Miniaturized Laser Heterodyne Radiometer
Laser heterodyne radiometry is a technique based on the radio receiver (still used in modern radios) that amplifies weak signals from a radio antenna by mixing them with a strong local oscillator. We use a variation of this technique to measure the concentration of trace gases in the atmosphere by measuring their absorption of sunlight in the infrared. Each absorption signal is mixed with laser light (the local oscillator) at a near-by frequency in a fast photoreceiver. The resulting beat signal is sensitive to changes in absorption, and located at an easier-to-process RF frequency. Scanning the laser through an absorption feature in the infrared, results in a scanned beat signal in the RF. Deconvolution of this signal through the retrieval algorithm allows for the extraction of altitude contributions to the column signal.
The mini-LHR instrument (in yellow case) has been developed as an add-on to an AERONET sun photometer so that both aerosols and carbon cycle gases can be monitored simultaneously.
Vision for a Global Network
Our ultimate goal is to develop a low-cost global surface instrument network for monitoring key greenhouse gases in the atmospheric column including carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO), as well as oxygen (O2) for atmospheric pressure. The emerging network will produce a carefully characterized data product appropriate for calibration and validation of Earth observing missions such as ASCENDS, OCO-2, and OCO-3.
The passive instrument that measures CO2, CH4, and CO in the atmospheric column is a miniaturized laser heterodyne radiometer (mini-LHR) that has been developed at NASA/GSFC and has been designed to operate in tandem with an AERONET sun photometer. This partnership offers an established ground network for expansion (AERONET has >450 sites worldwide) as well as a simultaneous measure of aerosols . known to be important modulators in regional carbon cycles.
Benefits of this emerging network will include:
- Coverage in key regions missed by satellite passes: This network will include arctic regions (not covered by OCO-2) where accelerated warming due to the release of CO2 and CH4 from thawing tundra and permafrost is a concern.
- Improved attribution of carbon sources and sinks: The suite of proposed measurements in conjunction with existing aerosol measurements will provide needed insight into the processes governing atmospheric composition and climate change.
- Continuous record of greenhouse gases: The continuous record from a ground network adds continuity to limited time-line data sets from flight missions.