CASPER (Years 6-7)

Coupled Air-Sea Processes and EM Ducting Research (CASPER): Effects of Atmospheric Boundary Layer Dynamics on Propagation (Years 6-7)

Sponsor: Office of Naval Research (Grant #N00014-21-1-2126)

PI: Harindra Joseph Fernando (Civil and Environmental Engineering and Earth Sciences and Aerospace and Mechanical Engineering, University of Notre Dame)



Qing Wang, Naval Postgraduate School  (PI: CASPER MURI)

Caglar Yardim, Ohio State University

Kipp Shearman, Oregon State University

Lian Shen, University of Minnesota


Under an ONR 2014 MURI, the PIs of this project were funded to conduct collaborative research on electromagnetic (EM) wave propagation in coastal Marine Atmospheric Boundary Layers (MABL). Dubbed Coupled Air-Sea Processes and EM ducting Research (CASPER), the aim of this MURI was to fully characterize MABL as an EM propagation environment. CASPER involved extensive field observations and analyses as well as Numerical Weather Prediction (NWP) and Large Eddy Simulation (LES) modeling. The field campaigns included CASPER-Pilot (Monterey, CA, Spring of 2015), CASPER-East (Duck, NC, October 2015) and CASPER-West (Point Mugu, CA, October 2017). The measurements were comprehensive, and probed simultaneously a full volume of the environment encompassing upper ocean, surface waves, atmospheric boundary layer (ABL), upper air conditions and EM propagation, with well-designed sampling strategies and by deploying multiple measurement platforms. The CASPER group investigated surface-layer physics, modeling concepts (e.g., Monin-Obukhov similarity theory MOST), evaporation-duct refractive profiles and their variability, and internal boundary layer development. As well, CASPER developed new sampling and measurement techniques, for example, for EM propagation over a broad range of frequencies using vertical arrays of transmitters and modeling approaches based on LES and single column models.

The voluminous and multifaceted dataset of CASPER is unique, and invites further explorations on EM propagation in a dynamic ABL. This proposal seeks an additional year of funding to undertake such research of consequence. The work of this project consists of collaborative in-depth analyses and modeling studies to tackle unresolved scientific issues previously pursued or newly identified. The goals are to: (i) Further explore factors governing evaporation duct evolution, beyond simple descriptions of duct height and strength and their relation to signal quality in and outside the duct; (ii) Educe new physical and dynamical processes impacting EM propagation in MABL over coastal regions and across the Gulf Stream; (iii) Quantify internal boundary layer development in the presence of background stratification and thermal wind effects; (iv) Develop new approaches for modeling ducting characteristics through variable atmosphere; and (v) Further testing and development of evaporation-duct parametrizations in mesoscale models. Analysis of the CASPER database, theoretical analyses as well LES and mesoscale NWP modeling are the main tools to be employed.

The research will be conducted by the CASPER PIs from University of Notre Dame (UND), Naval Postgraduate School (NPS), The Ohio State University (OhSU), Oregon State University (OrSU) and University of Minnesota (UMN). Their collaborative work will integrate information on EM propagating in a volume of coastal environment: across upper ocean and lower atmosphere. The research will broadly cover (i) Variability of turbulent kinetic energy dissipation and strain rates in the upper ocean mixed layer influenced by internal tides/waves, (ii) Effect of such mixed-layer signatures on surface waves and swell in determining the atmospheric surface layer vertical profiles and fluxes and hence the evaporation ducts, (iii) Implications of horizontal variability of meteorological parameters due to internal boundary layers, (iv) The slow fading due to turbulence and fast fading due to sea surface clutter of EM signals that help retrieve information on atmospheric reflectivity from measured fluctuations.

Research dissemination plans via scientific meetings and publications are in place. Special emphasis is placed on collaborating with Navy laboratories and the transition of our results to improve Navy's operational environmental forecasting and EM propagation models for tactical applications.