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geodesy > Geod quiz 1 - Sheet1 > Flashcards

Geod quiz 1 - Sheet1 Flashcards

1
Q

definition of geodesy

A

the science of the measurement and mapping of earth’s surface

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2
Q

global geodesy includes:

A

the determination fo the shape and size of earth, its orientation in space, its gravity field

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3
Q

what is a geodetic survey

A

the determiniation of the earth’s surface and gravity field over a region (usually a country/ group of countries)

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4
Q

what needs to be considered in geodetic surveys?

A

the earth’s curvature and gravity field

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5
Q

what is plane surveying

A

when the details of the earth’s surface are determined on a local level (ignoring curvature and gravity effects)

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6
Q

geodesy applications

A

agriculture, aviation, space, public safety, survey and mapping, roads and highways

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7
Q

wht does tectonic geodesy include?

A

crustal deformation, plate boundaries, microplates, earthquakes, post seismic relaxation, volcanoes

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8
Q

hazards applications of geodesy

A

real time gnss/gps data, real time algorithims for seismic and volcanic hazards, sea level rise calculations, ice mass variations, land water storage

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9
Q

what do reference frames describe

A

orientation of the earth in space, earth’s surface geomoetry, the gravity field

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10
Q

what was the first idea about earth’s shape

A

a disk encircled by oceans (homer in the illiad, 800BC)

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11
Q

what shape did pythagoras propose?

A

spherical earth (580-500BC)

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12
Q

when was the spherical model accepted and why

A

around aristotle’s time (382-322BC), because of 1) the round shadow of earth in lunar eclipses and 2) the apparent rising of an aproaching ship on the horizon

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13
Q

who is the founder of geodesy and what did he do?

A

eratosthenes of alexandria, deduced the earth’s radius from measurements, developed arc measurement method. found that raus of sun descended vertically into a well in syene at summer solstice, then comapred to alexandria. estiamted 6366km (actual= 6367 km)

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14
Q

who suggested ellipsoidal earth

A

newton (ssuggested flattening of earth)

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15
Q

what are the WGS84 and ITRF?

A

really similar global ellipsoidal models. both are geocentric (relative to the center of earth’s mass), WGS= world geodetic service, ITRF = international terrestrial ref. frame

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16
Q

what is the NAD84

A

north americal ellipsoidal model (north american datum = NAD). NON geocentric

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17
Q

how do we take present day geodetic surveys?

A

1) control points (might be in shallow concrete) 2) geodetic benchmarks (installed in very stable bedrock or on a deep steel rod)

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18
Q

who is gladys west?

A

mathmatician that layed groundwork for gps. she made a model of the earth accounting for gravitational, tidal, and other forces

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19
Q

who were laplace, gauss, and bessel

A

dudes who determined that the ellipsoid was NOT accurate

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20
Q

how did laplace, gauss, and bessel figure our that the elliposoid wasn’t accurate?

A

they used the deflection of vertical (aka the deviation of a plumbline from the ellipsoidal normal)

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21
Q

what is the geoid and who defined it

A

the mathmatical surface of the earth. all points on a geoid have the same effective potential. gauss and bessel defined it

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22
Q

how is the geoid currently measured?

A

recent satellite missions (Gravity FIeld and Steady STate Ocean Circulation (GOCE) and GRACE)

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23
Q

what is a terrestrial refernce system

A

a spatial refernece system co-rotating with the Earth

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24
Q

what’s special about a TRS

A

positions of points attached to the solid earth have coords. which undergo only small variations with time (due to geophysical effects - tectonic or tidal deformations)

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25
Q

what are reference systems good for?

A

describing the positions and motions of the earth, other celestial bodies, artificial satellites, the surface fo the earth, the stationary and time variable parts of earth’s gravity field

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26
Q

what are refrence systems represented by?

A

coordiante systems

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27
Q

how does time play into reference systems?

A

the mutual motion of the earth and other celest. bodies, temporal variations of the earth’s shape, gravity field, and orientation

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28
Q

how are reference systems and frames related?

A

refernce systems are realized through reference frames. ref. systems are theoretical, ref. frames are REAL and ppl have access to them

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29
Q

what do reference frames consist of

A

a set of well determined, fixed points or objectss (given by their coords and -if necessary- their velocities)

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30
Q

what are time systems based on

A

processes of quantum physics, motions in the solar system, daily rotation of earth

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31
Q

what is the equation for flattening?

A

F = (a-b)/a

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32
Q

why are time systems important

A

need uniform time scale to: model motion of artificial satellites, describe motion of earth w/ respect to inertial space, date all measurements and results

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33
Q

what is the difference between control points and benchmarks

A

benchmarks are in bedrock (representative of tectonic motion), control points are in shallow conrete (measure shallow surface processes)

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34
Q

how does sea level factor into the geoid defintion?

A

Mean sea level is used ( without tides/ waves)

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35
Q

what is the difference between ref. systems and frames?

A

ref system = theoretical, frames = application (you tie measurements to reference frames)

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36
Q

what defined mass?

A

plank’s constant expressed in Joules

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37
Q

how is the realtization of the meter possible?

A

atomic clocks and GPS satellites

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38
Q

what is sexagesimal graduation

A

system of measurement using degrees, minutes, and seconds to measure angles and time

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39
Q

what are some key equations in sexagesimal graduation

A

1 degree = 60 arcmin, 1 arcmin= 60 arcsec, 2pie = 360, angle in degrees = (180/pie) angle in radians

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40
Q

what are other important constants in geodesy

A

speed of light, gravitational constant (henry cavendish figured out G)

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41
Q

what do most geodetic measurements use for positioning

A

time or frequency measurements of electromagnetic waves

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42
Q

what are forier’s theroem and equations

A

he said that any wave form in the time domain can be represented by the weighted sum of sins and cosines. F(v) = integral of neg infinity to infinity of f(t) times e^(-2pi times i times vt)

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43
Q

what is a big takeaway about general relativity

A

the observed gravitational effect between masses results from their warping of space time. so, systems of space time coords withing ht egravity field must be defined and used for modelling

44
Q

are ref. systems defined within the frame of relatitivty theory

A

yes, now they are

45
Q

when do you have to pay attention to relativistic effects?

A

when you are off of earth - satellite orbits, space geodetic observations (on earth you don’t need to worry about it)

46
Q

what is the definition of the SI second?

A

86,400 s/ day

47
Q

what time does the origin of international atomic time (TAI) correspond to?

A

Jan 1, 1958

48
Q

what are some versions of universal time?

A

UT1 and UTC

49
Q

what’s the difference between UT1 and UTC?

A

UT1: principal form of universal time, cocmputed of observations of distant quasars using long baseline inferometry. UTC; (coordinated universal time) approximates UT1, international standard for civil time, ticks SI seconds and is in step with TAI

50
Q

do the UTC and TAI account for leap seconds?

A

yes

51
Q

how do we get TAI?

A

by weighing the averages of time kept by over 400 atomic clocks (cesium) in different labs

52
Q

what is terrestrial time? and what is it used for

A

an astronomical time standard ddefined by the international astronomical union. it’s used for the relativistic treatment of space geodetic techniques ALSO it is basically equal to international atomic time (TAI)

53
Q

is terrestial time (TT) adjusted so that it agress with the SI unit of a second on the geoid?

A

yes

54
Q

what is GPS time? (GPST)

A

runs parallel to TT, doesn’t have leap seconds, implemented by atomic clocks in the GPS ground control stations and GPS satellites. is ahead of UTC (bc no leap seconds)

55
Q

how many dimenstions are ref. systems?

A

4d

56
Q

what are refernece coordiante systems defined by?

A

the origin and orientation of planes or axes of a cartesian coord. system

57
Q

how do you go from cartesian coordinates to spherical coordinates?

A

that matrix with cos(v)cos(lamda), etc.

58
Q

what are earth centered earht fixed coordiantes (ECEF)

A

show the relationship to the geodetic lat, long, and height. consideres earth’s flattening

59
Q

what is precession

A

a secular effect due to gravitation of the moon and sun on the equitorial buldge of earth. it rotates between vega and the north star. it creates torque

60
Q

what does precession cause

A

the vernal equinox moves clockwise along the ecliptic with one rotation every 25,800 years.

61
Q

what is nutation

A

rotation of the true pole about precession (precession is superimpsoed by nutation), slight fluxuation during precession due to small oscillations

62
Q

what defines the rotation of the earth

A

a vector directed to the north pole of the instantaneous axis of rotation AND the angular velocity (w)

63
Q

how long is one siderial day

A

86,164.10s

64
Q

what is the equation for angular velocity

A

delta theta/ delta time (anngle/time)

65
Q

what is a sidereal day

A

the time it takes for the earth to complete on erotation about its axis with respect to the ‘fixed’ stars (like the sun)

66
Q

what causes the direction and magnitude of the rotational axis vector to change with time (with repect to solid earth)

A

time variable lunar, solar and planetary gravitation AND mass redistributions in the atmo and hydrospheres over tectonic plate movements AND post-glacial isostatic adjustment AND mantle convection DUE TO LIQUID OUTER CORE MOTION

67
Q

what are the earth rotation parameters

A

polar motion (wobble) and the earth rotation angle

68
Q

what is polar motion (wobble)

A

the motion of the earth’s rotation (spin) axis with repect to the earth fixed ref. system

69
Q

what is the chandler wobble

A

a free oscillation period of abt 435 days

70
Q

why does the chandler wobble occur?

A

the spin axis of the earth doesn’t aligh exactly witht he polar axis of moment moment of inertia

71
Q

what is the annual wobble? why does it occur?

A

a wobble that superimposes the chandler wobble. it is caused by mass redistributions and mass motions in the earth

72
Q

what is the secular motion wobble? why does it occur?

A

supeimposes chandler wobble. due to glacial isostatic adjustment. ALSO caused by sea level changes, large scale tectonic movements, mass schifts inthe earth’s interior, and polar ice melting

73
Q

what casues periodic, quasiperiodic, and irregular variations with respect to polar motion

A

ocean tides, atmospheric and hydrologic processes, oceanic and continental water variations

74
Q

what casues other free motions with respect to polar motion

A

the misalignment of rotational axis and figure axes. related to the flattening of the earth’s mantle, inner, and outer core

75
Q

what do earth orientation parameters describe and how many are there

A

the irregularities of the earth’s rotation. there are five (celestial pole offsets, pole coordinates, universal time (UT1))

76
Q

what is the ephemerides

A

the positions of naturally occuring and artificial satellites in the sky at a given time

77
Q

what is a celestial reference system characterized by (CRS)

A

newton’s laws of motion

78
Q

what is a dynamical CRS based on? and how have they been realized?

A

the ephemerides of solar system bodies. they’ve been realized through various optical measurements and radio data

79
Q

what is a kinematic CRS defined by?

A

the positons and proper motions of stars or quasars

80
Q

what ar the X Y and Z coords in a CRS and what do they entail

A

Z coincides with earth’s rotational axis (north pole), X and Y axis span equitorial plane (y on equator, x pointing out from equator- like radius). X points to the Vernal Equinox

81
Q

what is the vernal equinox

A

the point on the celestial sphere where the path of the sun crosses the celestial equator from south to north in March.

82
Q

what are hour circles

A

great circles perpendicular to the celest. equator

83
Q

whar are celestial parallels

A

small circles parallel to the equator

84
Q

what are declination and right ascention

A

declination: angle above/ below the equitorial plane. right ascention= angle in equitorial plane measured CW from vernal equinox

85
Q

how is a terrestial ref system represented by

A

3D cartesian coords (X,Y,Z)

86
Q

what iss the geocenter

A

the earth’s center of mass (including atmosphere and oceans)

87
Q

how are the axes aligned in the terrestial reference system?

A

Z axis aligned with mean terrestial north pole, mean equitorial plane is perp to Z axis and includes X and Y axes

88
Q

what is a terrestial system used to do?

A

describe positions on/ clsoe to the earth’s surface, national surveys, geoinformation systems, navigation, a frame for determining earth’s gravity field and other geophysical properties

89
Q

what celestial frame is used?

A

represented by the IAU; international celestial reference frame

90
Q

what is the international terrestrial reference system

A

a world spatial reference system co-rotating with the earth. it provides a set of coords of some points on earth’s surface

91
Q

who maintains the world spatial reference system

A

intrantional earth rotation and reference systems service (IERS)

92
Q

how many satellites do GPS, Galileo, and Glonass have

A

Gps has 6, the other two have 3

93
Q

what system has the most satellites

A

galileo (27), gps has 24 and glonass havs 21

94
Q

how do we utelize satellite laser ranging

A

satellites orbit earth, control stations on earth detect laser with satellite, then we can calulate the distances betweeen control stations

95
Q

what is DORIS

A

a french system where sations on earth send signals to satellites

96
Q

what is the International Terrestial Reference Frame and what does it do

A

the mathmatical realtization of the ITRS. it provides coords in geocentric ECEF cartesian positions (as well as their 3D velocities)

97
Q

what is a helmert transformation

A

transformation between different systems consisting of a shift in origin, change in orientation, and scale factor

98
Q

what ITRF is used now?

A

ITRF2020 (some ppl still use ITRF14)

99
Q

when does ITRF improve

A

when the number of sites with long time series increases, new techniques appear, estiamation procesures are improved

100
Q

why do we use the ITRF?

A

because it provides the msot accurate global ref. frame available, GNSS orbits use it, if everyone uses it then it’s easy to comapre data bc it’s standardized

101
Q

what is the no net rotation frame (NNR) and what does it do

A

represents velocities without referrring to a certain plate. it’s achieved by aligning the velocity field to the HORIZONTAL movement s of a plate tectonics model. HAS NO IMPACT ON RELATIVE PLATE VELOCITIES

102
Q

what are fixed plate, regional, and local reference frames

A

used for defining relative plate motions

103
Q

how do you chose a reference frame

A

based on geophysical objectives, maybe like the local surroundings of a volcano, one side of a fault, or the upper plate of a subduction zone

104
Q

what is the major plate reference frame

A

relative to eurasia, nubia, NA, SA, etc plates.

105
Q

what are regional ref. frames

A

smaller coherent regions (central valled of CA)

106
Q

what are local ref. frames

A

sites near (but outside the influence of) a volcano, geothermal field. etc.

geodesy (3 decks)

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