Radar Propagation in the Atmospheric Boundary Layer

I spent about 18 months at the Geography Department of Queen Mary, University of London.  Initially I worked on Phase 2 of the project on "Numerical Modelling of the Propagation Environment in the Atmospheric Boundary Layer over Coastal Areas" funded by the Meteorological Support Group of the MoD.

The refractive index of the atmosphere for radar frequencies can be determined to good accuracy using the semi-empirical relation

 

where a and b are empirical constants and N is the refractivity, a scaled refractive index. Thus, the refractive index can be obtained as a diagnostic from a numerical weather prediction model. Refractivity data derived from a mesoscale model can then be incorporated into radar propagation models. The project investigated the extent to which a mesoscale meteorological model can assist in obtaining genuinely useful predictions of the radar propagation environment in coastal areas. Coastal regions present a particularly difficult problem for radar applications since the meteorological conditions can vary quite significantly over both space and time. This is particularly true for the moisture variable e, the variations of which very often dominates the variations of refravtivity. It is not uncommon at present for predictions to be based on soundings taken at 12 hourly intervals, assuming horizontal homogeneity across distances of  around 100 km. These are not good approximations in coastal areas.

Simulations were performed for the Persian Gulf and compared reasonably well with aircraft observations of radar ducting in the area. Ducting refers to trapping of signals and can occur if the vertical refractivity gradient is strong, for example across the inversion that caps the marine boundary layer. Attempts to understand such inversions naturally led to work on the growth and temporal evolution of the marine boundary layer under conditions of offshore flow. The structure of the marine internal boundary layer is significantly affected by another coastal phenomenon, the sea breeze, and these interactions were also studied.

Some links for this work:

Papers:

1. A paper on the growth of the marine boundary layer, and its interaction with the sea breeze
2. A paper on simulations for the Persian Gulf

Posters:

1. A poster on radar propagation in coastal regions (html version), presented at the Royal Meteorological Society 2nd National Conference

Reports:

1. Project Report 1: Resolution Effects
2. Project Report 2: Horizontal Variations in the Marine Boundary Layer
3. Project Report 3: Application of the TERPEM Propagation Model
4. Project Report 4: Initial Conditions in the Mesoscale Model
5. Project Report 5: Summary of Findings from Phase 2