Radar as a Device for Tracking Different Objects - Essay Example

Waquas Mehmood Radar 101 March 19, 2006 ELECTRONIC POSITIONING SYSTEM (MARINE NAVIGATIONAL RADAR) Introduction RADAR is a device which is used totrack different objects in space as well as on the ground. These objects are generally air planes and ships. The RADAR that is used to track ships and other marine vessels is known as a Marine Navigational RADAR. This RADAR not only detects these vessels but also guides them for their movements in the water. In marine industry the RADAR is used to mainly accomplish the following things:- Detect an object It can detect an object (a vessel) moving in the waters or flying in the air from a distance. Sometimes it can also give the information about the type of the vessel which it has tracked. Detect the speed It can also detect the speed with which the object is moving towards or away from you. Weather report It also updates the mariners with weather conditions. Besides this RADAR (a sophisticated one) can also detect objects deep into the sea water or inside the ground. In addition to its use in marine industry a RADAR is also widely used at airports for tracking and guiding planes, by police for detecting the speed of vehicles, by NASA to map the earth. Basic principle The basic principle of working of RADAR is the concept of Echo and Doppler Shift. Echo is the reflection of a wave from a solid surface. When a wave is thrust upon an object it strikes it and returns back. This effect can be observed when a person shouts in a valley. The sound waves travel to the nearby mountains and get reflected. The person thus hears back his own voice. The time taken by the sound waves to return back depends upon the distance between the persons and the mountains. The similar concept is applied in RADAR. Here radio waves are emitted by the RADAR which travel in all directions. If an object comes in the way of these waves they get reflected back with the speed of light and detected by the RADAR. By knowing the time elapsed between sending and receiving back the waves, the position of the object can be determined by calculating the distance the wave has travelled. Now in order to calculate the speed of an object the concept of Doppler shift plays its role. When a wave is reflected by a moving object its nature depends upon the movement of that object. If the object is moving towards the source of the wave, then the pitch of the wave will be higher than if it is moving away from it. This can be observed in case of a car blowing its horn. When a moving car approaches a person the horn seems to be louder and when it moves away it become s somewhat fainter. Knowing the pitch of the sound wave the speed of the car can be detected. This principle is applied in case of RADAR where a radio wave is used instead of a sound wave. The pitch of the reflected radio wave determines the speed and the direction of motion of the object. Combining the Echo and Doppler Shift, we can exactly determine the position, speed and direction of motion of an object in the sea with the help of a Navigational RADAR. Components of Marine Navigational RADAR There are five main components of a Marine Navigational RADAR. Transmitter Modulator Antenna Receiver Indicator 1. Transmitter A transmitter is a device which transmits radio waves into the air. These waves are generated inside the RADAR. 2. Modulator It allows waves to be omitted as pulses (Integrated Publishing, n.d.). 3. Antenna An antenna is used to give direction to the radio waves being transmitted. These waves are sent as 'beams'. The antenna is always in rotating condition so that the whole of the area is covered. 4. Receiver It receives back the reflected waves from the objects and converts the information into usable data (Integrated Publishing, n.d.). 5. Indicator It is a device on which the received information is plotted. It shows the position of the object in the form of a mark on a screen. The standard indicator that is used mainly is known as Plan Position Indicator (PPI). It presents your ship in the centre and shows the rotation of the RADAR antenna in the form of a sweep indicated by a bright line. (Integrated Publishing, n.d.). The sweep rotates 360 degrees and a bright spot appears on the screen whenever an object is detected. How it works The working of marine navigational RADAR is explained in the step by step procedure shown below:- The RADAR turns 'on' its transmitter and shoots out a burst of radio waves lasting about a microsecond. The transmitter is then turned 'off' and receiver turned 'on'. The receiver detects an echo (if any) coming from an object. The RADAR measures the time taken by the echo to arrive and the Doppler shift. By measuring the time of echo and Doppler shift the RADAR detects the position and speed of the objects. Figure 8-31. PPI presentation. PPI Display Interpretation The scale of PPI can be adjusted according to the details required to be viewed. It can be decreased to view larger area and increased to view greater details.Range is either measured in yards or nautical miles from the centre of the scope representing your own ship to the target objectindicated. Beam width, pulse length, mechanical adjustment, and interpretation are some of the factors affecting the accuracy of RADAR. Because of beam width distortion, radar bearings are usually less accurate than radar ranges. Shorelines alsoappear on PPIin a manner similar to the representations on the electronic charts; however, the scale of area inPPI is lesser than that of charts.With increased practice one can judge exactly the position and the movements of different objects on PPI. How to Obtain a RADAR Bearing and Range Bearings The PPI comes with a 'bearing cursor' and a 'range strobe'. The bearing cursor, like the sweep, appears as a bright line and can be manually rotated through 360. Bearing information can be derived by rotating the cursor to the centre of the target. Bearing dial then directly reads the target bearing. On gyro-equipped ships (and most ships having radars are so equipped), the radar has a gyro input and bearings obtained from it are true . If a gyro failure occurs the radar presentation automatically re-orients to a relative picture and relative bearings may be taken from the PPI (Integrated Publishing, n.d.). Ranges The cursor has a bright spot which represents the range strobe. As the range crank is turned clockwise, the strobe moves out from the centre. Range is obtained by placing the strobe on the leading edge (edge closest to the centre of the PPI) of the target (Integrated Publishing, n.d.). The range dials then give the information about target range either in yards or in miles depending on the chosen system of measurement. How to Plot RADAR Fixes Following steps should be properly followed to plot a radar fix. Figure above shows how to obtain a fix using three radar ranges on a PPI. 1. Location ofthe distance scales or the latitude scale near the approximate location on the chart. 2. Measurement of the distance on the scale with a compass. 3. Location of the charted navigational point used for the range. 4. Placement of the sharp point of the compass on the chart where the range had been takenand draw an arc in the vicinity of DR position. 5. Repeat steps 2 to4 for all the ranges obtained. 6. Location of the area where the lines of position (arcs) all cross each other. 7. Label the radar fix by putting a small mark around the intersection of the ranges, with the time of the fix noted besides the symbol. RADAR Integration Systems Automatic identification system (AIS) is a shipboard broadcast system based on latest technology where an AIS acts just like a transponder operating in VHF maritime band (USCG Navigation Center, 2005). It is a device used for tracking other ships offshore thereby identifying and exchanging information with them. Targets from the radar and from AIS can simultaneously be plotted on an electronic chart (Strenge, Rainer, & Bober, Stefan, 2004). Thus signals from both radar and AIS can be acquired and depending on the requirement, the information can be collected from either of the two sources or from both of them. The positioning of the target on the electronic chart is carried out by DGPS positioning system and in addition through radar map matching process that was developed by Stuttgart University (Strenge, Rainer, & Bober, Stefan, 2004). The ships have large electronic chart displays (ECDIS) installed on them on which AIS data and radar information from other ships is superimposed. These large displays have nowadays been replaced by small and portable computers. Present and future of Marine Navigational Radar RADAR is nowadays being confined to airports only. In navigation AIS is replacing RADAR completely. Presently AIS is used in integration with RADAR but day by day improvements in it, the simplicity of operation and varied functions make it completely independent for operation. In the near future RADAR will not be associated with marine industry. AIS-ECDIS system has numerous advantages over traditional systems such as radar. One of such advantages is the collision avoidance by knowing the speed, heading and direction of turn, which cannot be provided by radar (Motz , Florian,& Widdel, Heino,& Oei, Parry,& Kiat, Lim Wee, n.d.) . On suspecting a collision risk, the ECDIS can obtain the parameters of the target after identifying it and establish communication by transmitting a message (safety message) through AIS if the target does not respond to normal communication (Andrianov, Mikhail, n.d.). This message will be prompted on the screen of the target ship. The AIS-ECDIS system is extremely helpful in limited visibility conditions as AIS also provides information about motion status of the target (Andrianov, Mikhail, n.d.). Apart from target data AIS-ECDIS system also provides the navigator with weather information. It also provides data about the real time tidal height, tidal stream, etc. This system also allows the navigators to monitor the routes as well as the targets simultaneously as the ECDIS displays both of them (Andrianov, Mikhail, n.d.). References USCG Navigation Center. (July 12, 2005). How AIS Works. Retrieved February 27, 2006, from < http://www.navcen.uscg.gov/enav/ais/how_AIS_works.htm > Motz , Florian,& Widdel, Heino,& Oei, Parry,& Kiat, Lim Wee. (n.d.).Evaluation and Design of AIS Target Information on ECDIS. Retrieved February 27, 2006, from < http://www.ecdisnow.org/ecdisconf03pdf/Presentations%20-%20Session4/ Evaluation%20design%20-AIS-FlorianMotz.pdf > Andrianov, Mikhail (n.d.). Transas AIS and ECDIS integration. Retrieved February 28, 2006, from < www.thedigitalship.com/DSmagazine/ds%20april%202003/ transas%20ais%20and%20ecdis%20integration.doc > Integrated publishing (n.d.) Navigational Radar. Retrieved March 18, 2006, from < www.tpub.com/content/administration/ 14220/css/14220_251.htm > Howstuff works.com (n.d.) How Radar Works. Retrieved March 18, 2006, from < http://www.howstuffworks.com/radar.htm> Read More