Influence of Horizontal Inhomogeneity of Refractivity Vertical Profiles on Electromagnetic Measurements in Application to Refractivity Inversions
Abstract
The environment impacts system performance prediction and evaluation of shipcommunication and sensing technologies that involve transmission and receipt of electromagnetic (EM) waves. The complex fluid dynamics of the marine atmospheric boundary layer (MABL) and its interaction with the ocean surface layer cause changes in temperature and humidity over a wide range of scales. These changes result in variability of radio refractivity that in extreme cases causes ducting layers to form. Evaporation ducts are prevalent over marine surfaces and can cause significant changes to performance of ship communication and sensing systems, such as extended ranges. Direct measurement of humidity and temperature at all the relevant scales in the MABLis difficult and costly; thus, inversion methods that infer the refractive environment based on EM measurements have gained favor as a means to retrieve environmental information in-situ. There are numerous considerations for optimizing an inversion approach beyond the inversion methodology itself, including, treatment of the sea surface (or other non-refractive environmental effects), amount and location of data, data quality, sufficiency of the refractivity model, and inclusion of horizontal inhomogeneity effects. The influence of horizontal inhomogeneity has been relatively sparsely examined over the last few decades and few inversion approaches have attempted to account for it. The proposed work will examine radio refractivity horizontal inhomogeneity using both numerical and experimental datasets with the goal of determining typical scopes for magnitudes and spatial scales of variation in range. Refractivity and its typical variations will then be used to compute propagation path loss estimates using a parabolic equation propagation simulation. The resulting variations in path loss will be compared to othertypical sources of variation in EM data, such as variations due to multipath over rough surfaces and turbulence scintillation effects, which provide insight into what scales of variation of horizontal inhomogeneity are significant sources of propagation variability.Finally, these studies will be utilized to develop a range-dependent refractivity vertical profile parameterization for incorporation into refractivity inversions for evaporative ducting scenarios. The parameterizations will include scales of variation that were found to be influential on propagation while neglecting scales that were found to be insignificant; thereby minimizing the complexity of the model as much as possible. Inversions using both range-independent and range-dependent refractivity models will be performed and compared to each other as well as to measured propagation and refractivity data. Collectively, the proposed research extends our understanding of the relative importance of refractivity horizontal variations on EM propagation in application to refractivity inversions. This knowledge can improve assessments of systemperformance and susceptibility.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 23, 2019
- Source ID
- N000141912350
Entities
People
- Erin E Hackett
Organizations
- Coastal Carolina University
- Office of Naval Research
- United States Navy