Chapter 5 Introduction Introduction This chapter presents the basic features and working principles of major navigational instruments used onboard, which is crucial to the safe and efficient navigation on the sea. This chapter presents the basic features and working principles of major navigational instruments used onboard, which is crucial to the safe and efficient navigation on the sea. It should be borne in mind that no single navigational aid should ever be relied upon as the exclusive method for navigating your vessel. The navigator is responsible for checking all aids available to confirm his position. Electronic aids are meant to assist the navigator, not replace him. Various navigational aids should be used in a combined operation on a vessel to ensure the safety of navigation. The contents: Radar & Radar Plotting Radar & Radar Plotting Magnetic Compass & Gyro Magnetic Compass & Gyro GPS, VDR, AIS, GPS, VDR, AIS, Part I Radar I. Vocabulary Study radio detection and ranging (radar) crucial / kru l / adj. exclusive /iks klu:siv/ adj. transmitter n. pulse /p ls / n. pulse length / pulse width / pulse duration pulse durationpulse duration modulate / m djuleit/ vt. e.g. In marine navigation application, the radar signal is pulse modulated. e.g. The cabin is for the exclusive use of Master. Speed is crucial to our success. Radar is crucial to the safe navigation at sea. low average power low average power Plan Position Indicator PPI Plan Position Indicator PPI radial adj. radial adj. radial line radial line synchronize vt. synchronization n. synchronize vt. synchronization n. luminescent / lu:mi nesnt / adj. luminescent / lu:mi nesnt / adj. luminescent tube luminescent tube proportional adj. proportional adj. be proportional to be proportional to Payment will be proportional to the amount of work done. On a PPI, a targets actual range is proportional to its echos distance from the scopes center. e.g. If there is any difference between the readings of master compass and its repeater, make sure to synchronize them. Strong signals can be provided with low average power synchronization The plan position indicator (PPI), is the most common type of radar display. The radar antenna is usually represented in the center of the display, so the distance from it and height above ground can be drawn as concentric circles. As the radar antenna rotates, a radial line on the PPI sweeps in synchronization with it about the center point. A detection is indicated by a brightening of the screen at the bearing and range of the return. Because of a luminescent tube face coating, the glow continues after the radial line rotates past the target. relating to rays of light, beams of light cursor n. moveable cursor cursor n. moveable cursor heading-upward presentation heading-upward presentation north-upward presentation north-upward presentation unstabilized adj. stabilized unstabilized adj. stabilized orientation / :rien tei n / n. orientation / :rien tei n / n. (position relative to points of the compass) (position relative to points of the compass) e.g. In this unstabilized presentation, the orientation changes as the ship changes heading e.g. In the stabilized north-upward presentation, gyro north is always at the top of the scope. A ship's head up (un-stabilized) display has the ship's heading marker fixed at 0 at the top of the screen All targets fixed or moving move relative to the ship's position in the centre of the screen and the heading marker As the ship moves through the water fixed targets appear to track down the screen on a reciprocal heading at the speed the ship is moving and when the ship alters course, targets appear to rotate in the opposite direction to that of the ship so targets appear to move on the radar screen while the ship's heading remains fixed A moveable cursor helps to measure ranges and bearings. II. Passage Reading Warming-up Questions: 1. Which measurement of radar is more accurate, bearing or distance? 2. What is the PRR of a radar signal? 3. Can you name radar components? 4. What is the most common type of radar display? 5. Which presentation is stabilized, heading- upward or north-upward? Passage one Passage one General Characteristics General Characteristics Radar determines distance to an object by measuring the time required for a radio signal to travel from a transmitter to an object and return. Since most radars use directional antenna, they can also determine an object s bearing. However, a radar s bearing measurement will be less accurate than its distance measurement. Understanding this concept is crucial to ensuring the optimal employment of the radar for safe navigation. Radar determines distance to an object by measuring the time required for a radio signal to travel from a transmitter to an object and return. Since most radars use directional antenna, they can also determine an object s bearing. However, a radar s bearing measurement will be less accurate than its distance measurement. Understanding this concept is crucial to ensuring the optimal employment of the radar for safe navigation. A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. All practical antennas are at least somewhat directional. Radar determines distance to an object [by measuring the time (required for a radio signal to travel from a transmitter to an object and return.)] The distance from a ship to an object can be calculated by counting the cycle time taken by a radar signal. 1.1 Signal Characteristics In most marine navigation applications, the radar signal is pulse modulated. Signals are generated by a timing circuit so that energy leaves the antenna in very short pulses. When transmitting, the antenna is connected to the transmitter but not the receiver. As soon as the pulse leaves, an electronic switch disconnects the antenna from the transmitter and connects it to the receiver. Another pulse is not transmitted until after the preceding one has had time to travel to the most distant target within range and return. Since the interval between pulses is long compared with the length of a pulse, strong signals can be provided with low average power. The duration or length of a single pulse is called pulse length, pulse duration, or pulse width. This pulse emission sequence repeats a great many times, perhaps 1,000 per second. This rate defines the pulse repetition rate (PRR). The returned pulses are displayed on an indicator screen. In most marine navigation applications, the radar signal is pulse modulated. Signals are generated by a timing circuit so that energy leaves the antenna in very short pulses. When transmitting, the antenna is connected to the transmitter but not the receiver. As soon as the pulse leaves, an electronic switch disconnects the antenna from the transmitter and connects it to the receiver. Another pulse is not transmitted until after the preceding one has had time to travel to the most distant target within range and return. Since the interval between pulses is long compared with the length of a pulse, strong signals can be provided with low average power. The duration or length of a single pulse is called pulse length, pulse duration, or pulse width. This pulse emission sequence repeats a great many times, perhaps 1,000 per second. This rate defines the pulse repetition rate (PRR). The returned pulses are displayed on an indicator screen.returned pulses returned pulses so that Since interval 1.2. The Display The most common type of radar display used in the navigation is the plan position indicator (PPI). On a PPI, the sweep starts at the center of the display and moves outward along a radial line rotating in synchronization with the antenna. A detection is indicated by a brightening of the display screen at the bearing and range of the return. Because of a luminescent tube face coating, the glow continues after the trace rotates past the target. bearing range In synchronization with e.g. Set the clock in synchronization with the internet. On a PPI, a target s actual range is proportional to its echo s distance from the scope s center. A moveable cursor helps to measure ranges and bearings. In the heading-upward presentation, which indicates relative bearings, the top of the scope represents the direction of the ship s head. In this unstabilized presentation, the orientation changes as the ship changes heading. In the stabilized north-upward presentation, gyro north is always at the top of the scope. scope = radar display screen head-up cg(cursor gyro) mode, course-up mode, north-up true motion Language points to remember: Radar, transmitter, receiver, antenna, screen(scope), sweep, bearing, range Radar, transmitter, receiver, antenna, screen(scope), sweep, bearing, range timing circuit timing circuit be crucial to be crucial to exclusive exclusive pulse modulated pulse modulated Pulse length/pulse duration/pulse width Pulse length/pulse duration/pulse width PRR---pulse repetition rate PRR---pulse repetition rate PPI---plan position indicator PPI---plan position indicator in synchronization with in synchronization with be proportional to be proportional to moveable cursor moveable cursor heading-upward presentation; north-upward presentation heading-upward presentation; north-upward presentation stabilized; unstabilized stabilized; unstabilized / / Home Work: Be capable of using key words and expressions in this lesson Be capable of using key words and expressions in this lesson Be able to express the ideas about radar in English Be able to express the ideas about radar in English Look up the words which are new to you in the dictionary and read the text globally for main ideas Look up the words which are new to you in the dictionary and read the text globally for main ideas