The Model UVMFR-7 Ultraviolet Multi-Filter
Rotating Shadowband Radiometer is an instrument
that measures diffuse and total global irradiance,
and computes direct irradiance at four or seven
narrow-bandwidth wavelengths in the UV-B and
UV-A regions
. It extends the YES shadowband
instrument family into the UV-B, providing the
atmospheric scientist with a low-cost precision tool
for measuring narrowband UV-B total, direct, and
diffuse spectral irradiance. Real-time UVMFR-7
data is available at sites across the US by browsing
http://uvb.nrel.colostate.edu
The UVMFR-7 provides spectral irradiance data
with stability equal to that of spectroradiometers but
at a fraction of the cost. In addition, unlike most
global spectroradiometers that only provide total
horizontal irradiance, the UVMFR-7 makes diffuse,
and direct normal measurements. Direct beam
spectral irradiance data provides optical depth
information that can be used to track the absolute
calibration stability of the instrument.
Most UV-B field spectroradiometers for making
narrowband irradiance measurements demand
constant attention by highly skilled personnel. The
UVMFR-7 is designed to operate automatically and
autonomously in remote locations with only periodic
manual cleaning of the fore optic. A unique optical
design coupled with the flexible and powerful
YESDAS-2 data acquisition and control system,
gives the instrument high performance at a modest
price.
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Compared to scanning spectroradiometers the
UVMFR is a cost-effective solution for measuring
UV-B spectral irradiance in a number of important
applications:
- Meteorological networks used for prediction of
UV-B hazards to the public
- Global climate change and ozone studies
- UV-B and aerosol research
- Biological effects studies
The UVMFR-7 consists of two basic components: a
Detector Assembly and an Electronics Enclosure.
The Detector Assembly consists of the UVMFR-7
sensor head and the stepper-motor-driven rotating
shadowband, which are mounted on a common
base. An electronics enclosure, mounted below the
Detector Assembly, contains a YESDAS-2
microprocessor-driven data acquisition and control
system with 13-bit A/D conversion accuracy and the
capability of collecting data from an additional 24
analog and 6 pulse/counting-type met sensors.
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- All radiation components are measured with the
same photodetector
- Thermally controlled sensor head eliminates
ambient temperature-induced errors, and
prevents dew/snow/ice buildup on aperture
- Data acquisition system has inputs for up to 24
other analog and 6 pulse-type met sensors
- Durable, state-of-the-art design
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The UVMFR-7 uses an automated rotating
shadowband to make measurements of the global and
diffuse components of solar irradiance. Once these two
components are known, a CPU can readily compute
the direct-normal component.
The geometry of the rotating shadowband instrument is
shown in the figure below. The shadowband is a strip
of metal formed into a circular arc and mounted along
a celestial meridian with the instrument's entrance
aperture at the center of the arc. The shadowband
blocks a strip of sky with a 3.3° umbral angle, sufficient
to block the sun. It can be positioned with an accuracy
of 0.4° by the microprocessor-controlled stepper motor.
The motor housing is adjusted for the latitude of the
instrument. When the instrument is installed at the field
site, it must be azimuthally aligned to the Earth's pole
(North or South, depending on the hemisphere). Once
aligned, no further mechanical adjustment is necessary
and the instrument may operate for extended periods
without any operator intervention, unlike trackers that
require nearly constant attention.
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UVMFR-7 Detector Assembly Side View 
UVMFR-7 Diffuser Shading View |
The operation of the instrument is controlled by its
microprocessor. At each measurement interval, the
microprocessor computes the solar position using an
approximation for the solar ephemeris. The first
measurement is made with the band rotated to its nadir
position (global or total horizontal irradiance). The band
is then rotated to make three more measurements.
One measurement is made with the sun completely
blocked (diffuse horizontal irradiance) and the other
two are made with the band rotated to 9° on either side
of the sun. The side measurements permit a correction
for the "excess sky" that is blocked by the shadowband
when the sun-blocking measurement is made. The
microprocessor then subtracts the corrected diffuse
component value from the global irradiance to obtain
the direct-horizontal component. Finally, division of the
direct- horizontal component value by the cosine of the
solar zenith angle (available from the ephemeris
calculation) results in the value of the direct-normal component. The entire sequence is completed in less
than 20 seconds and can be programmed to occur up
to 3 times per minute. |
The use of the computed solar ephemeris in the
UVMFR-7 instrument gives it a significant advantage
over instruments that use a continuously moving
shadowband to make the global and diffuse
measurements. The UVMFR-7 method permits much
longer integration time for each measurement because
it requires measurements at only four shadowband
positions rather than making many measurements
during a continuous scan across the sky. Longer
integration time substantially improves measurement
precision and permits operation at wavelengths and
passbands that would not be possible with a continuously moving shadowband. The excess sky
blockage correction significantly improves
measurement accuracy, particularly under skies with
fractional cloud cover.
The filter wavelengths were carefully chosen by the
atmospheric research community to maximize the
utility of the data. For example, the 311.5 nm filter was
chosen to land on a small but somewhat “flat” area of
the spectrum, and the 332.4 nm was selected as a
Dobson reference. Each filter-detector channel is
individually characterized, yielding spectral irradiance
in W/m2-nm.
The UVMFR-7's unique ability to make simultaneous
spectral measurements of the three solar irradiance
components makes it an extremely versatile
instrument. For example, in order to obtain the data
collected at least two instruments would have to be
used: a global filter radiometer, and either a
tracker-mounted normal incidence sun photometer or a
second, shaded global radiometer. When making
spectral measurements, the UVMFR-7 has the
advantage of sensing the global and diffuse irradiance
components with the same detector. This eliminates
the error introduced into the measurement of solar
irradiance components by the use of different detectors
to measure the different components, reducing
concerns about the intercalibration of multiple sensors.
The UVMFR-7 is simpler, less expensive and more
robust. Finally, the UVMFR-7 instrument ensures that
the measurements of the irradiance components are
synchronous in time.
Changing ambient temperatures can cause unwanted
response changes in semiconductor detectors,
resulting in measurement errors. To avoid these errors
the instrument utilizes a computer-controlled thermal
regulation circuit that maintains the detectors and filters
above ambient temperature, thereby preventing
thermal transients from affecting the solid state
detectors. A side benefit is that the additional thermal
energy helps to keep the sensor free of dew, ice, and
snow. A separate thermistor permits the user to
monitor the temperature. The solid state photodiodes,
interference filters, and sensitive electronic
components are all held inside a desiccated enclosure,
further eliminating environmentally-induced
measurement errors.
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The UVMFR-7 instrument operation and data logging
are controlled by a microprocessor. This on-board
CPU, 1) performs the required ephemeris calculations,
2) controls the stepper motor which positions the
shadowband, 3) controls the acquisition, processing
and storage of sensor data for the MFR-7 and up to 24
additional analog meteorological sensors, and 4)
permits simultaneous data telemetry. The ultra-stable
system time-keeping (with an accuracy of 1 second per
month) ensures that the positioning of the shadowband
will be precise over extended time periods, with no
need for operator intervention or adjustment. The
system data logger includes a state-of-the-art 13 bit
self-calibrating analog-to-digital converter and onboard
data storage capability of up to 2 Mbytes via the
PCMCIA-2 memory option (most users want more
memory to permit higher time-resolution sampling.)
You can communicate directly through the 3m serial
cable provided, or over a telephone lines using a usersupplied
modem. Using YESDAS Manager software,
data are automatically downloaded, corrected,
calibrated and presented to the web. Modem
communication allows a remote instrument to be
controlled from a laboratory or office without
interrupting its data acquisition, making it ideal for
large, geographically widespread networks. |
| Each UVMFR-7 instrument is individually tested and characterized before shipment. First, the response to a
direct beam at different angles is measured in our
cosine facility, where an instrument-specific cosine
correction file is generated. Next, each head is
spectrally scanned with a narrowband spectrometer to
determine the precise full width at half-maximum
(FWHM) bandwidth and center wavelength. Finally,
each head is calibrated against a NIST-traceable FEL
lamp to determine its absolute response. |
The usefulness of any instrument depends critically on
the quality and long-term stability of its calibration. YES
has fully-equipped optical laboratories to completely
characterize the performance and calibrate each
instrument. The cosine, spectral and absolute
responses of each wavelength channel of the
instrument are measured with NIST-traceable optical
and electronic equipment and test results are supplied
with each system. A comprehensive document is
available on our web site (Calibration Services.)
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| The interference filters and photodiodes used in the
UVMFR-7 are of the highest quality and result in an
instrument with exceptional ruggedness, long term
stability of calibration, and excellent unit-to-unit
repeatability of response. The spectral response of
each wavelength channel of the UVMFR-7 instrument
is measured using an Acton Research AM-511 one
meter monochrometer. |
The unique spectral irradiance voltage transfer function
calibration data provided by the FEL lamp is convolved
(in conjunction with each channel's individually
measured relative spectral response) to calculate each
channel’s spectral irradiance in W/m2-nm units, as well
as identify effective bandwidth and effective center
wavelength. By doing this, unlike the integrated dose
output from broadband UV-B instruments, the UVMFR-
7’s spectral irradiance output data is readily
comparable to spectroradiometer data.
The ability to measure direct and diffuse spectral
irradiance allows the user to conduct automated
Langley analysis with the software tools provided. As in
the visible wavelength MFR instrument, the automated
Langley analysis results can be used to track the
UVMFR-7’s absolute calibration, since the direct-todiffuse
ratio is independent of the UVMFR’s absolute
calibration. As filter solarization gradually occurs under
normal exposure, these shifts can be monitored and
accounted for. Using the same method, the calibration
of other more sophisticated UV-B instruments (such as
spectroradiometers) can be checked against the
UVMFR-7's direct-to-diffuse ratios.
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The UVMFR-7 belongs to a class of instruments that
measure flux incident on a horizontal surface from a
moving light source. Ideally, one would like these
instruments to be uniformly sensitive to incident
radiation coming from any direction. The response of
such instruments to radiation incident at an angle, q,
with respect to the surface normal is called the cosine
response. The ideal cosine response is proportional to
the cosine of the angle q, and any deviation from this
response introduces measurement errors.
The UVMFR-7 uses a novel diffuser input optic that
provides superb cosine response and long-term
stability. The radiation receiver element is a computerdesigned,
specially shaped TeflonÔ diffuser disk that
is directly coupled to an optical integrating cavity.
Teflon is a halocarbon with excellent resistance to
chemical and ultraviolet degradation, thus ensuring
calibration stability in the field. In addition, instruments
with diffusing input optics are inherently less sensitive
to surface soiling than are instruments with
transmission windows such as domes.
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| The cosine response of each UVMFR-7 is fully
characterized in our angular test facility. Each
instrument is placed on a computer- controlled rotary
actuator and the instrument's relative response as a
function of its angle measured using a feedbackstabilized,
parallel, uniform light beam. The individually
characterized cosine response, supplied with each
instrument, is used by system software to correct, in
real time, for deviations from the ideal cosine
response. |
A primary use of UV-B irradiance data is for tracking
long-term changes in column ozone. The calculated
direct beam data is stored and later used for optical
depth determination. Optical depth is a dimensionless
quantity closely related to the extinction coefficient
used in visibility studies. An automatic angular
correction procedure corrects raw data for cosine
errors based on the factory-measured, instrumentspecific
angular response. Next, factory-determined
spectral irradiance calibration constants are applied to
the data to derive engineering units. The software also
performs automated Langley analysis on the data for
retrieval of optical depth information.
Once calibration constants are applied to the data via
the host software, spectral irradiance data can be used
for studies such as determining scattering due to
aerosols. Aerosols have recently been shown to have
a great effect on UV-B radiation at the earth’s surface,
possibly impacting total irradiance as much as cloud
conditions do.
The direct-normal UVMFR-7 data can be used to
measure both ozone and aerosols. In addition, by
using the automated Langley analysis software
(provided with the system) a self-check on the absolute
calibration can be performed based on the stability of
the extraterrestrial solar constant and the known
optical depth. |
UVMFR-7 instruments are controlled by an included
YESDAS-2 data acquisition and control system that
controls the shadowband and thermal subsystems,
stores and telemeters the data. Data are anglecorrected,
calibrated and analyzed via the YESDAS
Manager software running on a user-supplied Windows
9x/NT PC. This system is a reliable and well tested
remote data acquisition and display platform that even
provides web access to the data. Calibration
information is applied to the data in a foolproof and
flexible architecture yet permits users to reconstruct
data streams when instruments are recalibrated.
Multiple systems can be automatically polled and the
data provided on the web letting users efficiently
manage networks with many field sites. |
The UVMFR-7 instrument is easy to install; it needs a
user-provided level mounting platform approximately
17" in diameter. Set the latitude adjustment on the
shadowband motor assembly (this is usually done at
the factory). Place the Detector Assembly on a flat
stable platform. Orient the instrument with the
shadowband support post toward geographic north in
the Northern hemisphere (south in the southern). Stepby-
step instructions for this procedure are in the
instrument manual. You need to perform this
orientation procedure only once, at the time of
installation; no further orientation adjustments are
necessary.
The UVMFR-7 detector assembly is fabricated from
anodized aluminum and stainless steel; all hardware is
stainless steel and all connectors are potted and
weatherproof. The system electronics (including the
DC power supply, data acquisition board and ancillary
electronics is housed in a NEMA-4X enclosure. The
DC power supply is high quality a medical-grade, linear
type, with a dual bobbin transformer for maximum
power line transient signal and noise rejection. A 3m
null modem cable is provided for direct connection with
a local PC or laptop. A telephone line connection
terminal with spark gap lightning arrestor is provided
for connecting a user-supplied Hayes-compatible
modem to the system. Screw terminal connections are
provided for the 16 auxiliary sensor connections.
Use the three leveling screws and the precision bubble
level to position the instrument with the receiver
surface in the horizontal plane. Once you have
completed this step, secure the instrument to your
mounting platform via a #10 screw through-hole
located in the center of the base. Connect the two
cables from the system electronics enclosure to the
mating receptacles on the Detector Assembly. Connect
the DC standby battery and apply AC power.
Depending on whether the system will be local or
remote, either connect the serial cable to the PC
running YESDAS Manager or connect a modem to the
system serial port. The instrument is now installed and
ready to take data.
You will need to provide a deep cycle marine/RV 12
Vdc standby battery, as well as 115/230 Vac 50/60 Hz
power to the instrument. A 2m power cord is provided
(please specify 115 or 230 Vac when ordering the
instrument.) The entire system can also optionally be
configured to operate from a 12 Vdc solar panel/battery
system. You must also furnish a ground rod to ensure
a static discharge path independent from the path
through the power grounding system to help protect
against lightning. |
The UVMFR-7 is designed for long-term continuous
field use. The entire housing is O-ring sealed and
polyester-powder-coated for long life. A userremovable
desiccant is provided to ensure that any
water entering the housing is absorbed. The only
required maintenance is periodic cleaning of the optical
diffuser to remove aerosols and other particulates. The
action of the shadowband coupled with the internal
heater help to reduce bird landings and snow and ice
build up. UVMFR-7 heads can be swapped without
shipping the entire system back to the factory.
Alternatively, the instrument can be calibrated against
a co-located research grade UV-B spectroradiometer
such as a YES Model UVRSS-1024. Calibration should
be performed at least every 12 months. |
instruments have gained a reputation for relatively poor
long-term stability, especially in the UV-B region. Some
manufacturers have responded by using wideband
channels (e.g. 280-305 nm bandpass) that produce
data that cannot be separated into the constituent
wavelengths. The UVMFR-7 reverses this trend by
offering narrow band channels deep into the UV-B
region at 317, 311, 305 and 300 nm. Nevertheless,
rigid quality control standards are necessary during the
filter fabrication steps as well as strict handling
precautions during the final assembly process. For
long life, environmental thermal stabilization is
necessary. Earlier filter-photometer instruments often
did not provide adequate thermal stabilization or
humidity protection for their filters.
Recently, advances in interference filter technology
have resulted in next-generation coatings that make
them much more mechanically durable and resistant to
changes in throughput due to solarization. The
UVMFR-7 uses these s-called Ion-Assisted Deposition
filters, as well as a diffuser fore optic to reduce the flux
level the filters are exposed to by an order of
magnitude. This diffuser design, similar to that used in
the MFR instrument has demonstrated greatly
improved calibration stability over earlier instruments. |
The UVMFR-7 is part of the MFR family of solar
radiation instrumentation that includes the Model SDR-
1, MFR-7 and RSS-1024. The UVMFR-4 is a four
channel version of the UVMFR-7 that contains only the
UV-B channels at slightly reduced cost. For
applications requiring visible spectral irradiance, the
Model MFR-7 instrument has a broadband channel
plus six 10 nm wide (FWHM) visible channels
extending from 415 to 940 nm. The broadband channel
measures the global, diffuse, and direct-normal
components of total solar radiation making it equivalent
to a total solar pyranometer and a solar trackermounted
normal incidence pyrheliometer. A full suite of
UVMFR-7, MFR-7 and UVB-1 instruments forms the
backbone of several national monitoring networks.
The UVMFR-7's data acquisition and control system
can also be purchased separately. A YESDAS-2
system collects and store data from up to 32
meteorological sensors while giving the user total
flexibility in controlling the data acquisition. For more
information, refer to the YESDAS-2 and YESDAS
Manager data sheets.
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The visible Multi-Filter Rotating Shadowband
Radiometer was initially developed for the U.S.
Department of Energy (DOE) Atmospheric Radiation
Measurement (ARM) program by researchers at the
State University of New York at Albany and the Battelle
Memorial Institute at DOE's PNNL. It was designed as
a rugged field instrument to perform the required
spectral measurements of solar irradiance components
and to serve as the primary data logging station for a
suite of associated meteorological sensors. In 1993,
YES was granted an exclusive worldwide license by
the State University of New York at Albany to
manufacture the UVMFR-7 instrument. |
| Spectral
Response |
UVMFR-4: 300, 305.5, 311.4 and
317.6 nm, (2nm FWHM)
UVMFR-7: 300, 305.5, 311.4, 317.6,
325.4, 332.4, 368 nm, (2nm FWHM). |
| Radiometric
Accuracy |
2-3%, with angle corrections applied. |
| Electrical
Interface |
YESDAS-2 system interfaces via
RS-232 DB-9 Male (DTE) or modem.
Telephone input is lightning
protected. Cable lengths are 2m
Detector Assembly, 2m AC power |
| Power
Requirements |
Can be operated from 110/220 VAC
50/60 Hz or 12 VDC @ 3A.
Customer-supplied 12 VDC deepcycle
battery is required, and a
ground rod |
| Weight
Mechanical |
YESDAS: 10 kg; UVMFR-7 Asy: 5 kg
Center bolt hold-down, compatible
with all MFR mounts. A level and
stable 40 cm x 40 cm platform is
required for mounting. |
| Note: Included MFR-to-YESDAS system cables are
fixed length and cannot be lengthened. |
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