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Eng ID Term Definition
2781
levelling plate
A plate designed to support the LEVEL­LING ROD as an aid to ACCURACY in LEVELLING.
2782
levelling rod
A straight rod or bar, designed for use in measuring a vertical distance between a point on the ground and the LINE OF COLLIMATION of a LEVE... more
A straight rod or bar, designed for use in measuring a vertical distance between a point on the ground and the LINE OF COLLIMATION of a LEVELLING INSTRUMENT which has been adjusted to horizontal position. Also called levelling staff.
2783
levelling screw
One of the three screws of surveying and astronomic instruments used for levelling same. Also called footscrew.
2784
levelling staff
See LEVELLING ROD.
2785
level net
Lines of SPIRIT LEVELLING connected together to form a system of loops and circuits extending over an area. Also called survey net.
2786
level surface
A surface which, at every point, is perpendicular to the DIREC­TION OF GRAVITY. A level surface is an EQUIPOTENTIAL SURFACE. The GEOID or, i... more
A surface which, at every point, is perpendicular to the DIREC­TION OF GRAVITY. A level surface is an EQUIPOTENTIAL SURFACE. The GEOID or, in general, any surface parallel to it, is a level sur­face. If changes in ELEVATION due to TIDES, WINDS, etc. are neglected, the surface of the SEA is a level surface. A level surface is not a plane surface, but it is sometimes so regarded in SURVEYS of limited areas.
2787
librations of moon
Motions of the MOON due to which certain margins round the MOON's LIMB occasionally pass out of view while a cor­responding margin on the ot... more
Motions of the MOON due to which certain margins round the MOON's LIMB occasionally pass out of view while a cor­responding margin on the other side comes into view. The librations enable 59 per cent of the MOON's surface to be seen at one time or another.
2788
lidar
(LIght Detection And Ranging) An instrument that measures distance to a reflecting object by emitting timed pulses of LASER light and measur... more
(LIght Detection And Ranging) An instrument that measures distance to a reflecting object by emitting timed pulses of LASER light and measuring the time between emission and reception of reflected pulses.  The measured time interval is converted to distance.  In survey use, the lidar system usually scans the light PULSEs across the TRACK of the SURVEY platform (usually an aircraft) so that successive PULSEs cover a SWATH(E) either side of the platform's track.  Infra-red LASERS will reflect off land and water, and are normally used for TOPOGRAPHIC lidar SURVEYs.  Blue-green LASERS will penetrate water and are used in HYDROGRAPHIC lidar SURVEYs.
2789
life buoy
See BUOY.
2790
life saving station
A place where equipment for saving life at SEA is maintained. Also called rescue station.
2791
light
A luminous or lighted AID TO NAVIGATION. For internationally agreed abbreviations of light characteristics see the International Chart Speci... more
A luminous or lighted AID TO NAVIGATION. For internationally agreed abbreviations of light characteristics see the International Chart Specifica­tions.
2792
light: aerial obstruction
LIGHT marking an obstacle which constitutes a danger to AIR NAVIGATION.
2793
light: aeromarine
A marine-type LIGHT in which a pro­portion of the BEAM is deflected to an angle of 10°-15° above the HORIZON for the use of aircraft.
2794
light: aeronautical ground
Any LIGHT specially provi­ded as an AID TO NAVIGATION, other than a LIGHT dis­played on an aircraft.
2795
light: alternating
A signal LIGHT that shows, in any given direction, two or more colours in a regularly repeated sequence with a regular periodicity.
2796
light(s): boundary
LIGHTS marking the BOUNDARY of a LANDING AREA.
2797
light: catoptric
A LIGHT concentrated into a narrow BEAM by means of one or more REFLECTORS (as opposed to DIOPTRIC).
2798
light: composite group-flashing
A flashing light in which a sequence of groups of one or more flashes, which are specified in number, is regularly repeated, and the groups ... more
A flashing light in which a sequence of groups of one or more flashes, which are specified in number, is regularly repeated, and the groups comprise different numbers of flashes.
2799
light: composite group-occulting
An occulting light in which a sequence of groups of one or more eclipses, which are specified in number, is regularly repeated, and the grou... more
An occulting light in which a sequence of groups of one or more eclipses, which are specified in number, is regularly repeated, and the groups comprise different numbers of eclip­ses.
2800
light: continuous ultra quick
A light showing 160 or more, usually 240 to 300, flashes per minute.