Campbell Scientific NR01 User Manual
NR01 Four-Component
Net Radiation Sensor
Revision: 8/11
Copyright © 2008-2011
Campbell Scientific, Inc.
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NR01 Table of Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. Introduction..................................................................1
2. Measurement Principle ...............................................3
2.1 General......................................................................................................3
2.2 NR01 Construction ...................................................................................4
2.3 Pyranometers ............................................................................................5
2.4 Pyrgeometers ............................................................................................6
2.5 Expected Measurement Results................................................................8
2.6 Heating....................................................................................................10
2.7 Data Quality Assurance ..........................................................................10
3. Specifications of NR01..............................................10
3.1 NR01 General Specifications .................................................................11
3.2 SR01 Pyranometer Specifications ..........................................................12
3.3 IR01 Pyrgeometer Specifications ...........................................................13
3.4 Dimensions .............................................................................................14
4. Installation..................................................................14
4.1 Installation ..............................................................................................14
4.2 Electrical Connections ............................................................................16
4.3 Connecting the Sensor to Campbell Scientific Dataloggers ...................17
4.3.1 Connecting and Using the Heater .................................................19
4.4 Installation of the Radiation Shields.......................................................20
4.5 Instrument-Inversion-Test ......................................................................20
5. Datalogger Programming.......................................... 20
5.1 Calibration Factors..................................................................................21
5.2 Example Programs..................................................................................22
5.2.1 Example 1, CR1000 Using Differential Channels ........................22
5.2.2 Example 2, CR3000/CR5000 Using Differential Channels
(no 4WPB100) ..........................................................................25
5.2.3 Example 3, CR23X Program Using Differential Channels...........27
5.2.4 Example 4, CR23X Program Using Single-Ended Channels .......31
6. Maintenance and Troubleshooting ..........................33
6.1 Maintenance............................................................................................33
6.2 Troubleshooting......................................................................................34
Appendix
A. CR3000 Program that Controls the Heater ........................................... A-1
i
NR01 Table of Contents
Figures
Tables
1-1. Atmospheric Radiation as a Function of Wavelength ............................ 2
2.2-1. The NR01 Four-Component Net Radiation Sensor............................. 4
2.3-1. Spectral Response of the Pyranometer Compared to the Solar
Spectrum.......................................................................................... 5
2.4-1. Spectral Response of the Pyrgeometer Compared to the Atmospheric
LW Spectrum................................................................................... 7
3.4-1. Dimensions of the NR01 in mm ........................................................ 14
4.1-1. NR01 with Reducer (P/N 21271) and Mounting Arm....................... 15
4.4-1. Installation and Removal of Radiation Shields.................................. 20
5-1. 4WPB100 Module ................................................................................ 21
2.3-1. Main Measurement Errors in the SW Signal....................................... 6
2.4-2. Main Measurement Errors in the LW Signal....................................... 8
2.5-1. Average Global Radiation Values at the Earth Surface....................... 9
2.5-2. Expected SENSOR Outputs when Measuring with the NR01 ............ 9
3.1-1. General Specifications of the NR01 .................................................. 11
3.2-1. Specifications of SR01 ...................................................................... 12
3.3-1. Specifications of IR01 ....................................................................... 13
4.1-1. Recommendations for Installation of the NR01 ................................ 15
4.2-1. Internal Electrical Diagram of the NR01........................................... 17
4.3-1. Datalogger Connections for Differential Measurement,
when using a 4WPB100................................................................. 18
4.3-2. Datalogger Connections for Single-Ended Measurement,
when using a 4WPB100................................................................. 18
4.3-3. Pt-100 Temperature Sensor Connections to 4WPB100 and
Datalogger...................................................................................... 18
4.3-4. CR3000 and CR5000 Connections for Differential Measurement
and using the Current Excitation to Measure the PT100 Sensor ... 19
6.1-1. The NR01 Recommendations for Maintenance................................. 33
6.2-1. Troubleshooting for the NR01........................................................... 34
ii
NR01 Four-Component Net Radiation Sensor
The NR01 is a four-component net radiation sensor that is used for scientific-grade energy
balance studies.
1. Introduction
The NR01 has separate measurements of solar (Short Wave or SW) and Far
Infra-Red (Long Wave or LW) radiation. It offers a professional solution to
the measurement of net radiation and its four main components. The NR01 is
robust and requires only limited maintenance.
Measurement of the separate components of the net radiation is useful because
it:
• Enhances accuracy by having separately calibrated instruments (similar
accuracy cannot be attained with sensors with single outputs or dual
outputs). Single-output or dual-output instruments will always suffer from
instrument asymmetry or from errors due to sensitivity differences for LW
and SW radiation.
• Provides more detailed information than sensors with single or dual
outputs (e.g., albedo of the ground, cloud condition).
• Allows more thorough quality assurance of the instrument data (compared
to sensors with single or dual outputs). Quality assurance with fourcomponent radiometers is done by analyzing trends in SW
signal, SW albedo, correlation of SW
and correlation LW
and surface temperature.
out
and LWin, SW night time signals,
in
absolute
in
1
NR01 Four-Component Net Radiation Sensor
FIGURE 1-1. Atmospheric Radiation as a Function of Wavelength
LW or FIR radiation is mainly present in the 4500 to 50000 nm region, while SW or solar radiation is
mainly present in the 300 to 3000 nm region. The two are measured separately.
Major improvements of the NR01 relative to comparable instruments include
reduced weight, reduced solar offsets in the LW signal, ease of leveling
(because a 2-axis leveling assembly is built-in).
The NR01 serves to measure the four separate components of the surface
radiation balance. Working completely passive, using thermopile sensors, the
NR01 generates four small output voltages proportional to the incoming and
outgoing SW and LW fluxes; SW
solar radiation, LW
or infrared emitted by the sky and LW
in
or global solar radiation, SW
in
or reflected
out
or infrared
out
emitted by the ground surface.
From these also parameter like SW “albedo”, “sky temperature”, “(ground)
surface temperature” and off course “net-radiation” (net value of all SW and
LW fluxes) can be calculated.
The SW sensors are also called pyranometers (type SR01); the LW sensors are
called pyrgeometers (type IR01). For calculation of the sky and surface
temperature, a PT100 temperature sensor is included in the connection body of
the pyrgeometers. A heater is also included in the pyrgeometers’ connection
body to heat the pyrgeometers, which prevents the deposition of dew.
The NR01 requires leveling; a two-axis leveling facility is incorporated in the
design. See the chapter on installation.
Using the NR01 is easy. For readout one only needs four analog input
channels, and, only if sky and surface temperature are required, a way to
measure the PT100. If power is available, Campbell Scientific recommends
heating the pyrgeometers from sundown to sunset.
2
NR01 Four-Component Net Radiation Sensor
The NR01 is supplied with four separate instrument sensitivities. As a brief
explanation, to calculate the radiation level, the sensor output voltage, U, must
be divided by the sensor sensitivity; a constant, E, that is supplied with each
individual instrument. For example:
Φ = SW
in
= U
pyrano, up
More information can be found in the chapter on instrument performance.
WARNING
The NR01 is a passive sensor, and does not need any
power. The NR01 pyrgeometer can, however, be
heated to prevent dew-deposition.
Putting more than 12 Volt across the NR01 sensor
wiring can permanently damage the sensor.
2. Measurement Principle
The following chapters explain the measurement principles of the NR01.
Pyranometers and pyrgeometers are treated in different paragraphs. The last
section is about expected measurement results.
2.1 General
In its most common application, the NR01 measures net-radiation. The four
components of net radiation are measured and the net radiation is calculated:
/ E
pyrano, up
NOTE
The temperature (T
) for the following formula is in Kelvin.
pyrgeo
If the temperature is measured in degrees Celsius, add 273.15 to
pyrgeo
out
= (U
in
out
net
net
= U
= (U
= U
= U
value.
pyrano, up
pyrano, down
pyrgeo, up
pyrgeo, down
pyrgeo, up
pyrano, up
+ LW
net
/ E
/ E
/ E
net
/ E
/ E
net
2.1-1
pyrano, up
pyrano, down
pyrgeo, up
/ E
pyrgeo, down
2.1-2
) + 5.67.10-8 (T
) + 5.67.10-8 (T
pyrgeo
4
)
)4 2.1-4
pyrgeo
the instrument temperature is cancelled:
pyrgeo, up
pyrano, up
- U
- U
pyrgeo, down
pyrano, down
/ E
/ E
pyrano, down
pyrgeo, down
2.1-5
2.1-6
2.1-7
the T
SWin = U
SW
LW
LW
NOTE: in the LW
LW
SW
NR = SW
Special parameters that could be deducted:
SW albedo = SW
/ SW
in
out
2.1-3
2.1-8
3
NR01 Four-Component Net Radiation Sensor
NOTE
The following equations assume the temperature is in Kelvin.
Add 273.15 to equations 2.1-9 and 2.1-10 for temperature in
degree Celsius.
T
= (LW
surface
T
= (LW
sky
in
2.2 NR01 Construction
/5.67.10-8)
out
/5.67.10-8)
1/4
2.1-9
1/4
2.1-10
FIGURE 2.2-1. The NR01 Four-Component Net Radiation Sensor
(1) SW
(2) LW
solar radiation sensor or pyranometer,
in
Far Infrared radiation sensor or pyrgeometer
in
(3) radiation shield
(4) leveling assembly for x- and y axis, block plus bolts for x-axis
adjustment
(5) leveling assembly for x- and y axis, horizontal rod
(6) connection body containing the Pt100 temperature sensor, heater,
and hole for user-supplied temperature sensor (add cable gland M8)
(7) LW
Far Infrared radiation sensor or pyrgeometer
out
(8) leveling assembly for x- and y-axis, bolts for y-axis adjustment
(9) SW
solar radiation sensor or pyranometer
out
A level is located under the radiation screens.
4
2.3 Pyranometers
A pyranometer should measure the solar or SW radiation flux from a field of
view of 180 degrees. The atmospheric SW radiation spectrum extends roughly
from 300 to 2800 nm. It follows that a pyranometer should cover that
spectrum with a spectral sensitivity that is as “flat” as possible.
For a flux measurement, it is required by definition that the response to “beam”
radiation varies with the cosine of the angle of incidence. For example, full
response occurs when the solar radiation hits the sensor perpendicularly
(normal to the surface, sun at zenith, 0 degrees angle of incidence); zero
response occurs when the sun is at the horizon (90 degrees angle of incidence,
90 degrees zenith angle), and half a response occurs at 60 degrees angle of
incidence. It follows from the definition that a pyranometer should have a socalled “directional response” or “cosine response” that is close to the ideal
cosine characteristic.
In order to attain the proper directional and spectral characteristics, a
pyranometer’s main components are:
1. Thermopile sensor with a black coating—absorbs all solar radiation,
NR01 Four-Component Net Radiation Sensor
provides a flat spectrum covering the 300 to 50000-nanometer range, and
has a near-perfect cosine response.
2. Glass dome—limits the spectral response from 300 to 2800 nanometers
(cutting off the part above 2800 nm) while preserving the 180 degrees
field of view. Another function of the dome is that it shields the
thermopile sensor from convection.
FIGURE 2.3-1. Spectral Response of the Pyranometer Compared to the Solar Spectrum
The pyranometer only cuts off a negligible part of the total solar spectrum.
5
NR01 Four-Component Net Radiation Sensor
The black coating on the thermopile sensor absorbs the solar radiation. This
radiation is converted to heat. The heat flows through the sensor to the
pyranometer housing. The thermopile sensor generates a voltage output signal
that is proportional to the solar radiation.
SW
in
= U
pyrano, up
/ E
2.3-1
pyrano, up
In case of the NR01, the pyranometer is type SR01. This is a second-class
pyranometer according to the WMO and ISO classification system (ISO 9060).
The atmospheric solar radiation consists of two components—direct radiation
(in a beam from the sun) and diffuse radiation from the sky.
For down facing instruments, the earth surface reflects part of the solar
radiation, depending on the local surface properties. If there is direct radiation,
this often is the dominant source of energy. Because the solar position is
changing, this implies that for a pyranometer the directional response is quite
important.
Table 2.3-1 summarizes the main sources of measurement errors for the SR01.
The error in the directional response is caused by non-perfect optical properties
of the dome and coating. The infrared offset is produced when the low
temperature “sky” cools off the instrument dome. Because the LW radiation
balance between dome and sky is negative, a negative sensor offset occurs as
the dome cools.
TABLE 2.3-1. Main Measurement Errors in the SW Signal
Source Maximum Error
Directional response +/- 30 W/m2 on SW
+/- 15 W/m
2
on SW
in practice this level is
in
at 1000 W/m
in
2
SWin
Infrared offset - 15 W/m2 on SW
Temperature dependence +/- 5 % for the entire range
2.4 Pyrgeometers
A pyrgeometer should measure the far infrared or LW radiation flux from a
field of view of 180 degrees. The atmospheric LW radiation spectrum extends
roughly from 4500 to 50000 nm. The pyrgeometer should cover that spectrum
with a spectral sensitivity that is as “flat” as possible.
For a flux measurement, by definition, the response to “beam” radiation varies
with the cosine of the angle of incidence. For example, full response occurs
when the radiation hits the sensor perpendicularly (normal to the surface,
source at zenith, 0 degrees angle of incidence); zero response occurs when the
radiation comes from the horizon (90 degrees angle of incidence, 90 degrees
zenith angle), and half a response occurs at 60 degrees angle of incidence. It
follows from the definition that a pyrgeometer should have a so-called
“directional response” or “cosine response” that is close to the ideal cosine
characteristic.
at -200 W/m2 LW
in
net
6
NR01 Four-Component Net Radiation Sensor
To attain the proper directional and spectral characteristics, a pyrgeometer’s
main components are:
1 Thermopile sensor with a black coating—absorbs all LW and SW
radiation, provides a flat spectrum covering the 300 to 50000 nanometer
range, and has a near-perfect cosine response.
2 Silicon window with solar blocking—limits the spectral response from
4500 to 50000 nanometers (cutting off the part below 4500 nm) while
preserving the 150 degrees field of view (not the ideal 180 degrees).
Another function of the window is that it shields the thermopile sensor
from convection.
FIGURE 2.4-1. Spectral Response of the Pyrgeometer Compared to
the Atmospheric LW Spectrum
The black coating on the thermopile sensor absorbs the LW radiation. This
radiation is converted to heat. The heat flows through the sensor to the
housing. The thermopile sensor generates a voltage output signal that is
proportional to the LW radiation that is exchanged between sensor and source.
However, the sensor itself also irradiates LW radiation. This is according to
Plank’s law, so that the pyrgeometer thermopile signal is composed of the
incoming radiation minus the outgoing radiation. In order to estimate the
outgoing component, the pyrgeometer temperature is measured independently,
using a Pt100 or a user-supplied temperature sensor. Equation 2.4-1 calculates
the incoming LW radiation assuming T
LW
= (U
in
For LW
out
pyrgeo, up
/ E
) + 5.67.10-8 (T
pyrgeo, up
a similar formula is valid. The equations are the same for up- and
is in Kelvin:
pyrgeo
)4 2.4-1
pyrgeo
down facing instruments.
It is possible to calculate temperatures of the objects within the field of view of
the instrument, assuming these are uniform- temperature blackbodies (emission
7
NR01 Four-Component Net Radiation Sensor
coefficient of 1). For example, equation 2.4-2 calculates, in Kelvin, the sky
temperature:
T
sky
= (LW
/5.67.10-8)
in
1/4
2.4-2
The NR01’s pyrgeometers are type IR01. Pyrgeometers are not classified by
the ISO or WMO.
The atmospheric LW
radiation essentially consists of two components:
in
1 Low temperature radiation from the universe, filtered by the atmosphere.
The atmosphere is transparent for this radiation in the so-called
atmospheric window (around 10 to 15 micrometer wavelength).
2 Higher temperature radiation emitted by atmospheric gasses.
Down facing instruments are presumably looking directly at the surface, which
behaves like a normal blackbody.
As a first approximation, the sky can, be seen as a cold temperature source
with its lowest temperatures at zenith and getting warmer at the horizon. The
uniformity of this LW source is much better than that in the solar (SW) range,
where the sun is a dominant and non-uniform contributor. This explains why a
pyrgeometer with 150 degrees field of view can perform a good measurement.
Table 2.4-2 summarizes the main measurement errors for the IR01. The error
in the directional response is caused by non-perfect field of view. The windowheating offset occurs when solar radiation heats up the instrument window,
producing a positive sensor offset.
TABLE 2.4-2. Main Measurement Errors in the LW Signal
Source Maximum Error
Directional response 8 W/m2 on LWin at -100 W/m2 LW
Window heating offset +15 W/m2 on LW
SW
in
Temperature
dependence
+/- 5 % for the entire range
2.5 Expected Measurement Results
The average energy balance at the earth surface strongly depends on the:
• Latitude (mostly for SW)
• Local surface properties (SW and LW)
• Local surface temperature (LW)
Table 2.5-1 summarizes the average global values. The average net radiation at
the earth surface is positive, and the remaining energy is used for convective
heat transport and evaporation.
net
at 1000 W/m2
in
8
NR01 Four-Component Net Radiation Sensor
TABLE 2.5-1. Average Global Radiation Values
at the Earth Surface
Type SW in SW
SW
out
LW in LW
net
LW
out
Net
net
Units W/m2 W/m2 W/m2 W/m2 W/m2 W/m2 W/m2
Value 198 - 30 168 324* -390** -66 102
value assumes a sky temperature of 2ºC.
in
value assumes a surface temperature of 14ºC.
out
NOTE
* LW
** LW
The LW radiation values in Table 2.5-1 are corrected for sensor
temperature. The values in Table 2.5-2 are not corrected for
sensor temperature.
On a smaller timescale, the most important factors are:
• solar position
• cloud cover
The ambient air temperature is less important because cloud base temperature
tends to follow surface temperature.
TABLE 2.5-2. Expected SENSOR Outputs when Measuring with the NR01
D / N CD / CR
Ambient
air temp.
pyrgeo
#
down
pyrgeo
up#
pyrano
down
pyrano
up
T
T
sky
ground
°C W/m2 W/m2 W/m2 W/m2 °C °C
D CD +20 0 0 0-500 0-150 20 +20
D CD -20 0 0 0-500 0-150 -20 -20
D CR +20 -70** 0 0-1500 0-400 +1 +20
D CR -20 -70** 0 0-1500 0-400 -50 -20
N CD +20 0 0 0 0 +20 +20
N CD -20 0 0 0 0 -20 -20
N CR +20 -70* 0 0*** 0 1 +20
N CR -20 -70* 0 0*** 0 50 -20
The table makes a distinction between the day and night (D/N), cloudy and
clear (CD / CR) conditions, and high and low ambient air temperatures.
The instrument temperature is normally close to air temperature.
9
NR01 Four-Component Net Radiation Sensor
#Outputs listed for both of the pyrgeometers are not compensated for sensor
temperature. For example, to correct for sensor temperature when the sensor
temperature is 14 ºC, you should add 385 W/m
The raw reading of the upward facing pyrgeometer will generally be close to
zero when the sensor temperature is close to the ground temperature. You
should expect small negative readings when the sensor is located above cooled
surfaces (e.g. water or transpiring vegetation) or small positive readings when
the surface is emitting heat (e.g. warm soil at night).
2
to the pyrgeometer signals.
* At night, dew deposition may affect the downward facing pyrgeometer’s
output. In that case, the signal may drop to 0 W/m
error of +100 W/m
avoid dew deposition.
** During the day, the window-heating offset may affect the downward facing
pyrgeometer’s output. This can produce a maximum error of +15 W/m
***At night, the infrared offset may affect the downward facing pyranometer’s
output. The maximum error of this offset is -25 W/m
2.6 Heating
A heater is located in the connection body of the pyrgeometers to prevent dew
deposits on the sensor that may occur at night. Because of the heater’s current
drain, Campbell Scientific recommends using the heater only when necessary.
A relay can turn the heater on when the solar radiation is less than 20 W/m
See Section 4.3.1.
2.7 Data Quality Assurance
To assure quality data, look for unrealistic values when analyzing:
• Trends in SW
• SW albedo
• Correlation of SW
• SW night time signals
• Correlation of relation LW
in
2
2
. Campbell Scientific recommends activating the heater to
absolute signal,
and LWin
in
and surface temperature
out
, producing a maximum
2
.
2
.
2
.
3. Specifications of NR01
The NR01 is a four-component net-radiometer consisting of two pyranometers
of type SR01, two pyrgeometers of type IR01, a heater, and a Pt100
temperature sensor.
10
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