Model of the Month: October 2003
UGVs are becoming increasingly important to numerous industries, especially for defense. To protect its investment, the defense industry needs to consider the thermal (infrared) signature of the system under various operating conditions and environments. This type of analysis is best carried out in our MuSES software. MuSES performs a full thermal analysis followed by a radiance solution in specific IR wave bands corresponding to the sensor of interest. Signature drivers such as solar loading, hot surfaces, interior heat loads, and reflections are all accounted for in MuSES.
This model includes a hybrid electric drive train with battery storage in the rear of the vehicle. Additional heat sources are the internal electronics, sensor tower, lights, and transient solar loads. The engine and exhaust inlet are active for models where the vehicle is idling or exercised. The battery is active to simulate heat losses during a short period of vehicle exercise. In this case, only the battery is being used to draw power—the engine is not engaged. The battery power curve is shown below.
Materials and Surfaces
A number of materials were employed in creating this model, including steel, aluminum, lead, glass, and hard rubber. Material properties affect not only conductive behavior but also the thermal mass effects in transient analysis. Since the outdoor environment is always changing, transient effects must be accounted for.
In order to predict the intensity of radiation in specific IR wave bands, MuSES employs spectrally dependent surface conditions called "Paints." The emissivity VS wavelength is shown below for the paint "Desert Tan." This curve is used in the radiance prediction. Note that the emissivity scale varies from 0 to 1 and wavelength from 0 to 16 microns.
An important aspect of signature analysis is accurate background temperatures and radiance. In this case, we are modeling sand dunes and therefore define our faceted terrain appropriately, using the paint code for Desert Sand as the surface condition.
Diurnal Signature Analysis
A Diurnal thermal solution was generated and then the IR Signature predicted for a 24-hour period with engine off and lights on. The results below are from 09:00, 15:00, 21:00, and 03:00.
Signatures - Contrast with Background
To get a graphical understanding of the contrast level for a vehicle of this type against a realistic background, we created a rolling terrain. The vehicle was placed upon it, to provide accurate reflections and shadows in both the thermal band and the IR signature solution.
The image at left shows the full terrain and the vehicle located approximately in the center. This image is facing southward from above, near midday. Note the shadowing on the north (bottom) side of the hills and also on the UGV.
View Animation of Diurnal Thermal Results:
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Sample unmanned ground vehicle signature analysis featuring a simple hybrid drive engine and exhaust system and sensor tower. The defense industry needs to consider the thermal (infrared) signature of its systems under various operating conditions and environments. MuSES performs a full thermal analysis followed by a radiance solution in specific IR wave bands corresponding to the sensor of interest.
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