ARM TR-039

> Absolute Solar Transmittance Interferometer (ASTI) Handbook
>
> January 2005
>
> C. Flynn
>
> 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 3](#data-quality)

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

# General Overview

The absolute solar transmittance interferometer (ASTI) provides
calibrated spectra of the solar irradiance at the surface of the earth
over a wavelength region from 1 to 5 microns at a resolution of 2
wavenumbers. The system consists of a BOMEM MB-120 interferometer
equipped with a CaF2 beamsplitter and an InSb detector. The
interferometer is coupled with a scanning mirror and automated
solar-tracking system permitting collection of relative solar irradiance
spectra throughout the day. Periodic calibration against a National
Institute of Standards and Technology (NIST) standard lamp source yields
absolute solar irradiance at the surface of the earth.

# Contacts

## Mentor

Connor Flynn\
Pacific Northwest National Laboratory\
P.O. Box 999\
Richland, WA 99352\
Phone: 509-375-2041\
Fax: 509-375-4545\
<connor.flynn@pnl.gov>

## Instrument Developer

University of Denver\
Department of Physics and Astronomy\
Dr. Frank Murcray, Chairman\
2112 Wesley Avenue\
Denver, CO 80208\
Phone: 303-871-2238\
<murcray@ram.phys.du.edu>

**Primary Contacts**:\
Art Dybdahl\
Phone: 303-871-3389\
<adybdahl@du.edu>

Joe Landry\
Phone: 303-871-4351\
<jland@fox.phys.du.edu>

# Deployment Locations and History 

Updated 5/15/00:

The ASTI is used during intensive operational periods (IOPs) and is not
run routinely. However, there is a permanent location at the Southern
Great Plains (SGP) to host this instrument while it is on location. This
is a concrete pad with power and network connections located within 50
yards of the central cluster, permitting an unobstructed view within 10
degrees of both east and west horizons.

Data available from the [Archive](http://www.archive.arm.gov/):

1997 - June 24, 25, 27\
1998 - August 6, 7, 9, 15-24, 27, September 15, 17, 30\
1999 - March 3, 20, 21

# Near-Real-Time Data Plots

This section is not applicable to this instrument.

# Data Description and Examples

Data available from the [ARM Archive](http://www.archive.arm.gov/):

1997 - June 24, 25, 27\
1998 - August 6, 7, 9, 15-24, 27, September 15, 17, 30\
1999 - March 3, 20, 21

## Data File Contents

### Primary Variables and Expected Uncertainty

Solar irradiance spectra are measured in milliwatts/square
meter\*wavenumber\*steradian (mW/m^2^\*n\*sr) from wavelengths of 1 to 5
microns.

Integrated column amounts of O~3~, N~2~O, and other trace molecules are
derived from data streams.

#### Definition of Uncertainty

Determination of wavenumbers: What uncertainty inherent?

Absolute calibration of irradiance: Uncertainty from NIST lamps of 3-4
percent over range.\
Detector non-linearity?\
Uncertainty in column retrievals?

### Secondary/Underlying Variables

This section is not applicable to this instrument.

### Diagnostic Variables

This section is not applicable to this instrument.

### Data Quality Flags

This section is not applicable to this instrument.

### 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 the
Atmospheric Radiation Measurement (ARM) Program's data quality analysts,
instrument mentors, and site scientists to monitor and diagnose data
quality.

## Data Reviews by Instrument Mentor

-   **QC frequency**: Not specified; automatic after each data
    integration interval is planned

-   **QC delay**: Not specified

-   **QC type**: Comparison to similar measurements

-   **Inputs**: Raw data files, and SORTI data

-   **Outputs**: Not specified

-   **Reference**: N/A

Automated data quality products have not yet been implemented for the
ASTI and the solar radiance transmission interferometer (SORTI). Initial
work has been carried out that is similar to that done for the SORTI;
see the entry for the SORTI. The ASTI is used primarily during IOPs and
is not run routinely. Instrument mentor Connor Flynn is working with Tim
Shippert to ensure that the ingested files be configured for efficient
use in a shortwave line-by-line Quality Measurement Experiment (LBL
QME). A case study with the ingested data should be carried out to test
procedures and further evaluate ASTI performance.

## Data Assessments by Site Scientist/Data Quality Office

All Data Quality 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
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 to fill unmet measurement needs,
but 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 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 web
page](http://www.arm.gov/data/vaps.stm).

# Instrument Details

## Detailed Description

### List of Components

BOMEM Model MB 120 interferometer NIST calibration lamp(s):

Optical Interference Filters:

Computer type:

Operating system:

Quadrant Sensor:

Solar Tracker:

Overall dimensions:

### System Configuration and Measurement Methods

This section is not applicable to this instrument.

### Specifications

Wavelength range: 1 to 5 microns (10000 to 2000 wavenumber).

Resolution:

Accuracy:

Precision:

Decimal resolution:

Height: Views from bottom to top of atmosphere on clear-sky days.

## Theory of Operation

Theory of operation of interferometer, introduction to Fourier
Transform, and discrete Fourier Transform.

## Calibration

### Theory

Direct calibration against standard lamps.

Caveats:

1.  Lamps have a finite lifetime, and must be used carefully and
    precisely to get stated performance.

2.  Both lamps and solar spectra have fine structure at this resolution.

### Procedures

This section is not applicable to this instrument.

### History

Repeated on a daily basis during use. Calibration files are found with
relative spectra from the same day.

## 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

This section is not applicable to this instrument.

### Additional Documentation

This section is not applicable to this instrument.

## Glossary

Irradiance - Radiative flux per square meter (W/m^2^)

Radiance - Radiative flux per steradian (W/sr)

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

## Acronyms

ASTI: Absolute Solar Transmittance Interferometer

IOP intensive operational period

LBL line-by-line

NIST National Institute of Standards and Technology

QC quality control

QME Quality Measurement Experiment

SGP Southern Great Plains

SORTI solar radiance transmission interferometer

VAP value-added product

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

## Citable References

This section is not applicable to this instrument.