Environmental Effects on Radar Performance using COAMPS High

Environmental Effects on Radar Performance using COAMPS High Resolution Modeling
Tracy Haack*,
Naval Research Laboratory-Monterey
Marine Meteorology Division
The environment presents significant challenges on radar and communications performance due
primarily to sensitivity of electromagnetic propagation to vertical variations in water vapor. Weather
across an operating region often contains substantial variation especially in littoral regions where the
land/sea transition, topography and coastline features contribute to abrupt changes in stability.
Horizontal gradients in surface stability drive sea-breezes in benign weather conditions in which the
marine atmospheric boundary layer (MABL) encroaches inland. In strong off-shore flow regimes,
internal boundary layers (IBL) can advect seaward several hundreds of kilometers resulting in shallow,
near surface ducting. These conditions contribute to sharp temperature and moisture inversions that
produce extended signal strength and signal ranges.
In this presentation we describe the influence of spatial and temporal variations in weather on notional
sensors operating in the X and S-frequency band. Using validation data from several field experiments,
we evaluate observed propagation path loss values against modeled propagation path loss using a link
between COAMPS1 numerical weather prediction (NWP) forecasts, the NPS surface layer model, and the
Advanced Propagation Model (APM). Here the surface layer is blended with the COAMPS levels to
provide spatio-temporal changes in the atmosphere to the propagation code. Data from Wallops-2000
MPME field campaigns over the eastern seaboard of the U.S. and the RED experiment on Oahu’s
windward side provide very different operating regimes to evaluate model and radar/communications
Several key NWP modeling criteria have been established for supporting EM propagation predictions
from this study. The first requirement is accuracy in the large-scale forcing from global models that
generate synoptic weather patterns, frontal passage and air-mass transitions at initialization and lateral
boundaries. The second requirement involves accuracy in the mesoscale from 1) high spatial resolution
of the model grid, 2) mesoscale detail allowed to develop on model grid which is necessary for the buildup of moisture content and vertical gradient structures in the MABL, 3) high resolution sea surface
temperature (SST) analysis updated at least 12-hrly or fully coupled air-sea modeling in which the SST
evolves with each ocean model time step. The third requirement is use of advanced observational data
assimilation schemes to permit accuracy in over water moisture analysis, from 3D- or 4D-variational DA.
Examples of these NWP model issues and their impact on radar/communications performance will be
shown at the conference.