Direct Measurement of Plume Velocity to Characterize Point Source Emissions

An explosion of recent research uses remote imaging spectroscopy from aircraft and spacecraft to detect greenhouse gas point sources. These instruments first map the concentration field below the sensor, and then combine this information with the effective wind speed to estimate the source emission rate. The wind speed at the surface is the largest uncertainty in this process, since it is estimated from coarse-resolution meteorological databases and may not match the actual currents experienced by the gas plume. Here we measure plume velocity remotely using the same spectrometer that performs the detection. Our approach acquires multiple views of the same point source, with visual tracking of plume features to estimate its ground velocity. This resolves the representational mismatch between database records and effective wind speeds. It provides data with exact spatiotemporal coincidence to the plume being measured. The approach points to new instruments and operational methods to dramatically improve the precision of remote greenhouse gas measurements.