ARM TR-058

> Multi-Filter Radiometer (MFR) Handbook
>
> January 2005
>
> D. Flynn
>
> G. Hodges
>
> 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
2](#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 6](#data-quality)

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

**Figures**

[1. 2](#__RefHeading___Toc95720300)

**Tables**

[1. MFRSR Status as of January 1, 2005 2](#__RefHeading___Toc95719922)

[2. Wavelengths of Narrowband (10-nm) Filters Used in the MFRSR, and
Main Trace Species Measured (Michalsky et al. 1995).
3](#__RefHeading___Toc95719923)

# General Overview

The multi-filter radiometer (MFR) is simply the head from a multi-filter
rotating shadowband radiometer (MFRSR) mounted on a tower pointing at
the surface. Like the MFRSR, it has six narrowband channels (415, 500,
615, 673, 870, and 940 nm) and one broadband channel. Pointing the head
at the surface provides spectral measurements of reflected irradiance.
Measurements are taken every 20 seconds. No averaging is performed.

# Contacts

## Mentor

Gary Hodges

NOAA/ARL/SRRB

325 Broadway Street

Boulder, CO 80305**\
**Phone: 303-497-6460\
Email: <Gary.Hodges@noaa.gov>

Donna Flynn (data analysis)\
Pacific Northwest National Laboratory\
P.O. Box 999, Mailstop: K9-24

Richland, WA 99352\
Phone: 509-375-6978\
Email: <Donna.Flynn@pnl.gov>

John Schmelzer\
Pacific Northwest National Laboratory

P.O. Box 999, Mailstop: K5-08

Richland, WA 99352\
Phone: 509-375-3729

Fax: 509-375-3614\
Email: <john.schmelzer@pnl.gov>

## Instrument Developer

[Yankee Environmental Systems, Inc.](http://www.yesinc.com/)

[Airport Industrial Park](http://www.yesinc.com/)

101 Industrial Blvd.

Turners Falls, MA 01376

Phone: 413-863-0200

# Deployment Locations and History 

[]{#__RefHeading___Toc95719922 .anchor}Table 1. MFRSR Status as of
January 1, 2005

  ----------------------------- ---------------------- -------------------
  **Site**                      **Collect Data**       **Ingest Data**

  NSA C1 (Barrow) @ 10 m        YES                    YES

  NSA C2 (Atqasuk) @ 10 m       YES                    YES

  SGP C1(Central Facility) @ 10 YES                    YES
  m                                                    

  SGP C1 (Central Facility) @   YES                    YES
  25 m                                                 

  TWP C1 (Manus) @ 10 m         YES                    YES

  TWP C2 (Nauru) @ 10 m         YES                    YES

  TWP C3 (Darwin) @ 10 m        YES                    YES
  ----------------------------- ---------------------- -------------------

# Near-Real-Time Data Plots

See the [MFRSR General
Plots](http://education.arm.gov/nsdl/visualization.shtml).

See the [MFR General
Plots](http://education.arm.gov/nsdl/visualization.shtml).

# Data Description and Examples

## Data File Contents

### Primary Variables and Expected Uncertainty

As mentioned above, the primary quantities measured by the system are:

-   Six wavelengths of reflected solar spectral irradiance (W m^-2^
    nm^-1^).

The spectral data are at wavelengths of 500, 615, 673, 870, and 940 nm.
The measurements at each wavelength are made by a single filtered
detector with a nominal 10-nm full width at half maximum (FWHM)
bandwidth.

[]{#__RefHeading___Toc95719923 .anchor}Table 2. Wavelengths of
Narrowband (10-nm) Filters Used in the MFRSR, and Main Trace Species
Measured (Michalsky et al. 1995).

  ------------------------------------- ---------------------------------
  **Wavelength (nm)**                   **Trace Species**

  415                                   aerosol

  500                                   aerosol, ozone

  615                                   aerosol, ozone

  673                                   aerosol, ozone

  870                                   aerosol

  940                                   water vapor
  ------------------------------------- ---------------------------------

Ozone abundances may be inferred by measurements made by the 500-, 615-,
and 673-nm channels. These wavelengths, particularly the 615- and 673-nm
wavelengths, are influenced by the Chappuis band of ozone \[Goody and
Yung 1989). Water vapor primarily affects the 940-nm channel. Rayleigh
scattering most strongly affects the lower wavelength channels. This
phenomenon is well understood and, therefore, can be removed from an
analysis of the optical depth measurements made at all wavelengths.

The uncalibrated silicon detector provides a measure of the:

-   Reflected broadband solar irradiance (counts).

These quantities are uncalibrated and reported in "counts." Note that
the actual output of the instrument is millivolts, and the use of
"counts" is historical and has been attached to the MFRSR (and related
instruments) since it was developed. The counts are linearly scaled
using broadband radiometers to be roughly equivalent to W m^-2^. Zhou et
al. (1995) discusses the proportionality between the MFRSR broadband
channels and broadband irradiances measured by World Meteorological
Organization (WMO) first-class thermopile radiometers.

#### Definition of Uncertainty

The following notes are from the MFRSR instrument pages, but because the
MFR is merely a MFRSR head, they are included as they relate to the MFR.

**Note about MFRSR calibration as of May 30, 2000**:

We have long suspected that the amplitude of measured irradiances from
the MFRSR is sensitive to the ambient temperature. For example, if one
examines a year-long time series of so-called \"Ios\" (top-of-atmosphere
(TOA) values derived from Langley regressions, a sinusoidal pattern in
the time series will be seen. The period of this pattern is exactly one
year; the peak of the sine wave corresponds to the warmest part of the
year while the valley corresponds to the coldest part of the year.

This pattern, in itself, is not sufficient evidence to implicate
sensitivity to temperature. However, we retrieved the MFRSR head
associated with these data, and we put the head and logger board in an
"environmental chamber" and measured the temperature responsiveness of
the system. The responsiveness can be characterized by temperature
coefficients for each wavelength channel; these coefficients indicate
about a 1 to 2% change in MFRSR output for each 1-degree change in head
temperature. Typically, the MFRSR head temperature changes about 2
degrees over a diurnal period and about 5 degrees over the year.
Therefore, the potential for output fluctuations over the course of a
year may be as high as -+ 5%. If we consider the atmosphere to be gray,
the temperature sensitivity errors induce an equivalent broadband error
of about +- 50 w/m\^2 error (by contrast, a drifting filter may
contribute errors on the order of 500w/m\^2!!). In short, the
temperature sensitivity errors may be significant.

After measuring the temperature sensitivity we devised a way to correct
the data based on the measured temperature coefficients. When these
corrections were applied, the sinusoidal pattern in the MFRSR Ios
disappeared, and the calibration stability of the MFRSR was essentially
flat over the entire year. Furthermore, the temperature-corrected MFRSR
data was used to drive a broadband model and the output of this model
was compared with broadband measurements. In many cases, the use of
temperature-corrected MFRSR data (as opposed to the uncorrected data)
caused the agreement between the model and the broadband data to improve
significantly. (Note: these calculations are not yet finished, so we
can't be sure this conclusion will hold). All this evidence taken
together strongly suggests that the temperature sensitivity is real.

Independent evidence of the temperature sensitivity comes from MFRSR
data collected as part of old, defunct, non-Atmospheric Radiation
Measurement (ARM) programs in which the sinusoidal wave had been
observed but not explained until now. Again, in these old data sets the
peak of the sine wave occurs during the warm times of the year and the
valley into the coldest times of the year.

We (Pacific Northwest National Laboratory \[PNNL\], Yankee Environmental
Systems, and the Atmospheric Sciences Research Center \[ASRC\]) don't
know what's causing this problem, and we don't know if the magnitude of
the problem is different from head to head. The analysis and temperature
chamber operation is costly, and we don't have the time or budget needed
to get to the bottom of this problem. The data can be partially
corrected by using monitoring the Ios from Langley regressions, but this
is at best, an imperfect solution.

Yankee knows about this problem, and they may try to fix it (this could
take a very long time).

**Note about MFRSR calibration as of November 1, 1999**:

Installation of new interference filters has significantly reduced the
calibration drift. To date, the calibrations (for MFRSRs that contain
the new filters) appear to be very stable. The new units have been
installed at the E13 and C1 sites at the Southern Great Plains (SGP),
and at all Tropical Western Pacific (TWP) and North Slope of Alaska
(NSA) sites.

**Note about MFRSR calibration as of March 11, 1998**:

As of 11 March 1998, the calibration of the MFRSR is problematic. For
some channels (i.e., wavelengths), the calibration drifts significantly
with time. For other channels the calibration is stable but not very
accurate; in some cases, the error in the spectral fluxes may be as much
as 50%. The poor calibrations affect some of the flux measurements but
do not affect any of the optical depths derived from the MFRSR.

### Secondary/Underlying Variables

This section is not applicable to this instrument.

### Diagnostic Variables

This section is not applicable to this instrument.

### Data Quality Flags

-9999.0 signifies missing data.

See [MFRSR](http://science.arm.gov/tool/dod/showdod.php?Inst=mfrsr),
[MFR10M](http://science.arm.gov/tool/dod/showdod.php?Inst=mfr10m), and
[MFR25M](../%20http://science.arm.gov/tool/dod/showdod.php%3FInst=mfr25m)
Data Object Design files for the ARM netCDF file header descriptions.

### Dimension Variables

This section is not applicable to this instrument.

## Annotated Examples

> ![](media/image1.png){width="3.692361111111111in"
> height="4.5993055555555555in"}

[]{#__RefHeading___Toc95720300 .anchor}Figure 1.

## User Notes and Known Problems

None to add at this time.

## Frequently Asked Questions

Currently there is no FAQ for 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 \[DQ\] 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 DQ
analysts, instrument mentors, and site scientists to monitor and
diagnose DQ.

## Data Reviews by Instrument Mentor

-   **QC frequency**: Weekly

-   **QC delay**: Up to one week

-   **QC type**: Graphical plots

-   **Inputs**: Raw and processed data

-   **Outputs**: Summary reports

-   **Reference**:

Once a week the instrument mentor downloads both the raw and processed
(NetCDF) files from the ARM Data Archive. Time series plots of the
NetCDF files for each instrument (every channel) are produced and
examined. In addition, the raw data files are processed independently of
the ARM Archive and compared to the NetCDF files from the archive for
inconsistencies. Any problems found are reported so technicians can make
the appropriate repairs. Once a month the mentor submits a report
summarizing the general health and status of all the MFRs.

## Data Assessments by Site Scientist/DQ 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 Products and Quality Measurement Experiments

Currently there are no value-added products for this instrument.

# Instrument Details

## Detailed Description

### List of Components

Many of the MFRSRs deployed at the SGP site have been manufactured by
PNNL. The other MFRSRs are manufactured by Yankee Environmental Systems
(Model MFR-6).

### System Configuration and Measurement Methods

The MFR instrument is a MFRSR without the rotating shadowband. The
sensors associated with each wavelength are all located in a small
canister capped by a level, upward-looking, Lambertian diffuser.
Radiation that strikes the diffuser is directed towards the sensors.
These sensors consist of a single silicon photodetector for measuring
broadband radiation, and a set of interference-filter-photodiode
detectors for measuring spectral irradiances. Even though there is no
shadowband, the instrument is configured to log data on the same
interval as the MFRSR. A measurement is taken once every 20 seconds.

### Specifications

The spectral irradiances are measured at or close to, the following
wavelengths: 415, 500, 615, 673, 870 and 940 nm. These measurements are
made over a passband of nominally 10 nm. A silicon photodiode measures
broadband irradiances. These irradiances are reported in \"counts\" and
are not calibrated per se, but rather linearly scaled to broadband
instruments.

## Theory of Operation

The MFR contains seven sensors. Six are interference-filter-photodiode
detectors for measuring spectral irradiances, and one is a single
silicon photodetector for measuring broadband radiation. The instrument
is connected to a datalogger and measurements in mV are taken every 20
seconds.

## Calibration

### Theory

ARM employs two methods for calibrating MFRSRs. Primarily a standard
lamp is used to produce calibration factors for the six narrowband
channels. A secondary method, often used as a check of the lamp
calibrations, is a set of Langley plots. Langley plots are used to
extrapolate the values that would be read if the instrument was at the
TOA. The TOA value, or I~0~, is divided by the extraterrestrial spectrum
to give a calibration factor for each channel. A lamp calibration of the
MFR is straightforward. To perform a Langley calibration it would need
to be configured with a rotating shadowband. Typically only lamp
calibrations are performed on the MFR.

### Procedures

To perform a standard lamp calibration, a MFRSR is placed in a
calibration chamber and a lamp with a known spectral output is used. The
known spectral distribution in (W m^-2^ nm^-1^) is convolved with the
output of each channel to produce calibration factors in (V W^-1^
m^-2^). Langley plots can also be done for channels 415, 500, 615, 673
and 870 nm (channel 940 nm is a special case). On a clear day a Langley
plot will give a stable I~0~ for each channel when the data are
extrapolated to the TOA. With several I~0~s from clear days, an average
I~0~ for each channel is obtained. The average I~0~ for each channel is
divided by the extraterrestrial spectrum to give a calibration factor.
Because water vapor is highly variable, the Langley method of
calibrating is impractical for the 940-nm channel so only lamp
calibrations are performed.

### History

A detailed calibration history of all the ARM MFRs is too lengthy to be
given here. To date, the instrument's calibration has been driven by
instrument failure; that is, when either an instrument head or board
fails, the offending component is replaced with a new one that has been
freshly calibrated. This constitutes a "calibration" of the instrument.
(This "calibration" procedure may change in the future.)

## Operation and Maintenance

### User Manual

Not available in electronic format at this time.

### Routine and Corrective Maintenance Documentation

Time series plots are monitored to ensure the instrument is operating
properly. Careful monitoring of the data can also interfere with filters
that are failing.

### Software Documentation

ARM netCDF file header descriptions may be found at
[MFRSR](http://science.arm.gov/tool/dod/showdod.php?Inst=mfrsr),
[MFR10M](http://science.arm.gov/tool/dod/showdod.php?Inst=mfr10m), and
[MFR25M](../%20http://science.arm.gov/tool/dod/showdod.php%3FInst=mfr25m)
Data Object Design Changes.

### Additional Documentation

**March 1998**: The laboratory calibration of the instruments is
problematic. By comparing the laboratory calibrations to an estimate of
the calibrations obtained by a Langley analysis, it appears that some
calibration factors can be in error by as much as 50%. The user of the
MFRSR flux data should be aware that some of these data might not be
very accurate.

**November 1999**: The laboratory calibrations of the MFRSR heads have
significantly improved and are now being checked before field deployment
by calibrations performed using the Langley method. This
"pre-deployment" checking has resulted in a significant improvement in
initial calibration accuracy; an estimate of this accuracy is plus or
minus 4% (or maybe even a little better).

The maintenance procedures seem adequate, although some of the
instruments are "out of alignment"; this lack of alignment can corrupt
data taken during certain times of day.

## Glossary

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

## Acronyms

ARM Atmospheric Radiation Measurement (Program)

ASRC Atmospheric Sciences Research Center

DQ data quality

FWHM full width at half maximum

MFR multi-filter radiometer

MFRSR multi-filter rotating shadowband radiometer

PNNL Pacific Northwest National Laboratory\
SGP Southern Great Plains

TOA top-of-atmosphere\
TWP Tropical Western Pacific

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

## Citable References

Goody, RM and YL Yung. 1989. *Atmospheric Radiation Theoretical Basis*.
Oxford University Press, New York.

Harrison, L and J Michalsky. 1994. "Automated multifilter rotating
shadow-band radiometer: An instrument for optical depth and radiation
measurements." *Applied Optics* 33(22):5118-5125.

Harrison, L, and J Michalsky. 1994. "Objective algorithms for the
retrieval of optical depths from ground-based measurements." *Applied
Optics* 33(22):5126-5132.

Michalsky, J, J Schlemmer, N Larson, L Harrison, W Berkheiser III, and N
Laulainen. 1994. "Measurement of the seasonal and annual variability of
total column aerosol in the northeastern U. S. network." In *Proceedings
of Aerosols and Atmospheric Optics: Radiative Balance and Visual Air
Quality, Air and Water Management Association*, Pittsburgh,
Pennsylvania, 247-258.

Michalsky, J, J Liljegren, and L Harrison. 1995. "A comparison of sun
photometer derivations of total column water vapor and ozone to standard
measures of same at the Southern Great Plains Atmospheric Radiation
Measurement site." *Journal of Geophysical Res*earch
100(D12):25995-26003.

Zhou, C, J Michalsky, and L Harrison. 1995. "Comparison of irradiance
measurements made with the multi-filter rotating shadowband radiometer
and first-class thermopile radiometers." *Solar Energy* 55:487-491.