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Term Definition/Description Source
label point A reference point used for displaying map and chart text to assist in feature identification. EXAMPLE - reference point for a feature name. ISO/TC 211
labeling (digital) The process of assigning attributes to polygons. HDBK-850
Laborde map projection Similar to the transverse Mercator projection, except that the Laborde projects a spheroid rather than a sphere onto a plane. This conformal projection is best suited for regions which are elongated in a direction which is at a considerable angle to the meridian. [USAF Special Flight Charts are based on this projection.] HDBK-850
LaCoste-Romberg gravimeter A long-period spring suspended cantilevered weight system adapted to the measurement of gravity differences. HDBK-850
ladder grid numbers Those grid numbers which identify the grid lines within the neatline. HDBK-850
Lambert azimuthal equal-area map projection See Lambert zenithal equal-area map projection. HDBK-850
Lambert azimuthal polar map projection A Lambert equal-area map projection with the pole of projection at the pole of the sphere, and the radii of the circles which represent the geographic parallels corresponding to the chords of those parallels. HDBK-850
Lambert bearing A bearing as measured on a Lambert conformal chart or plotting sheet. This approximates a great-circle bearing. HDBK-850
Lambert central equivalent map projection upon the plane of the meridian An azimuthal map projection having the pole of the projection on the Equator. Also called Lambert equal area meridional map projection. HDBK-850
Lambert conformal chart A chart on the Lambert conformal projection. HDBK-850
Lambert conformal conic map projection A conformal map projection of the so-called conical type, on which all geographic meridians are represented by straight lines which meet in a common point outside the limits of the map, and the geographic parallels are represented by a series of arcs of circles having this common point for a center. Meridians and parallels intersect at right angles, and angles on the Earth are correctly represented on the projection. This projection may have one standard parallel along which the scale is held exact; or there may be two such standard parallels, both maintaining exact scale. At any point on the map, the scale is the same in every direction. It changes along the meridians and is constant along each parallel. Where there are two standard parallels, the scale between those parallels is too small; beyond them, too large. Also called Lambert conformal map projection. HDBK-850
Lambert conformal map projection See Lambert conformal conic map projection. HDBK-850
Lambert equal-area meridional map projection See Lambert central equivalent map projection upon the plane of the meridian. HDBK-850
Lambert grid An informal designation for a coordinate system based on a Lambert conformal map projection. HDBK-850
Lambert zenithal equal-area map projection An azimuthal map projection having the pole of the projection at the center of the area mapped. The azimuths of great circles radiating from this center (pole) are truly represented on the map: equal distances on those great circles are represented by equal linear distances on the map, but the scale along those great circle lines so varies with distance from the pole of the projection, that an equal-area projection is produced. Also called Lambert azimuthal equal-area map projection. HDBK-850
laminate 1. The process of preserving a map sheet or other graphic by sandwiching between two sheets of clear synthetic material (polyethylene polyester plastic). The laminating equipment uses heat and pressure but no adhesive. 2. (relief model) See plastic block. HDBK-850
land boundary A line of demarcation between two parcels of land. HDBK-850
land effect See coastal refraction. HDBK-850
land mass simulator plate See factored transparency. HDBK-850
land survey The process of determining boundaries and areas of tracts of land. The term cadastral survey is sometimes used to designate a land survey, but in this country its use should be restricted to the surveys of public lands of the United States. Also called boundary survey; property survey. See also cadastral survey. HDBK-850
land-line adjustment Positioning the public land lines on a topographic map to indicate their true, theoretical, or approximate location relative to the adjacent terrain and culture. HDBK-850
landmark 1. An object of enough interest or prominence in relation to its surroundings to make it outstanding or to make it useful in determining a location or a direction. 2. Any monument, material mark, or fixed object used to designate the location of a land boundary on the ground. HDBK-850
LANDSAT The generic name for a series of earth observing satellites, first launched in 1972 by NASA. LANDSAT serves as platforms for several sensors, including the Return Beam Vidicon (RBV), the Multispectral Scanner (MSS), and the Thematic Mapper (TM). Originally named ERTS, for Earth Resources Technology Satellite. [Landsat 7 is not expected to launch before February, 1999.] HDBK-850
landscape map A topographic map made to a relatively large scale and showing all details. Such maps are required by architects and landscape gardeners for use in planning buildings to fit the natural topographic features and for landscaping parks, playgrounds, and private estates. These are generally maps of small areas, and scales vary from 1 inch = 20 feet to 1 foot = 50 feet, depending on the amount of detail. HDBK-850
language binding or mapping The means and conventions by which a programmer writing in a specific programming language accesses ORB capabilities. CORBA 2.2
language independent Describes a standard or specification which is not specified in terms of a specific programming language, but is implementable in a variety of languages. OpenGIS Guide
language schema A conceptual schema for a lexical language. CEN/TC 287
language-binding API specification A specification that documents the source code method, consistent with a specific programming language, used by an application to access services provided by an application platform. IEEE P1003.0
language-independent service specification A specification that defines a set of required functional semantics independent of the syntax and semantics of a programming language. IEEE P1003.0
Laplace azimuth A geodetic azimuth derived from an astronomic azimuth by use of the Laplace equation. HDBK-850
Laplace azimuth mark An astronomic azimuth mark at a Laplace Station. HDBK-850
Laplace condition The Laplace condition, expressed by the Laplace equation, arises from the fact that a deflection of the vertical in the plane of the prime vertical will give a difference between astronomic and geodetic longitude and between astronomic and geodetic azimuth; or, conversely, that the observed differences between astronomic and geodetic values of the longitude and of the azimuth may both be used to determine the deflection in the plane of the prime vertical. HDBK-850
Laplace control Control and correction of astronomic azimuths through observations of the deflection of the plumb line in the prime vertical (comparison of astronomic and geodetic longitude). HDBK-850
Laplace equation 1. The equation which expresses the relationship between astronomic and geodetic azimuths in terms of astronomic and geodetic longitudes and geodetic latitude. 2. (potential) A partial differential equation of the second-order which is satisfied by the Newtonian potential of every finite body at all exterior points. HDBK-850
Laplace station A triangulation or traverse station at which a Laplace azimuth is determined. At a Laplace station both astronomic longitude and astronomic azimuth are determined. HDBK-850
Laptop Imagery Transmission Equipment (LITE) The LITE is one of four variants of a system designed as a flexible open architecture for secondary imagery dissemination. The other three are: Base Station, Compaq, and Ultra. USIS 95
Large Diameter Target A point target, which due to geometric constraints, requires more than one image to achieve full coverage USIS 95
large-scale map (JCS) A map having a scale of 1:75,000 or larger. See also map. HDBK-850
laser A device producing coherent energy beams in the spectrum of light or near-light frequencies. A laser-equipped Geodimeter makes it possible to measure greater distances. HDBK-850
laser terrain profile recorder An electronic instrument that emits a continuous wave laser beam from an aircraft to measure vertical distances between the aircraft and the Earth's surface. HDBK-850
latent image The invisible image produced in radiation-sensitive materials which becomes visible upon processing. HDBK-850
lateral chromatic aberration An aberration which affects the sharpness of images off the lens axis because different colors undergo different magnifications. HDBK-850
lateral gain (JCS) The amount of new ground covered laterally by successive photographic runs over an area. HDBK-850
lateral magnification The ratio of a length in the image, perpendicular to the lens axis, to a corresponding length in the object. HDBK-850
lateral refraction The horizontal component of the refraction of light through the atmosphere. HDBK-850
lateral shift The offset of the position of the peak of an anomaly with the mass of magnetization (or gravitation). HDBK-850
lateral tilt See roll, definition 2. HDBK-850
latitude Angle from the equatorial plane to the considered direction at the given point, northwards treated as positive. The considered direction is the perpendicular to the reference surface through the given point; see astronomical latitude, geodetic latitude and geographic latitude. CEN/TC 287
latitude 1. (general) A linear or angular distance measured north or south of the Equator on a sphere or spheroid. 2. (plane surveying) The perpendicular distance in a horizontal plane of a pointfrom an east-west axis of reference. See also difference of latitude, definition 2. 3. (on a sphere) The angle at the center of a sphere between the plane of the Equator and the line to the point on the surface of the sphere. 4. (traverse) The north-south component of a traverse course. 5. (photography) The ability of an emulsion to record a range of brightness values. See also argument of latitude; assumed latitude; astronomic latitude; authalic (equal-area) latitude; celestial latitude; circle of latitude; difference of latitude; fictitious latitude; galactic latitude; geocentric latitude; geodetic latitude; geographic latitude; geomagnetic latitude; grid latitude; isometric (conformal) latitude; latitude correction; middle latitude; oblique latitude; parallel; parametric latitude; rectifying latitude; terrestrial latitude; transverse latitude; variation of latitude. HDBK-850
latitude band (JCS) Any latitudinal strip designated by accepted units of linear or angular measurement, which circumscribes the Earth. Also called band; latitudinal band. HDBK-850
latitude coordinate The value that represents the location of a point relative to the equator. Latitude is positive northward and negative southward from the equator. USIGS/CDM-A
latitude correction The amount of the adjustment of observed gravity values to an arbitrarily chosen base latitude. Also, correction to latitude in a traverse course. HDBK-850
latitude determination, zenith-telescope method A precise method of determining astronomic latitude by measuring the difference of the meridional zenith distances of two stars of known declination, one north and the other south of zenith. Also called Horrebow-Talcott method of latitude determination. HDBK-850
latitude difference (plane surveying) Length of the projection of a traverse course onto a meridian. Also called northing; southing. HDBK-850
latitude equation A condition equation which expresses the relationship between the fixed latitudes of two points which are connected by triangulation or traverse. HDBK-850
latitude factor The change in latitude along a celestial line of position per one minute change in longitude. HDBK-850
latitude level A sensitive spirit level attached to the telescope of an instrument employed for observing astronomic latitude, in such manner that when the telescope is clamped in position, the level measures, in a vertical plane, variations in the direction of the line of collimation. HDBK-850
latitude of the line See difference of latitude, definition 2. HDBK-850
latitudinal band See latitude band. HDBK-850
latitudinal curve This term denotes an easterly and westerly property line adjusted to the same mean bearing from each monument to the next one in regular order, as distinguished from the long chord or great circle that would connect the initial and terminal points. HDBK-850
lattice (JCS) A network of intersecting positional lines printed on a map or chart from which a fix may be obtained. HDBK-850
law of propagation of error The probable (standard) error of the sum of two or more quantities is equal to the square root of the sum of the squares of their probable (standard) errors. HDBK-850
law of universal gravitation See constant of gravitation. HDBK-850
Lawrence Livermore National Laboratory A University of California facility performing advanced physics work for the DoE. Located in Livermore, CA. USIS 95
lay 1. See layout. 2. To assemble a photomosaic. Often referred to by the method used in assembly, such as wet lay, staple lay, etc. HDBK-850
laydown Often used to designate a mosaic temporarily assembled from uncropped prints. HDBK-850
layer (digital mapping) A logical separation of data base information according to theme. Many geographical information systems and CAD/CAM systems allow the user to choose and work on a single thematic layer or any combination of thematic layers at a time. HDBK-850
layer tints See hypsometric tinting. HDBK-850
layered data Thematically separated data. The geographic equivalent of third normal form. HDBK-850
layout The planned positioning of reproduction material to fit the requirements and limitations of lithographic plates, paper, and finishing. Also called lay. See also flat, definition 1. HDBK-850
layout guide See key flat. HDBK-850
lead line A long, graduated chain or line at the end of which is attached a lead weight, used to measure depths of water. The lead line is usually used when making soundings by hand in water less than 25 fathoms deep. HDBK-850
Lead Standardization Activity (LSA) A management activity within a Military Department or Defense agency that guides DOD standardization efforts for a Federal Supply Group (FSG), Federal Supply Category (FSC), or Standardization Area through the development of standardization program plans, authorization of standardization projects, and identification and resolution of standardization issues. SD-1 identifies the LSAs. [DOD 4120.3-M] DISA CFS
Leading Edge Services (LES) A DISA proof of concept evaluating the feasibility of an asynchronous transfer mode (ATM) based global communications network. USIS 95
Leap Second (DOD) A second of time that is added to or removed from Coordinated Universal Time (UTC) to keep UTC within 0.9 seconds of UT1 (see Universal Time). Leap Seconds are normally introduced at the end of June or December if required. The decision to introduce a Leap Second is announced by the International Time Bureau (Bureau International de l'Heure, or BIH) approximately eight to ten weeks in advance. See also Coordinated Universal Time (UTC). JPUB 1-02
leap-frog method A rapid means of obtaining elevations of stations along a route between two base stations, or to obtain a closed loop of altimeter elevations. The system uses four barometers operating in pairs. One pair of barometers remains at the base station while the other pair is advanced to the first station at which time barometer and weather conditions are read and recorded simultaneously. The original base station pair are advanced to the second station and the process repeated. This method does not produce reliable elevations. The two-base method is considered better. HDBK-850
least count (micrometer or vernier) The finest reading that can be made directly (without estimation) from a vernier or micrometer. HDBK-850
least squares The theory of least squares states that in a set of redundant observations, the most probable adjusted values of the observations are obtained when the sum of the squares of the adjustments to the observations to obtain mathematical compatibility is a minimum. A least squares adjustment imposes this condition on a set of redundant and incompatible observations so that the set of equations may be solved uniquely for these most probable values. See also adjustment of observations. HDBK-850
left bank That bank of a stream or river on the left of the observer when he is facing in the direction of flow, or downstream. HDBK-850
legacy environments Legacy environments could be called legacy architectures or infrastructures and as a minimum consist of a hardware platform and an operating system. Legacy environments are identified for phase-out, upgrade, or replacement. All data and applications software that operate in a legacy environment must be categorized for phase-out, upgrade, or replacement. TAFIM 3.0
legacy standard {JTA} A JTA standard that is a candidate for phase-out, upgrade, or replacement. A legacy standard may be an obsolete standard without an upgrade path, or an older version of a currently mandated JTA standard. A legacy standard is generally associated with an existing or 'legacy system', although it may be necessary in a new or upgraded system when an interface to a legacy system is required. (JTADG) JTA 2.0
legacy system Software or database components inherited from a previous computing model which do not fit into an open system environment without some modification. In the case of the OpenGIS Specification, legacy systems are modified to include an OpenGIS-compliant interface. OpenGIS Guide
legacy systems Systems that are candidates for phase-out, upgrade, or replacement. Generally legacy systems are in this category because they do not comply with data standards or other standards. Legacy system workloads must be converted, transitioned, or phased out (eliminated). Such systems may or may not operate in a legacy environment. TAFIM 3.0
Legendre polynomial A special case of the associated Legendre function in which the function becomes a polynomial. HDBK-850
Legendre's theorem A mathematical theorem stating that the lengths of the sides of a spherical triangle (very short by comparison with the radius of the sphere) are equal to the lengths of the corresponding sides of a plane triangle in which the plane angles are derived by reducing each of the spherical angles by approximately one-third of the spherical excess. HDBK-850
Lehmann's method See triangle-of-error method. HDBK-850
length correction (taping) The difference between the nominal length of a tape and its effective length under conditions of standardization. The standard length of a tape is usually expressed by a number of whole units (the nominal length) plus or minus a small distance which is the length correction defined above. HDBK-850
length equation A condition equation which expresses the relationship between the fixed lengths of two lines which are connected by triangulation. HDBK-850
length of degree The length of a degree of latitude measured along a meridian of longitude. The length varies somewhat with the degrees of latitude. Those near the pole are longer and those near the Equator are shorter. The length also varies with different selections of spheroids. HDBK-850
Lenoir level An instrument which has the telescope passing through steel blocks, one near each end, whose upper and lower faces are plane and closely parallel; the lower faces rest upon a brass circle; the upper faces support a spirit level, which is reversed in leveling the instrument. HDBK-850
lens A disk of optical glass, or plastic, or a combination of two or more such disks, by which rays of light may be made to converge or to diverge. Such disks have two surfaces, which may both be spherical, one plane and one spherical, or various other combinations (cylindrical, paraboloid, or hyperboloid). See also achromatic lens; anastigmatic lens; aplanatic lens; apochromatic lens; aspherical lens; astigmatizer; coated lens; compensating lens; convertible lens; cylindrical lens; eyepiece; Fresnel lens; Metrogon lens: narrow-angle lens; negative lens; normal-angle lens; objective lens; positive lens; process lens; spherical lens; superwide-angle lens; thick lens; thin lens; wide-angle lens. HDBK-850
lens axis See optical axis. HDBK-850
lens calibration See camera calibration. HDBK-850
lens component See lens element. HDBK-850
lens distortion (JCS) Image displacement caused by lens irregularities and aberrations. HDBK-850
lens element One lens of a complex lens system. In a photographic lens, the terms front element and rear element are often used. Also called lens component. HDBK-850
lens speed See relative aperture. HDBK-850
lensatic compass A type of compass equipped with a lens which permits the observer to read the far side of the movable dial. HDBK-850
level A partition within an MC&G data subgroup that is an aggregation of data elements distinguishable by data characteristics (e.g, resolution, scale, accuracy). HDBK-850
Level 0 topology A topological surface which contains a set of entity points and edges. Edges contain only coordinate and attribute information. See also spaghetti vector data. HDBK-850
Level 1 topology A topological surface which consists of a set of entity points and edges that meet at nodes. Edges contain start node, end node, next edge, and previous edge information. See also chain-node data structure. HDBK-850
Level 2 topology A topological surface which consists of a set of edges and entity points, when projected on a planar surface, the edges meet only at nodes. Edges contain start node, end node, and next and previous edge information. Edges meet only at nodes. See also planar graph. HDBK-850
Level 3 topology A topological surface which is partitioned by a set of mutually exclusive and collectively exhaustive faces. Edges contain left face, right face, start and end node, and next and previous edge information. Edges meet only at nodes. See also full topology. HDBK-850
level constant The amount by which the actual line of sight through a leveling instrument (when the bubble is centered in its vial) departs from the truly horizontal line through the center of the instrument, computed in millimeters per millimeter of stadia interval. When leveling rods graduated in yards instead of meters are used, the level constant, C, would be expressed in milliyards per milliyard of stadia interval. Also called C-constant. HDBK-850
level control A series of bench marks or other points of known elevation, established throughout a project. HDBK-850
level correction That correction which is applied to an observed difference of elevation to correct for the error introduced by the fact that the line of sight through the leveling instrument is not absolutely horizontal when the bubble is centered in its vial. See also level constant. HDBK-850
level line 1. A line on a level surface; therefore a curved line. 2. A line over which leveling operations are accomplished. See also duplicate level line; line of levels; multiple level line; simultaneous level line; spur line of levels. HDBK-850
level net See survey net, definition 2. HDBK-850
level rod See leveling rod. HDBK-850
level surface See equipotential surface. HDBK-850
level trier An apparatus for use in measuring the angular value of the divisions of a spirit level. HDBK-850
leveling 1. (surveying) The operations of measuring vertical distances, directly or indirectly, to determine elevations. See also astrogeodetic leveling; astrogravimetric leveling; barometric leveling; differential leveling; direct leveling; first-order leveling; flying levels; geodetic leveling; profile leveling; reciprocal leveling; second-order leveling; spirit leveling; stadia trigonometric leveling; thermometric leveling; third-order leveling; three-wire leveling; trigonometric leveling; vertical angulation; water leveling. 2. (photogrammetry) In absolute orientation, the operation of bringing the model datum parallel to a reference plane, usually the tabletop of the stereoplotting instrument. Also called horizontalizing the model; leveling the model. See also aeroleveling; orientation, definition 7. HDBK-850
leveling error of closure See error of closure, definition 4. HDBK-850
leveling instrument An instrument used for determining differences of elevations between points. See also Abney level; dumpy level; Egault level; eng'neer's level; first-order level; Fischer level; Gravatt level; hand level; hanging level; latitude level; Lenoir level; lo'ator's hand level; military level; pendulum level; plate level; precise level; reversible level; self-leveling level; spirit level; Stampfer level; striding level; telescope level; tilting level; Troughton level; U.S. Geological Survey level; wye (Y) level. HDBK-850
leveling 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 leveling instrument which has been adjusted to a horizontal position. Also called level rod; rod. See also Barlow leveling rod; Boston leveling rod; double-target leveling rod; foot-meter rod; Gravatt leveling rod; Invar leveling rod; long rod; Molitor precise leveling rod; New York leveling rod; Pemberton leveling rod; Philadelphia leveling rod; precise leveling rod; range rod; self-reading leveling rod; short rod; single-target leveling rod; Stephenson leveling rod; tape rod; target leveling rod; U.S. Engineer precise leveling rod; U.S. Geological Survey precise leveling rod. HDBK-850
leveling the model See leveling, definition 2. HDBK-850
Levels of Information Systems Interoperability (LISI) LISI is oriented by levels that represent increasing degrees of sophistication required to accomplish interactions between information systems. A level in the LISI model is characterized by the most demanding exchanges the level embodies, as well as the enabling capabilities it requires. The LISI Reference Model defines five levels, currently numbered 0, 1, 2, 3, and 4: Level 0 -- Isolated: Level 0 systems have no direct electronic connection. Data exchange between these systems typically occurs via either manual keyboard entry or an extractable common media format (e.g., diskette). Level 1 -- Connected: Level 1 systems are linked electronically. These systems conduct peer-to- peer exchange of homogeneous data types, such as simple "text," e-mail, or fixed graphic files (e.g., GIF, TIFF images). Generally, level 1 systems allow decision makers to simply exchange files with one another. Level 2 -- Functional: Level 2 systems are distributed, i.e., they reside on local networks that allow complex, heterogeneous data sets (e.g., annotated images, maps with overlays) to be passed from system to system. Formal data models (logical and physical) are present; but generally, only the logical data model is agreed to across programs and each program defines its own physical data model. Generally, decision makers are able to share fused information between systems or functions. Level 3 -- Domain: Level 3 systems are integrated, i.e., capable of being connected via wide area networks (WAN) that allow multiple users to access data. Information at this level is shared between independent applications. A domain-based data model is present (logical and physical) that is understood, accepted, and implemented across a functional area or group of organizations that comprises a domain. Systems are capable of implementing business-rules and processes to facilitate direct database-to-database interactions, such as those required support database replication servers. Individual applications at this level may share central or distributed data repositories. Systems at this level support group collaboration on fused information products. Generally, decision-making is supported by fused information from a localized problem domain. Level 4 -- Enterprise: Level 4 systems are capable of operating using a distributed global information space across multiple domains. Multiple users can access and interact with complex data simultaneously. Data and applications are fully independent and can be distributed throughout this space to support information fusion. Advanced forms of collaboration (the virtual office concept) are possible. Data has a common interpretation regardless of form, and applies across the entire enterprise. The need for redundant, functionally equivalent applications is diminished since applications can be shared as readily as data at this level. Decision-making takes place in the context of, and is facilitated by, enterprise-wide information found in this global information space. C4ISR AF
Lewis and Clark See Small Spacecraft Technology Initiative (SSTI). NASA Web Site
lexical language A formal language using words and mathematical symbols. Lexical languages can be used to present conceptual schemata. CEN/TC 287
library A repository of digital data. Each library maintains a catalog of its holdings to support discovery functions, such as search and browse. Users may retrieve items from a given library by selecting them from the catalog responses to their queries. The content of a library may be limited to specific types of data (e.g., imagery, image products, SIGINT, etc.) USIS 95
library negative mold A negative mold which has been extended to a size compatible with the printed plastic map and forming equipment, and which is kept in file for subsequent castings. HDBK-850
libration A real or apparent oscillatory motion, particularly the apparent oscillation of the Moon, which results in more than half of the'Moon's surface being revealed to an observer on the Earth, even though the same side of the Moon is always toward the Earth because the'Moon's periods of rotation and revolution are the same. HDBK-850
license (UCDM Entity: "LICENSE") Official or legal permission granted to use a specified thing. USIGS/CDM-A
life cycle The period of time that begins when a system is conceived and ends when the system is no longer available for use. [IEEE STD 610.12]. AIS life cycle is defined within the context of life-cycle management in various DOD publications. It generally refers to the usable system life. DISA CFS
Life-Cycle Management (LCM) Life-cycle management means the management of an item or system from inception/Pre-Milestone 0 through program termination. The term is also used in relation to Supply Management as management of an item from the time it first comes into the government inventory until it is disposed of at the end of its service life. The Services/Agencies have organizations to perform this level of management, but it can also be done under contract. LCM includes the procurement of initial and sustainment spare and repair parts; item management of those parts; oversight of the maintenance process (government or contractor); configuration control; planning for product improvements; the collection of failure and demand data, analysis and appropriate support process modification; and proper disposal action at the end of the life cycle. [DISA/D4] DISA CFS
lift See selection overlay. HDBK-850
Light Table Mensuration System A system that can be mounted on imagery interpretation light tables and provides automated mensuration capabilities. USIS 95
limb 1. The graduated curved part of an instrument for measuring angles, as that part of a marine sextant carrying the altitude scale, or arc. 2. The circular outer edge of a celestial body. See also lower limb; upper limb. HDBK-850
limit of reliable photo coverage A label placed along a dashed line separating reliable photo compilation from map compilation on a chart. The label is always placed on the photo compilation side of the limit line. HDBK-850
line A bounded, contiguous 1-dimensional geometric primitive. ISO/TC 211
line A one dimentional geometric-spatial-element that is defined by a set of points connected by straight line segments in an ordered sequence. USIGS/CDM-A
line copy Any copy suitable for reproduction without using a screen. Copy composed of lines as distinguished from continuous tone copy. HDBK-850
line drawing A graphical representation of imagery exploitation results, often incorporating information from other sources, that may include precision mensuration and the results of detailed analysis. USIS 2-1.1
line map See planimetric map. HDBK-850
line of apsides The major axis of an elliptical orbit extended indefinitely in both directions. Also called apse line. HDBK-850
line of collimation (optics) The line through the second nodal point of the objective lens of a telescope and the center of the reticle. Also called aiming line; line of sight; pointing line; sight line. HDBK-850
line of constant scale Any line on a photograph which is parallel to the true horizon or to the isometric parallel. Also called line of equal scale. HDBK-850
line of equal scale See line of constant scale. HDBK-850
line of force A line indicating the direction in which a force acts, as in a magnetic field. HDBK-850
line of levels A continuous series of measured differences of elevation. The individual measured differences may be single observations in the case of single-run Ieveling or the means of repeated observations in the case of double-run leveling. HDBK-850
line of nodes The straight line connecting the two points of intersection of the ecliptic with the orbit of a planet, planetoid or comet; or the line of intersection of the planes of the orbit of a satellite and the equator of its primary. HDBK-850
line of position A line indicating a series of possible positions, determined by observation or measurement. HDBK-850
line of sight 1. The straight line between two points. This line is in the direction of a great circle, but does not follow the curvature of the Earth. 2. The line extending from an instrument along which distant objects are seen, when viewed with a telescope or other sighting device. Also called aiming line. 3. (optics) See line of collimation. HDBK-850
line of sight The distance to the horizon from an elevated point, including the effects of atmospheric refraction. A straight line between an observer or radar antenna and a target. An unobstructed, or optical path between two points. The vector from the imaging sensor position to a ground point. USIS 95
line of soundings A series of soundings obtained by a vessel underway, usually at regular intervals. HDBK-850
line pattern A photographic negative containing parallel lines of equal-sized widths, which are equally spaced. Line patterns are used for printing tones of a color or to present a pattern of coverage for a chart feature. See also area pattern screen. HDBK-850
line rod See range rod. HDBK-850
line segment A direct line between two points. ISO/TC 211
line string A set of coordinate points and the lines that join them. OpenGIS Guide
line thinning (generalization) 1. (vector) Reducing the quantity of coordinates necessary to portray the basic shape at a feature by using a series of rules. 2. (raster) Process whereby a linear feature is represented in a grid by a continuous series of cells, each of which touches along its sides and corners, no more than two other cells belonging to the feature. HDBK-850
line tree A tree intersected by a surveyed line, reported in the field notes of the survey, and marked with two hacks or notches cut on each of the sides facing the line. Also called sight tree. HDBK-850
lineage The quality element describing the history of a geographic subset in terms of source material, dates, processing applied, and responsible organisations. CEN/TC 287
lineage Information about the data source, particularly the original scale and accuracy. HDBK-850
lineal convergency The length by which meridians approach one another when extended from one parallel to another. HDBK-850
linear building frontage In air photographic interpretation, the side elevation of structures of homogeneous area. HDBK-850
linear distortion The failure of a lens to reproduce accurately to scale all distances in the object. HDBK-850
linear error A one-dimensional error (such as an error in elevation) defined by the normal distribution function. HDBK-850
linear error Vertical error at the target. The accuracy with which the elevation of the target can be determined. LE at a point is a value such that the true elevation of the point can be expected to have the given value plus or minus LE with same degree of probability (usually 0.9 P). USIS 95
linear error of closure The straight-line distance by which a traverse fails to close. HDBK-850
linear feature A feature that is portrayed by a line that does not represent an area. Also called line feature. HDBK-850
linear magnification The ratio of a linear quantity in the image to a corresponding linear quantity in the object. It may be lateral magnification or longitudinal magnification. HDBK-850
linear parallax See absolute stereoscopic parallax. HDBK-850
linearization The process of redefining a set of nonlinear equations to a set of approximate linear equations to facilitate solution computations. HDBK-850
line-route map A map or overlay for signal communication operations that shows the actual routes and types of construction of wire circuits in the field. It also gives the locations of switchboards and telegraph stations. HDBK-850
lines of communications (LOC) (JCS) All the routes, land, water, and air, which connect an operating military force with a base of operations, and along which supplies and reinforcements move. HDBK-850
lines on a spheroid Any direct line between two positions on a spheroid, represented by two points on the Earth. Such a line may be one of mathematical definition, or it may result from a direct survey between the points on the Earth. See also curve of alignment; geodesic line; normal section line. HDBK-850
lining pole See range rod. HDBK-850
link 1. (leveling) A line, a part of a line, or a combination of lines or parts of lines of levels, which, taken as a unit, make a continuous piece of leveling directly from one junction bench mark to another junction bench mark without passing through or over any other junction bench marks. Also called link of levels. 2. A unit of linear measure, one one-hundredth of a chain, and equivalent to 7.92 inches. See also chain. 3. A line between two consecutive nodes. HDBK-850
link and node A data structure characterized by data in which one or more links are related to one or more features. The beginning and end points of each link are identified by node identifiers either explicitly or implicitly. HDBK-850
link of levels See link, definition 1. HDBK-850
Linked Operations /Intelligence Center Europe (LOCE) Unted States European Command's (USEUCOM) intelligence fusion network for producing a common picture of the battlefield, shared among U.S. and allied command intelligence centers. LOCE provides automatically correlated near-real-time, multisource sensor data including ELINT, IMINT, and ship location reports; it provides a consolidated, multisource order of battle data base with ground, electronic, air, missile, target, and naval data; and it assists intelligence analysts with situation monitoring, collection management, targeting, and battlefield intelligence analysis. Located at Molesworth, U.K. USIS 95
Liquid Crystal Display (LCD) Display operated by polarizing light in which the nonactive segment reflects incident light and thus appears invisible against its background. [HCI Style Guide] DISA CFS
Liquid Crystal Stereoscopic Shutter (LCSS) Type of display that utilizes liquid crystal shutters, one for each eye synchronized to alternate fields of the display, and representing one of the two images necessary to achieve the third dimension. [HCI Style Guide] DISA CFS
liquid hand compass A type of hand held compass wherein the compass card is damped through the action of a liquid. HDBK-850
list See x-tilt. HDBK-850
list of directions A listing of objects observed at a triangulation station, together with the horizontal directions in terms of arc of the circle, referred to one of the objects observed as a zero initial. HDBK-850
List of Lights The NIMA publication which identifies and describes lights and fog signals in foreign waters of the world. This information is also accessible on the Navigation Information Network (NAVINFONET). HDBK-850
litho copy See lithographic copy. HDBK-850
lithographic copy A graphic reproduced by the lithographic process. Also called litho copy. HDBK-850
lithographic drafting See tusching. HDBK-850
lithography A planographic method of printing based on the chemical repulsion between grease and water to separate the printing from nonprinting areas. See also offset lithography; photolithography. HDBK-850
lithosphere The solid part of the Earth or other spatial body. Distinguished from the atmosphere and the hydrosphere. HDBK-850
Littoral Warfare Data (LWD™) LWD™ is a vector-based digital product that portrays selected marine and coastal features in littoral (shallow water) regions. LWD™ is a dataset which contains feature, sounding and attribute information relevant to amphibious operations and mine warfare. LWD™ is the combined deconflicted data content of a group of available standard NIMA products. NIMA Web Site
Live, Virtual, and Constructive Simulation The categorization of simulation into live, virtual, and constructive is problematic, because there is no clear division between these categories. The degree of human participation in the simulation is infinitely variable, as is the degree of equipment realism. This categorization of simulations also suffers by excluding a category for simulated people working real equipment (e.g., smart vehicles).
a. Live Simulation. A simulation involving real people operating real systems.
b. Virtual Simulation. A simulation involving real people operating simulated systems. Virtual simulations inject human-in-the-loop (HITL) in a central role by exercising motor control skills (e.g., flying an airplane), decision skills (e.g., committing fire control resources to action), or communication skills (e.g., as members of a C4I team).
c. Constructive Model or Simulation. Models and simulations that involve simulated people operating simulated systems. Real people stimulate (make inputs) to such simulations, but are not involved in determining the outcomes.
local adaptation The process of modifying a product that is specific to one culture to make it specific to another culture. IEEE P1003.0
local adjustment See station adjustment. HDBK-850
local apparent time The apparent solar time for the meridian of the observer. HDBK-850
local area network (LAN) A data communications system that (a) lies within a limited spatial area, (b) has a specific user group, (c) has a specific topology, and (d) is not a public switched telecommunications network, but may be connected to one. Note 1: LANs are usually restricted to relatively small areas, such as rooms, buildings, ships, and aircraft. Note 2: An interconnection of LANs within a limited geographical area, such as a military base, is commonly referred to as a campus area network. An interconnection of LANs over a city-wide geographical area is commonly called a metropolitan area network (MAN). An interconnection of LANs over large geographical areas, such as nationwide, is commonly called a wide area network (WAN). Note 3: LANs are not subject to public telecommunications regulations. FED STD 1037C
local astronomic time Mean time reckoned from the upper branch of the local meridian. HDBK-850
local attraction See local magnetic anomaly. HDBK-850
local cartesian coordinates Cartesian coordinates in the case where the origin of the axis is at a point to the Earth's surface. CEN/TC 287
local chart A large-scale aeronautical chart designed for contact flight in a congested area. HDBK-850
local civil time See local mean time. HDBK-850
local coordinate system A right-handed rectangular coordinate system of which the z-axis coincides with the plumb line through the origin . HDBK-850
local datum A datum which serves as a reference for defining local cartesian coordinates. CEN/TC 287
local datum The point of reference of the geodetic control used exclusively in a small area. Usually identified by a proper name. HDBK-850
local horizon See apparent horizon. HDBK-850
local hour angle Angular distance west of the local celestial meridian; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the local celestial meridian and the hour circle of a point on the celestial sphere, measured westward from the local celestial meridian through 360. HDBK-850
local lunar time The arc of the celestial equator, or the angle at the celestial pole, between the lower branch of the local celestial meridian and the hour circle of the Moon, measured westward from the lower branch of the local celestial meridian through 24 hours; local hour angle of the Moon, expressed in time units, plus 12 hours. See also Greenwich lunar time. HDBK-850
local magnetic anomaly Abnormal or irregular variation of the Earth's magnetic field extending over a relatively small area, due to local magnetic influences. Also called anomalous magnetic variation; local attraction; local magnetic disturbance; magnetic anomaly. HDBK-850
local magnetic disturbance See local magnetic anomaly. HDBK-850
local mean time 1. (JCS) The time interval elapsed since the mean sun's transit of the observer's antemeridian. 2. The arc of the celestial equator, or the angle at the celestial pole, between the lower branch of the local celestial meridian and the hour circle of the mean sun, measured westward from the lower branch of the local celestial meridian through 24 hours; local hour angle of the mean sun, expressed in time units, plus 12 hours. Called local civil time in United States terminology from 1925 through 1952. See also local astronomic time; Universal Time. HDBK-850
local meridian The meridian through any particular place or observer, serving as the reference for local time. Also called reference meridian. HDBK-850
local sidereal time The local hour angle of the vernal equinox, expressed in time units. Local sidereal time at the Greenwich meridian is called Greenwich sidereal time. HDBK-850
local sun time The apparent time of day at a given spot on the Earth, relative to the sun's position. The time at which the sun is at its highest point is noon, which defines the remaining 24 hours. It is also the time that would be read from a sundial. USIS 95
local time 1. Time based upon the local meridian as reference, as contrasted with that based upon a time zone meridian, or the meridian of Greenwich. 2. Any time kept locally. HDBK-850
local time of day The time of day, at a particular point on the Earth, measured in terms of the local time zone. These times generally vary slightly from the local sun time. See local sun time. USIS 95
local vertical The direction of the acceleration of gravity, as opposed to the normal to a reference surface. HDBK-850
locale The definition of the user environment that depends on language and cultural conventions. IEEE P1003.0
localization The process of utilizing the internationalization features to adapt an internationalized product to a specific cultural environment. (See also internationalization.) IEEE P1003.0
location survey The establishment on the ground of points and lines in positions which have been previously determined by computation or by graphical methods, or by description obtained from data supplied by documents of record, such as deeds, maps, or other sources. HDBK-850
locator's hand level A hand held type of level used to measure approximate differences in elevation . HDBK-850
locking angle In tilt analysis of oblique photographs, the complement of the interlocking angle. The depression angle of the oblique when the tilt of the vertical photograph is zero. HDBK-850
logical consistency The primary quality parameter describing the degree of conformance of a geographic subset compared to its nominal ground with respect to the constraints defined in the application schema. CEN/TC 287
logical consistency (digital mapping) The correctness of the relationships encoded in the data structure of the data set. HDBK-850
logical contouring A procedure, based on the facts that contours are spaced equally along a uniform slope, which permits the sketching of contours from field notes with considerable accuracy and without the need of running a level line for every contour. Contour lines are interpolated by spacing them proportionately between spot elevations established at every point where there is a change in slope. HDBK-850
logical data model (LDM) A data model that represents the meaning of the data contained in a data structure. [IEEE 610.5] Compare to conceptual data model (CDM) and physical data model (PDM). IEEE 610-1990
logical entity (A&D LDM Entity: "LOGICAL-ENTITY") The set of entities identified in the logical data model. An entity represents a set of real or abstract things (people, places, events, etc.) which have common attributes or characteristics. The logical equivalent of a table A&D LDM
logical relationship A subtype of feature relationship covering any logical association between features except aggregation, generalisation and topological relationship. ISO/TC 211
logical work unit (LWU) An LWU contains up to 1850 FAF [fast access format] blocks or 995 FAF blocks of imagery including full and reduced resolution data sets. USIS 95
Log-On Process of gaining access to the system, usually involving a password and a recognition of the specific user by the computer. [HCI Style Guide] DISA CFS
long chord (route surveying) On a simple curve, the chord, or straight line, that extends from the point of curvature to the point of tangency; on a compound curve, the chord that extends from the point of compound curvature to the point of curvature or to the point of tangency. In a description of a circular land boundary, the length and bearing of the long chord is an important factor. HDBK-850
long line azimuth (LOLA) surveys A measurement by use of photorecording theodolites and airborne strobe lights of long azimuth lines not visible between ground stations. HDBK-850
long rod A level rod, usually a Philadelphia rod, permitting readings of 13 feet when fully extended. Also called high rod. See also short rod. HDBK-850
long-dwell platforms Collection platforms capable of loitering over a specified area for long periods of time for the purpose of providing continuous coverage. USIS 95
longitude Angle from the zero meridian plane to the meridian plane of the given point, eastward treated positive. See astronomical longitude, geodetic longitude and geographic longitude. CEN/TC 287
longitude A linear or angular distance measured east or west from a reference meridian (usually Greenwich) on a sphere or spheroid. See also assumed longitude; astronomic longitude; celestial longitude; circle of longitude; difference of longitude; fictitious longitude; galactic longitude; geodetic longitude; geographic longitude; grid longitude; meridian; oblique longitude; terrestrial longitude; transverse longitude. HDBK-850
longitude coordinate The value that represents the location of a point relative to the prime meridian. Longitude is positive eastward and newative westward from the prime meridian. USIGS/CDM-A
longitude difference See departure, definition 1. HDBK-850
longitude equation A condition equation which expresses the relationship between the fixed longitudes of two points which are connected by triangulation or traverse. HDBK-850
longitude factor The change in longitude along a celestial line of position per one minute change in latitude. HDBK-850
longitude of the Moon's nodes The angular distances along the ecliptic of the Moon's nodes from the vernal equinox; the nodes have a retrograde motion, and complete a cycle of 360 in approximately 19 years. HDBK-850
longitude signal A sign indicating a time event, observable at different stations, and used in comparing local times of those stations, and determining the difference of their longitudes. HDBK-850
longitude term gravity formula An additional term in the formula for theoretical gravity which expresses the variation with longitude due to a triaxial ellipsoid of reference. See also Helmert's gravity formula of 1915. HDBK-850
longitudinal chromatic aberration An aberration which affects the sharpness of all parts of an image because different colors come to a focus at different distances from the lens. HDBK-850
longitudinal magnification The ratio of a length in the image, parallel to the axis, to a corresponding length in the object. HDBK-850
longitudinal separation Time separation. HDBK-850
longitudinal tilt See pitch, definition 2. HDBK-850
long-period constituent A tide or tidal current constituent with a period that is independent of the rotation of the Earth but which depends upon the orbital movement of the Moon or of the Earth. The period is usually longer than a day and in general a half-month or larger. HDBK-850
long-period perturbations Periodic perturbations in the orbit of a planet or satellite which require more than one orbital period to execute one complete periodic variation. HDBK-850
long-range chart See long-range navigation chart. HDBK-850
long-range navigation chart Any one of a series of small scale, 1:3,000,000 or smaller, aeronautical charts designed for long flights using dead reckoning and celestial navigation as the principal means of navigation. Also called long-range chart. HDBK-850
longwave infrared see infrared, longwave. USIS 95
look angles The elevation and azimuth at which a particular satellite is predicted to be found at a specified time. See also alerts. HDBK-850
look elevation angle The angle between the local horizontal plane at the target and the line-of-sight vector to the imaging satellite. USIS 95
look-up table Used to provide filtering parameters for sensors. USIS 95
loop A set of one or more connected edges and bounded at both ends by one and the same node. ISO/TC 211
loop closure (leveling) The difference between the rod sum on the run out and the rod sum on the run back. HDBK-850
loop error of closure See error of closure, definition 5. HDBK-850
loop traverse A closed traverse that starts and ends at the same station. The traverse provides neither inherent validation of starting position and azimuth, nor validation against systematic distance error. See also connecting traverse. HDBK-850
LORAN chart A plotting chart on which loran ground wave line of positions and sky wave correction values have been printed, for use in loran navigation. HDBK-850
LORAN lines Lines of constant time difference between signals from a master and a slave loran station. HDBK-850
LORAN tables Publications containing tabular data for constructing loran hyperbolic lines of position. HDBK-850
LORAN-C A long-range radio navigation position fixing system using a combination of time difference of reception and phase difference of signals from two stations to provide a line of position. HDBK-850
LORAN-C Secondary Phase Correction Table Tabulated secondary phase corrections for LORAN-C in a given service area for each appropriate transmitter pair or station. These corrections account for overland radio wave phase retardation. HDBK-850
lorhumb line A line along which the rates of change of the values of two families of hyperbolae are constants. HDBK-850
LOROP photography A general term referring to any photographs taken with a long focal length (in excess of 100 inches) camera with a narrow-angle lens. [The term is derived from the words "long-range oblique photography."] HDBK-850
Los Alamos National Laboratory (LANL) Owned by the Department of Energy, Los Alamos has been managed by the University of California since 1943, when the Laboratory was born as part of the Manhattan Project to create the first atomic weapons during World War II. Today, LANL's central mission is reducing the danger of nuclear weapons and nuclear materials worldwide. LANL's statutory responsibility is the stewardship and management of the nuclear stockpile. LANL is located in Los Alamos, NM. LANL Web Site
loss-less compression A compression technique that compresses data (or an image) without losing any bits or deteriorating the resolution of an image. Compression ratios are not tremendously high in this type of compression. ITSG Vol. 1
lossy compression A compression technique that compresses data (or an image) but loses bits in the process. The quality of the image may deteriorate; however, extremely high compression ratios may be obtained in this type of compression. ITSG Vol. 1
lost corner A corner whose position cannot be determined, beyond reasonable doubt, either from traces of the original marks or from acceptable evidence or testimony that bears on the original position, and whose location can be restored only by reference to one or more interdependent corners. HDBK-850
Lovar A steel alloy having a low coefficient of expansion used in construction of precise Lovar tapes. See also Invar. HDBK-850
Lovar tape A newer version of the Invar tape used in surveying operations. Lovar tape possesses properties and cost factors between that of the less accurate steel tape and the more accurate Invar tape. HDBK-850
low intensity conflict Political-military confrontation between contending states or groups below conventional war and above the routine, peaceful competition among states. It frequently involves protracted struggles of competing principles and ideologies. Low intensity conflict ranges from subversion to the use of armed force. It is waged by a combination of means employing political, economic, informational, and military instruments. Low intensity conflicts are often localized, generally in the Third World, but contain regional and global security implications. USIS 95
low tide See low water. HDBK-850
low water (LW) The lowest limit of the surface water level reached by the lowering tide. Low water is caused by the astronomic tide-producing forces and/or the effects of meteorological conditions. Also called low tide. HDBK-850
low water datum An approximation of the plane of mean low water, adopted as a standard datum plane for a limited area, and retained for an indefinite period, even though it might differ slightly from a better determination of mean low water from later observations. HDBK-850
low water full and change The average interval of time between the transit (upper or lower) of the full or new Moon and the next low water. HDBK-850
low water inequality See diurnal inequality. HDBK-850
low water interval See lunitidal interval. HDBK-850
low water line The line defined by the boundary of a body of water at its lowest stage (elevation). In tidal waters, the low water line is, strictly, the intersection of the plane of mean low water with the shore. HDBK-850
low water lunitidal interval See lunitidal interval. HDBK-850
low water springs See mean low water springs. HDBK-850
low water springs datum An approximation of the plane of mean low water springs, used as a datum in local areas, and retained for an indefinite period, even though it might differ slightly from a better determination of mean low water springs from later observations. HDBK-850
lower branch That half of a meridian or celestial meridian from pole to pole which passes through the antipode or nadir of a place. HDBK-850
lower culmination See culmination. HDBK-850
lower high water (LHW) The lower of two high waters of any tidal day where the tide exhibits mixed characteristics. HDBK-850
lower high water interval (LHWI) The interval of time between the transit (upper or lower) of the Moon over the local or Greenwich meridian and the next lower high water. This expression is used when there is considerable diurnal inequality. See also lunitidal interval. HDBK-850
lower limb That half of the outer edge of a celestial body having the least altitude, in contrast with the upper limb, that half having the greatest altitude. HDBK-850
lower low water (LLW) The lower of two low waters of any tidal day where the tide exhibits mixed characteristics. HDBK-850
lower low water datum An approximation of the plane of mean lower low water, adopted as a standard datum plane for a limited area, and retained for an indefinite period, even though it might differ slightly from a better determination of mean lower low water from later observations. Used in engineering design of harbor facilities and dredging, when there is a material difference between mean lower low and mean low datums. HDBK-850
lower low water interval (LLWI) The interval of time between the transit (upper or lower) of the Moon over the local or Greenwich meridian and the next lower low water. This expression is used when there is considerable diurnal inequality. See also lunitidal interval. HDBK-850
lower motion (surveying) The rotation of the lower plate of a repeating instrument. HDBK-850
lower transit Transit of the lower branch of the celestial meridian. Also called inferior transit. HDBK-850
lowest low water A plane of reference whose distance below mean sea level corresponds with the mean level of lowest low water of any normal tide. Also called lowest normal low water. HDBK-850
lowest low water springs A plane of reference approximating the mean lowest low water during syzygy (spring tides). HDBK-850
lowest normal low water See lowest low water. HDBK-850
low-oblique photograph See oblique air photograph. HDBK-850
loxodrome A line on the surface of the Earth cutting all meridians at the same angle. Also called a rhumb line. HDBK-850
loxodromic curve See rhumb line. HDBK-850
lunar celestial equator A great circle on the celestial sphere in the plane of the Moon's equator, i.e., in a plane perpendicular to the Moon's axis of rotation. HDBK-850
lunar chart A chart showing the surface of the Moon. HDBK-850
lunar cycle Any cycle related to the Moon, particularly the Callippic cycle or the Metonic cycle. See also saros. HDBK-850
lunar day The interval between two successive upper transits of the Moon over a local meridian. The period of the mean lunar day, approximately 24.84 solar hours, is derived from the rotation of the Earth on its axis relative to the movement of the Moon about the Earth. Also called tidal day. HDBK-850
lunar declination Angular distance of the Moon expressed in degrees north or south of the celestial equator; it is indicated as positive when north, and negative when south of the equator. Also called declination of the Moon. HDBK-850
lunar distance The angle between the line of sight toward the Moon and the line of sight toward another celestial body at the point of an observer on the Earth. HDBK-850
lunar earthside chart A chart showing that portion of the Moon's surface visible from the Earth. HDBK-850
lunar eclipse The phenomenon observed when the Moon enters the shadow of the Earth. A lunar eclipse is partial if only part of its surface is obscured; and total if the entire surface is obscured. HDBK-850
lunar equation A factor used to reduce observations of celestial bodies to the barycenter of the Earth-Moon system. HDBK-850
lunar farside chart A chart showing that portion of the Moon's surface not visible from the Earth. HDBK-850
lunar inequality 1. Variation in the Moon's motion in its orbit, due to attraction by other bodies of the solar system. See also evection; perturbation. 2. A minute fluctuation of a magnetic needle from its mean position, caused by the Moon. HDBK-850
lunar interval The difference in time between the transit of the Moon over the Greenwich meridian and a local meridian. The lunar interval equals the difference between the Greenwich and local intervals of a tide or current phase. HDBK-850
lunar month See synodical month. HDBK-850
lunar node A node of the Moon's orbit. HDBK-850
lunar parallax The horizontal parallax or the geocentric parallax of the Moon. HDBK-850
lunar satellite A man-made satellite that makes one or more revolutions about the Moon. HDBK-850
lunar tide That part of the tide caused solely by the tide-producing forces of the Moon as distinguished from that part caused by the forces of the Sun. HDBK-850
lunar time 1. Time based upon the rotation of the Earth relative to the Moon. 2. Time on the Moon. See also Greenwich lunar time; local lunar time. HDBK-850
lunation See synodical month. HDBK-850
lune That part of the surface of a sphere bounded by halves of two great circles. HDBK-850
lunicentric See selenocentric. HDBK-850
lunisolar effect Gravitational effects caused by the attraction of the Moon and of the Sun. HDBK-850
lunisolar perturbation Perturbations of artificial satellite orbits due to the attractions of the Sun and the Moon. The most important effects are secular variations in the mean anomaly, in the right ascension of the ascending node, and in the argument of perigee. All other orbital elements, except the major semiaxis, undergo long periodic changes. HDBK-850
lunisolar precession That component of general precession caused by the combined effect of the Sun and Moon on the equatorial perturbance of the Earth, producing a westward motion of the equinoxes along the ecliptic. HDBK-850
lunitidal interval The interval between the Moon's transit (upper or lower) over the local or Greenwich meridian and the following high or low water. The average of all high water intervals for all phases of the Moon, the mean high water lunitidal interval, is abbreviated to high water interval. Similarly, the mean low water lunitidal interval is abbreviated to low water interval. The high water or low water interval is described as local or Greenwich according to whether the reference is to the transit over the local or the Greenwich meridian. Also called establishment. HDBK-850

Last Updated by Mark Owens 6 January 1999.