Characterizing thawing permafrost with the Miniaturized Laser Heterodyne Radiometer (mini-LHR) through column measurements of methane

Abstract:

We present mini-LHR measurements of column CH₄ from our preliminary field campaign outside of Fairbanks, AK in June 2015. The mini-LHR is fully automated and works in tandem with the AERONET sun photometer for collection of column CH₄ every 15 minutes. As part of a comprehensive array of ground based instruments, measurements made by the mini-LHR will aid in monitoring of changes in atmospheric greenhouse gas emissions and help interpret data collected by space-born instruments.

The mini-LHR is a passive variation of typical heterodyne radiometry instruments, using sunlight as the light source for measuring CH₄ in the infrared. Collecting through collimation optics mounted on the AERONET tracker, the sunlight is chopped in an optical chopper and mixed with a local oscillator in a fast photoreciever (InGaAs detector). The amplitude of the resultant RF (radio frequency) beat signal directly correlates with the concentration of the column gas being measured.

Working in conjunction with ground penetrating radar, covariance flux tower, and high-resolution surface CO₂ and CH₄ measurements, our column CH₄ measurements contribute to a holistic view of the atmospheric evolution and response to permafrost thaw. With the intent to expand our observational network to other North American sites, our column CH₄ measurements will be instrumental in showing the effects of permafrost thaw on global CH₄ levels, as well as benefiting ongoing efforts in retrospective and predictive simulations of greenhouse gasses.