A NASA scientist, who has played a key role in developing and demonstrating a new technique for gathering carbon-dioxide (CO2) measurements, is applying the same general principles to develop a new laser instrument sensitive to another greenhouse gas, methane.
A team, led by the NASA researcher Haris Riris, demonstrated a prototype Methane Sounder. The next-generation instrument will be able to provide remotely collected, high-resolution, highly accurate, around-the-clock global methane measurements should it ultimately fly as a spaceborne instrument.
Although carbon dioxide, another greenhouse gas, lingers in the atmosphere longer, methane is in some respects more worrisome. It is more potent and effective at absorbing heat. Exacerbating concerns is the fact that large quantities of the gas reside beneath permanently frozen ground in the Arctic. As the permafrost melts, which scientists say currently is occurring, more of this gas is released into the atmosphere, creating a feedback mechanism, where emissions lead to more warming, which in turn accelerates the melting.
Although some satellite instruments can detect and map Earth’s methane, Riris’ concept gives scientists something they don’t currently have — 24-hour coverage at all latitudes.
In sharp contrast to many methane instruments, the Methane Sounder also employs its own light source — tunable laser transmitters. Although laser light cannot penetrate thick clouds, it can measure through thin clouds and particles and at night, which is impossible for passive systems that rely on reflected sunlight for their source of illumination.
To gather methane data, the team’s instrument works much like the CO2 Sounder. The system bounces a laser light tuned to a specific wavelength band — in this case, 1.65 microns — off Earth’s surface. Like all atmospheric gases, methane will absorb the light as it travels back to the orbiting instrument. The more methane molecules along the path, the deeper the absorption lines as measured by the instrument’s detectors.
Also: Learn about an Oxygen-Methane Thruster.