Characterizing Boundary Layer Properties for Estimating Urban Greenhouse Gas Emissions

The Indianapolis Flux Experiment (INFLUX) aims to develop, evaluate and improve methodologies for quantification of greenhouse gas fluxes from urban areas through a multi-year modeling and observational study. The study incorporates measurements of greenhouse gases from periodic aircraft observations as well as from a surface-based network of towers in the area. Recently, we installed a scanning Doppler lidar east of downtown Indianapolis to characterize boundary layer properties important for the aircraft and modeling studies. A scan sequence, including conical scans, vertical scans along two orthogonal directions, and zenith staring is repeated every 20 minutes. The lidar measurements of the radial velocity and backscatter intensity are processed to estimate boundary layer depth, turbulent mixing, aerosol distribution, and wind speed and direction. These lidar-derived boundary layer parameters are used in conjunction with the aircraft greenhouse gas concentration measurements in mass-balance studies and for investigating model performance. The lidar wind profile measurements can also be ingested into models to improve inverse flux estimates. We present here an overview of the first several months of lidar observations from Indianapolis, including performance evaluation, comparison with model estimates, diurnal and seasonal variability of the measurements, and use of the data for model ingest. We also discuss different techniques for estimating boundary layer depth from the observations and the application for mass-balance studies, and introduce plans for deploying a second instrument to study horizontal variability of the measured boundary layer properties.