7.4. Tutorials
Two tutorials are presented in this section. They are provided as a means to ensure THERM is working properly within DIRSIG and also to demonstrate some of the features. The first tutorial will provide the basic steps and requirements to use THERM within DIRSIG. It will also provide a look at DIRSIG truth maps, specifically the temperature map. The second tutorial will demonstrate DIRSIG's ability to model thermal scarring.
7.4.1. Running DIRSIG with THERM
This first tutorial sets up DIRSIG with two different configuration files to run at two different times of day. We will view the truth imagery, specifically the temperature maps, to verify that the general thermal phenomenology is correct. The foxbat scene is used for both tutorials as it has sufficient thermal properties specified in the material file. Having said that, the general procedure for creating the configuration files and adding thermal properties is described below.
Running THERM at two different times
Assigning Material Properties
The first step is to assign thermal properties to the materials in the scene. As stated above, the foxbat material file included in the delivery already has thermal properties assigned to the materials. This is included for completeness. The thermal properties and the units expected by DIRSIG are listed in the table below.
Table 7-2. Thermal Property Units
Material Property Units Specific Heat Langley/C Thermal Conductivity W/m/K Thermal Emissivity fraction Mass Density gm/cm^3 Thickness cm Exposed Area -1 to 1 These properties can be set for the materials using the mat_edit tool as described in Section 11.4.3.2. This tool has many features, one of which is to simulate the diurnal cycle of a given material based on the assigned properties. It is often a good idea to run these quick simulations to get a rough idea how the properties affect the simulation, and if the values make sense.
The material properties can also be set by directly editing the Material Database File. An example of a material file entry is shown below:
MATERIAL_ENTRY { NAME = Metal, Red, Shiny, New ID = 1003 SPECIFIC_HEAT = 0.11 THERMAL_CONDUCTIVITY = 559 MASS_DENSITY = 7.35 THERMAL_EMISSIVITY = 0.49 EXPOSED_AREA = 0.5 THICKNESS = 1.0 OPTICAL_DESCRIPTION = OPAQUE SPECULARITY = 0.0 EMISSIVITY_FILE = hood2_red.ems EDITOR_COLOR = 0.9000, 0.0000, 0.0000 }Enabling thermal sub model
The next step is to enable the THERM model. By default, DIRSIG will not calculate the facet temperatures. This is changed by setting a flag in the configuration file. The configuration file can be edited using cfg_edit. Click the Options button from the main window. It will open the window shown below. Check the box labeled Enable thermal model under the Model Complexity Options.
This can also be done by editing the configuration (.cfg) file directly and setting the appropriate flag to TRUE again under the OPTIONS section. An excerpt of this section from a configuration file is shown below:
. . . # flags for optional modeling OPTIONS { ENABLE_TRUTH_IMAGES = TRUE ENABLE_MAPS = TRUE ENABLE_THERMAL_MODEL = TRUE } . . .Enable Truth Imagery
In order to view the temperatures that THERM calculates for the facets, you must enable truth imagery output, and specifically the temperature map output. This is a two step process. First, to enable truth imagery output check the Generate truth images box on the Options screen, shown in the above figure. After clicking OK at the bottom, that window will close and the main cfg_edit window will remain. The Truth Images button is now activated. Clicking it will open the window shown below. In this window select the Temperature Maps option and change the output truth image filename (the filename assigned to the Image File variable, if desired. Dismiss this window by clicking OK.
Note: Truth images are an excellent way of debugging a simulation. Select all relevant in this window.
Make two simulation configuration files
At this point we have one configuration file. Make a copy of this configuration file. One will be used for the early simulation, and one for the night time simulation. The configuration files use many of the same settings. The things that need to be changed are the atmospheric database filename, the output image and truth image filenames, and of course the time of day of the simulation. All of these are set using the cfg_edit program. For information about the specifics of using the cfg_edit program see Section 4.1.1.
Build the atmospheric databases
After the configuration files are finalized, the Atmospheric Database File (.adb) must be constructed for each. For more information about the make_adb program, please refer to the The make_adb User Manual. At the prompt type:
prompt> make_adb name.cfgwhere name.cfg is the name of one of the configuration files created above. Run make_adb for both of the configuration files. Making the atmospheric database file is often time consuming since the MODTRAN model being employed under-the-hood is itself a very complex model.
Run the DIRSIG model
Once the ADB files have been created we can now run DIRSIG. It is often a good idea to verify the output image and truth image filenames are all different before the start of the simulation, to ensure no data is overwritten. The DIRSIG simulation can now be run using the following command:
prompt> dirsig name.cfgwhere name corresponds to the configuration files created previously. Run DIRSIG for both configuration files.
Review the simulation results
At this point, DIRSIG has created radiance and truth images along with the ENVI headers, for both configuration files described above. They can be viewed in ENVI. Below are the temperature maps which are stored in the truth image file. The image on the left was created at noon, and the image on the right was created at midnight. The pixel values are the temperatures calculate by DIRSIG (and THERM). The cursor is located on the top of one of the aircraft. In the cursor location window, Disp #1 Data refers to the temperature of the aircraft at noon, while Disp #2 Data refers to the temperature of the aircraft at midnight. There is a difference in the temperature of the aircraft of approximately 39 degrees Celsius. The temperature map shows a higher temperature for the aircraft that was simulated at noon, the result we expect. Examining other points in the scene confirms that the basic thermal phenomenology is correct.
7.4.2. Thermal Scarring
This tutorial will demonstrate DIRSIG's capability to perform basic geometry movement, and to simulate thermal scarring. Thermal scarring is the phenomenon that occurs as evidence of activity in the scene. For example consider the foxbat scene where there are aircraft on the ground. What happens when one of those planes moves at time A during the middle of the day? Remember, DIRSIG incorporates an entire 24 hours of sun/shadow history. Therefore, we would expect the ground under the aircraft that has been shielded throughout the day from the sun to be at a different temperature than the ground immediately surrounding the plane. If the plane moves, there will be a thermal scar. This scar will "fade" as the ground returns to an equilibrium temperature after a certain amount of time. The amount of time depends on the thermal properties assigned to the material, the location, as well as, the environmental parameters. It is obvious that things like the material's specific heat, the time of day, and air temperature (as well as all of the parameters listed in the Table of THERM Inputs).
Again, the foxbat scene delivered with DIRSIG will be used for this tutorial. This scene has the necessary thermal material parameters. As above, the standard mls.wth will be used to supply the weather history. The user can change parameters as desired using the procedures described in the first tutorial, as well as throughout the manual.
Thermal scarring procedure
Moving objects using the ODB
This step describes how to move objects using DIRSIG. At this time, the GUI tools does not support editing of the Object Database Files. Therefore, the user must manually edit the file using a simple text editor like vi. Below is a section from the Object Database File foxbat3.odb.
OBJECT { GDB_FILENAME = helicopter.gdb UNITS = INCHES INSTANCES { TIME_INFO = 11.99, 15850.0, 2300.0, 15.24, 1.0, 1.0, 1.0, 0.0, 0.0, 20.0 } }The Object Database File is a collection of Geometric Database Files (or object) instances. The example above shows one instance of the helicopter.gdb with the specified location, scale, and rotation in the TIME_INFO line. By default, an INFO variable is used for instancing. The TIME_INFO line adds a field at the beginning that specifies a LOCAL TIME for the object to leave the scene. In other words, at 11.99 local time, the helicopter leaves the scene. Therefore, the helicopter will not be present in a simulation performed for 12.00 local time, and only the thermal scar will remain. Also, simulations at subsequent time intervals will show the strength of the thermal scar decreasing.
Creating configuration files for different times
The tutorial will run a simulation at 12.00 local time, 12.17 local time, and 13.00 local time; or in other words, 1, 10 and 60 minutes respectively after the helicopter leaves the scene. For information on how DIRSIG interprets time fields refer to the section on the Object Database File.
Configuring DIRSIG
Make three copies of the configuration file from the first tutorial that was set up to run the simulation at 12.00pm. There are only a couple of settings that need to be changed. First, ensure that the configuration files are pointing to foxbat3.odb, the ODB file with the TIME_INFO field. Also, change the output filenames as desired. The configuration file for noon is complete, as it can even run with the same ADB file from the first tutorial.
In the other configuration files, change the time of simulation to correspond to a local time of 12.17 and 13.00. For example, a GMT of 17.17 will correspond to an EST of 12.17 (12:10pm). It is crucial to remember that the time in the ODB is local time, and not GMT time. Also change the adb filenames in the other configuration files. Two new atmospheric databases must be created since the times of simulations have changed. After making all necessary changes to the configuration file, run make_adb. The configuration files are complete and DIRSIG can be run as in the first tutorial. Note also that the focal length has been changed to 150mm to provide a close up shot of the helicopter and the thermal scars.
Review the results
Below are four images. The first image is a simulation without the helicopter removed from the scene for comparison purposes. The next three images correspond to simulations 1, 10 and 60 minutes after the helicopter has left the scene. The table below shows the temperatures for different times after the helicopter has left the scene. At t=0, the temperature corresponds to the actual temperature of some part on the helicopter. Immediately following the removal of the helicopter, the tarmac is only at 20 degrees, as it has been shaded from the sun. Temperatures for the tarmac after 10 and 60 minutes are also provided. In the third column is the approximate temperature of the surrounding tarmac. Even after 60 minutes, there is still a thermal scar as the tarmac in the scar area is approximately 5 degrees colder. However, recall that the duration of this scar is dependent on many factors. The material parameters have an effect as well as the environmental parameters (wind speed). The user can perform simulations to understand how these other parameters affect the thermal scarring.
