618  | "F3" implied  |     |      |
| 4 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > DD Calibration      | > 102.5  | W/sq m per mv |     |      |
| 5 | > Factor              |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > US Serial No.       | > 30802  | "F3" implied  |     |      |
| 6 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > US Calibration      | > 108.19 | W/sq m per mv |     |      |
| 7 | > Factor              |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > DNI S/N             | > 29737  | "E6" implied  |     |      |
| 8 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 6 | > DNI Calibration     | > 117.51 | W/sq m per mv |     |      |
| 9 | > Factor              |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 7 | > DS S/N              | > 30891  | "F3" implied  |     |      |
| 0 |                       |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+
| 7 | > DS Calibration      | > 118.2  | W/sq m per mv |     |      |
| 1 | > Factor              |          |               |     |      |
+---+-----------------------+----------+---------------+-----+------+

Note: All PIR and PSP serial numbers are "xxxxx.F3". All NIP s/n are
"xxxxx.E6"

**Reconstructing the 1-Minute Averages from Three 20-Second Samples**

Use the average of the three samples for each of the elements described
below to compute an average irradiance (W/sq m). The data acquisition
system program uses these same procedures to compute the 1-minute
statistics from the 2-second scans.

### Global DS = DSTp (mV) \* DS Cal Factor (W/sq m per mV) 

### Upwelling Shortwave US = USTp (mV) \* US Calibration Factor (W/sq m per mV)

### Diffuse DD = DDTp (mV) \* DD Calibration Factor (W/sq m per mV)

### Direct Normal DNI = DNITp (mV) \* DNI Calibration Factor (W/sq m per mV)

### Down / Upwelling Infrared (DIR or UIR)  Step 1. Compute Temperature (K) from thermistor resistance (KOhm) 

T = 1 / \[A + BX + CX^3^\]\
where,

T = Temperature (K)\
A = 10.425E-04\
B = 2.37E-04\
C = 1.64E-03\
X = 5 \* Ln(10) + Ln(R/100), and R = Resistance (KOhm)

Step 2. Compute Irradiance from PIR Temperatures (K) and Thermopile
Voltages (mV)

Irrad = T~p~ \* C1 + Sig \* T~c~^4^ - C2 \* Sig \*(T~d~^4^ - T~c~^4^)\
where,

Irrad = Irradiance (W/sq m)\
T~p~ = PIR thermopile voltage (mV)\
T~c~ = PIR case temperature (K)\
T~d~ = PIR dome temperature (K)\
C1 = PIR Calibration Factor (W/sq m per mV)\
C2 = PIR Dome Correction Factor (4.0 = default for all PIRs)\
Sig = Stephan-Boltzman Constant = 5.67E-08 W/m^2^ K^4^)

### Specifications

Selected theoretical measurement parameters of the SIRS radiometers are
listed below in Table 5.

[]{#__RefHeading___Toc87419584 .anchor}Table 5.

  ----------------- -------------- -------------- -------------- --------------
  **Measurement**   **Radiometer   **Wavelength   **Minimum      **Maximum
                    Field of       Range\         Irradiance\    Irradiance\
                    View**         (microns)**    (Wm^-2^)**     (Wm^-2^)**

  Direct Normal\    5.7°           0.3 to 3.0     0.0            1100
  (beam) \[DNI\]                                                 

  Diffuse           2π sr          0.3 to 3.0     0.0            600
  Horizontal\                                                    
  (sky) \[DD\]                                                   

  Downwelling       2π sr          0.3 to 3.0     0.0            1400
  Shortwave\                                                     
  (global) \[DS\]                                                

  Downwelling       2π sr          4.0 to 50      50             800
  Longwave\                                                      
  (atmospheric)                                                  
  \[DIR\]                                                        

  Upwelling         2π sr          0.3 to 3.0     0.0            1100
  Shortwave\                                                     
  (reflected)                                                    
  \[US\]                                                         

  Upwelling         2π sr          4.0 to 50      100            800
  Longwave\                                                      
  (terrestrial)                                                  
  \[UIR\]                                                        
  ----------------- -------------- -------------- -------------- --------------

### Field of View and Angular Response  {#field-of-view-and-angular-response .unnumbered}

The SIRS pyrheliometer (Eppley Laboratory, Inc. Model NIP) field of view
was designed to meet the World Meteorological Organization's design
requirements circa 1960. Without the scattering effects of a clear
atmosphere, the solar disc would appear to be about 0.5° at the earth's
surface. The NIP geometry allows for solar tracker alignment tolerances
possible at the time of the WMO specification and includes, therefore,
an amount of circumsolar (forward scatter) radiation.

The SIRS pyranometers (Eppley Laboratory, Inc. Model PSP) have unique
angular response characteristics that can be determined and verified
with calibration (see separate section). The angular response of the
pyranometer is a major contributor to the estimated measurement
uncertainty for the

various shortwave irradiance elements.

### Spectral Response  {#spectral-response .unnumbered}

The spectral response of the SIRS radiometers listed above are nominal
values. The precise values vary with instrument model. [Figures 2
&]{.mark} [3??]{.mark}

\<\<Insert John's Spectral Response Plot here\>\>

### Thermal Offsets  {#thermal-offsets .unnumbered}

Shortwave radiometers should produce a null signal in the absence of
solar radiation. However, all commercially available pyranometers based
on thermoelectric transducers, exhibit a non-zero output signal in the
absence of solar radiation. These signals are believed to be a result of
thermal gradients within the pyranometer.

The Eppley Laboratory, Inc. Model PSP is a thermoelectric, single-black
detector design with well-established performance characteristics
(Thekaekara , 1972, Hulstrom, 1989, McCluney, 1994). As shown in
[Figure]{.mark} [4]{.mark}, the two Schott Glass hemispheres protect the
thermopile detector from the weather. These inner and outer domes are
used to also reduce the thermal exchange between the detector, or
thermopile "hot" junction, and the environment. The body of the
instrument is a relatively massive bronze casting that is used to
control the "cold" or reference junction of the thermopile. Recent
studies of this and other models of pyranometers suggest thermal offsets
are producing as much as 30 Wm^-2^ during clear-sky, nighttime
conditions. Similarly, daytime measurements of downwelling diffuse
shortwave irradiance must be corrected for thermal offsets. ARM will use
a correction method based on correlations with the net infrared and
observed diffuse irradiances [\[Dutton, et al,]{.mark} [2001\]]{.mark}.

## Theory of Operation

### Shortwave Irradiance {#shortwave-irradiance .unnumbered}

Three pyranometers are positioned to measure the hemispheric irradiance
fields:

DS Unshaded, ventilated, and mounted in horizontal orientation\
US Inverted, unventilated and mounted 10m above the ground level\
DD Shaded, ventilated, and mounted on automatic solar tracker in
horizontal orientation.

A single pyrheliometer is mounted on an automatic solar tracker and
aligned to the sun's disc.

The following relationships are expected from the SIRS measurement
system for the various broadband shortwave irradiance elements.

### ![](media/image7.png){width="2.2395833333333335in" height="1.2291666666666667in"} {#section-2 .unnumbered}

where,

DS = Downwelling Hemispheric Shortwave (Global) Irradiance

DNI = Direct Normal Shortwave (Beam) Irradiance

Z = Solar Zenith Angle (sunrise/sunset = 90°)

DD = Downwelling Diffuse Shortwave (sky) Irradiance

US = Upwelling Diffuse Shortwave (reflected) Irradiance

![](media/image8.png){width="0.19791666666666666in"
height="0.17708333333333334in"}= Surface Shortwave Albedo (typically 0.2
for vegetation, 0.8 for fresh snow)

ETR = Extraterrestrial (exo-atmospheric) Radiation on horizontal surface

ETRN = Extraterrestrial Radiation Normal (beam) to the sun (1366 ±5
Wm^-2^ [\[REF??\]]{.mark}).

###  {#section-3 .unnumbered}

### Longwave Irradiance {#longwave-irradiance .unnumbered}

Elements of the pyrgeometer measurements are used to compute the
infrared:

### ![](media/image9.png){width="2.8854166666666665in" height="0.3333333333333333in"} {#section-4 .unnumbered}

where,

IR = Infrared Irradiance (W/sq m)\
T~tp~ = PIR thermopile voltage (mV)\
T~c~ = PIR case temperature (K)\
T~d~ = PIR dome temperature (K)\
C~1~ = PIR Calibration Factor (W/sq m per mV)\
C~2~ = PIR Dome Correction Factor (4.0 = default for all PIRs)\
![](media/image10.png){width="0.19791666666666666in" height="0.125in"} =
Stephan-Boltzman Constant = 5.67E-08 W/m^2^ K^4^.

## Calibration

### Theory

The calibration of all SIRS *shortwave* radiometers (pyrheliometers and
pyranometers) is traceable to the World Radiometric Reference (WRR)
maintained by the World Radiation Center (WRC) for the World
Meteorological Organization. Calibrations are performed at the SGP
Radiometer Calibration Facility (RCF-see separate entry) using the
Broadband Outdoor Radiometer CALibration (BORCAL) methods developed at
NREL. A group of three electrically self-calibrating absolute cavity
radiometers is maintained by NREL as the reference standards for the
U.S. Department of Energy (DOE) and ARM. WRR calibration traceability of
these reference standards is maintained for all DOE programs by
participation in the International Pyrheliometer Comparisons (IPC) held
every five years at the WRC. NREL Pyrheliometer Comparisons (NPCs) are
held annually at the Solar Radiation Research Laboratory (SRRL) in
Golden to transfer the WRR to participating instruments and ensure the
measurement performance of the reference standards.

The calibration of all SIRS *longwave* radiometers (pyrgeometers) are
traceable to temperature standards maintained by the National Institute
of Standards and Technology (NIST). SIRS pyrgeometers are to be
calibrated in the new Pyrgeometer Blackbody Calibration System developed
by The Eppley Laboratory, Inc. for the ARM Program and/or by outdoor
comparisons with transfer standards. Standard operating procedures are
currently under development at NREL for later use at the RCF to provide
routine pyrgeometer calibrations.

**Shortwave Radiometer Calibrations**

The *Component Summation Method* used for all BORCAL events is a
modified version of the shading method described in the American Society
for Testing and Materials (ASTM) Standard E913-82, \"Standard Method for
Calibration of Reference Pyranometers with Axis Vertical by the Shading
Method.\"

The direct normal (beam) irradiance is measured with one or two absolute
cavity radiometers, and the diffuse (sky) irradiance is measured with
one or two pyranometers shaded with a tracking disk ([Figure]{.mark} 6)
The two pyranometers providing the reference diffuse irradiance are
calibrated by a shade/unshade method involving only the absolute cavity
radiometer as a reference ([Figure]{.mark}7). The output voltage of
these standards and the radiometers under test are measured at
approximate 30-second intervals throughout each day during clear-sky
conditions (no clouds near the solar disk).

The responsivity for a pyrheliometer is calculated for each data point
by dividing the value of the instrument\'s output signal (microvolts) by
the mean value of the absolute cavity radiometer(s) output (W/sq m).

The responsivity for a pyranometer is calculated by dividing the value
of the instrument\'s output signal (microvolts) by the computed
reference global horizontal irradiance (W/sq m). The computed reference
irradiance is the sum of the diffuse radiation and the vertical
component of the direct beam irradiance (cavity radiometer irradiance
multiplied by the cosine of the solar zenith angle at the time of
measurement). This assumes that the pyranometer has a perfect angular
response. The solar zenith angle calculations are corrected for
atmospheric refraction effects at the calibration facility.

During a calibration event, one or more pyranometers (The Eppley
Laboratory, Inc. Model PSP) and pyrheliometers (The Eppley Laboratory,
Inc. Model NIP) are used as control standards to monitor the calibration
process.

[]{#__RefHeading___Toc87419577 .anchor}[Figure 6. [Component Summation
Calibration]{.underline}]{.mark}

### []{.mark} {#section-5 .unnumbered}

[]{#__RefHeading___Toc87419578 .anchor}[Figure 7. Shade/Unshade
Calibration]{.mark}

[]{.mark}

[]{.mark}

### Longwave Radiometer Calibrations  {#longwave-radiometer-calibrations .unnumbered}

As of January 2001, all SIRS pyrgeometers have the calibration factors
assigned by the manufacturer. A new blackbody calibration system has
been developed for the recalibration of all SIRS pyrgeometers and is
under test and evaluation at NREL. The specifications relative to the
temperature ranges to be attained by the blackbody source and the PIR
instrument were adapted from the BSRN (WMO\'s Baseline Surface Radiation
Network) operating specifications.

The model PIR pyrgeometer is an instrument for measuring infrared
radiation from the atmosphere, or from the ground if used in an inverted
position. It defines the radiative transfer relative to the longwave
irradiance. A PIR can be calibrated using a blackbody radiator with
temperatures in the range given in the cited specification. The
blackbody radiator itself is a copper hemisphere mounted in a fluid
containing vessel, which is insulated. The geometry is such that the PIR
will be in the "up-looking\" position when it is inserted into the
radiator. The surface of the hemispherical cavity is coated with
Parson's black paint over a layer of Parson's black primer. This should
yield a surface emissivity greater than 0.98. When the PIR instrument is
inserted in the hemispherical cavity the effective emissivity approaches
1.0, due to the cavitation and enhancement from reflection of its own
radiation. The reason for this approach is that the PIR instrument has a
180° Field of view (FOV). While this concept is simple in principle it
is not as straight forward in operation. One reason is that for
temperature differences between blackbody radiator and the PIR
instrument thermal conduction and convection interfere with achieving
the strictly radiative heat transfer desired for a calibration.

In nature, the ambient temperature determines the temperature of the PIR
to a high degree. The cold radiative temperatures of the sky are
actually affecting the instrument temperature to a high degree. It has
been reported that solar radiation heats the hemisphere and/or
hemisphere collar during some field use. However, some investigators use
ventilation and / or shading to reduce this effect. Correction terms
have been added to the data reduction algorithms to reduce such effects.
The prototype PIR calibration system offered an opportunity to assess
some of these effects. There is a history of relatively good agreement
among different calibration laboratories as reported elsewhere. It was
intended that information gathered by use of the prototype would allow
development of the production units.

The prototype system was based on the system used at Eppley Laboratory
for over 20 years. The main differences for the new systems:

### Operates over a larger temperature range (see discussion of BSRN spec.) 

### Is to be fully automatic for a number of functions and all measurements 

### The temperature of the PIR is controlled (EPLAB system at ambient). 

To understand the design and operation of the calibrator, the actual
desired result must be defined. The radiation measured by a PIR is
calculated from the measurement of the parameters of the instrument. The
primary parameters are:

### The thermopile output signal 

### The case temperature (approximation of the cold junction temperature) 

### The silicon hemisphere temperature.

Note that some users also measure a quantity termed the pyrgeometer
output signal. This is a modified output signal from the PIR by virtue
of a radiation compensation circuit which act like an analog computer
which automatically corrects for the outgoing (emitted) radiation from
the thermopile surface.

Generally speaking, investigators define the calibration as the
determination of the sensitivity of the thermopile and the correction
parameters associated with the temperatures and temperature differences
experienced. A thermopile signal is related to the NET radiation at its
receiver. This leads to the fact that the outgoing radiation must be
assessed to calculate the incoming radiation, which is the desired
result of the measurement. This is accomplished by calculating the
outgoing radiation using the measured case temperature and making such
corrections as deemed necessary. The measured hemisphere (or dome)
temperature is also used to calculate correction terms related to other
effects due to temperature gradients in the instrument during
calibration and/or use.

![](media/image11.jpeg){width="2.1680555555555556in"
height="3.3743055555555554in"}-\
[]{#__RefHeading___Toc87419579 .anchor}Figure 8. Photo of PIR BB
Production 0809Unit Blackbody Unit in Enclosure front view

Figure 8 shows the PIR BB system enclosure consists of 2 chambers: upper
Blackbody chamber and lower PIR chamber which are separately purged with
dry gas. Dry air is also directed to the Blackbody hemisphere. The lower
section with lab jack for height adjustment is outside the purged
volume.

### Procedures

This section is not applicable to this instrument.

### History

Pyranometers and pyrheliometers are re-calibrated annually at the SGP
Radiometer Calibration Facility (RCF). Calibration results and
instrument deployment records are available from NREL's ARM Instrument
Management (AIM) System at <http://www.nrel.gov/aim/>.

## Operation and Maintenance

### User Manual

This section is not applicable to this instrument.

### Routine and Corrective Maintenance Documentation

This section is not applicable to this instrument.

### Software Documentation

ARM netCDF file header descriptions may be found at [SIRS Data Object
Design Changes](http://science.arm.gov/tool/dod/showdod.php?Inst=sirs).

### Additional Documentation

In order to provide research-quality irradiance measurements, the SIRS
radiometers are re-calibrated annually. The existing radiometer
inventory allows for 50% spares, reducing the down time for station
operation due to calibration. Maintenance of the SIRS equipment is
performed during the biweekly maintenance visits to the SGP facilities.
Detailed information is available from the Operations Management
Information System (OMIS) at
[http://ops.sgp.arm.gov](http://ops.sgp.arm.gov/).

## Glossary

See the [ARM Glossary](http://www.arm.gov/about/glossary.stm).

## Acronyms

See the [ARM Acronyms and
Abbreviations](http://www.arm.gov/about/acronyms.stm).

## Citable References

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Applied to the Measurement of Total, Direct and Diffuse Shortwave
Radiation at the Surface. *J. Geophys.* *Res*.

Coulson, K.L. 1975. *Solar and Terrestrial Radiation Methods and
Measurements*. Academic Press, New York, New York. ISBN 0-12-192950-7,
pp. 322.

Dutton, E.G., J.J. Michalsky, T. Stoffel, B.W. Forgan, J. Hickey, D.W.
Nelson, T.L. Alberta, and I. Reda. 2001. Measurement of Broadband
Diffuse Solar Irradiance Using Current Commercial Instrumentation with a
Correction for Thermal Offset Errors. *J. Atmospheric & Oceanic
Technology*, Vol. 18, pp. 297-314. American Meteorological Society,
Boston, MA.

Gulbrandsen, A. 1978. On the Use of Pyranometers in the Study of
Spectral Solar Radiation and Atmospheric Aerosols. *J. Appl. Meteorol*.,
17, 899-904.

Hickey, J.R., and A.R. Karoli. 1974. Radiometer Calibrations for the
Earth Radiation Budget Experiment. *Applied Optics*, Vol. 13, No. 3, pp.
523-533. ISSN 0003-6935.

Hickey, J.R. 1975. Solar Radiation Measuring Instruments: Terrestrial
and Extraterrestrial. *Proc. of Soc. of Photo-Optical Instrumentation
Engineers*, Vol. 68. *Optics in Solar Energy Utilization*, Y.H. Katz
(ed). ISBN 0892520809.

Hill, A.N., J.R. Latimer, A.J. Drummond, and H.W. Greer. 1966.
Standardized Procedures in the North American Continent for the
Calibration of Solar Radiation Pyranometers. *Solar Energy*, Vol. 10,
No. 4, pp. 1-11.

Hulstrom, R.L. 1989. *Solar Resources*. The MIT Press, Cambridge,
Massachusetts. ISBN 0-262-08184-9, pp. 408.

Iqbal, M. 1983. *An Introduction to Solar Radiation*. Academic Press,
New York, New York. ISBN 0-12-373750-8 (ISBN 0-12-373752-4 for
paperback), pp. 390.

Karoli, A.R., J.R. Hickey, and R.G. Frieden. 1983. Self-calibrating
Cavity Radiometers at the Epley Laboratory: Capabilities and
Applications. *Proc. of SPIE-Int. Soc. Opt. Eng*., Vol. 416, pp. 43-49.
Conference: Arlington, Virginia, April 7-8, 1983. ISSN: 0277-786X.

Latimer, J.R. 1964. An Integrating Sphere for Pyranometer Calibration.
*J. of Applied Meteorology*, Vol. 3, No. 3, pp. 323-326. American
Meteorological Society, Boston, Massachusetts.

Maxwell, E.L, and D.R. Myers. 1992. Daily Estimates of Aerosol Optical
Depth for Solar Radiation Models. *Solar \'92, Proceedings of 1992
Annual Conference of the American Solar Energy Society*, p. 323. Cocoa
Beach, Florida, June 15-18, 1992.

McCluney, W.R. 1994. *Introduction to Radiometry and Photometry*. Artech
House, Inc., 685 Canton Street, Norweed, Massachusetts 02062. ISBN
0-89006-678-7, p. 402.

Reda, I. 1999. *Improving the Shade/Unshade Method to Calculate the
Responsivities of Solar Pyranometers*. NREL/TR-26483 (June 1999).

Thekaekara, M.P., R.H. Collingbourne, and A.J. Drummond. 1972. A
Comparison of Working Standard Pyranometers. *Bulletin of the American
Meteorological Society*, Vol. 53, No. 1, pp. 8-15.

World Meteorological Organization. 1971. *Guide to Meteorological
Instrument and Observing Practices*. 4^th^ edition, WMO-No. 8, TP. 3,
Geneva, Switzerland. (Note: Most WMO publications are available in the
U.S. from the American Meteorological Society, 45 Beacon St., Boston,
Massachusetts 02108-3693, Telephone: 617-227-2425.)