Sensor Design in STK

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

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 STK Capabilities:

  • STK Pro

Problem Statement

You are using STK for preliminary analysis of a future air traffic control radar system that will track aircraft flying through an airport's control zone. You are also interested in determining if a low earth orbit (LEO) satellite can take pictures of a ground site in the training area.

Solution

Use STK to model a scenario that allows you to consider and compare all of your system options. Simulate an aircraft traveling in the vicinity of the airport and use a Sensor object to simulate the radar's field of view. Determine which portion of the aircraft's route can be tracked by the various radars. Model a LEO satellite and use a Sensor object to model the satellite's camera. Determine if the LEO can take pictures of a ground site in the training area.

Video Guidance

Watch the following video. Then follow the steps below, which incorporate the systems and missions you work on (sample inputs provided).

Create a Scenario

Start by creating a scenario.

  1. Click the Create a Scenario button.
  2. Enter the following in the New Scenario Wizard:
    3. Option Value
    Name SensorIntro
    Location C:\Users\<username>\Documents\STK 12\
    Start 1 Jul 2016 16:00:00.000 UTCG (Change this if you plan to take the L3 quiz at the end of this tutorial; if not, model the default Start time)
    End + 1 day
  3. When you finish, click OK.
  4. When the scenario loads, click Save (). A folder with the same name as your scenario is created for you in the location specified above.
  5. Verify the scenario name and location and click Save.
  6. If you plan to complete the L3 quiz at the end of the tutorial, turn off the Terrain Server.Closed
    1. Right-click on the scenario () and open the Properties ().
    2. Select the Basic - Terrain page.
    3. Disable the Use terrain for analysis option.
    4. Click OK to apply changes and dismiss the Properties Browser.

Save Often!

Create the Airport Radar Site

Start by creating the radar site.

  1. Using the Insert STK Objects tool, insert a Place () object using the Insert Default method.
  2. In the Object Browser, rename the Place object "RadarSite."
  3. Open RadarSite's () properties ().
  4. On the Basic - Definition page, make the following changes:
    5. Option Value
    Latitude 38.8006 deg
    Longitude -104.6784 deg
    Height Above Ground: 50 ft

    The additional 50 feet of altitude above the ground is to simulate the height of the radar antenna.

  5. Click OK.
  6. In the Object Browser, right click on RadarSite () and select Zoom To.
  7. Bring the 3D Graphics window to the front.
  8. Use your left and right mouse buttons to obtain situational awareness of where your radar site is located.

Create Waypoints

The test aircraft will fly between two waypoints. For the test, you will insert two additional Place objects using the City Database.

  1. Using the Insert STK Objects tool, insert a Place () object using the From City Database method ().
  2. In the Search Standard Object Data window, type Cheyenne in the Name: field.
  3. Click the Search button.
  4. In the Results: list, select Cheyenne Wyoming and click the Insert button.
  5. Return to the Name: field and type Raton.
  6. Click the Search button.
  7. In the Results: list, select Raton New Mexico and click the Insert button.
  8. Close the Search Standard Object Data window.
  9. Bring the 2D Graphics window to the front.
  10. Locate your Place objects and zoom in until you are centered on RadarSite with Cheyenne and Raton visible at the top and bottom of your map.

Place Object Locations

Model the Test Flight Aircraft

The aircraft performing the test flight will fly from Raton to Cheyenne. Since this is a preliminary analysis of the radar system, you can use the Great Arc Propagator.

You can also use the mouse to enter waypoints directly in the 2D Graphics window. Simply click anywhere in the 2D Graphics window to add new waypoints (latitude/longitude values) in the waypoint table. However, you must use the Route page to enter altitude, speed, and turn radius values. When you use the mouse to define a great arc route, it is recommended that you specify the altitude and speed for the first point before you create the second point, so that the initial route information become the default for all additional points.

  1. Using the Insert STK Objects tool, insert an Aircraft () object using the Insert Default method.
  2. In the Object Browser, rename the Aircraft object "TestFlight".
  3. Open TestFlight's () properties ().
    1. If you plan to complete the L3 quiz at the end of the tutorial, follow these steps.Closed
      1. On the Basic - Route page, click Insert Point twice to add two waypoints.
      2. Manually enter the waypoint values in the table:
        3. Waypoint Latitude Longitude
        1 36.9034 deg -104.439 deg
        2 41.14 deg -104.82 deg
      3. Click OK.
    2. If you do not plan to complete the L3 quiz at the end of this tutorial, follow the steps below to create the aircraft route:Closed
      1. Return to the 2D Graphics window.
      2. Click on the Place marker () for Raton.
      3. Click on the place marker () for Cheyenne.

        4. Be careful! Each time you click on the 2D Graphics window, you will create a new waypoint. Ensure you only click on the map where you want a waypoint.

      4. Return to TestFlight's () properties ().
      5. On the Basic - Route page, you will see your waypoints in the waypoints table.
      6. Click OK.
  4. Return to the 2D Graphics window and make sure you can see the entire flight route of TestFlight.
  5. In the Animation toolbar, use the Decrease Time Step () button to decrease the time step to 3.00 sec.
  6. Click the Start () button and observe your aircraft as it flies from Raton to Cheyenne.
  7. When done, click the Reset () button.

Model a LEO Satellite

Add a Satellite object to the scenario. You need to analyze when the satellite's camera (Sensor object) can take pictures of Raton.

  1. Using the Insert STK Objects tool, insert a Satellite () object using the Orbit Wizard () method.
  2. Make the following changes to the Orbit Wizard:
    3. Option Value
    Type: Circular
    Satellite ImageSat
    Inclination: 60 deg
    Altitude: 800 km
    RAAN: 20 deg
  3. Click OK.

Sensor Design

Use Sensor objects to model the various components that make up the detection system.

Fixed Sensors On Moving Objects

The default Sensor Object that STK creates when you introduce a Sensor object is a simple conic sensor with a 45 degree cone angle. The default view is fixed at zero (0) degrees azimuth and 90 degrees elevation which is nadir pointing. When a Sensor object is attached to a moving object it points with respect to the parent object’s reference frame. A fixed sensor is always pointing in a fixed direction with respect to its parent object.

  1. Using the Insert STK Objects tool, insert a Sensor () object using the Insert Default method.
  2. When the Select Object window opens, select ImageSat ().
  3. Click OK.
  4. In the Object Browser, rename the Sensor object "Fixed".
  5. Bring the 3D Graphics window to the front.
  6. In the Object Browser, right click on ImageSat () and select Zoom To.
  7. Use your left and right mouse buttons to get a good view of ImageSat and the Sensor object's field of view and the locations of your ground sites.

Targeted

Access

The first analysis to perform is to check, whether or not, if Fixed will see Raton during your analysis period (24 hours).

  1. In the Object Browser, right click on Fixed () and select Access.
  2. When the Access Tool () opens, select Raton in the Associated Objects list.
  3. In the Reports field, click the Access... button. During the 24 hour exercise, Raton will be in Fixed's field of view (FOV) a couple of times.
  4. Note the Total Duration time in the report.
  5. Close the report and the Access Tool.
  6. In the Timeline View, click Add Time Components ().
  7. Select the ImageSat Fixed sensor to Raton access on the left and Access Intervals on the right.
  8. Click Apply and OK to add the intervals to the Timeline View and close the Select Timeline Component window.

    9. Access Intervals are automatically added to the Timeline. If you are using a version older than STK 11.3, you will need to add them manually to the Timeline.

Moving Sensors On Moving Objects

When you attached Fixed, you used the default fixed pointing type. Many satellites can gimbal their sensors to track other objects (stationary and moving). STK provides a variety of Sensor object definition and pointing types that allow you to model this type of movement.

  1. Using the Insert STK Objects tool, insert a Sensor () object using the Insert Default method.
  2. When the Select Object window opens, select ImageSat ().
  3. Click OK.
  4. In the Object Browser, rename the Sensor object "Targeted."
  5. Open Targeted's () properties ().
  6. On the Basic - Definition page, ensure the Sensor Type is set to Simple Conic, and change the Cone Half Angle: to 5 deg.
  7. Browse to the Basic - Pointing page.
  8. Change Pointing Type: to Targeted.
  9. Select Raton () in the Available Targets list and move () it to the Assigned Targets list by click the right arrow.
  10. Click OK.

Targeted Access

Compare the access time for Targeted to Fixed.

  1. In the Object Browser, right click on Targeted () and select Access ().
  2. In the Associated Objects list, select Raton ().
  3. In the Reports field, click the Access... button.
  4. Note the Total Duration time.
  5. In the Timeline View, click Add Time Components ().
  6. Select the ImageSat Targeted sensor to Raton access on the left and Access Intervals on the right.
  7. Click Apply and OK to add the intervals to the Timeline View and close the Select Timeline Component window.

How does the access time for Targeted compare to Fixed? When you target the Sensor object, it locks onto the assigned target using the Sensor objects boresight. It's a point-to-point access. You're using the line-of-site constraint. Therefore, Targeted accesses Raton from horizon to horizon. The field of view for Fixed had to pass over Raton. So, the access time for Targeted is much higher.

View in 3D

  1. Bring the 3D Graphics window to the front.
  2. If required, Zoom To ImageSat ().
  3. Use your left and right mouse buttons to get a good view of ImageSat and the Sensor object's field of view and the locations of your ground sites.
  4. Using the Animation toolbar, click the Start () button to view any accesses that occur.

    5. Targeted Access

  5. When you are finished, reset the scenario.

Remove Accesses

  1. Close the report and the Access Tool.
  2. Open the Analysis menu and select Remove All Accesses.
  3. In the Object Browser, disable Fixed and Targeted ().

Your preliminary analysis shows that both cameras attached to ImageSat will have opportunities to take pictures of Raton.

Fixed Sensors On Stationary Objects

You are now ready to model the radar field of view for RadarSite. In the previous examples, you attached sensors to moving objects to model a fixed camera field of view and a camera that can gimbal. Sensors can also be used to model instruments attached to stationary objects, such as Facility, Place and Target objects. Fixed Sensor objects attached to stationary objects also point with respect to the parent object’s reference frame. Since stationary objects never change position or direction, a fixed Sensor object will always point in a fixed direction with respect to the parent object.

  1. Using the Insert STK Objects tool, insert a Sensor () object using the Insert Default method.
  2. When the Select Object window opens, select RadarSite ().
  3. Click OK.
  4. In the Object Browser, rename the Sensor object "RadarDome."
  5. Open RadarDome's () properties ().
  6. On the Basic - Definition page, in the Simple Conic field, change the Cone Half Angle to 90 deg.
  7. Click Apply.

Add Constraints

The Sensor object created here is similar to the fixed Sensor object attached to ImageSat. However, it has a larger field-of-view, and instead of pointing straight down this one points straight up from RadarSite. It has an up looking field-of-view that covers everything above RadarSite. That’s not very realistic. Let’s limit its range so that the field-of-view spans a constrained area mimicking the field-of-view of the actual air traffic control radar.

  1. Browse to the Constraints - Basic page.
  2. In the Range field, change Max: to 150 km.
  3. Click Apply.
  4. Bring the 3D Graphics window to the front.
  5. Zoom To RadarSite ().
  6. Using your mouse, zoom out far enough so that you can see RadarDome's () full field-of-view.

Radar Dome Field-of-View

2D Projection properties

2D Graphics Projection properties for Sensor objects control the display of sensor projection graphics in the 2D Graphics window. Sensor objects attached to Facility, Place and Target objects differ in their display behavior from those attached to vehicles. The intersections of Sensor objects with the Earth are displayed during animation. The Extension Distances option indicates whether the Sensor object’s field-of-view crossings at specified distances are computed and displayed in the 2D Graphics window. When the Sensor object display is set to project to the range constraint, STK projects the Sensor object's field-of-view to the maximum range specified on the Basic Constraints properties page for the Facility, Place, or Target object.

  1. Bring the 2D Graphics window to the front.
  2. Locate your Place objects and zoom in until you are centered on RadarSite with Cheyenne and Raton visible at the top and bottom of your map. At this point, there is no indication of RadarDome's field-of-view.
  3. Return to RadarDome's () properties (), and browse to the 2D Graphics - Projection page.
  4. In the Extension Distances field, enable Use.
  5. Open the pull down menu for Project to: and select Use Range Constraint.
  6. Click OK.
  7. Return to the 2D Graphics window.

2D Graphics Projection

You can see the range constraint of 150 km projecting out from RadarDome.

Access

There's no doubt visually, that RadarDome can access TestFlight. For the purposes of the analysis, we need to know for how long.

  1. In the Object Browser, right click on RadarDome () and select Access ().
  2. In the Access Tool, select TestFlight () in the Associated Objects list.
  3. In the Reports field, click the Access... button.

    4. This is pretty straight forward. The access report tells you when and for how long you have access to TestFlight. For briefing purposes, you might want to change the duration from seconds to minutes.

  4. At the top of the access report, click the Report Units icon.
  5. When the Units: Access window opens, ensure Time Dimension is selected.
  6. In the New Unit list, select Minutes (min) and click OK.

Save as Quick Report

Sometimes it's useful to change report units. You can save the report inside or outside of STK. Later, you will be sending this scenario to someone who does not have STK. Therefore, you can create a Quick Report. If you make any property changes to the objects being used in the access calculation, the changes will appear in the Quick Report. Therefore, if you want to compare numbers, sometimes it's a good idea to save reports externally. For the purposes of this scenario, there's no need. Should you decide to do this, you can use the Save as .csv icon.

  1. At the top of the access report, click the Save as quick report () button.
  2. Close the report.
  3. At the top of STK, click the Quick Report Manager ().

    4. All of your Quick Reports will be available by simply opening the Quick Report Manager. You can rename your reports, add descriptions, delete them, etc.

  4. Select the Access Quick Report and click the Create button.
  5. Return to the Quick Report Manager and click OK.
  6. Return to the Access report.

Zoom To Access Start Time

You can use the report to quickly jump to the time in the scenario when RadarDome first accesses TestFlight.

  1. In the report, place your cursor on the access start time.
  2. Right click and select Start Time.
  3. When the sub-menu window appears, select Set Animation Time.
  4. Bring the 3D Graphics window to the front.
  5. Zoom To TestFlight.

Generate an AER Report

This gives you a good idea of the location of TestFlight when it first enters RadarDome's field-of-view. You'll recall, that the maximum distance constraint for RadarDome is 150 km. Also, an air traffic controller might need to know TestFlight's azimuth and elevation data.

  1. Return to the Access Tool.
  2. Make sure RadarDome is selected as the Access For: object and TestFlight () is selected in the Associated Objects list.
  3. In the Reports field, click the AER... button.

    4. This report not only tells you what time RadarDome accesses TestFlight, but it reports the azimuth, elevation, and range.

  4. When you are finished, close both reports and the Access Tool.
  5. At the top of STK, open the Analysis menu and select Remove All Access.
  6. In the Object Browser, disable RadarDome ().
  7. Reset () the scenario.

Moving Sensors On Stationary Objects

Often, the dome created by a Sensor object is used to model a field-of-view, or the overall volume of space in which radar looks. The radar itself often sweeps or scans through that field-of-view in a repeating cycle. The area of space represented by such a scanning or spinning radar at any given instant is its field-of-view. Add another level of fidelity to your scenario and build a sweeping radar beam using a moving Sensor object.

  1. Using the Insert STK Objects tool, insert a Sensor () object using the Insert Default method.
  2. When the Select Object window opens, select RadarSite ().
  3. Click OK.
  4. In the Object Browser, rename the Sensor object "RadarSweep."

Define the Sensor's Properties

You want to simulate the actual field-of-view, antenna height, and spinning properties of your air traffic control radar. The antenna height was set when you increased RadarSite's altitude earlier in the scenario.

Often, the area created by a sensor’s projection is used to model a field-of-view. Rectangular sensor types are typically used for modeling the field-of-view of instruments such as push broom sensors and star trackers. Rectangular sensors are defined according to specified vertical and horizontal half-angles.

The radar that you are modeling sweeps or scans in a repeating cycle. Since the radar “scans”, the full range of the radar is not always covered. You can configure the sensor’s field-of-view to provide a visual representation of the area that the radar does cover at any given point in time.

  1. Open RadarSweep's () properties ().
  2. On the Basic - Definition page, make the following changes:
    3. Option Value
    Sensor Type: Rectangular
    Vertical Half Angle 5 deg
    Horizontal Half Angle 35 deg

The above configuration should create a wedge type field-of-view. Right now, that “wedge” is just pointing straight up. Set the properties of the Sensor object to rotate and point at 35 degrees elevation. You can set the spin axis elevation to 90 degrees for horizontal rotation with a cone angle of 55 degrees for a 35 degree elevation from the horizon.

Set the Pointing Properties

  1. Return to RadarSweep's () properties () and browse to the Basic - Pointing page and make the following changes:
    2. Option Value
    Pointing Type: Spinning
    Spin Rate (Revs/Min) 12
    Spin Axis Cone Angle 55 deg
  2. Click Apply.

Set the Constraints of the Sensor

Right now, the field-of-view extends beyond the limits of the actual radar because you haven’t constrained it. The airport’s primary surveillance radar has a range of 150 km. You need to limit the range of the radar to model that constraint.

  1. Return to RadarSweep's () properties () and browse to the Constraints - Basic page.
  2. In the Range field, enable Max: and change the value to 150 km.
  3. Click OK.
  4. Bring the 3D Graphics window to the front.
  5. Zoom to RadarSite ().
  6. Use your mouse and mouse buttons to get a good view the RadarSweep's () field-of-view.

    7. Rectangular Sensor

  7. In order to view the RadarSweep () in real time, click the X Real-time Animation Mode icon in the Animation toolbar.
  8. Click the Play () to play the scenario. You can see RadarSweep as it turns 12 revolutions a minute.
  9. When done, reset () the scenario.

Visual RadarSweep on the 2D Graphics Window

  1. Bring the 2D Graphics window to the front.
  2. Locate your Place objects and zoom in until you are centered on RadarSite with Cheyenne and Raton visible at the top and bottom of your map. At this point, there is no indication of RadarSweep's field-of-view.
  3. Return to RadarSweep's () properties (), and browse to the 2D Graphics - Projection page.
  4. In the Extension Distances field, enable Use.
  5. Open the pull down menu for Project to: and select Use Range Constraint.
  6. Click OK.
  7. Return to the 2D Graphics window.
  8. Play the scenario.
  9. When you are finished, reset the scenario.

Access

  1. In the Object Browser, right click on RadarSweep () and select Access ().
  2. In the Access Tool, select TestFlight () in the Associated Objects list.
  3. In the Graphs field, click the Access... button.

    4. This graph is interesting because it's graphing each instance RadarSweep accesses TestFlight while it is spinning. The Zoom In tool is embedded in the functionality of the mouse. If you left-click on your mouse and hover over an item on the graph, you can draw a box around the item and zoom closer. Try it.

  4. When finish, close the access graph and return to the Access Tool.
  5. Generate an Access report.

Stored Views

At times, you may desire to quickly return to a particular 3D Graphics view. For instance, you might use this scenario for a briefing. During the briefing, you desire to jump to the 3D Graphics window view of when TestFlight is first detected by RadarSweep. Store a view that depicts just that.

  1. In the report, place your cursor on the access start time.
  2. Right click and select Start Time.
  3. When the sub-menu window appears, select Set Animation Time.
  4. Bring the 3D Graphics window to the front.
  5. Zoom To RadarSite ().
  6. Mouse around until you are happy with the view.

    7. First Access

  7. Click Stored Views on the 3D Graphics toolbar.
  8. Click New.
  9. Rename View0 First Access.
  10. Click OK.
  11. Close the Access report.
  12. Go to the Animation toolbar and click the Reset button.
  13. In the 3D Graphics window toolbar, click the Home View icon.
  14. Click on the pull-down arrow of the Stored Views icon and select First Access.

Multiple Accesses

You can quickly create an access graph that shows all the Sensor objects at the same time. You can create the graph from TestFlight to the Sensor objects. The Sensor properties will still be used.

  1. Return to the Access Tool.
  2. At the Top of the Access Tool, click the Select Object... button.
  3. When the Select Object window opens, select TestFlight.
  4. Click OK.
  5. In the Associated Objects list, using your Ctrl key and mouse, select all four Sensor objects. You may need to expand ImageSat or RadarSite to see all the Sensor objects.
  6. Generate an Access graph.

Multiple Access Graph

This graph shows you when each Sensor object accesses TestFlight.

Save Your Work

  1. When you are finished, close the Access graph and the Access Tool.
  2. Save () your work.