TIREM Atmospheric Model 3.31

The Terrain Integrated Rough Earth Model (TIREM) adds fidelity to the calculation and dynamic modeling of point-to-point line-of-sight effects for link performance in STK Communications, by taking into account the effect of irregular terrain, sea water, and non-line-of-sight effects. Among other things, TIREM predicts radio frequency propagation loss over irregular terrain and seawater. The maximum height for these models is 30 km.

This model supersedes all previous versions of the TIREM atmospheric model. The use of TIREM can be used in conjunction with the Communications and Radar modules.

Parameter	Description
Surface Temperature	Surface temperature along the path.
Surface Humidity	Absolute humidity along the path.
Surface Conductivity (S/m)	The effective conductivity (reciprocal of receptivity) of the Earth along the path to a depth corresponding to the penetration depth appropriate for the frequency.
Surface Refractivity (N-Units)	Surface refractivity of the atmosphere along the path.
Relative Permittivity	The relative permittivity of the Earth along the path to a depth corresponding to the penetration depth appropriate for the frequency (unitless).
Override available terrain resolution	By default, terrain data is sampled at the available terrain resolution for use with TIREM. The "Override available terrain resolution" option allows the user to specify a custom sample resolution, and thus accommodates both long and short range link budget calculations using TIREM. In case the resolution specified by the user differs from the available terrain resolution, samples will be obtained through interpolation to satisfy the requirement. To specify a custom sample resolution, select this option and enter a value in the Terrain Sample Res. field.

The Terrain Integrated Rough Earth Model (TIREM) model only applies when both the transmitter and the receiver are below 30,000 meters. The computation time is proportional to the terrain resolution, dynamic nature of the scenario, proximity to ground and length of the simulation. It is recommended to use incremental steps and short initial scenario durations when using TIREM.

The TIREM models are listed as an option only if you have a valid TIREM for STK Communications and STK Radar license.
The scenario must have terrain to use TIREM, and the terrain must be from a local terrain file and not from a Terrain Server.
Any terrain format that STK can read can be used by TIREM. STK searches for terrain data for each object location. If the object moves out of the available terrain data, STK issues an error message that provides the object's time, latitude, and longitude when it crossed over the terrain's boundary.

Using Terrain with Scenario Objects

Scenario objects must use Terrain as the altitude reference.

For a facility, select Use Terrain Data and set Height Above Ground to at least half a meter on the Basic Position properties page.

For a vehicle, select Terrain as the Altitude Reference for vehicles and set the waypoint altitude to at least half a meter above terrain on the Basic Route properties page.

If you do not set the altitude reference to terrain for an object, STK will check the object height above ground (as determined by terrain) and issue a message in the message viewer each time the height drops below half a meter. TIREM will accept 0.5 meter height above ground, but the recommended minimum height is one meter above the ground level.

TIREM Tutorial

For more information on using TIREM, see TIREM Best Practices and Tutorial