Comparison of atmospheric refractivity estimation methods and their influence on radar wave propagation predictions

Environmental predictions in the marine atmospheric surface layer (MASL)
are imperative to optimize X-band radar system performance in marine
environments.  Evaporation ducts (ED) lead to anomalous
propagation where characterization of EDs in the MASL occurs primarily
through two methods: in-situ measurements and numerical modeling. This
study investigates differences in co-located and synchronous refractivity
estimations from the CASPER-East campaign. Propagation predictions are
generated for refractive profiles from in-situ measurements, Monin-Obukov
boundary layer similarity theory, and numerical weather prediction
forecasts. Variations in evaporation duct height (EDH) are found to be a
primary driver of differences in propagation between the estimated
refractivity profiles, where location of the EDH relative to the
transmitter changes the sensitivity of propagation predictions to EDH
estimates. Differences in propagation are large when EDH estimates span
the transmitter height and the lowest EDH across the methods is small,
regardless of how much variation there is in EDH estimates. When the
lowest EDH is small and EDH estimates span the transmitter height there
are differences in physical regimes causing large propagation
discrepancies – e.g., leakage into versus trapping within the duct.
Variation in EDH between the methods is greatest in stable environments.
M-deficit and curvature of the refractive profiles also influence
propagation specifically in scenarios when EDH spans the transmitter. When
all EDHs are below the transmitter, EDH variance is the primary
contributor to propagation variance, but M-deficit and profile curvature
variance play a secondary role. M-deficits and curvature between the
methods agree most often during periods of atmospheric stability.