Detecting and characterizing enhanced methane emissions from coastal wetland vegetation with airborne imaging spectroscopy in Louisiana’s Terrebonne Basin

Abstract:

Methane is naturally emitted in wetland ecosystems as organic matter within the soil’s aerobic zone decays. This represents a feedback process in wetlands threatened by relative sea level rise and anthropogenic degradation, as degrading wetlands may emit increased methane and worsen climate warming and sea level rise. Recent airborne remote sensing campaigns have demonstrated imaging spectroscopy’s utility for detecting both point-source methane plumes and more diffuse emissions in natural environments. The latter represents enhanced methane emissions relative to background levels within each flightline, or “enhancement” features. Here we apply mosaicked flightlines captured by NASA’s Airborne Visible/Infrared Imaging Spectrometer—Next Generation (AVIRIS-NG) to investigate the distribution and spectral characteristics of methane enhancements in coastal wetlands throughout Louisiana’s Terrebonne Basin. Using Multiple Endmember Spectral Mixture Analysis (MESMA), we map vegetation types and the fractional composition of green vegetation, non-photosynthetic vegetation, and soil for each pixel. The methane enhancements observed in the AVIRIS-NG methane products coincide with certain wetland vegetation types and exposed soils. With these observations, we calculated the Poisson rates of methane enhancement occurrence for each vegetation type and soil coverage. A partial least squares regression reveals the vegetation and soil spectral features that are associated with enhanced methane emissions.