keywords: thermal, THERM

Summary

This scene demonstrates various ways to assign temperatures to and compute temperature for objects in a DIRSIG scene. Temperatures are shown to be assigned to individual facets in GDB files and to built-in geometry defined in an ODB file. For the remaining objects, the built-in THERM temperature code is used to predict the temperatures of surfaces.

Details

The scene uses a variety of methods to either assign or compute the temperatures of these panels. The following three methods are demonstrated:

  1. Setting the temperature field for a facet in a GDB file (Celcius)

  2. Setting the TEMPERATURE variable for a built-in geometry object (e.g. BOX, SPHERE, etc.) defined in an ODB file (Kelvin).

  3. Forcing THERM to compute a temperature based on the material properties and environmental conditions.

demo
Figure 1. An image of the 4 x 4 array of panels in this demo.

Important Files

The scene is composed of a 4 x 4 array of square panels on a background:

  • The 1st row of objects are blackbody (emissivity = 1) panels described by individual GDB files with temperature computed by THERM (the temperature field of the facets in the GDB files are set to -1).

  • The 2nd row of objects are graybody (emissivity = 0.9) panels created using the built-in BOX object, with the temperatures set to 250 K, 300 K, 320 K, and 350 K via the TEMPERATURE variable in ODB file.

  • The 3rd row of objects are blackbody (emissivity = 1) panels created using the built-in BOX object, with the temperatures set to 250 K, 300 K, 320 K, and 350 K via the TEMPERATURE variable in ODB file.

  • The 4th row of objects are blackbody (emissivity = 1) panels described individual GDB files with temperatures set to 250 K, 300 K, 320 K, and 350 K (the temperature field of the facets in the GDB files are set to -23.15, 26.85, 46.85, and 76.85, respectively).

The single GDB files with user-defined temperatures of 250, 300, 320 and 350 K can be found in the plate_250.gdb, plate_300.gdb, plate_320.gdb and plate_350.gdb files, respectively. Note that the temperature field in each facet description is in degrees Celcius.

The set single facet GDB files and built-in BOX panel objects are laid out in the geometry/thermal.odb file.

The materials are defined in the materials/thermal.mat file, with only two unique optical property files used (see materials/blackbody.ems and materials/graybody.ems).

The atmospheric setup uses a MODTRAN-driven atmosphere.

The platform has a single focal plane that uses the Raw capture method to output a spectral radiance cube from 7.5 to 12.5 microns at 0.1 micron spectral resolution. This focal plane also has material, intersection and temperature truth collectors configured.

Setup

The primary simulation is defined in the thermal.sim simulation file. Running the simulation will produce the output radiance and truth image files configured

Results

The results of the simulation are a radiance image cube (see thermal.img) and a truth image cube (see thermal_truth.img).

Since the path (distance from the sensor to the scene) is short and most of the panels are blackbodies, the atmospheric impacts are hard to notice. However, the spectral structure of the atmosphere can be observed in the lower emissivity (0.9) panels which reflect the downwelled sky.