Melanie Engram will share findings from her study using SAR to quantify lake ebullition at the March 30 WERC Friday Seminar.
Detecting methane ebullition in winter from Alaska lakes using synthetic aperture radar (SAR) remote sensing
Methane (CH4) is a greenhouse gas with a high radiative forcing attribute, yet large uncertainties remain in constraining atmospheric CH4 sources and sinks. While freshwater lakes are known atmospheric CH4 sources, flux through ebullition (bubbling) is difficult to quantify in situ due to uneven spatial distribution and temporally irregular gas eruptions. This heterogeneous distribution of CH4 ebullition also creates error when scaling up field measurements for flux estimations.
My research investigates various imaging parameters of space-borne synthetic aperture radar (SAR) to constrain current CH4 emissions from northern lakes. In a GIS spatial analysis of lakes on the northern Seward Peninsula, Alaska, comparing field data of ebullition to SAR, I found that SAR L-band backscatter from lake ice was high from lakes with CH4 bubbles trapped by lake ice and low from lakes with low ebullition activity. The ‘roughness’ component of a Pauli polarimetric decomposition of quad-pol SAR showed a significant correlation with the percentage of lake ice area containing CH4 bubbles and with CH4 ebullition flux. This indicates that the mechanism of SAR scattering from ebullition bubbles trapped by lake ice is single bounce. I conclude that SAR remote sensing could improve our ability to quantify lake ebullition at larger spatial scales than field measurements alone, could offer between-lake comparison of CH4 ebullition activity, and is a potential tool for developing regional estimations of lake-source CH4.
Melanie Engram
Methane ebullition bubbles trapped in ice on a thermokarst lake.
Friday Seminar Series
- What:Detecting methane ebullition in winter from Alaska lakes using synthetic aperture radar (SAR) remote sensing
- Who: Presenter Melanie Engram
- When: 3:30-4:30 p.m. Friday, March 30
- Where: 531 Duckering
Seminar schedule in PDF
