The Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD19) is an ongoing National Science Foundation project based on an intensive field campaign that occurred from June-October 2019. The purpose of the study is to examine how the atmospheric boundary layer responds to spatial heterogeneity in surface energy fluxes. One of the main objectives is to test whether lack of energy balance closure measured by eddy covariance (EC) towers is related to mesoscale atmospheric processes. Finally, the project evaluates data-driven methods for scaling surface energy fluxes, with the aim to improve model-data comparison and integration. To address these questions, an extensive suite of ground, tower, profiling, and airborne instrumentation was deployed over a 10×10 km domain of a heterogeneous forest ecosystem in the Chequamegon-Nicolet National Forest in northern Wisconsin USA, centered on the existing Park Falls 447-m tower that anchors an Ameriflux/NOAA supersite (US-PFa / WLEF). The project deployed one of the world’s highest-density networks of above-canopy EC measurements of surface energy fluxes. This tower EC network was coupled with spatial measurements of EC fluxes from aircraft, maps of leaf and canopy properties derived from airborne spectroscopy, ground-based measurements of plant productivity, phenology, and physiology, and atmospheric profiles of wind, water vapor, and temperature using radar, sodar, lidar, microwave radiometers, infrared interferometers, and radiosondes. These observations are being used with large eddy simulation and scaling experiments to better understand sub-mesoscale processes and improve formulations of sub-grid scale processes in numerical weather and climate models.

We present an intercomparison and consistency study of aerosol optical depth (AOD) retrievals from the 1625 nm channel that has recently been added to the SURFRAD’s Multi-Filter Rotating Shadowband Radiometer (MFRSR) instruments. In addition, a Multi-Filter Radiometer (MFR) has been installed at the SURFRAD sites to measure upwelling radiation in the same wavelength bands. SURFRAD (Surface Radiation Budget Monitoring) is a NOAA measurement network with the prime directive to determine the surface radiative budget. It is composed of seven sites across the United States and two mobile facilities. Each site is equipped with an MFRSR which measures global and diffuse solar radiation in one broadband and six narrow band spectral channels. MFRSR retrivals include several aerosol optical properties including the spectrally resolved AOD at 415, 500, 673, 870, 940, and 1625 nm. With particular focus on the AOD from the 1625 nm channel we discuss measurement uncertainties based on instrument limitations, uncertainties from the retrieval algorithm, and statistical considerations. Some of the SURFRAD sites have a colocated CIMEL sunphotometer that in some instances is equipped with a 1625 nm channel. While the two datasets are highly correlated we observe various deviations. We furthermore present an aerosol particle size distribution retrieval based on the AOD from 5 narrow band MFRSR channels. Here we put particular emphasis on the 1625 nm channel and its potential to improve the retrieval of the coarse mode fraction of the size distribution.