ARM TR-061

> Normal Incidence Multi-Filter Radiometer (NIMFR) 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
1](#deployment-locations-and-history)

[4. Near-Real-Time Data Plots 1](#near-real-time-data-plots)

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

[6. Data Quality 3](#data-quality)

[7. Instrument Details 4](#instrument-details)

# General Overview

The Normal Incidence Multi-Filter Radiometer (NIMFR) is a ground-based
instrument that provides a time series of the shortwave spectral direct
normal irradiance. Additionally, there is a broadband silicon detector
that can crudely measure the direct normal broadband irradiance. These
irradiance measurements can be used to infer clear sky aerosol optical
depth and columnar abundances of ozone and water vapor. The NIMFR is one
of a class of instruments known as sun photometers.

# Contacts

## Mentor

Gary Hodges**\
**Phone: 303-497-6460\
E-mail: <Gary.Hodges@noaa.gov>

Donna Flynn (data analysis)\
Pacific Northwest National Laboratory\
K9-24, P.O. Box 999\
Richland, WA 99352\
Phone: 509-375-6978\
E-mail: <Donna.Flynn@pnl.gov>

John Schmelzer\
Pacific Northwest National Laboratory\
K5-08, P.O. Box 999\
Richland, WA 99352\
Phone: 509-375-3729

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

## Instrument Developer

This section is not applicable to this instrument.

# Deployment Locations and History 

The SHEBA NIMFR has been removed from service. There has been and will
be a NIMFR deployed at the Barrow NSA site during the time of the year
that the sun is up.

# Near-Real-Time Data Plots

See [General Quick
Looks](http://education.arm.gov/nsdl/visualization.shtml).

# Data Description and Examples

This section is not applicable to this instrument.

## Data File Contents

### Primary Variables and Expected Uncertainty

The primary quantities measured by the NIMFR are direct normal spectral
irradiances at six discrete wavelengths (with units of W/m\^2/nm) as
well as a broadband measurement from the silicon detector.

#### Definition of Uncertainty

The uncertainties in the measurement depend on the state of calibration
of the instrument. A well-calibrated instrument can measure the spectral
irradiances to within 2% (or maybe even a little better). A calibration
of this accuracy can only be obtained using sun photometry and it
assumes that the extraterrestrial radiation upon which the calibration
depends is known with negligible error. At the present time, sun
photometry is not used to calibrate the NIMFR; instead the instrument is
calibrated using a standard lamp that is uncertain to +/- 5%. With
proper calibration, the broadband measurement is accurate to about 5%.

The calibration stability of the instrument depends on the several
factors, including the stability of the interference filters used to
make the spectral observations and the temperature stability of the
MFRSR head. Although there have been problems in the past with
interference filter stability (the transmission of these devices can
change over time), these problems have been largely solved for the
NIMFRs \... or so we hope. Time will tell if the problem has indeed been
solved, but so far the filters are staying stable.

The head temperature affects the magnitude of the signal coming out of
the MFRSR head, and this sensitivity has been estimated to be a 0% to 2%
change in output per 1^o^ C change in head temperature. It is not
unusual for the head temperature to fluctuate over a range of +/- 1^o^
over the course of a day, and +/- 3^o^ over the course of a year. Such
fluctuations can cause the calibration to change significantly in step
with the temperature variations. To date, this problem has not been
solved. The extent to which this problem affects measurements from any
given NIMFR has not been determined. All we can say is that the error
could be as large as +/- 6% for some wavelengths. Not all instruments
will exhibit errors of this magnitude and for a given instrument the
error may be small for one wavelength channel and large for another. The
6% figure cited above should be considered a worse-case scenario.

### Secondary/Underlying Variables

This section is not applicable to this instrument.

### Diagnostic Variables

This section is not applicable to this instrument.

### Data Quality Flags

See [NIMFR Data Object Design
Changes](../%20http://science.arm.gov/tool/dod/showdod.php%3FInst=nimfr)
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

This section is not applicable to this instrument.

## 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 instrument consists of a "head" from an MFRSR to which a collimating
tube is attached. This assembly is mounted in a solar tracker so that
the instrument points directly at the sun (i.e., the collimating tube
points at the sun). The collimating tube has a narrow field of view
designed to admit only the direct normal irradiance; this radiation hits
the detectors housed in the MFRSR head. A very small amount of diffuse
radiation is also admitted by the tube and sensed by the detectors. The
amount of diffuse radiation that strikes the detector is so small in
relation to the direct beam radiation that it is usually neglected. For
the spectral measurements, the detector for each wavelength channel
consists of a combination interference filter/silicon photodiode. The
instrument's head is kept at a relatively constant temperature of about
35^o^ C.

### System Configuration and Measurement Methods

The NIMFR is mounted on a solar tracker that is usually about 2 or 3
meters above the ground. At a specified time interval (20 sec at the NSA
sites), the instrument takes a reading (six spectral irradiances and one
broadband irradiance). The readings are stored on a nearby data logger.

### Specifications

The spectral measurements are made at nominal wavelengths of 415, 500,
615, 673, 870, and 940 nm. The nominal width of the interference
filters' passband is 10 nm. The broadband silicon detector responds only
to radiation in an interval from about 300 and 1100 nm.

## Theory of Operation

This section is not applicable to this instrument.

## Calibration

### Theory

This section is not applicable to this instrument.

### Procedures

This section is not applicable to this instrument.

### History

The SHEBA NIMFR was calibrated by a standard lamp on March 6, 1998.\
The Barrow NIMFR was calibrated by a standard lamp on March 6, 1998.

## 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 [NIMFR Data Object
Design Changes](http://science.arm.gov/tool/dod/showdod.php?Inst=nimfr).

### Additional Documentation

This section is not applicable to this instrument.

## Glossary

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

## Acronyms

NSA: North Slope of Alaska\
SHEBA: Surface Heat Budget of the Arctic Program

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

## Citable References

This section is not applicable to this instrument.