Signal Science TERPEM


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TERPEM PACKAGE

The TERPEM propagation package provides a powerful tool for forecasting and analysis of refraction, ducting and terrain effects on radiowave links. It is based on state-of-the-art hybrid models combining parabolic equation and ray-trace techniques. The TERPEM package is the result of on-going algorithm and software development that began in 1989 with the release of PCPEM.

Computer platform:	PC with Windows 95, 98 or NT, 100 MHz or higher Pentium processor and at least 32 Mbytes of RAM.
Frequency range:	30 MHz to 100 GHz.
TERPEM package components:	interface for specification of input parameters
	meteorological module
	propagation engine
	coverage diagrams
	path loss plots

TERPEM interface screen

Input scenarios including system and environmental parameters are specified via a Windows interface. The propagation engine computes path loss arrays on a user-specified range/height grid.

TERPEM GUI

Typical TERPEM computation times on 200 MHz Pentium

The TERPEM propagation engine uses hybrid techniques that combine the accuracy of the full-wave parabolic equation method with the speed of ray-trace methods. This leads to rapid computation times, even for large range-height domains:

Antenna height	Frequency	Range/height domain	Environment	Timings
25 m	3 GHz	250 km by 2500 m	evaporation duct/sea	2 s
25 m	10 GHz	250 km by 2500 m	evaporation duct/sea	5 s
10000 m	3 GHz	500 km by 10000 m	multiple ducts/mountains	2 min
1000 m	10 GHz	250 km by 2500 m	elevated duct/coastal	1 min

TGRAPH: the TERPEM postprocessor

TGRAPH provides postprocessing graphics and facilities for ASCII output. Options include coverage diagrams and path loss graphs along vertical, horizontal or user-defined trajectories. Alternatively users can write their own analysis software accessing TERPEM output files, using the format description given in the TERPEM documentation.

TGRAPH GUI

Capabilities of TERPEM propagation models

oversea and overland propagation. Terrain profiles are specified through an ASCII input file.

range-dependent refractivity environments. Refractivity profiles may be specified at several ranges, with a choice of horizontal interpolation techniques. The meteorological module includes evaporation duct models and a variety of options for upper air data. Evaporation duct and upper air data are merged to obtain a smooth function of height.

flexible specification of antenna. Standard or user-defined patterns can be used. Other parameters include polarization and antenna elevation.

fast field-strength computation for both surface and airborne antennas. Novel hybrid PE techniques are used to minimize the parabolic equation domain. The use of "incoming energy" boundary conditions coupled with ray-tracing provides a very efficient algorithm for high antenna problems. A generalized horizontal PE method is used to extend the coverage upwards, and ray-optics are used for high propagation angles. Integration times essentially depend on frequency, maximum range and terrain/refractivity environment.

modelling of finite impedance and rough surfaces. Mixed Fourier transform techniques propagate the field correctly over a surface with range-dependent impedance. Sea surface roughness is taken into account with a modified impedance using the Miller-Brown model and locally determined incidence angles on the surface, using wind speed as the basic parameter.

modelling of atmospheric absorption. Line-by-line spectral calculations of absorption using the Liebe MPM model are performed if required, based on temperature and humidity.

Additional TERPEM modules

Radar probability of detection analysis: integrates standard radar/target calculations with TERPEM to provide probability of detection contours and one-dimensional plots along target trajectory. Available now.

Refractivity database: includes ducting statistics extracted from a large worldwide database of radiosonde measurements, together with individual ascents from selected stations. Available now. This module is fully integrated with TERPEM, but can also be used as a stand-alone package (TERMET) for analysis of global radiosonde upper-air data.

Clutter analysis: calculates clutter returns based on field values and incidence angle at the surface, together with the Georgia Institute of Technology empirical clutter model. Available March 2001.

Terrain interface: includes terrain profile selection, extraction and plotting tools. Designed for NATO Digital Terrain Elevation Database initially. In preparation.

Customised versions of TERPEM

As well as the "off-the-shelf" TERPEM package described above, TERPEM can also be integrated into larger software suites. For example TERPEM provides the propagation backbone for EEMS (Environmental Electromagnetic Modelling System), the UK Royal Navy operational replacement for IREPS. TERPEM has also been incorporated in Unix-based propagation packages.

The TERPEM propagation engine can be tailored to your particular needs. For example, versions have been developed for customers that include the effects of clutter, and that predict phase effects (for synthetic aperture array applications).

If you have an application that you would like to discuss, please contact us.