Sensor Calibration and Ground Imaging with EOIR

STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this tutorial by contacting AGI Support at support@agi.com or 1-800-924-7244.

Required Capability Install: This lesson requires an additional installation for the STK software's EOIR capability. The EOIR installer is included in the STK Premium software download, but requires a separate installation process. Read the Readme.htm found in the STK software install folder for installation instructions. You can obtain the necessary install by visiting https://support.agi.com/downloads or calling AGI support.

This lesson requires version 12.9 of the STK software or newer to complete in its entirety. If you have an earlier version of the STK software, you can complete a legacy version of this lesson.

Optional Software Install: This lesson uses the MATLAB programming platform for analysis. If you do not have access to MATLAB or an equivalent software, the necessary files produced using that platform are available for download. An internet connection is required to download these files.

The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Capabilities covered

This lesson covers the following capabilities of the Ansys System Tool Kit® (STK®) digital mission engineering software:

  • STK Pro
  • Analysis Workbench
  • Electro-Optical Infrared Sensor Performance (EOIR)

Problem statement

Engineers and operators need to understand how onboard cameras will behave within the context of a mission. They want to simulate what a sensor will see if it looks at a target under different conditions, which is important. If they own the sensor, field tests are expensive and complicated, results are uncertain, and there are no do-overs. If they don't own the sensor, they may want a better understanding of what kind of results it can achieve, or what kind of threat it might present. Many simulation tools are proprietary, classified, or compartmented, and may not be available for downstream analytical purposes.

Solution

Use the STK software's Electro-Optical Infrared Sensor Performance (EOIR) capability, a commercial-off-the-shelf (COTS) solution, to create a realistic model of a ground-imaging sensor from reference images. First, you will construct a sensor scene of a known location at a specific time and insert an artificial object into the scene. This will result in a sensor image with the target object overlaid on the background reference image. You will then use the image to perform in-scene calibration of the sensor and target models. Once you have an acceptably accurate model, you will explore the potential performance of the sensor in varying conditions, including the impact of various atmosphere models and low-light illumination conditions.

What you will learn

Upon completion of this tutorial, you will be able to:

  • Create system models such as satellite orbits, EOIR system specs, and sample target objects
  • Load custom image texture maps into your scenario
  • Conduct in-scene model calibrations with regard to the resolution and sensitivity

Creating a new scenario

Create a new scenario.

  1. Launch the STK application ().
  2. Click Create a Scenario in the Welcome to STK dialog box.
  3. Enter the following in the STK: New Scenario Wizard:
    4. Option Value
    Name Ground_Imaging_EOIR
    Start 30 Jul 2017 00:00:00.000 UTCG
    Stop + 1 day
  4. Click OK when you finish.
  5. Click Save () when the scenario loads. A folder with the same name as your scenario is created for you in the location specified above.
  6. Verify the scenario name and location in the Save As dialog box.
  7. Click Save.

Save () often!

Downloading files

This lesson will walk you through how to use the MATLAB programming platform to convert an image into a comma-separated values (CSV) file. Any utility that can extract pixel data from an image into a CSV file will work for this study, however.

If you do not have access to MATLAB, the converted files are available for download. If you want to use the converted files in this tutorial, follow these steps to download the files:

  1. Download the zipped folder here: https://support.agi.com/download/?type=training&dir=sdf/help&file=EOIRSensorCalibrationGroundImaging.zip

    If you are not already logged in, you will be prompted to log in to agi.com to download the file. If you do not have an agi.com account, you will need to create one. The user approval process can take up to three (3) business days. Please contact support@agi.com if you need access sooner.

  2. Navigate to the downloaded folder.
  3. Right-click on EOIRSensorCalibrationGroundImaging.zip.
  4. Select Extract All... in the shortcut menu.
  5. Set the Files will be extracted to this folder: path to be within your scenario folder (e.g. C:\Users\<username>\Documents\STK  12\Ground_Imaging_EOIR\EOIRSensorCalibrationGroundImaging).
  6. Click Extract.
  7. Go to your scenario folder.

    8. The following files will be in the EOIRSensorCalibrationGroundImaging folder:

    • Airport.bmp
    • Airport.csv
    • Airport.jp2
    • Aiport_v2.csv

Displaying the EOIR toolbar

Update your workspace to show the EOIR toolbar.

  1. Select View in the Menu Bar.
  2. Select Toolbars in the View menu.
  3. Select EOIR in the Toolbars submenu to display the EOIR toolbar.

    4. If you do not see the EOIR option in the Toolbars submenu, check the status of your STK software license and whether you have the EOIR capability installed.

  4. Locate the EOIR toolbar ().

Here, you can access the EOIR configuration and EOIR sensor scene for a particular sensor.

Disabling streaming terrain

You will not be using streaming terrain for this analysis. You can disable it in the scenario object's properties.

  1. Right-click on Ground_Imaging_EOIR () in the Object Browser.
  2. Select Properties ().
  3. Select the Basic – Terrain page when the Properties Browser opens.
  4. Clear the Use terrain server for analysis check box.
  5. Click OK to accept the changes and close the Properties Browser.

Inserting a Satellite object

You will use the SkySat C3 satellite (SSCN 41774), which is a part of a constellation of 15 high-resolution imaging satellites operated by Planet Labs PBC, in your mission to image the ground. Insert this satellite into your scenario from the Standard Object Database.

  1. Bring the Insert STK Objects tool () to the front.
  2. Select Satellite () in the Select An Object To Be Inserted list.
  3. Select From Standard Object Database () in the Select A Method list.
  4. Click Insert....
  5. Enter 41774 into the Name or ID field of the Search Standard Object Data dialog box.
  6. Click Search.
  7. Select SKYSAT-C3 from the AGI’s Standard Object Data Service data source.
  8. Click Insert.
  9. Click Close after SKYSAT-C3_41774 () finishes propagating to close the Search Standard Object Data dialog box.

Modeling your sensor target at Boston Logan International Airport

Insert a Target object and locate it near one of Boston Logan International Airport's terminals. This will be the "target" location for the SkySat C3 satellite's onboard imaging sensor.

  1. Insert a Target () object using the Define Properties () method.
  2. Select the Basic - Position page when the Properties Browser opens.
  3. Enter the following values in the Position frame:
    4. Option Value
    Latitude 42.3639 deg
    Longitude -71.0242 deg
  4. Click OK to accept your changes and to close the Properties Browser.
  5. Right-click on Target1 () in the Object Browser.
  6. Select Rename in the shortcut menu.
  7. Rename Target1 () Boston.

Setting the scenario animation time

Modify the scenario animation time to match the "acquired" time of the image. From an external source, you know that during the below specified period, the SkySat C3 satellite was overhead and was able to capture an image of the ground.

  1. Open Ground_Imaging_EOIR's () Properties ().
  2. Select the Basic - Time page when the Properties Browser opens.
  3. Clear Use Analysis Start Time in the Animation frame.
  4. Enter 30 Jul 2017 15:32:11.507 UTCG in the Start Time field.
  5. Click OK to accept your changes and to close the Properties Browser.
  6. Click Reset () in the Animation toolbar to reset the scenario to the animation start time.

    7. When changing the animation start time in the Scenario object's properties, it doesn't affect the analysis period. You can also update the animation time directly in the Animation toolbar.

Computing Access to the target

Now that the animation time is set, you can compute Access from the SkySat C3 satellite to Boston.

  1. Right-click on SKYSAT-C3_41774 () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select Boston () in the Associated Objects list when the Access Tool opens.
  4. Click .

Finding the viewing angle

Generate an azimuth-elevation-range (AER) report to find the elevation angle at the animation start time.

  1. Click AER... in the Reports frame.
  2. Click Show Step Value.
  3. Enter 1 sec in the Step field.
  4. Select the Enter key.
  5. Scroll to 30 Jul 2017 15:32:11.000 in the Time (UTCG) column.
  6. Make note of the Elevation Angle.

    7. It is approximately -77 deg. This is a good angle to view your sensor "target" at Boston ().

  7. Close the AER report and the Access Tool when finished.

Modeling an EOIR Sensor object

Next, you will insert a Sensor object to model EOIR capabilities. The STK software's EOIR capability models the detection, tracking, and imaging performance of electro-optical and infrared sensors. You can use the EOIR capability to a support concept development, design, field testing, and operations. The STK software takes this modeling to the big picture by considering electro-optical and infrared performance in conjunction with sensor platform dynamics, communications, and other mission architecture elements to assess integrated performance.

Inserting a sensor object

Insert a Sensor object and attach it to SKYSAT-C3_41774.

  1. Insert a Sensor () object using the Define Properties () method.
  2. Select SKYSAT-C3_41774 () in the Select Object dialog box.
  3. Click OK.
  4. Rename Sensor1 () Default_EOIR_1deg.

Setting the EOIR sensor type

You will start with a general model of an EOIR sensor. You don't have to enter every sensor specification at the start; you will iteratively refine the sensor settings throughout your analysis. Start by updating Default_EOIR_1deg's properties to model an EOIR sensor type.

  1. Select the Basic - Definition page in the Properties Browser.
  2. Open the Sensor Type drop-down list.
  3. Select EOIR.

Selecting EOIR will display both the band-specific and sensor-level EOIR sensor properties on the Definition page.

Setting the EOIR sensor's spatial properties

Adjust the sensor's spatial properties to specify a 1-degree field of view.

  1. Select the Spatial tab.
  2. Open the Input drop-down list.
  3. Select Field-of-View and Number of Pixels.
  4. Set the following values in the Field of View frame:
    5. Option Value
    Horizontal Half Angle 1 deg
    Vertical Half Angle 1 deg
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Targeting Boston with an along vector

Update Default_EOIR_1deg's sensor pointing definition to target Boston using an along vector. While you could use the Targeted pointing type, the view would be opposite to the view in the 2D and 3D Graphics windows. This is due to the velocity vector of the satellite at the time of the EOIR sensor scene you will generate later in this tutorial.

  1. Select the Basic - Pointing page.
  2. Open the Pointing Type drop-down list.
  3. Select Along Vector.
  4. Click Select.... next to the Alignment vector field.
  5. Select Default_EOIR_1deg () in the object list in the Select Alignment Vector dialog box.
  6. Expand () the To Vectors () directory in the Vectors for: Default_EOIR_1deg list.
  7. Select Boston ().
  8. Click OK to close the Select Alignment Vector dialog box.

Setting the constraint vector

You want to orient the sensor view so that north is at the top of the image, meaning that it will match what you will see in the 2D and 3D Graphics windows. You can do so by defining a an appropriate vector towards which the sensor will be constrained: the SkySat satellite's North vector.

  1. Click Select.... next to the Constraint vector field.
  2. Select SKYSAT-C3_41774 () in the object list in the Select Constraint Vector dialog box.
  3. Expand () the Installed Components () directory in the Vectors for: SKYSAT-C3_41774 list.
  4. Select North ().
  5. Click OK to confirm your selection and to close the Select Constraint Vector dialog box.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Generating an EOIR sensor scene

With your sensor pointing at Boston, you can now generate a sensor scene. The EOIR Line of Sight and Field of View are synchronized to the STK Sensor object. The input scene represents the analog world by sampling the digital "modeled universe" at four times the sensor's pixel's spatial frequency, 16 spatial samples per sensor pixel, and over the passband and at wavelengths defined by the sensor model. The input scene is thus a "box" of floating point numbers of dimension (Horizontal spatial resolution × Vertical spatial resolution × Spectral resolution). The sensor scene is output as an image with mapped pixel values for false color display.

Creating a new EOIR sensor scene

Create an EOIR sensor scene for Default_EOIR_1deg at the animation time you set (30 Jul 2017 15:32:11.507 UTCG), then update its calculation detail of the image to produce a more-detailed surface map.

  1. Select Default_EOIR_1deg () in the Object Browser.
  2. Click EOIR Sensor Scene... () in the EOIR toolbar.
  3. Right-click in the EOIR Sensor Scene window.
  4. Select Details... in the shortcut menu.
  5. Select Fine in the Scene Detail frame when the EOIR Scene Visual Details dialog box opens.
  6. Click Apply.
  7. Examine the EOIR Sensor Scene.

    8. You should now see the default Earth background texture rendered in gray scale. This 1 km texture map that comes with the EOIR capability is adequate for very broad area applications.

    GRAY SCALE color map

Changing the color map

Explore the scene's details by applying a different "false color" mapping of the display.

  1. Select the BGRY option in the Color Map frame.
  2. Click Apply.

    3. Areas that were varying shades of gray are now blue, green, red and yellow.

    BGRY color map

  3. Click on the different colors in the scene.

    4. Note the Material type in the EOIR Scene Visual Details dialog box changes depending on which part of the scene you have selected. As you click, you should see various kinds of materials listed in the field including Urban, WaterBody, GrassLands, and more.

  4. Select the Gray Scale option in the Color Map frame.
  5. Click OK to close the EOIR Scene Visual Details dialog box.
  6. Close () the EOIR Sensor Scene window.

Creating a reflectance texture map

Texture maps, like the reflectance map you will use in this scenario, can come from your own sources, or you can create them from within the STK application. Next, you will walk through a workflow for creating your own texture maps. The example file will be generated from Bing Maps imagery data, which only has red, green, and blue pixels. You will use the data you have available and extend it to the wavebands you are using in this study

Cleaning up the 3D Graphics window

Remove unneeded data from the 3D Graphics window before you create your reflectance map.

  1. Bring the 3D Graphics window to the front.
  2. Click Properties () in the 3D Graphics window toolbar.
  3. Select the Annotation page when the Properties Browser opens.
  4. Clear the following check boxes in the Time frame:
    • Show Time
    • Show Time Step
  5. Clear the Show check box in the View Reference Frame.
  6. Click OK to close the Properties Browser.
  7. Clear the check box for Boston () in the Object Browser.

Using the 3D Graphics Snap Frame tool to create a bitmap image

Create an image of Boston using the STK software's Bing Maps imagery and the 3D Graphics Snap tool.

Use this procedure if you are going to use MATLAB to create a reflectance map. Please note, the example file has already been converted and is available for download from agi.com. The link to the file is in this tutorial’s Downloading files section. If you are going to use the downloaded Airport.csv file, you can skip to the Importing the reflectance map section.

  1. Right-click on Boston () in the Object Browser.
  2. Select Zoom To in the shortcut menu.
  3. Click Orient North () in the 3D Graphics window toolbar.
  4. Zoom out slightly in the 3D Graphics window, so your view looks something like this:

    5. 3D Graphics window view of boston

    It is OK if your airport looks different than the picture above. The STK application automatically updates ground imagery with the latest Bing Maps imagery available. If you want to use the same imagery as used in this lesson, you can load in the airport.jp2 image file provided in the Downloading files section to the 3D Graphics display. You can also use your own imagery. Please review the Working with Imagery Help page for more information.

  5. Click Snap Frame () in the 3D Graphics window toolbar.
  6. Enter Airport in the File name field when the Save As dialog box opens.
  7. Make sure Save as type is set to *.bmp, the default option.
  8. Select your scenario directory.
  9. Click Save.

Converting the image into a CSV file

Your bitmap image has three channels: red, green, and blue. Copy and modify the following MATLAB code to create a texture map that is normalized across each of the three channels. The MATLAB script below was used to create Airport.csv.

  1. Open the MATLAB application.
  2. Copy the following script into MATLAB, replacing C:\Airport.bmp with the full file path to your bitmap file (for example, C:\Users\<username>\Desktop\Airport.bmp):

    a=imread('C:\Airport.bmp');

    b=mean(a,3);

    imagesc(b)

    b=b/max(b(:));

    csvwrite('C:\Airport.csv',b);

  3. Select the Enter key.
  4. Go to your directory where you saved Airport.csv to confirm that is has been created.

Importing the reflectance map

Load the Airport.csv texture map file into your scenario for your camera to view.

Adjusting the EOIR Configuration

To select STK objects for possible inclusion in the generated scene and make sensors available to generate radiometric results, open the EOIR Configuration dialog box. You can also add texture maps and specify their associated parameters in the EOIR configuration.

  1. Click EOIR Configuration... () on the EOIR toolbar.
  2. Click Atmosphere and Textures... in the EOIR Configuration dialog box.
  3. Select the Texture Maps page in the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  4. Click New Texture Map () in the EOIR Atmosphere, Clouds, and Texture Maps dialog box toolbar.
  5. Set the following options:
    Option Value
    Name Reflectance
    Type Reflectance

Loading the texture map file

Load in the Airport.csv texture map file.

  1. Open the Value drop-down list.
  2. Select File:.
  3. Click the ellipsis () beside the File field.
  4. Browse to the location of the Airport.csv file you created or downloaded.
  5. Select the Airport.csv file.
  6. Click Open.
  7. Set the following corner points:
    8. Point Latitude (deg) Longitude (deg)
    NW Corner 42.3654 -71.0271
    NE Corner 42.3654 -71.0232
    SW Corner 42.3631 -71.0271
    SE Corner 42.3631 -71.0232
  8. Click OK to accept your changes and to close the EOIR Atmosphere, Clouds, and Texture Maps dialog box.

    9. You'll need to have some patience here. Loading a texture map can take a while depending on the amount of data required.

  9. Click OK to close the EOIR Configuration dialog box once the map has loaded.

Revisiting the sensor scene

Examine the changes in the EOIR Sensor Scene. If you left the window open, then the scene will have automatically refreshed when you updated the EOIR configuration.

If you closed it, reopen the EOIR Sensor Scene window.

  1. Select the Default_EOIR_1deg () in the Object Browser.
  2. Click EOIR Sensor Scene... () on the EOIR toolbar to generate an image that represents the sensor output.
  3. Examine the changes. They are subtle.

    4. You will see the custom imagery overlaid on the default Earth background.

    Custom EOIR sensor scene

  4. Close the EOIR sensor scene.

Improving EOIR sensor realism

You can improve EOIR sensor model's realism with published specs and some understanding of engineering. The following references provide some helpful information about the SkySat imaging sensor:

Here are the relevant details:

  • The EOIR sensor has an effective nadir resolution (also called Ground Sample Distance, or GSD) at 450 kilometers of 50 centimeters after super-resolution processing. See the GSD formula help page for more information.
  • The optics have a 3.6-meter focal length and 35-centimeter aperture.
  • The effective detector pitch value you get from solving the GSD equation using the values above is 4.0 microns. However, one of the sources gives a value of 6.5 microns. This gives you a range of values to begin with.

Attaching a new Sensor object to the SkySat C3 satellite

You will begin to refine your EOIR system specifications. The system specifications can come from open source or published documentation, as you will use here. Over the course of the scenario, you will look at the aperture and focal length, modify the spectral bands, change the optical and radiometric inputs, and examine the detector pitch.

Inserting a Sensor object

Insert a Sensor object to model EOIR capabilities.

  1. Insert a Sensor () object using the Define Properties () method.
  2. Select SKYSAT-C3_41774 () in the Select Object dialog box.
  3. Click OK.
  4. Rename Sensor2 () to SKYSAT_EOIR.

Updating the sensor type

Update the sensor's properties to model an EOIR Sensor Type.

  1. Select the Basic - Definition page in the Properties Browser.
  2. Open the Sensor Type drop-down list.
  3. Select EOIR.
  4. Select the Spatial tab.
  5. Rename Band1 to PAN in the Band Name list.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the sensor's spatial properties

Set the number of pixels for your scene to 128 × 128 and detector pitch to 6.5 microns by updating the sensor's spatial properties. Even though the SkySat C3 satellite's sensor has a pixel count that is much higher, considering only a subset of its image area will speed up the processing time. You can also do this because you will ensure the STK application points the sensor directly at the desired target and will not need to search a large scene to find it.

  1. Open the Input drop-down list.
  2. Select Number of Pixels and Detector Pitch.
  3. Set the following values in the Number of Pixels frame:
    4. Option Value
    Horizontal 128
    Vertical 128
  4. Set the following values in the Related Detector Parameters frame:
    5. Option Value
    Horiz Pixel Pitch 6.5 (um)
    Vertical Pixel Pitch 6.5 (um)
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the sensor's spectral properties

Set the lowest and highest wavelengths that the sensor responds to by updating the sensor's spectral properties.

  1. Select the Spectral tab.
  2.  Set the following values in the Spectral Band Edge Wavelengths frame:
    3. Option Value
    Low 0.45 (um)
    High 0.90 (um)
  3. Click Apply to accept your changes and to keep the Properties Browser open.

Setting the sensor's optical properties

Adjust the optical properties of the sensor.

  1. Select the Optical tab.
  2. Open the Input drop-down list.
  3. Select Focal Length and Entrance Pupil Diameter
  4.  Set the following parameters:
    5. Option Value
    Effective Focal Length 350 (cm)
    Entrance Pupil Diameter 35 (cm)
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Targeting Boston with an along vector

Update SKYSAT_EOIR's properties to target Boston using an along vector.

  1. Select the Basic - Pointing page.
  2. Open the Pointing Type drop-down list.
  3. Select Along Vector.
  4. Click Select.... next to the Alignment vector field.
  5. Select SKYSAT_EOIR () in the object list in the Select Alignment Vector dialog box.
  6. Expand () the To Vectors () directory in the Vectors for: SKYSAT_EOIR list.
  7. Select Boston ().
  8. Click OK to close the Select Alignment Vector dialog box.

Setting the constraint vector

You must select an constraint vector in addition to the alignment vector.

  1. Click Select.... next to the Constraint vector field.
  2. Select SKYSAT-C3_41774 () in the object list in the Select Constraint Vector dialog box.
  3. Expand () the Installed Components () directory in the Vectors for: SKYSAT-C3_41774 list.
  4. Select North ().
  5. Click OK to confirm your selection and to close the Select Constraint Vector dialog box.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Unlike when you targeted Boston with the Default_EOIR_1deg Sensor () object, this time, the North vector is marked with a green check mark (). This indicates it has already been computed. It was computed for the SKYSAT-C3_41774 Satellite () object when you used it as the constraint vector in Default_EOIR_1deg's pointing definition.

Changing the projection translucency

Change SKYSAT_EOIR's projection translucency. This can make it easier to see your ground objects while still seeing SKYSAT_EOIR's field of view in the 3D Graphics window.

  1. Select the 3D Graphics - Attributes page.
  2. Enter 90 in the % Translucency field in the Projection frame.
  3. Click OK to accept your changes and to close the Properties Browser.

Modeling an Aircraft for imaging

Now, model an aircraft that is parked at the airport by inserting an Aircraft object as a target model.

Adjusting your view

Zoom to you analysis target area at Boston Logan International Airport.

  1. Bring the 3D Graphics window to the front.
  2. Right-click on Boston () in the Object Browser.
  3. Select Zoom To in the shortcut menu.
  4. Click Orient North () in the 3D Graphics window toolbar.
  5. Zoom out slightly in the 3D Graphics window so your view looks something like this:

    6. Tarmac in SKYSAT_EOIR's field of view

As you can see in the 3D Graphics window, you can see the tarmac. Your view might be different depending on if the Bing Maps imagery has been updated when you complete this scenario.

Inserting an Aircraft object

Load your own aircraft into the scenario, so you can compare it to what the sensor sees in the ground imagery.

  1. Insert an Aircraft () object using the Insert Default () method.
  2. Rename Aircraft1 () 737.

Setting the aircraft's location

Park the aircraft at the terminal for one day.

  1. Open 737's () Properties ().
  2. Select the Basic - Route page in the Properties Browser.
  3. Open the Route Calculation Method drop-down list.
  4. Select Specify Time.

    5. Specify Time uses the Time properties of each waypoint.

  5. Click Insert Point.
  6. Set the following properties:
    7. Option Value
    Latitude 42.3639 deg
    Longitude -71.0242 deg
    Altitude 3 m
  7. Click Insert Point to insert a second point at that same location.
  8. Enter 31 Jul 2017 00:00:00.000 UTCG in the Time field of the second point.

    9. This will "park" 737 () at the same spot for 24 hours.

  9. Click Apply to accept your changes and to keep the Properties Browser open.

Adding a Sun vector

By adding a Sun vector, you can better understand why and where shadows appear around your aircraft 3D Graphics model.

  1. Select the 3D Graphics - Vector page.
  2. Select the Vectors tab.
  3. Select the Sun Vector - Show check box.
  4. Enter 10 in the Thickness field.
  5. Click Apply to accept your changes and to keep the Properties Browser open.

Examining the changes to your scenario

Review your changes in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Zoom to 737 ().
  3. Using your mouse, set your view to see your simulated 737 from an aerial oblique angle.

    4. You can easily distinguish the 3D model of 737 from the other aircraft imaged on the ground, especially at this angle.

    Oblique View of 737

Defining the EOIR shape of the aircraft

The EOIR capability supports the use custom 3D mesh files to generate vehicle shapes in a sensor scene. The models can be user-supplied and samples are included with your STK software installation. You can set the image generation properties for selected STK objects included as targets in an EOIR configuration to define their EOIR shapes and properties.

Loading the custom shape file

Load a custom mesh file that models the shape of a 737 aircraft. You will use a sample external model (*.obj) file included with your STK software installation.

  1. Return to 737's () Properties ().
  2. Select the Basic - EOIR Shape page.
  3. Open the Shape drop-down list.
  4. Select CustomMesh.
  5. Enter 37 m in the Max Dimension field.

    6. It’s important to use realistic dimensions for the 3D model you choose, as the EOIR capability will scale the model to match the Max Dimension you enter.

  6. Click the Mesh File ellipsis ().
  7. Go to <STK install folder>EOIR_Databases\PropertyFiles\CustomMeshes\Air.
  8. Select Boeing-737.obj.
  9. Click Open.

Updating the model's reflectance

Each surface material has optical properties used in the sensor scene calculation. One of these is reflectance. Light bouncing off a surface is selectively reflected by wavelength; i.e., some wavelengths are absorbed instead of reflected. In the visible wavelengths, this is what gives objects color. The reflectance can vary from no light reflected (0%) to all light reflected (100%). Adjust the model's reflectance to better simulate the real-world properties of an aircraft.

  1. Enter 25% in the Reflectance field.
  2. View the other default settings if desired.
  3. Click OK to accept your changes and to close the Properties Browser.

Adding the simulated 737 to the EOIR configuration

Now that the model 737 is defined analytically, set up the EOIR configuration so that SKYSAT_EOIR sees it.

  1. Click EOIR Configuration... () on the EOIR toolbar.
  2. Select Aircraft/737 () in the list of Available STK Objects in the EOIR Configuration dialog box.
  3. Move () Aircraft/737 () to the Selected Targets list.
  4. Click OK to close the EOIR Configuration dialog box.

Generating an EOIR sensor scene

Generate an image that represents the radiometric input to SKYSAT_EOIR.

  1. Select the SKYSAT_EOIR () in the Object Browser.
  2. Click EOIR Sensor Scene... () in the EOIR toolbar.
  3. Right-click in the EOIR Sensor Scene window.
  4. Select Details... in the shortcut menu.
  5. Select the Scene Detail – Fine check box in the EOIR Scene Visual Details dialog box.
  6. Click OK to close the EOIR Scene Visual Details dialog box.
  7. Examine the scene. 737 () should now appear within the EOIR sensor scene.

    8. EOIR Sensor Scene with 737

Adjusting the EOIR sensor scene

Compare the simulated 737 with any other aircraft that are in the scene. Although the model 737 looks very similar to any other aircraft in the image, there are a few differences worth noting between in the display of its shadows and its contrast.

Exploring the shadows

The EOIR capability does not render shadows cast from custom 3D mesh objects onto the ground or onto themselves, such as the shadow of the simulated 737's vertical stabilizer onto its horizontal stabilizer. However, you can see that one side of the fuselage is shaded due to the sun’s position and is consistent with other objects in the background image.

  1. Look at the 737's () fuselage in the scene.
  2. Notice that one side of the fuselage is shaded due to the sun’s position. This is consistent with the other objects' shading in the background image.

Exploring the scene contrast

The shaded regions of the simulated 737's fuselage show a darker black than almost any other part of the scene. This is especially noticeable between comparable locations on the aircraft fuselage in the background image. There are a couple of potential reasons for this:

  • The EOIR capability does not compute reflections from the sky, which will result in less ambient light and thus starker shadows.
  • The white balance of the background image could be a bit off. One approach to work around this is to convert the image background to a percentile map. Essentially, it will cut out the top 5% brightest and top 5% darkest pixels and rescale the reflectance values accordingly. This is a crude approximation of scaling the image to the dark pixel and light pixel reflectance values, or using the Empirical Line Method (ELM) to calibrate all pixel values. You can do this in MATLAB by recreating the CSV file. You will add a few commands to the end of the code you used above. The additional commands are in bold below. The script in the section below was used to create Airport_v2.csv.

Scaling the image

Cut out the top 5% brightest and top 5% darkest pixels and rescale the reflectance values accordingly by creating a new EOIR texture map. You can create your own CSV file or use the Airport_v2.csv file you downloaded earlier. The MATLAB script was used to create the Airport_v2.csv file.

If you are using the downloaded file, skip to Loading the texture map file section.

  1. Open MATLAB.
  2. Copy the below script into MATLAB, replacing C:\Airport.bmp with the full file path to your bitmap file:

    3. a=imread('C:\Airport.bmp');

    b=mean(a,3);

    imagesc(b)

    b=b/max(b(:));

    b=b-0.1;

    b(b<0)=0;

    csvwrite('C:\Airport_v2.csv',b);

  3. Select the Enter key.

Loading the texture map file

Load in the new Airport_v2.csv texture map file.

  1. Return to your STK scenario.
  2. Click EOIR Configuration... () on the EOIR toolbar.
  3. Click Atmosphere and Textures... in the EOIR Configuration dialog box.
  4. Select the Texture Maps page in the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  5. Click the ellipsis () beside the File field.
  6. Browse to the location of the Airport_v2.csv file that you created or downloaded earlier.
  7. Select the Airport_v2.csv file.
  8. Click Open.
  9. Click OK to load the texture map and to close the EOIR Atmosphere, Clouds, and Texture Maps dialog box.

    10. Be patient. It will take a while to load.

  10. Click OK to close the EOIR Configuration dialog box.

    11. Your EOIR scene will look similar to this. The darkness from the EOIR target aircraft’s shaded fuselage is now much closer to that of the background image.

    737 view with texture map

Changing the simulated 737's target reflectance

Besides the shadows, the model 737 aircraft itself still appears a little darker than the adjacent aircraft. This could easily be due to the actual reflectance of the real aircraft in the background image, paint color, surface treatments, etc. If your goal is to create an aircraft that matches the imaged aircraft even more closely, you could change the 737 model’s EOIR Shape Reflectance value to 22%. For more advanced applications, you may want to supply a Spectral Reflectance File. For more information, see the EOIR General Vehicle Shape Properties help page.

  1. Open 737's () Properties ().
  2. Select the Basic - EOIR Shape page.
  3. Enter 22% in the Reflectance field.
  4. Click OK to accept your change and to close the Properties Browser.

Investigating the model 737's target edge sharpness

The model 737 aircraft seems to be slightly sharper, or more "in focus," than the rest of the scene, especially along the wings. Part of the reason may be that your EOIR sensor model is using a few idealized parameters. One of these parameters is jitter along the line of sight. It is currently set to 0 milliradians, representing a perfectly stable platform. A more appropriate value for a real platform might be 0.1 to 1.0 times the Instantaneous FOV (IFOV) of a single pixel. For a resolution of 128 × 128 pixels and 6.5 micron pixel pitch, the IFOV is 0.0019 milliradians. Set the Line of Sight Jitter to 0.001 milliradians, or about 0.5 times the IFOV.

  1. Open SKYSAT_EOIR's () Properties ().
  2. Select the Basic - Definition page.
  3. Scroll to the Jitter frame below the band-specific tabs in the Definition panel.
  4. Enter 0.001 in the Line of Sight Jitter field.
  5. Click OK to accept your change and to close the Properties Browser.
  6. Examine your sensor scene.

    7. The scene now looks very blurred.

    Blurred EOIR Sensor scene from the effects of jitter

Now that you’ve been able to insert a false object into a collected image that is fairly consistent with an actual target, you can declare victory for your model calibration!

Comparing the scenes

Compare the sensor scene with the 3D Graphics window.

  1. Compare the EOIR sensor scene above and your simulated 737 aircraft object to the 3D Graphics window.
  2. Optionally, you can open the saved Airport.bmp file outside of the STK application, which would better preserve the original pixelation.

    3. 3D Graphics vs EOIR sensor scene

  3. Compare the apparent resolution, or Ground Sample Distance (GSD), between the two images.
  4. Compare the detail in the scene.

    5. Is there enough detail in the scene to discern the various 737 variants, or a 737 from an Airbus A320?

  5. Examine the scene to determine if the scenario produces a sufficiently accurate model of this sensor's performance.

    6. Does this give you confidence in evaluating the sensor performance in other scenes and against other targets?

Verifying the sensor resolution

Earlier in the exercise, you found a potential range of values to use for detector pitch, and thus, GSD. You initially picked the largest value, 6.5 microns, for the detector pitch. Now is a good time to revisit that assumption. You can also reference the earlier SkySat sensor parameters and find the detector pitch required to achieve 0.8 m/pixel for the sensor. The STK application includes the ability to compute GSD geometrically for accesses involving a sensor object when you specify the sensor resolution values of Focal Length and Detector Pitch.

Updating the sensor's properties

Update the sensor's focal length and detector pitch.

  1. Open SKYSAT_EOIR's () Properties ().
  2. Select the Basic - Resolution page.
  3. Set the following in the Focus Constraints frame:
    4. Option Value
    Focal Length 3.5 m
    Detector Pitch 6.5 um
  4. Click Apply to accept your changes and to keep the Properties Browser open.

Computing Access

Compute access from SKYSAT_EOIR to Boston.

  1. Right-click on SKYSAT_EOIR () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select Boston () in the Associated Objects list of the Access Tool.
  4. Click .

Creating a custom report

Create a custom report to display constraint data.

  1. Click Report & Graph Manager....
  2. Click Create new report style () in the Styles toolbar.
  3. Name the report GSD.
  4. Press Enter on your keyboard.

Selecting a data provider and elements

Add select data providers to your custom GSD report.

  1. Select the Content page when the Properties Browser opens.
  2. Expand () Constraint Data () in the Data Provider list.
  3. Move () the following elements to the Report Contents list.
    • Time ()
    • ToElevationAngle ()

      • The elevation angle will change depending on if you compute access from the ground to the satellite versus from the satellite to the ground. When computing from SKYSAT_EOIR to Boston, use the ToElevationAngle to get the elevation of the SkySat C3 satellite above Earth’s horizon.

    • FromRange ()
    • FromGroundSampleDistance ()
  4. Click OK to accept your changes and to close the Properties Browser.

Analyzing the Ground Sampling Distance (GSD)

Generate a Dynamic Display to analyze the GSD.

  1. Confirm or set the scenario animation time to 30 Jul 2017 15:32:11.507.
  2. Select the GSD () report in My Styles () in the Styles frame.
  3. Select the Dynamic Display/Strip Chart option in the Generate As list.
  4. Click Generate....

    5. The STK software computes a GSD of 0.97 meters for this access.

Updating the detector pitch

Adjust the sensor's optical resolution by decreasing the detector pitch.

  1. Return to SKYSAT_EOIR's () Properties ().
  2. Select the Basic - Resolution page.
  3. Enter 5.3 um in the Detector Pitch field in the Focus Constants frame.
  4. Click Apply to accept your change and to keep the Properties Browser open.

Examining the changes in the report

Review the effects of decreasing the detector pitch on your access.

  1. Return to the GSD Dynamic Display.
  2. Review the data in the display.

The STK application now computes a GSD of 0.79 meters for this access. If you refer to the SkySat Sensor parameters linked earlier in the lesson, you find yourself in close range to the values reported by Planet Labs.

Updating the sensor's properties

Update the related detector parameters to represent a more-accurate effective detector pitch for your EOIR sensor scene.

  1. Return to SKYSAT_EOIR's () Properties ().
  2. Select the Basic - Definition page.
  3. Select the Spatial tab.
  4. Enter the following in the Related Detector Parameters frame:
    5. Option Value
    Horiz Pixel Pitch 5.3 (um)
    Vertical Pixel Pitch 5.3 (um)
  5. Click OK to accept your changes and to close the Properties Browser.

Verifying the GSD computation

In addition to inspecting the pixels in the sensor scene, the EOIR capability also computes a relevant value in its "EOIR Sensor to Target Metrics" data providers. The target is selected by the EOIR Configuration toolbar button().

Creating a new custom Ground Sampling Distance report

Create a new report to display Ground Sampling Distance (GSD) data.

  1. Bring the Report & Graph Manager back to the front.
  2. Open the Object Type drop-down list.
  3. Select Sensor.
  4. Select Satellite/SKYSAT-C3_41774/SKYSAT_EOIR () in the Object type list.
  5. Click Create new report style () in the Styles toolbar.
  6. Name the report EOIR Metrics.
  7. Select the Enter key.

Selecting a data provider and elements

Build your custom EOIR metrics report with select EOIR Sensor to Target Metrics data providers.

  1. Select the Content page when the Properties Browser opens.
  2. Expand () EOIR Sensor to Target Metrics () in the Data Provider list.
  3. Move () the following elements from the EOIR Sensor to Target Metrics data providers:
    • Time ()
    • Range to Target ()
    • Geometric instantaneous field of view footprint ()
  4. Click OK to accept your changes and to close the Properties Browser.

Analyzing the GSD

Generate a Dynamic Display to analyze GSD.

  1. Select the EOIR Metrics () report in My Styles ().
  2. Select the Dynamic Display/Strip Chart option in the Generate As list.
  3. Click Generate....

    4. EOIR sensor-to-target metrics compute more slowly than many other data providers. Be careful not to create a standard report using the default object time period and time step, as this would require significant computational time. The Dynamic Display computes these values only for the current time step.

    The STK application computes a Geometric Instantaneous field of view footprint of 0.615 at the time of the stored view. Assuming a square pixel, the square root of 0.615 is 0.784 m, in the range of the GSD values reported by Planet Labs.

  4. When finished, close all reports and dynamic displays, the Report & Graph Manager and the Access Tool.

Examining the impact of atmospheric models

Next, run some stress tests on the system. All of your work up to this point has not used any atmospheric models. You can verify this by looking in the EOIR Configuration's () Atmosphere definition page.

The EOIR capability includes a Simple Atmosphere and a MODTRAN Atmosphere model. Both models take the same input parameters: Aerosol models, Visibility, and Humidity. Begin by seeing what impact atmospheric modeling will have on the specific scene you have been recreating. To do this, you should use the most appropriate Aerosol, Visibility, and Humidity models and values for the time and location being imaged. Historical humidity and visibility information for Boston can be found online, for example here, https://www.wunderground.com/history/daily/us/ma/boston/KBOS/date/2017-7-30. The Visibility was 10 miles (16 km) and Humidity was 55%. Boston Logan International Airport is on Boston Harbor, so the Urban Aerosol Model is probably most appropriate.

You will generate two more scenes: one using the Simple Atmosphere model, and one using MODTRAN Atmosphere model. Then, you will compare these two scenes with the one previously created that did not use an atmospheric model.

Setting the Simple Atmosphere model

Set the atmospheric properties for the generated sensor scene to use the Simple Atmosphere model.

  1. Select SKYSAT_EOIR () in the Object Browser.
  2. Click EOIR Configuration... () on the EOIR toolbar.
  3. Click Atmosphere and Textures... in the EOIR Configuration dialog box.
  4. Select the Atmosphere page in when the EOIR Atmosphere, Clouds, and Texture Maps dialog box opens.
  5. Select the Simple Atmosphere option in the Modes frame.
  6. Set the following in the Parameters frame:
    7. Option Value
    Aerosol Models Urban
    Visibility 16.0 (km)
    Humidity 55 (%)
  7. Click OK to accept your changes and to close the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  8. Click OK to close the EOIR Configuration dialog box.
  9. Look at your regenerated sensor scene.
  10. If you closed your sensor scene, click EOIR Sensor Scene... () in the EOIR toolbar to generate an image.

EOIR sensor scene with Simple atmosphere

Setting the MODTRAN Atmosphere model

Set the atmospheric properties for the generated sensor scene to use the MODTRAN Atmosphere model. MODTRAN is a community standard, and the MODTRAN-derived atmosphere model is one of the highest-fidelity atmospheric models available with the EOIR capability.

The MODTRAN database samples, as well as the compression and interpolation methodology, maintain both a low absolute error and a low percentage error for transmission, thermal path radiance, and reflected path radiance calculations. For applications requiring higher fidelity than these error tolerances, the atmospheric database methodology might not be appropriate and the results may introduce a greater amount of uncertainty than the desired results. Therefore, you should take caution when using this model. You can contact AGI support to learn more about the applicability and limitations of using this model.

  1. Select SKYSAT_EOIR () sensor in the Object Browser.
  2. Click EOIR Configuration... () on the EOIR toolbar.
  3. Click Atmosphere and Textures... in the EOIR Configuration dialog box.
  4. Select the Atmosphere page in the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  5. Select the MODTRAN Atmosphere option in the Modes frame.
  6. Set the following in the Parameters frame:
    7. Option Value
    Aerosol Models Urban
    Visibility 16.0 (km)
    Humidity 55 (%)
  7. Click OK to accept your changes and to close the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  8. Click OK to close the EOIR Configuration dialog box.
  9. Note the increase in processing time when using MODTRAN.
  10. Review your regenerated sensor scene.

EOIR sensor scene with MODTRAN atmosphere model

Examining other atmospheric settings on your own

On your own, examine the image quality with the other atmospheric settings. Here are some examples to try:

  1. Try Simple Atmosphere test cases:
    2. Option Test Cases A Test Cases B Test Cases C Test Cases D
    Atmosphere Modes Simple Atmosphere Simple Atmosphere Simple Atmosphere Simple Atmosphere
    Aerosol Models Urban Urban Rural Rural
    Visibility 5 km, 10 km, 15 km, 30 km 10 km 5 km, 10 km, 15 km, 30 km 10 km
    Humidity 55% 15%, 50%, 85% 55% 15%, 50%, 85%
  2. Try MODTRAN Atmosphere test cases:
    3. Option Test Cases A Test Cases B Test Cases C Test Cases D
    Atmosphere Modes MODTRAN Atmosphere MODTRAN Atmosphere MODTRAN Atmosphere MODTRAN Atmosphere
    Aerosol Models Urban Urban Rural Rural
    Visibility 5 km, 10 km, 15 km, 30 km 10 km 5 km, 10 km, 15 km, 30 km 10 km
    Humidity 55% 15%, 50%, 85% 55% 15%, 50%, 85%
  3. Determine if atmospheric conditions change the answers to the above questions about detection or identification.
  4. Examine the image quality with a different elevation angle.
  5. You took your images at an elevation angle of about 77 deg. Consider what your scene would look like at a lower elevation angle.

EOIR sensor imaging under a full Moon

Thus far, you have imaged your simulated 737 during the daytime. Next, you will find some nighttime imaging opportunities under a full Moon.

You will make some modifications to the scenario, including extending the scenario time, adding constraints, modifying the 737 model's properties, and creating stored views.

Updating the scenario analysis period

Extend your scenario's analysis period to 30 days, a little more than a full lunar cycle.

  1. Open Ground_Imaging_EOIR's () Properties ().
  2. Select the Basic - Time page when the Properties Browser opens.
  3. Enter + 30 days in the Stop field in the Analysis Period frame.
  4. Click OK to accept your change and to close the Properties Browser.

Be patient. You data will be recomputed for 30 days and it'll take some time to complete.

Modifying the target aircraft's waypoints

Make the aircraft static for the full range of lighting conditions.

  1. Open 737's () Properties ().
  2. Select the Basic - Route page when the Properties Browser opens.
  3. Enter 30 Aug 2017 00:00:00 UTCG in the second waypoint's Time cell.

Recall that you extended the scenario analysis stop time to 30 days, so you are making a similar update here.

Adding a Moon vector

By creating a Moon vector, you will be later able to add constraints specific to certain illumination conditions provided by the moon.

  1. Select the 3D Graphics - Vector page.
  2. Select the Vectors tab.
  3. Click Add....
  4. Select 737 () in the object tree of the Add Components dialog box.
  5. Select Moon () in the Components for: 737 list.
  6. Click OK to close the Add Components dialog box.
  7. Click OK to accept your changes and to close the Properties Browser.

Calculating the lunar phase

Calculate the lunar phase using the vector geometry.

Creating an new angle

Use the Analysis Workbench capability to create a new angle.

  1. Click Analysis Workbench... () in the STK toolbar.
  2. Select the Vector Geometry tab in the Analysis Workbench.
  3. Open the Filter by drop-down list.
  4. Select Primary Central Bodies.
  5. Select Moon () in the Objects list.
  6. Click Create new Angle () in the Vector Geometry toolbar.

Specifying the vectors

The new angle will calculate the angle between the Moon-Earth vector and the Moon-Sun vector.

  1. Use the default Between Vectors Type in the Add Geometry Component dialog box.
  2. Enter Phase in the Name field.
  3. Check the following default setting and change them if required:
    4. Option Value
    From Vector Moon Earth
    To Vector Moon Sun
  4. Click OK to close the Add Geometry Component dialog box.
  5. Click Closeto close the Analysis Workbench.

Constraining Access

Use Access Constraints to find a good imaging opportunity for the SkySat C3 satellite with a nearly full Moon above the horizon.

Setting Sun constraints

Set Sun constraints so access can only occur when the Sun is five (5) degrees or more below the horizon.

  1. Open Boston's () Properties ().
  2. Select the Constraints - Active page when the Properties Browser opens.
  3. Click Add new constraints () in the Active Constraints toolbar.
  4. Select Sun Elevation Angle in the Constraint Name list in the Select Constraints to Add dialog box.
  5. Click Add.
  6. Click Close to close the Select Constraints to Add dialog box.
  7. Clear the Min check box in the Sun Elevation Angle frame in the Constraint Properties list.
  8. Select the Max check box.
  9. Enter -5 deg in the Max field.

    10. The Sun must be 5 deg or more below the horizon. This takes into account ambient light even though the Sun is below the horizon.

  10. Click Apply to accept your change and to keep the Properties Browser open.

Setting Lunar constraints

Set Moon constraints so access can only occur when the Moon is one (1) degree or more above the horizon.

  1. Click Add new constraints () in the Active Constraints toolbar.
  2. Select Lunar Elevation Angle in the Constraint Name list in the Select Constraints to Add dialog box.
  3. Click Add.
  4. Click Close to close the Select Constraints to Add dialog box.
  5. Enter 1 deg in the Min field of the Lunar Elevation Angle frame in the Constraint Properties frame.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Adding an Analysis Workbench angle constraint

You will set a 15 deg maximum phase angle constraint. First, you need to add the Analysis Workbench angle constraint name to the Active Constraints list.

  1. Click Add new constraints () in the Active Constraints toolbar.
  2. Clear All Categories in the Filter by Category list in the Select Constraints to Add dialog box.
  3. Select the Analysis Workbench (AWB) check box.
  4. Select AWB Angle in the Constraint Name list in the Select Constraints to Add dialog box.
  5. Click Add.
  6. Click Close to close the Select Constraints to Add dialog box.

Setting a phase angle constraint

Set a 15 deg max phase angle constraint.

  1. Click Select.. in the AWB Angle frame in Constraints Properties section.
  2. Open the Filter by drop-down list in the Select Angle dialog box.
  3. Select Primary Central Bodies.
  4. Select Moon () in the Objects list.
  5. Select Phase () in the Angles for: Moon list.
  6. Click OK to close the Select Angle dialog box.
  7. Clear the Min check box in the AWB Angle frame.
  8. Select the Max check box.
  9. Enter 15 deg in the Max field.

    10. This constrains the highest allowable phase angle to 15 deg. A phase angle of 0 deg would correspond to a perfectly "full" Moon.

  10. Click Apply to accept your changes and to keep the Properties Browser open.

Computing access elevation angles from Boston

Examine the max elevation angle when the SkySat C3 satellite has access to Boston.

Finding the access angle

Generate an AER report using the Access tool.

  1. Right-click on Boston () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select SKYSAT-C3_41774 () in the Associated Objects list of the Access Tool.
  4. Select the Specify Time Period option in the Compute Time Period frame.
  5. Click AER... in the Reports frame.
  6. Scroll to the bottom of the report.
  7. Locate Global Statistics.
  8. Examine the Max Elevation statistic to find the highest Max Elevation near 88.5 deg at approximately 8 Aug 2017 02:38:09 UTCG.

Setting the scenario's animation time to the time of maximum elevation

Set your scenario's animation time to produce a sensor view when the SkySat C3 satellite is nearly directly overhead.

  1. Right-click on the Max Elevation time in the report.
  2. Select Time in the shortcut menu.
  3. Select Set Animation Time in the Time submenu.

Creating a stored view

Create a stored view at this animation time called Full Moon Access. Having a stored view makes it easy to get back to the specific time at which you want to render your image.

  1. Bring the 3D Graphics window to the front.
  2. Zoom to Boston.
  3. Click Stored Views () in the 3D Graphics toolbar.
  4. Click New in the Stored View: 3D Graphics 1 - Earth dialog box.
  5. Change the View Name to Full Moon Access.
  6. Click OK to close the Stored View: 3D Graphics 1 - Earth dialog box.
  7. Using the 3D Graphics window, verify that the SkySat C3 satellite is directly overhead, the Sun is below the horizon, and the Moon is above the horizon and appears full from Boston.

You can verify all of the above by looking at the Sun and Moon vectors and SKYSAT_EOIR's field of view beaming straight down from the SkySat C3 satellite.

Full moon access

Turning off the EOIR atmosphere configuration

Remove atmosphere from the EOIR configuration.

  1. Select SKYSAT_EOIR () in the Object Browser.
  2. Click EOIR Configuration... () on the EOIR toolbar.
  3. Click Atmosphere and Textures... in the EOIR Configuration dialog box.
  4. Select the Atmosphere page in the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  5. Select the Atmosphere Off option in the Modes frame.
  6. Click OK to close the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  7. Click OK to close the EOIR Configuration dialog box.

Generating a sensor scene

Generate a sensor scene with the new constraints.

  1. Zoom to Boston ().
  2. Click Orient North () in the 3D Graphics window toolbar.
  3. Zoom out slightly in the 3D Graphics window.
  4. Select SKYSAT_EOIR () in the Object Browser.
  5. Click EOIR Sensor Scene... () in the EOIR toolbar to generate an image.

Full moon sensor scene

With a full Moon, typically there is enough light for the human eye to very easily make out distinct shapes and shadows and identify common objects. The EOIR sensor scene doesn’t look like much, does it? The settings used for this image are the default values:

  • Noise Equivalent Radiance: 1e-15 @ 100 milliseconds
  • Saturation Equivalent Irradiance: 3e-12 @ 100 milliseconds
  • Dynamic Range: 3000
  • Integration Time: 100 milliseconds

The sensor thus is either not sensitive enough or is simply not getting enough photons. You will need to make some adjustments to the sensitivity and integration time to get a usable image.

Modifying the sensor's sensitivity

Adjust the sensitivity (noise floor, or lowest detectable signal) and dynamic range (ratio of lowest to highest detectable signal) to compensate. To do this, you’ll need to determine the highest and lowest signal values in your scene, essentially the radiance values in the brightest and darkest pixels. Since there isn’t much to see in your sensor scene, tell the EOIR capability to render the Radiometric Input to the sensor — all the information the EOIR capability computes about all the photons — right before it hits your detector array.

Modeling radiometric input

Change SKYSAT_EOIR 's processing level to radiometric input.

  1. Open SKYSAT_EOIR's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Scroll to the Processing Level field below the band-specific tabs in the Definition panel.
  4. Open the Processing Level drop-down list.
  5. Select Radiometric Input.
  6. Click Apply to accept your change and to keep the Properties Browser open.

Examining the sensor scene

Review the changes to the sensor scene.

  1. Bring the EOIR sensor scene to the front.
  2. Examine the image.

    3. Radiometric EOIR sensor scene

Finding the inband radiance values

Use the scene pick information in the EOIR Scene Visual Details dialog box to find the total band radiance coming reaching the EOIR sensor of the darkest and brightest parts of the sensor scene.

  1. Right-click anywhere in the EOIR Sensor Scene window.
  2. Select Details… in the shortcut menu.
  3. Click the darkest part of the scene, somewhere on the shaded side of the target aircraft fuselage.
  4. Take note of the Inband Radiance value.
  5. Repeat the previous step, but for the brightest part of the scene, somewhere on the moonlit side of the fuselage.

Updating the sensor's radiometric properties

Update the EOIR sensor's radiometric properties based on what you just observed. The radiometric values may be different due to user settings.

  1. Return to SKYSAT_EOIR's () Properties ().
  2. Select the Radiometric tab.
  3. Select the Radiance option in the Units for Saturation and Sensitivity frame.

    4. This will match the units of the values you just measured.

  4. Enter 1.8e-12 in the EquivalentValue cell in the Sensitivity frame.

    5. This is the dark pixel value. This is the lowest detectable signal above the noise floor for a 100 millisecond integration time.

  5. Enter 5.8e-9 in the EquivalentValue cell in the Dynamic Range frame.

    6. This is the bright pixel value. This is the maximum detectable signal before the array is saturated.

    New radiometric settings

  6. Open the Processing Level drop-down list.
  7. Select Sensor Output.
  8. Click Apply to accept your changes and to keep the Properties Browser open.

Examining the sensor scene

Review the changes to the sensor scene.

  1. Bring the EOIR sensor scene to the front.
  2. Examine the image.

EOIR Sensor scene with New radiometric settings

The image is no longer just static, and you can make out some straight lines and brighter and darker regions. With a little difficulty, you may be able to recognize the building and some items on the tarmac. But it’s still not a very useable image.

Getting more photons

If you’ve ever tried to do any astrophotography, and image a dim object like a nebula or galaxy, you’ll know there are really only two ways to get more photons: you can increase the aperture or increase the exposure time. Your aperture is fixed at 35 cm based on specifications, but you can change the exposure time.

Updating the exposure time

Increase the exposure time of the sensor scene.

  1. Return to SKYSAT_EOIR's () Properties ().
  2. Enter 500 (msec) in the Integration Time field in the Current Integration Time, Sensitivity, and Dynamic Range frame.
  3. Click Apply to accept your change and to keep the Properties Browser open.

Examining the sensor scene

Review the changes to the sensor scene.

  1. Bring the sensor scene to the front.
  2. Examine the image.

EOIR sensor scene with Increased photons

This is much better! The aircraft fuselage is clearly visible, and the wings are even somewhat discernible.

Adding more realism

So far, so good, but see what happens when you add a bit more realism to the simulation. You'll do this by simulating quantization. This is especially important for low-light situations because you may be getting only a very few photons from the scene. This is an analog-to-digital converter; before, you may have been simulating half a photon, which would let you see artificially exaggerated resolution within the scene. With quantization on, you either get an electron out of your detector array, or you don’t, due to the quantum mechanical nature of photons and electrons.

Simulating quantization

Update the EOIR sensor to simulate quantization.

  1. Return to SKYSAT_EOIR's () Properties ().
  2. Select the Simulate Quantization check box.

    3. Turning on Quantization simulates the analog-to-digital conversion at the detector.

  3. Click OK to accept your changes and to close the Properties Browser.

Examining the sensor scene

Review your changes in the EOIR sensor scene.

  1. Bring the sensor scene to the front.
  2. Examine the results.

quantization simulation

Setting the atmosphere model

Set the atmosphere model to represent very good "seeing" conditions. Recall that for the daytime scene, adding an atmospheric model at high elevations had a minimal impact.

  1. Select SKYSAT_EOIR () sensor in the Object Browser.
  2. Click EOIR Configuration... () on the EOIR toolbar.
  3. Click Atmosphere and Textures... in the EOIR Configuration dialog box.
  4. Select the Atmosphere page in the EOIR Atmosphere, Clouds, and Texture Maps dialog box.
  5. Select the Simple Atmosphere option in the Modes frame.
  6. Set the following in the Parameters frame:
    7. Option Value
    Aerosol Models Urban
    Visibility 30 (km)
    Humidity 15 (%)
  7. Click OK to close the EOIR Atmosphere, Clouds, and Texture maps dialog box.
  8. Click OK to close the EOIR Configuration dialog box.

Examining the sensor scene

Review your changes in the EOIR sensor scene.

  1. Bring the sensor scene to the front.
  2. Examine the results.

radiometric EOIR sensor scene with atmosphere

The image quality is noticeably degraded; this is understandable, given your low-light and atmospheric settings. As you can see, through an iterative process, you're able to add realism to your scene.

Saving your work

Close out your scenario and save york work.

  1. When finished, close any reports, EOIR sensor scenes, and tools that are still open.
  2. Save () your work.

Summary

Using the EOIR modeling capabilities, you were able to create a realistic model of a ground imaging sensor. You began with default settings and iterated to a detailed setup. Using a sample ground image, you performed in-scene calibrations of the sensor and target model. Once it was set up, you were able to stress test the sensor's capability, such as comparing poor collection conditions to nominal conditions and varying lighting conditions.

On your own

You can adjust the scene further to balance the gray scale through the Radiometric settings. On your own, use the workflow you've learned to tweak the image. Explore the effects of atmospheric conditions on the sensor scene. If you have your own ground image, calculate the GSD by measuring a known object (such as street width) in both pixels and distance, as defined in the STK software. Use your results to calibrate the EOIR sensor. You examined a nighttime scene with a full moon; now reexamine the scenario but with a new Moon overhead.