F-16 radar display - focus on target

Transcription

1 Wild Tuna 1 Group: Wild Tuna Rathakan Leepraphantkul Nur Gadima Vita Ivanova Guo Yang Alireza Mahzoon F-16 radar display - focus on target Introduction Our group chose to investigate the radar display of F-16 A/B, the AN/APG-66 radar. The contact person is Group Captain Chanon Mungthaya who is a former Royal Thai Air Force pilot with 1500 hours logged on the F-16 and is currently a Defense and Air Force attaché at the Thai embassy in Sweden. The radar system uses some sort of raster scan display to produce a graphical representation of the objects detected by the radar. In this study we will analyze the air-to-air modes of the radar and the specific scenario - focus on target visualization. 1. System description The F-16 A/B uses the AN/APG-66 as its fire control radar. It is Pulse-Doppler radar. A series of short radio frequencies are pulsed out and the partial reflection of the said frequencies are then captured by the radar using Pulse-Doppler signal processing which uses the Doppler effect to calculate the distance of object based on the reflected waves. The AN/APG-66 radar is also multi-modal. It contains modes for air-to-air weapons delivery, ground-based modes for air-toground based weapons delivery and a weather mode for navigation (see figures below). Figure 1: Joystick and the grey nub used for moving the cursor on the radar screen and selecting the target

2 Wild Tuna 2 Figure 2: F16A Cockpit Figure 3: F16A radar screen

3 Wild Tuna 3 The modes for the radar for air-to-air combat allow the pilot to scan the airspace and lock on to a fighter-plane-sized target and track it, from up to 50 kilometers away, while continuously scanning. The radar can also enter ACM, air combat maneuver, mode which automatically locks and tracks are target within a smaller cone of detection. The primary missiles that the radar provides information for are the AIM-7 Sparrow, the AIM-9 Sidewinder and the AIM-120 AMRAAM. The Sparrow is a semi-active radar guided missile and relies on the radar s tracking to hit the target. The Sidewinder is an IR-guided, or heat-seeking, missile that is not directly guided by the radar. The radar aligns the Sidewinder s seeker head in the same direction of the target for lowered target acquisition time and accuracy. The AMRAAM is a beyond visual range fire-and-forget missile with active guidance. The missile has two stages, the first stage relying on the fire control radar to allow the missile to plot an intercept and give course corrections. It is in the second stage that the AMRAAM s own guidance system is used to guide itself to the target. 2. The method We chose the large-scale systematic approach because of careful and detailed documentation. In a user centered design we will look at three models: the role, the task and the content model. The user role model express needs, interests, expectations, behaviors and responsibilities between user and the system. Here we also plan to look at user role description and relations between the roles (for that purpose we will use user role model - form S6). The radar system is complex so we will narrow down the main user needs and divide the specific tasks. We are planning to have several meetings with the pilot in order to talk about different scenarios and specify use cases. We will identify the most significant use case problems, main expectations from the user and possible system responses. The final step is working on sketches and designing prototype. 2.2.Task modeling with the use cases The main focus of the method is to describe what the user is doing and what he/she tries to do. According to Larry L.Constantine suggestions in the book Software for use, A Practical Guide to the Models and Methods of User Centred Design (2006) the first step is to learn the roles that user will play in the relation with the system being built. The second step is to understand and model the nature of the work that must be supported within those roles. The aim of the task modeling is to build a joint understanding of the work and how to support it. The method to represent structure of the tasks and work is use case. According to Ivar Jacobson (1992) definition, a use case is in object-oriented software engineering, a narrative description of interaction between a user -in some role- and some system. We assume, that we will divide use case into two parts: the user action model, which shows what the user does, and the system response model, which shows what the system does in response (Wirfs-Brock, 1993). This form clearly divides the responsibilities and interests of the user from those of the system and its developers. The first step to identify use cases is to use role model. It means that we are looking for users needs and intentions in each use case by asking questions like - what are user in this role try to

4 Wild Tuna 4 accomplish and fulfill this role, what do user need to able to do, what capabilities are required to support whatever users in this role need to accomplish and so on. The second step is to name essential use cases. They should be in the language of user and we should have the same interpretation from the phrase in the user case. Here we focus on simplifying, generalizing and common understanding gathering (119). After that we will work on sketches part and prototype building. 3. Documentation of work and users your system supports 3.1.Specific use cases We came up with three possible user cases from the first interview (appendix 2) with the pilot. The intention of the pilot for doing the tasks are 1) Recognizing a target in the air 2) Dropping a bomb 3) Focus on a target. In the following table we analyzed the tasks into user actions and system responses in the form of essential use cases. 1. Recognize a target in the air User Action Turn on transceiver Looking at the information Recognize the target System Response Broadcasting ID Getting signal from the target Identifying the target Show information 2. Dropping a bomb User Action Looking on the location of target Input the information about the target Push the button System Response Generate location on the radar Calculate release point Line up the plane Release the bomb

5 Wild Tuna 5 3. Focus on a target User Action Finding the relevant information Identify the target Communicate the identified target System Response Supplying the relevant information Lock on the identified target Communicate to user that target is locked According to our user need we chose to investigate the last user task - focus on target. Here we want to find answers to several questions: - how can pilot move a cursor on the screen? - how can pilot select a target on the screen? - what are the relevant information that should be displayed on a screen? - how should communication process and feedback from system happen? The main requirements from pilot to use a radar for selecting the target is: - identify the target, - determine the distance to the target, - know which target is currently selected Problems in the existing system - in the old system, there is no possibility to show who is locked on who - the old system is monochrome. The problem with monochrome screens is to display more information on a screen ( some new symbology needs to be design) 3.2.Environment description The cockpit environment is relatively well shielded and allows the pilot to operate under high G conditions, high altitude and supersonic speed. To this end, the pilot wears a flight suit that helps blood circulation during high G manoeuvres in addition to a special breathing technique that allows him to maintain consciousness. As for other safety measures, the pilot is strapped to his seat by a 4-point harness, or a seat belt with 4 points of contact, and wears a helmet with a visor to protect his eyes. An oxygen is also provided for high altitude flight. The helmet also has a built in radio to allow communication. The pilot also wears gloves. The space in the cockpit is limited to allow only one person to sit comfortably inside. Additionally, the cockpit and its canopy is designed to allow for the greatest amount of visibility from inside. 3.3.User profile and task (User role model - form S6) See the appendix 1 Form S6 for detailed information.

6 Wild Tuna 6 4. Lo-fi prototype (paper and pen sketches) Our further sketches are based on display information visualization without the modification in existing selection buttons. According to user thoughts, the existing buttons functions and location is logical enough and there is no need for correction. The pilot could select the target just using the button left(<) and right(>) and the system will catch the target automatically based on their location. We think it s the best way to help the pilot to lock the target compared with using 4 buttons(left,right,up and down). In this way the pilot needs to focus on the right target. Before sketching we listed all the physical properties that are displayed on a screen. It helped us to take into account all the necessary information for sketching. Buttons: Change radar range Change between radar modes Show the radar warning receiver Weapon selection Things to display on screen (AA Mode): Contact - information that show in radar as dot Friendly or Enemy - visualization in blue or red Altitude of contact - how high of the ground plane is flying Bearing of contact - the direction of travel Azimuth of contact - a vector from the observer to a point of interest onto a reference plane Distance of contact - how far a contact is from the plane (usually in Nautical Miles) Speed of contact - how fast a contact is flying Type of aircraft - doesn t look likely Radar range information - the current radar range and cone of detection perhaps Sketches In the first sketch - track while scan mode, allows to track a target whilst scanning for enemies. Note the positions of the information on the screen. Weapon information is rather crude, only to give a cursory indication of how to engage. A full weapon s system screen is already present elsewhere. Target information displays speed, altitude and heading of the track. The radar s current range and mode settings are displayed in the top corners.

7 Wild Tuna 7 Sketch nr.1 This is the normal scanning mode. The contacts outside the radar cone is from an external system (friendly aircraft and radar sites). Sketch nr.2 Sketch nr.3

8 Wild Tuna 8 In a sketch nr. 3 the [ ] is the target selection cursor. It is moved by a nub on the joystick. It was not necessary to change the target selection cursor, as it is already present in the old system. Other sketch nr.4 shows all the necessary information in two steps. In the first step pilot can see all the enemies and friends in a triangular shape, number and different colors. Triangular colored edge shows the front of aircraft. Selection will be green square with dots. On background pilot can choose whether to see or not to see a navigation map. When target is locked on a display enemy aircraft symbol changes the color and the shape of square. The system will also show the distance to the locked aircraft. In a case there will be unidentified object on a screen, there appear round symbol. Sketch nr.4

9 Wild Tuna 9 5.The prototype We choose not to change the existing target selection, because according to pilot opinion, it is already fast solution. The process of selection happens with the help of joystick, by moving it with the thumb left or right. The first target of selection will be the target closer from pilot (in this case the plane nr.3). Figure 4: Selection of target When the number of allies is more than the number of enemies pilot can see the line between the aircrafts which shows the status of locking. The information about the aircraft is in the up right corner of the screen. Figure 5:The number of enemies is less than the number of allies

10 Wild Tuna 10 Using the gray nub on joystick pilot can move the cursor on the screen. When pilot put the cursor on the target, green brackets appears on the screen which shows the target that supposed to be locked. In figure 3 the enemies are shown in red and the allies in blue, going by the NATO convention. Figure 6: Selecting the target for locking Pilot can lock on the target by pressing the red button on joystick. The locked target is shown in figure 4 by yellow square around it. Figure 7: The low range Mode

11 Wild Tuna 11 In figure 8 you can see the high range mode. In this situation there are lots of aircraft on the screen. In this mode lines between the target are not shown. Maximum distance 180 km is shown on radar. Figure 8: The high range Mode In the second interview (appendix 2),the pilot suggested removing all unnecessary information. Additionally, he explained that though the color coding may be convenient, we should be mindful of nighttime conditions and to not employ too many colors that could lead to confusion. Figure 9 is the final version of the prototype for selecting the target. In the figure 9 the aircrafts, which are locked, are shown in pink. The lines between the aircrafts, numbers and information about the selected target are removed in this version. In the final version of locking on the target,all unnecessary information are removed as well. The two circles inside the radar are for the pilot to be able to estimate the range of the contacts on screen without having to look up a number. The bullseye is a pre-defined reference point that is used to determine the position of an object. Here our prototype displays 016 and 189, which is the heading and distance respectively. This was not changed from the original system.

12 Wild Tuna 12 Figure 9:selecting the target 6.Conclusion The main advantages of this solution allows for the display of additional information without detracting from the overall qualities of a radar system that grants the pilot situational awareness. The main challenge of the solution was to determine which information was relevant and important enough to be displayed on the radar screen. Reference Constantine, L.L. (2006). Software for use, A Practical Guide to the Models and Methods of User Centred Design, ACM Press: New York Jacobson, I., Christerson, M., Jonsson, P., Övergaard, G. (1992). Object Oriented Software Engineering: A Use Case Driven Approach. Reading, Mass: Addision-Wesley Wirfs-Brock, R. (1993). Designing Scenarios: Making the Case for a Use Case for a Use Case Framework. Smalltalk Report, November-December

13 Appendix 1-S6 form Wild Tuna 13

14 Wild Tuna 14 Appendix 2-Interview Session 1 Actions (Questions about what a pilot has to do) 1) What is standard procedure when an unknown contact/bogey appears on radar? Use of external surveillance system. They are always identification from these external systems. But it is visual confirmation. Intercept by flying abeam. Rock the wing. Ask for permission to shoot. Immediate self-defense. Commercial airlines use IFF. IFF squawks provide information. IFF is Identification Friend or Foe. 2) What is standard procedure when an enemy contact/bandit appears on radar? info is like a doubt on a screen (symbol in colors-my square box symbol). Datalink from AWACS. Square box on radar. Must manually remember who is who on on-board radar. Use of reference point, distance and bearing to identify the square boxes on the radar. 3) What are possible reasons to switch to ground mode? How? Use for drop the bomb on a target with a distinctive return signature. Use a button. Guess what the mountain looks like on the radar. When the radar sweeps to the ground. The impact changes return image. Light and darkness. Tilt the radar to determine the shape of the target. Targeting pods/external sensors. Can penetrate moisture and ground better. 4) What are possible reasons to switch to weather mode? How? Change pulse, PRF, Pulse Radio Frequency. Changes the radar the characteristics to show shapes you want to see. Uses a knobs. 5) At the moment how free you are as pilot to make a decisions based on information displayed in a radar? Is your reaction based on system information or otherwise? Who says the last word? No. Only gives information. Gives it to the Fire Control System. Displays whether in-range or not. 6) How do you handle multiple contacts, enemy or otherwise, in a radar display? The radar can lock onto one target but still display information. 7) How do you handle multiple modes for instance handle enemy in air and ground at the same time? No. Cannot handle more than one mode. Can only handle one target on lock-on mode. Visibility (Questions about the display etc.) 8) Are there some problems identifying things on radar? In the old system, the heading of the target is hard to identify. The newer system displays a bit more information. The more information is given in a shorter span of time, it is easier to understand to the pilot, adding situational awareness.

15 Wild Tuna 15 9) What are the common difficulties new pilots face when using the radar system? What are your personal experiences during training or in flight? Difficulties in old system. Physical switch is a problem. Has to look down to the radar and use his fingers to try to lock on. Throttle switch, or the control stick requires familiar. Uses simulations but cannot simulate gravitational forces in air combat manoeuvres. Typical problem. Physiological problem. If the design in the switch is easier to remember, this can be mitigated. 10) How important is it for you to be able to visualize some specific information in a radar system? Are the symbols representative or easily interpreted? Symbology is easy to understand. Uses triangles, circles and squares. Good for glances. Very important. You don t have the luxury of time. 11) How important is it for you to have a description of a contact in the radar system? Some numbers are displayed when the target is selected. Requires lock-on, from someone and information. In the newer everything it will display everything. Old system is square boxes. Important for situational awareness. 12) Is being visible to the the enemy when the radar on is a concern? Important when you turn on your radar. Emission of radio waves can be captured. Know when to turn on radar. Data-link information is best from a friendly aircraft. Higher PRF = more accuracy, can say that you are targeting the RWR of the enemy. 13) Are there delays in displaying information on the radar? And when you track objects? There can be a delay. Impossible to have no delay. Near real-time. Delay is not a big problem, inherent to the aircraft design. This is not a concern at all. Near light speed. Future Systems (for the latest fighter aircraft radar systems, look up AESA Radar ) 14) Think of current radar technologies compared to the past ones. Which values are important or are a must have function? The radar should be easy to understand, contributes to situational awareness. How the brain interprets symbols and how it changes it into situational. How fast can your brain recognise the airspace situation. Analog or digital clock metaphor, digital clock is precise at a glance, but not how long that you have. 15) Can you define your ideal radar? What are possible features? Which are important? Is your radar a decision support tool? Do you want it to interpret data for you or just show all the raw data? What about other pilots? Without touching the radar, it will give all the data that is needed. AI controlled radar. Only important information is needed. You want to have it prioritise. More information = complications. Customisation to suit users. Maybe the symbols, layout or something that handles or displays the information. Grid display or radar range lines. 16) What are your expectations for future passive and active sensors for military aircraft? These passive sensors are radar information from your friend. IR sensors/flir or RWR. Right now radar is the best.

16 Wild Tuna 16 17) What is your opinion on radar systems that allow you to see but remain undetected? Example: AESA Radars Better, faster scan and smarter when emitting. Not keen on improvement. 18)Future radar - is it more like decision support tool, tool for interpretation of data, just raw data place, computer interpreted version about the objects or... Radar system embedded in your eye? Ocular implants. Understand everything. Extends visuals. Displays information that you can t see. Other things Situational awareness is important. Data-link with friends. Who targets what, etc. If the system displays such life would be easier. Familiarity, such as positions of indicators and such. Managing their tasks, must prioritise. Mitigated What are some of the most important things a pilot must have? Situational awareness

17 Wild Tuna 17 Appendix 3-Interview Session 2 1)How do you identify ground targets? Picture of the target on the return of the radar. Must learn of the return of the radar. If the ground target is fixed target, like a building or bridge, and you have an aerial photo and you study it and compare it to the radar screen. If it is a moving target like a tank or truck, the return will change. At a longer distance, when you know the location from GPS or something, the radar can zoom in to that point. In some cases we need to use the radar, especially at night without IR or NVG. The radar itself can sharpen the image of the return. Radar is only used for weapons targeting if the target is close enough to be identified by visual. 2)How do you determine your location? There is GPS and INS. Separate from the radar. 3)How can pilot move the cursor on the screen? On the control stick, two axes nub. Thumb. 4)How can pilot can select a target on the screen? Acquire the target by pressing down on the nub. 5)When you select targets on the throttle, do you push another button? No. It doesn t happen too much when you try to select the target but move the switch instead. Its not that sensitive. 6)What should pilot do to release a bomb? Requires intelligence, you input the coordinates into the aircraft computer. The computer generates the location on the radar. Then go through the process of identifying the target. Requires fine-tuning. Find the angle of approach and compare to what you see on the radar. Another button close to the nub. 7)How can pilot line up the plane for this purpose? Angle of approach isn t too necessary. But it is part of a plan. The aircraft computer can calculate your weapons release point. Weapons will not release unless the pilot physically flies the aircraft to meet the weapons release criteria as determined flight computer.

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