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 on a roof.

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.