Atmospheric Emitted Radiance Interferometer (AERI) Handbook
Reference handbook for the ARM Program's ground-based Fourier transform infrared radiometer
J. Demirgian, R. Dedecker — Argonne National Laboratory & University of Wisconsin-Madison (ARM TR-054, January 2005)
Overview
The Atmospheric Emitted Radiance Interferometer (AERI) is a ground-based instrument that measures the absolute infrared spectral radiance of the sky from 520 to 3300 cm⁻¹ (3–19.2 µm). Developed under the DOE Atmospheric Radiation Measurement (ARM) program, it uses a Fourier transform interferometric design with a scene mirror driven by a flex-pivot-supported mechanism to switch between sky, hot blackbody, and ambient blackbody views for absolute calibration.
Key Highlights
Spectral Range
3300 to 520 cm⁻¹ (3–19.2 µm); extended polar instruments to 400 cm⁻¹ (25 µm)
1.0 cm⁻¹ Resolution
Spectral resolution suitable for line-by-line radiative transport code evaluation
Calibrated Every 8 Min
Absolute sky radiance spectrum produced every 8 minutes in normal mode
Flex Pivot Scene Mirror
Scene mirror mechanism uses flexural pivots for frictionless, repeatable view switching
Triple View Design
Switches between sky, hot blackbody (~60°C), and ambient blackbody (~12°C) for calibration
ARM Deployment
Deployed at SGP, NSA (Barrow), and TWP (Nauru, Darwin) ARM sites
Instrument Principle
The AERI measures absolute infrared spectral radiance of the sky directly above the instrument. A calibrated sky radiance spectrum is produced every 8 minutes in normal mode (or every ~20 seconds in rapid-sampling mode) by alternating between views of the sky and two blackbody calibration sources at known temperatures. The data supports evaluation of radiative transport codes, cloud property retrievals, and retrievals of vertical temperature and water vapor profiles.
Flexural Pivot Scene Mirror
The AERI's interferometer uses a scene mirror that alternates views between the sky and two blackbody calibration references (hot at ~60°C and ambient at ~12°C). This scene mirror is driven by a mechanism that requires highly repeatable, friction-free positioning — a role ideally suited to flexural pivots. The frictionless operation ensures the mirror returns to the same viewing angle each cycle, which is critical for the absolute calibration accuracy of the radiometric measurement.
Data Products
Primary outputs are absolute spectral radiance of the sky (W/m²/sr/cm⁻¹) and sky brightness temperature as a function of wavenumber (K). These feed value-added procedures (VAPs) for retrieving vertical profiles of atmospheric temperature, potential temperature, mixing ratio, and relative humidity. The data supports three primary uses: evaluating line-by-line radiative transport codes, detecting and quantifying cloud effects, and measuring trace gas concentrations.
ARM Network Deployment
AERI instruments are deployed at multiple ARM Climate Research Facility sites: the Southern Great Plains (SGP) Central Facility in Oklahoma, the North Slope of Alaska (NSA) at Barrow, and Tropical Western Pacific (TWP) sites at Nauru and Darwin. Instruments operate in both normal (8-min) and rapid (20-sec) sampling modes, with continuous automated data quality monitoring via diagnostic variables including encoder position confirm, detector temperature, and blackbody NEN (Noise-Equivalent Radiance).
Atmospheric Emitted Radiance Interferometer (AERI) Handbook — PDF
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