Passage TwoPassage Two

Recognition of Recognition of

Unwanted EchoesUnwanted Echoes and and

Radar PlottingRadar Plotting

Lesson Components:Lesson Components:

• Questions for global readingQuestions for global reading

• Vocabulary studyVocabulary study

• TextText

• ReviewReview

• ExercisesExercises

• HomeworkHomework

Questions for global Questions for global reading:reading:• 1. What are Unwanted Echoes? How to recog1. What are Unwanted Echoes? How to recog

nize them?nize them?

• 2. What are the methods of fixing a vessel’s p2. What are the methods of fixing a vessel’s position in radar plotting? And on what conditioosition in radar plotting? And on what conditions do we use them respectively?ns do we use them respectively?

• 3. As for radar fixes by two simultaneous range3. As for radar fixes by two simultaneous ranges, which object should be measured first, the os, which object should be measured first, the one to the beam or directly ahead/astern?ne to the beam or directly ahead/astern?

I. Vocabulary study:I. Vocabulary study:• lobe /llobe /ləəuub/ b/ nn. . 瓣瓣 (( 天线方向天线方向 ) main lobe ) main lobe 主瓣 主瓣 side lobeside lobe 旁旁

瓣瓣• stack /stæk/ stack /stæk/ nn. . 烟囱 同义词：烟囱 同义词： funnelfunnel• shadow sector shadow sector 阴影扇形区阴影扇形区• gain gain nn. . 增益 增益 gain controlgain control 增益控制旋钮 增益控制旋钮 receiver gainreceiver gain 接收器接收器

增益增益• clutterclutter / / ̍̍kklʌtəlʌtə//nn. . 杂乱回波 杂乱回波 • anti-clutter (A/C) control anti-clutter (A/C) control 抗回波干扰旋钮 抗回波干扰旋钮 • A/C Sea (rain, snow) control A/C Sea (rain, snow) control 抗海浪抗海浪 (( 雨、雪雨、雪 )) 抑制旋钮抑制旋钮• multiple (multiple (reflectionreflection) echo ) echo 多次反射回波 多次反射回波 second-trace echoesecond-trace echoe

ss 二次扫描回波二次扫描回波• refraction /ri refraction /ri ̍̍fræk n/ ʃəfræk n/ ʃə nn. . 折射折射 super-refraction super-refraction 超折射超折射• subtend /ssubtend /səbəb ̍̍tend/ tend/ vtvt. . 对着 对着 be subtended bybe subtended by(( 边边 // 弧）对弧）对

（角）（角）• spoke /spspoke /spəəuk/ uk/ nn. . 同频干扰回波 同频干扰回波 spoking spoking nn. . 同频干扰回波现象同频干扰回波现象

1. subtended: 对向的 2. subtended angle: 对角 3. subtended chord: 对弦 例句 A radian is the angle subtended by an arc of a circle whose length is just equal to the radius. 国际单位制采用的平面角单位；（弧度）即长度等于半径的弧所对的圆心角。

• Ramark / Ramark / ̍̍reireimɑmɑ:k/ :k/ nn. radar marker. radar marker 的缩写 的缩写 Ramark signal Ramark signal 雷达方位信标雷达方位信标• CRTCRT 阴极射线管阴极射线管 cathode-ray tube cathode-ray tube 的缩写的缩写• simultaneous /simultaneous /,,simsimələl ̍̍teinjəsteinjəs/ / adjadj. . 同时发生的同时发生的• coincident /kcoincident /kəuəu ̍̍ insidəntinsidənt/ / adjadj. . 同时发生的，同时发生的，

一致的，符合的一致的，符合的• precludepreclude / /pripri ̍̍klu:d/klu:d/vtvt. . 妨碍，排除妨碍，排除• disparity /dis disparity /dis ̍̍pærit/pærit/nn. . 差异 同义词：差异 同义词： differendifferen

ceceA prior engagement will preclude me from coming. " 我因有约在先 , 不能来了。 "

Recognition of Recognition of Unwanted EchoesUnwanted Echoes

• The navigator must be able to recognize various The navigator must be able to recognize various abnormal abnormal echoes and effects on the radarscope so as not to be echoes and effects on the radarscope so as not to be confused by their presence. confused by their presence. Indirect Indirect or or false echoesfalse echoes are are caused by reflection of the main lobe of the radar beam caused by reflection of the main lobe of the radar beam off ship’s structures such as stacks and kingposts.off ship’s structures such as stacks and kingposts. When When such reflection does occur, the echo will return from a such reflection does occur, the echo will return from a radar contactradar contact to the antenna by the same indirect path. to the antenna by the same indirect path. Consequently, the echo will appear on the PPI at the Consequently, the echo will appear on the PPI at the bearing of the reflecting surface. Characteristics by which bearing of the reflecting surface. Characteristics by which indirect echoes may be recognized are summarized as indirect echoes may be recognized are summarized as follows:follows:

• 1) The indirect echoes will usually occur in 1) The indirect echoes will usually occur in shadow shadow sectorssectors..

• 2) 2) They are received on substantially constant bearings, They are received on substantially constant bearings, although the true bearing of the radar contact may although the true bearing of the radar contact may change appreciably.change appreciably.

• 3) They appear at the same ranges as the corresponding 3) They appear at the same ranges as the corresponding direct echoes.direct echoes.

• 4) When plotted, their movements are usually abnormal.4) When plotted, their movements are usually abnormal.• 5) Their shapes may indicate that they are not direct 5) Their shapes may indicate that they are not direct

echoes.echoes.

间接回波或者假回波是由于雷达波束的主瓣碰到了船上的间接回波或者假回波是由于雷达波束的主瓣碰到了船上的烟囱、大桅等建筑物所造成的反射带来的。烟囱、大桅等建筑物所造成的反射带来的。

雷达捕捉（对象）雷达捕捉（对象）

尽管雷达捕捉对象的真方位可能明显变化，但尽管雷达捕捉对象的真方位可能明显变化，但是间接回波的方位基本不变。是间接回波的方位基本不变。

• Side-lobe effectsSide-lobe effects are readily recognized in that they produce a are readily recognized in that they produce a series of echoes on each side of the main lobe echo at the series of echoes on each side of the main lobe echo at the same range as the latter.same range as the latter. Semicircles, or even complete Semicircles, or even complete circles, may be produced. Because of the low energy of the circles, may be produced. Because of the low energy of the side-lobes, these effects will normally occur only at the side-lobes, these effects will normally occur only at the shorter ranges. The effects may be minimized or eliminated shorter ranges. The effects may be minimized or eliminated through use of thethrough use of the gaingain and and anti-clutter controlsanti-clutter controls. . Slotted wave Slotted wave guide antennasguide antennas have largely eliminated the side-lobe have largely eliminated the side-lobe problem.problem.

• Multiple echoesMultiple echoes may occur when a strong echo is received may occur when a strong echo is received from another ship at close range. from another ship at close range. A second or third or more A second or third or more echoes may be observed on the radarscope at double, triple, echoes may be observed on the radarscope at double, triple, or other multiples of the actual range of the radar contact.or other multiples of the actual range of the radar contact. Multiple reflection echoes can be reduced and often removed Multiple reflection echoes can be reduced and often removed by decreasing the gain or properly adjusting the by decreasing the gain or properly adjusting the A/C Sea A/C Sea controlcontrol..

• Second-trace echoesSecond-trace echoes are echoes received from a contact at are echoes received from a contact at an actual range greater than the radar range setting.an actual range greater than the radar range setting. If an If an echo from a distant target is received after the following pulse echo from a distant target is received after the following pulse has been transmitted, the echo will appear on the radarscope has been transmitted, the echo will appear on the radarscope at the correct bearing but not at the true range. at the correct bearing but not at the true range. Second-trace Second-trace echoes are unusual, except under abnormal atmospheric echoes are unusual, except under abnormal atmospheric conditions, or conditions under which super-refraction is conditions, or conditions under which super-refraction is present.present. Second-trace echoes may be recognized through Second-trace echoes may be recognized through changes in their positions on the radarscope in changing the changes in their positions on the radarscope in changing the pulse repetition rate (PRR). pulse repetition rate (PRR).

• 旁瓣效应很容易识别，这是因为旁瓣在主瓣回波的两侧产生旁瓣效应很容易识别，这是因为旁瓣在主瓣回波的两侧产生了一连串与主瓣回波同等距离的回波。了一连串与主瓣回波同等距离的回波。

• in thatin that 引导原因状语从句，后面跟原因。引导原因状语从句，后面跟原因。

屏幕上，在雷达捕捉对象实际距离两倍、三倍、或几倍距离处可能屏幕上，在雷达捕捉对象实际距离两倍、三倍、或几倍距离处可能观察到二次、三次或多次回波。观察到二次、三次或多次回波。

二次扫描回波是指实际距离超出雷达距离设定档的目标回波。二次扫描回波是指实际距离超出雷达距离设定档的目标回波。

• 二次扫描回波很少见，除非是有异常的大气状况，或者出二次扫描回波很少见，除非是有异常的大气状况，或者出现超折射现象。现超折射现象。

• How a Slotted Waveguide Antenna WorksHow a Slotted Waveguide Antenna Works

This antenna, called A slotted waveguide, is a very This antenna, called A slotted waveguide, is a very low loss transmission line.low loss transmission line.It allows to propagate signals to a number of smalIt allows to propagate signals to a number of smaller antennas (slots). The signal is coupled into the ler antennas (slots). The signal is coupled into the waveguide with a simple coaxial probe, and as it twaveguide with a simple coaxial probe, and as it travels along the guide it traverses the slots. ravels along the guide it traverses the slots. Each of these slots allows a little of the energy to rEach of these slots allows a little of the energy to radiate. The slots are in a linear array pattern. The adiate. The slots are in a linear array pattern. The waveguide antenna transmits almost all of its enewaveguide antenna transmits almost all of its energy at the horizon, usually exactly where we want rgy at the horizon, usually exactly where we want it to go. Its exceptional directivity in the elevation it to go. Its exceptional directivity in the elevation plane gives it quite high power gain. Additionally, plane gives it quite high power gain. Additionally, unlike vertical colinear antennas, the slotted wavunlike vertical colinear antennas, the slotted waveguide transmits its energy using eguide transmits its energy using HORIZONTALHORIZONTAL p polarization, the best type for distance transmissioolarization, the best type for distance transmission !!n !!

• Stacks, masts, samson posts, and other structures, may cause a reStacks, masts, samson posts, and other structures, may cause a reduction in the intensity of the radar beam beyond these obstructioduction in the intensity of the radar beam beyond these obstructions, especially if they are close to the radar antenna. ns, especially if they are close to the radar antenna. If the angle at If the angle at the antenna the antenna subtended bysubtended by the obstruction is more than a few degr the obstruction is more than a few degrees, the reduction of the intensity of the radar beam beyond the oees, the reduction of the intensity of the radar beam beyond the obstruction may produce bstruction may produce a blind sectora blind sector.. Within the blind sector, Within the blind sector, smsmall targets at close and long rangesall targets at close and long ranges may not be detected. Less redu may not be detected. Less reduction in the intensity of the beam beyond the obstructions may prction in the intensity of the beam beyond the obstructions may produce oduce shadow sectorsshadow sectors. Within a shadow sector, small targets at cl. Within a shadow sector, small targets at close range may not be detected, while larger targets at much greatose range may not be detected, while larger targets at much greater ranges will appear.er ranges will appear.

• Spoking Spoking appears on the PPI as a number of spokes or radial lines. appears on the PPI as a number of spokes or radial lines. Spoking is easily distinguished from interference effects because tSpoking is easily distinguished from interference effects because the lines are straight on all range-scale settings, and are lines rathehe lines are straight on all range-scale settings, and are lines rather than a series of dots. The spokes may appear all around the PPI, r than a series of dots. The spokes may appear all around the PPI, or they may be confined to a sector. or they may be confined to a sector. If spoking is confined to a narrIf spoking is confined to a narrow sector, the effect can be distinguished from a Ramark signal of ow sector, the effect can be distinguished from a Ramark signal of similar appearance through observation of the steady relative beasimilar appearance through observation of the steady relative bearing of the spoke in a situation where the bearing of the Ramark siring of the spoke in a situation where the bearing of the Ramark signal should change.gnal should change. Spoking indicates a need for maintenance or Spoking indicates a need for maintenance or adjustment.adjustment.

如果障碍物对着的天线角度超过了几度，那么障碍物外侧的雷达如果障碍物对着的天线角度超过了几度，那么障碍物外侧的雷达波束强度的降低会造成一个盲区。波束强度的降低会造成一个盲区。

• 长量程内离船近的物标长量程内离船近的物标• 如果同频干扰回波局限在一个狭窄的扇区，通过观察可以如果同频干扰回波局限在一个狭窄的扇区，通过观察可以把同频干扰回波的影响和外表相近似的雷达方位信标区别把同频干扰回波的影响和外表相近似的雷达方位信标区别开。因为在某些情况下，同频干扰回波的方位相对稳定，开。因为在某些情况下，同频干扰回波的方位相对稳定，而雷达方位信标的方位会改变。而雷达方位信标的方位会改变。

• be confined to…be confined to…：局限于…… ：局限于…… be distinguished frombe distinguished from……：与……区别开来：与……区别开来

• The PPI display may appear as normal sectors The PPI display may appear as normal sectors alternating with dark sectors. This is usually due to alternating with dark sectors. This is usually due to the automatic frequency control being out of the automatic frequency control being out of adjustment.adjustment. The appearance of The appearance of serrated range serrated range ringsrings indicates a need for maintenance. After the indicates a need for maintenance. After the radar set has been turned on, the display may not radar set has been turned on, the display may not spread immediately to the whole of the PPI spread immediately to the whole of the PPI because of static electricity inside the CRT. because of static electricity inside the CRT. Usually, the Usually, the static electricity effectstatic electricity effect, which , which produces a distorted PPI display, lasts no longer produces a distorted PPI display, lasts no longer than a few minutes.than a few minutes.

• The echo from an overhead power cable appears The echo from an overhead power cable appears on the PPI as a single echo always at right angles on the PPI as a single echo always at right angles to the line of the cable. If this phenomenon is not to the line of the cable. If this phenomenon is not recognized, the echo can be wrongly identified as recognized, the echo can be wrongly identified as the echo from a ship on a steady bearing. Avoiding the echo from a ship on a steady bearing. Avoiding action results in the echo remaining on a constant action results in the echo remaining on a constant bearing and moving to the same side of the bearing and moving to the same side of the channel as the ship alters course. This channel as the ship alters course. This phenomenon is particularly apparent for the power phenomenon is particularly apparent for the power cable spanning the cable spanning the Straits of MessinaStraits of Messina..

• 锯齿状距标圈锯齿状距标圈• 平面位置指示器的显示屏会有明暗扇形区交替出现平面位置指示器的显示屏会有明暗扇形区交替出现

的状况。这通常是由于自动频率调节没有调整好。的状况。这通常是由于自动频率调节没有调整好。• alternate with: alternate with: 交替，轮流 交替，轮流 be out of: be out of: 缺乏，没有 缺乏，没有

out of order out of order 失灵，失灵， out of stock out of stock 脱销，脱销， out of wout of workork失业失业

Radar PlottingRadar Plotting• When navigating in restricted waters, a mariner most often When navigating in restricted waters, a mariner most often

relies on visual piloting to provide the accuracy required to relies on visual piloting to provide the accuracy required to ensure ship safety. Visual piloting, however, requires clear ensure ship safety. Visual piloting, however, requires clear weather; often, mariners must navigate through fog. When weather; often, mariners must navigate through fog. When conditions conditions renderrender visual piloting visual piloting impossibleimpossible and a vessel is not and a vessel is not equipped with equipped with DGPSDGPS, radar navigation provides a method of , radar navigation provides a method of fixing a vessel’s position with sufficient accuracy to allow safe fixing a vessel’s position with sufficient accuracy to allow safe passage. passage.

• Fixing Position by Two or More Simultaneous RangesFixing Position by Two or More Simultaneous Ranges• The most accurate radar fixes result from measuring and The most accurate radar fixes result from measuring and

plotting ranges to two or more objects.plotting ranges to two or more objects. Measure objects directly Measure objects directly ahead or astern first; measure objects closest to the beam last.ahead or astern first; measure objects closest to the beam last. This procedure is the opposite to that recommended for taking This procedure is the opposite to that recommended for taking visual bearings, where objects closest to the beam are visual bearings, where objects closest to the beam are measured first; however, both recommendations rest on the measured first; however, both recommendations rest on the same principle. When measuring objects to determine a line of same principle. When measuring objects to determine a line of position, measure first those which have the greatest rate of position, measure first those which have the greatest rate of change in the quantity being measured; measure last those change in the quantity being measured; measure last those which have the least rate of change in that quantity. This which have the least rate of change in that quantity. This minimizes measurement time delay errors. Since the range of minimizes measurement time delay errors. Since the range of those objects directly ahead or astern of the ship changes more those objects directly ahead or astern of the ship changes more rapidly than those objects located abeam, measure objects rapidly than those objects located abeam, measure objects ahead or astern first.ahead or astern first.

• DifferentialGlobalPositioningSystemDifferentialGlobalPositioningSystem 差分全球定位系统差分全球定位系统

render---- 1)cause to become; make; getrender---- 1)cause to become; make; get e.g.e.g. Cheerfulness in doing Cheerfulness in doing render a deed more acceptable. a deed more acceptable. 常带三分笑，办事不烦恼。常带三分笑，办事不烦恼。 2)give; supply2)give; supply e.g. We are ready to e.g. We are ready to render them economic assistance. them economic assistance.

• 同时观测两标以上距离定位同时观测两标以上距离定位

应先测船首尾方向附近的物标，后测正横方向附近的物标。目应先测船首尾方向附近的物标，后测正横方向附近的物标。目测方位定位时正好相反，先测正横方向最近的物标。（ 即先测方位定位时正好相反，先测正横方向最近的物标。（ 即先测距离变化快的物标，后测距离变化慢的物标，以减少因不测距离变化快的物标，后测距离变化慢的物标，以减少因不能“同时”观测所产生的船位误差。能“同时”观测所产生的船位误差。国外按第一观测时间作国外按第一观测时间作为定位时间；我国是以第二观测时间作为定位时间，所以正为定位时间；我国是以第二观测时间作为定位时间，所以正好相反。好相反。） ）

• Record the ranges to the navigation aids used and Record the ranges to the navigation aids used and lay the resultinlay the resulting range arcs down on the chartg range arcs down on the chart. Theoretically, . Theoretically, these lines of positithese lines of position should intersect at a point coincident with the ship’s position on should intersect at a point coincident with the ship’s position at the time of the fix.at the time of the fix. However, the inherent inaccuracy of the radaHowever, the inherent inaccuracy of the radar coupled with the relatively large scale of most piloting charts usur coupled with the relatively large scale of most piloting charts usually precludes such a point fix. ally precludes such a point fix. In this case, the navigator must carIn this case, the navigator must carefully interpret the resulting fix. Check the echo sounder with the cefully interpret the resulting fix. Check the echo sounder with the charted depth where the fix lies. If both soundings consistently corrharted depth where the fix lies. If both soundings consistently correlate, that is an indication that the fixes are accurate. If there is diselate, that is an indication that the fixes are accurate. If there is disparity in the sounding data, then that is an indication that either tparity in the sounding data, then that is an indication that either the radar ranges were inaccurate or that the piloting party has mishe radar ranges were inaccurate or that the piloting party has misplotted them. plotted them. This practice of checking sounding data with each fiThis practice of checking sounding data with each fix cannot be overemphasized. x cannot be overemphasized.

• Fixing Position by A Range and Bearing to One ObjectFixing Position by A Range and Bearing to One Object• Visual piloting requires bearings from at least two objects; radar, Visual piloting requires bearings from at least two objects; radar,

with its ability to determine both bearing and range from one objewith its ability to determine both bearing and range from one object, allows the navigator to obtain a fix where only a single navigatict, allows the navigator to obtain a fix where only a single navigation aid is available. An example of using radar in this fashion occuron aid is available. An example of using radar in this fashion occurs in approaching a harbor whose entrance is marked with s in approaching a harbor whose entrance is marked with a single, a single, prominent lightprominent light such as Chesapeake Light at the entrance of the C such as Chesapeake Light at the entrance of the Chesapeake Bay. Well beyond the range of any land-based visual nahesapeake Bay. Well beyond the range of any land-based visual navigation aid, and beyond the visual range of the light itself, a shipbvigation aid, and beyond the visual range of the light itself, a shipboard radar can detect the light and provide bearings and ranges fooard radar can detect the light and provide bearings and ranges for the ship’s piloting party.r the ship’s piloting party.

plotplot he resulting range arcs on the he resulting range arcs on the chartchart

这些位置线应该正好相交于定位时的船位。这些位置线应该正好相交于定位时的船位。coincident withcoincident with 与…一致与…一致 // 符合符合 ;agreeable with; consist wit;agreeable with; consist wit

hh e.g. Find a job where desire is e.g. Find a job where desire is coincident withcoincident with need. need. 愿望和愿望和需求相一致的工作。需求相一致的工作。

• 但是，雷达固有的不精确性，再加上大多数导航图的比例但是，雷达固有的不精确性，再加上大多数导航图的比例尺相对较大，这样的定位点通常不会产生。尺相对较大，这样的定位点通常不会产生。

• couple withcouple with ：结合，成对地出现：结合，成对地出现 ;together with;together with• preclude: preclude: 妨碍妨碍 ; ; 使…行不通使…行不通 ; prevent (the possibility o; prevent (the possibility o

f)f)• 在每次定位的同时都要检查测深数据的做法十分重要。在每次定位的同时都要检查测深数据的做法十分重要。• … … cannot be overemphasized: cannot be overemphasized: 双重否定句式，表示其意义双重否定句式，表示其意义重大，需要重点强调。重大，需要重点强调。

• cannot be too…cannot be too…再…也不为过 再…也不为过 e.g. You cannot be too careful when you drive a car.e.g. You cannot be too careful when you drive a car. You cannot be too rich/young/thin.You cannot be too rich/young/thin.

单物标距离和方位定位单物标距离和方位定位

• 孤立、显著的灯标孤立、显著的灯标

• This methodology is limited by the inherent This methodology is limited by the inherent inaccuracy associated with radar bearings; inaccuracy associated with radar bearings; typically, a radar bearing is accurate to within 5° typically, a radar bearing is accurate to within 5° of the true bearing.of the true bearing. Therefore, the navigator must Therefore, the navigator must carefully evaluate the resulting position, checking carefully evaluate the resulting position, checking it particularly with the sounding obtained from the it particularly with the sounding obtained from the bottom sounder. If a visual bearing is available bottom sounder. If a visual bearing is available from the object, use that bearing instead of the from the object, use that bearing instead of the radar bearing when laying down the fix. This radar bearing when laying down the fix. This illustrates the basic concept discussed above: illustrates the basic concept discussed above: radar ranges are inherently more accurate than radar ranges are inherently more accurate than radar bearingsradar bearings..

• Prior to using this single object method, the Prior to using this single object method, the navigator must ensure that he has navigator must ensure that he has correctly correctly identified the objectidentified the object from which the bearing from which the bearing and range are to be taken. Using only one and range are to be taken. Using only one navigation aid for both lines of position can lead navigation aid for both lines of position can lead to disaster if the navigation aid is not properly to disaster if the navigation aid is not properly identified.identified.

• 雷达方位精确度（受天线尺寸等的影响）一般雷达方位精确度（受天线尺寸等的影响）一般≤≤ 5° 5°

Related exercises:Related exercises:1. ______ is not a job of the radar antenna1. ______ is not a job of the radar antenna ．．• AA．． To receive the high-frequency pulses from the transmitterTo receive the high-frequency pulses from the transmitter• BB ．． To focus the pulses into a beamTo focus the pulses into a beam ，， and send them into spaceand send them into space• CC ．． To pick up reflected pulses coming from objects that have been struTo pick up reflected pulses coming from objects that have been stru

ck by the beamck by the beam• DD ．． To reflect microwavesTo reflect microwaves2. Radar reflectors are required for ______2. Radar reflectors are required for ______ ．．• AA．． all fishing vessels over 39 feet in lengthall fishing vessels over 39 feet in length• BB ．． sail-propelled fishing vesselssail-propelled fishing vessels• CC ．． all fishing vessels of less than 200 GTall fishing vessels of less than 200 GT• DD ．． wooden hull fishing vessels with a poor radar echowooden hull fishing vessels with a poor radar echo3. The shoreline along Rocky Point should give a good radar return because 3. The shoreline along Rocky Point should give a good radar return because ____________ ．．

• AA．． The shore is bluff and rockyThe shore is bluff and rocky• BB ．． Of offshore exposed rocksOf offshore exposed rocks• CC ．． Submerged reefs cause prominent breakersSubmerged reefs cause prominent breakers• DD ．． The lookout tower is marked with radar reflectorsThe lookout tower is marked with radar reflectors4. Radar is not only to obtain ______, but also to measure their distance aw4. Radar is not only to obtain ______, but also to measure their distance aw

ay from you.ay from you.• A. brightness of objectsA. brightness of objects B. color of targets C. shape of targetsB. color of targets C. shape of targets• D. bearing of objects D. bearing of objects

• A steep headland, promontA steep headland, promontory, riverbank, or cliff.ory, riverbank, or cliff.

• 悬崖，峭壁，陡岸，绝壁悬崖，峭壁，陡岸，绝壁• adj.adj. （形容词）（形容词）• Having a broad, steep front.Having a broad, steep front.• 宽而垂直的宽而垂直的

5. When your vessel is proceeding to the area of traffic density, ______ is us5. When your vessel is proceeding to the area of traffic density, ______ is used to determine the exact ranges of other ships or objects in the vicinity.ed to determine the exact ranges of other ships or objects in the vicinity.

• A. radarA. radar• B. GPSB. GPS• C. DFC. DF D. satellite navigatorD. satellite navigator6. The fitting of an efficient radar reflector is likely to considerably increase 6. The fitting of an efficient radar reflector is likely to considerably increase

the ship’s probability of ______.the ship’s probability of ______.• A. detectionA. detection• B. being detectedB. being detected• C. the detectiveC. the detective D. the detected D. the detected7. The abbreviation PPI in the Sperry collision avoidance system means ___7. The abbreviation PPI in the Sperry collision avoidance system means ______.___.

• A. plan position indicator A. plan position indicator • B. plain position indicatorB. plain position indicator• C. plane position indicationC. plane position indication D. policy proof of interest D. policy proof of interest 8. It may be found that, in certain circumstances, radar beacon emissions c8. It may be found that, in certain circumstances, radar beacon emissions c

an cause ______ with the normal radar display, particularly at close rangan cause ______ with the normal radar display, particularly at close range.e.

• A. unwanted interferenceA. unwanted interference• B. unexpected figuresB. unexpected figures• C. abnormal dataC. abnormal data D. unwanted informationD. unwanted information

9. If there is any doubt as to the proper operation of a radar, which statement is true?9. If there is any doubt as to the proper operation of a radar, which statement is true?• A. Only a radar expert can determine if the radar is operating.A. Only a radar expert can determine if the radar is operating.• B. All radars have indicator lights and alarms to signal improper operation.B. All radars have indicator lights and alarms to signal improper operation.• C. A radar range compared to the actual range of a known object can be used to C. A radar range compared to the actual range of a known object can be used to

check the operation of the radar.check the operation of the radar.• D. The radar resolution detector must be energized to check the radar. D. The radar resolution detector must be energized to check the radar. 10. An indirect radar echo is caused by a reflection of the main lobe of the radar beam 10. An indirect radar echo is caused by a reflection of the main lobe of the radar beam

off the observer’s vessel. Which of the following is not a characteristic of indirect ecoff the observer’s vessel. Which of the following is not a characteristic of indirect echoes?hoes?

• A. Their bearing is almost constant, even when the true bearing of the contact chA. Their bearing is almost constant, even when the true bearing of the contact changes appreciably.anges appreciably.

• B. They always appear on a bearing of 90 degrees from the true bearing of the coB. They always appear on a bearing of 90 degrees from the true bearing of the contact.ntact.

• C. The indirect echoes usually appear in shadow sectors.C. The indirect echoes usually appear in shadow sectors.• D. When plotted, their movements are usually abnormal.D. When plotted, their movements are usually abnormal.11. A radar display in which north is always at the top of the screen is a(n)______.11. A radar display in which north is always at the top of the screen is a(n)______.• A. unstabilized displayA. unstabilized display• B. stabilized displayB. stabilized display• C. composition displayC. composition display D. relative displayD. relative display12. A radar contact will remain stationary on a relative motion radar display only whe12. A radar contact will remain stationary on a relative motion radar display only whe

n it is ______.n it is ______.• A. on the same course as your vesselA. on the same course as your vessel• B. at the same speed as your vesselB. at the same speed as your vessel• C. on the same course and speed as your vesselC. on the same course and speed as your vessel• D. on a reciprocal course at the same speed as your vessel D. on a reciprocal course at the same speed as your vessel