Geographical Model of Radio-Frequency Power Density

The text on this page is taken from an equivalent page of the IEHIAS-project.

GEOMORF is a GIS-based model, designed to simulate power density around EMF transmitters such as mobile phone masts.

Model description

Purpose

The Geographical Model of Radio-Frequency Power Density (Goemorf) is a GIS–based exposure model designed to estimate power densities at receptor locations around mobile phone base stations. The model uses a semi-Gaussian formulation to represent spatial variations in power densities around mobile phone masts, on the basis of power output, antenna height, tilt and the surrounding propagation environment.

Boundaries

Outdoor exposure

Spatial resolution: address or postcode

Input

Mx,My	Mast location	metres	x and y co-ordinates of the source mast
Rx,Ry	Receptor location	metres	x and y co-ordinates of the receptor
Em	Elevation of mast	metres	Height of the ground surface above ordnance datum, at the mast location
Er	Elevation of receptor	metres	Height of the ground surface above ordnance datum at the receptor location
Ha	Antenna height	metres	Height of the centre point of the antenna, above the ground surface. Default = surface height + 20 metres.
Hr	Receptor height	Metres	Height of the midpoint of the receptor, above the ground surface.
Tt	Net tilt	degrees	Total tilt due to electrical and mechanical tilt. Default = 6.5o
P	Power output	W	Maximum operational effective isotropic radiated power output of the source antenna
Zb	Azimuth	degrees	Direction (degrees from true north) of the centreline of the mainbeam of the antenna
BWd	Vertical beam width	degrees	Specified vertical beam width of the source antenna Default = 6o.
BWl	Horizontal beam width	degrees	Specified horizontal beam width of the source antenna. Default = 67o.
Tlos	Topographic line of site		Topographic line of site from antenna to receptor (0,1); modelled using visibility function in GIS.
C	Land cover type		Categorisation of land cover in area surrounding the receptor (urban, forested, open); determined by intersecting land cover data with receptor locations in GIS.

Output

Output: Power density (mW/m²)

Data type: point estimate(s)

Data sources: mobile phone operators

Data format: ESRI ArcGIS shape files

Description of processes modelled and of technical details

Operating System: WINDOWS
Software requirements: ArcGIS9.3 + Spatial Analyst extension
Programming language: VBA
Developed by Imperial College London
Model is free to use
Intellectual property rights Imperial College London
Canned model - cannot be modified

Rationale

THe GEOMORF model is based on the free-space equation for electromagnetic radiation, adapted to take account of the reduction in power density both along the beam and transverse to the beam. The model has been developed and validated on the basis of field measurements made around a series of mobile phone transmission masts (macrocells) in Great Britain, where it was shown to give good approximation of measured power densities (r² ~0.6) across a wide range of conditions. In densely built-up urban areas, performance is poorer, due to local variations caused by buildings.