Using P-band signals of opportunity for biomass remote sensing

Wednesday, May 22nd, 2019

Forests serve as important ‘“sponges” of atmospheric carbon dioxide, absorbing CO2 from the atmosphere and storing it in forest biomass. This stored carbon is released during wildfires, controlled burning, and deforestation; however, it is still difficult to assess how much these events are affecting the carbon cycle. This knowledge of carbon flows between forests and the atmosphere is critical to our understanding of future climate change. It is also essential for the development and implementation of mitigation programs, such as the United Nation’s Reducing Emissions from Deforestation and forest Degradation (REDD+) program. Despite the importance, monitoring of biomass globally, and especially in underdeveloped areas, is quite inaccurate.

Satellite remote sensing would be the most efficient approach for estimating biomass globally and in difficult to access areas (which includes many regions with the highest biomass density). Although biomass can be estimated through measurements of canopy height or forest extent using lidar or multispectral methods, only microwave observations in P-band or lower frequencies (< 500 MHz) are able to penetrate through dense biomass and provide observations directly related to the forest structure. Satellite measurements of P-bands have several limitations including radio frequency interference, high power requirements, and the need for large antennas. Despite these limitations, several airborne systems (AirMOSS, EcoSAR) are now operational, and investment in global biomass mapping using satellite remote sensing continues including from the European Space Agency for the BIOMASS satellite (scheduled for deployment in 2021).

An alternative method for microwave remote sensing was first proposed by Prof. James Garrison (Aeronautics and Astronautics) in the late 1990’s using Global Navigation Satellite Systems (GNSS) signals. This technique, now known as “signals of opportunity” (SoOp), re-utilizes existing transmissions (usually deployed for communications or navigation purposes) as illumination sources. In addition to overcoming issues with signal interference, this method allows for measurements to be made with small, omni directional antennas and lower power.

With a PCCRC seed grant, professors Janes Garrison, Brady Hardiman (Forestry and Natural Resources), John Couture (Entomology and Forestry and Natural Resources), and Dr. Lola Agues (NASA Goddard Space Flight Center), are conducting the first experimental demonstration of the sensitivity of P-band SoOp reflectivity to observe changes in forest biomass. The team is outfitting drones for observations over Martell Forest in West Lafayette, Indiana.

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