Geod quiz 2 - Sheet1 Flashcards
who formulated the law of gravitational attraction
newton (3 generations after galileo determined the magnitude of gravitational acceleration)
what was a strong argument for newton’s laws of motion?
the law of gravitational attraction
what are kelper’s laws?
1) each planet moves in an ellipse with the sun at one focus 2) the line connect a planet and the sun sweeps out equal areas in equal times 3) for all planets, the orbital period squared divided by the semimajor axis cubed is constant
what is the definition of gravity?
the force exerted on a mass (due to the combination of: 1) the gravitational attraction of the earth and 2) the rotation of the earth (2 componenets))
what are the two components of the rotation of the earth?
the centrifugal acceleration due to rotation with angular velocity and the existence of an equitorial buldge that results from the balance between self-gravitation and rotation
what kind of reference frame is there at the surface of the earth?
a rotating one
what is the earth’s center (with reference to a reference frame?)
the non-rotating intertial reference frame
what is the relationship between centrifugal acceleration and earth’s axis of rotation
they are normal to each other (perp)
what is the equation of motion inthe rotating reference frame?
mg = f(force of gravity) - m * omega times (omega * R)
how many parts foes apparent gravitational acceleration have?
2 (9.8 m/s^2 AND centrigugal acceleration ( omega * (omega * R)
what is the equation for apparent gravitational acceleration?
g (subscript a) = g - omega ^2 * R * cos^2 lamda
who first discovered g (gravitational acceleration)
galileo
what are gravimeters used for
to measure gravity anomalies
who discovered G and what is it
6.67 X 10 ^-11, Cavendish
what does G suggest
because this 6.67 number is much higher than the density of rocks at earth’s surface, earth’s density must increase with depth
what happened as a result of the discovery of G?
many measurements of g (lowercase) were calculated at different locations on earth (demonstrating the variation of g at different latitudes)
what is the difference between gravitational acceleration, centrifugal acceleration, and apparent gravitational acceleration
gravitational A = constant g (9.8 m/s^2), centrifugal A = outward effect of the earth’s rotation (like forces parallel to the equator), apparent gravitational A = gravity that includes the impact of earth’s rotation
what is the formula for gravitational PE
U = pgz (density * g * depth)
do higher or lower elevations have higer GPE?
higher
what is the mean potential energy of the lithosphere (U) used for?
1) defining the tectonic reference state of the Earth and 2) constraining the ambient state of stress in the plates
what is the compensation level?
a depth where the pressure is hydrostatic (the same). so if you take cross sections with the same area from any line along / below the comensation level up to the crust, the weight of vertical matter will be the same
what is a result of isostatic adjustments?
high mountain belts and plateus are usually underlain by thicker crust (that extends deeper into the upper mantle than do lower areas of elevation)
what does isostasy control?
surface elevation
what is isostasy?
the state of gravitational equilibrium between the earth’s crst and mantle (as if the crust were floating on the mantle)
what is the difference between Pratt and Aity isostasy?
prat’s includes a flat line between the crust and mantle. airy’s has the crust extending deeper into the mantle when there are mountains on the crust.
what is the geoid
a refined model for the figure of the earth. described as “the equipotential surface of the earth’s gravity field coinciding with the MSL”
what does solid earth physics use the geoid for?
as a gravity field representation revealing the distribution of deeper located masses
what is the equation of the geoid
W = W(r) = Wo (Wo = gravity potential value)
what is the free air correction?
the point at which the measurement is made is typically not at sea level (usually gravity is measured on a mountain top of in an oceanic basin) so we take into account that we are not at sea level
what is the free air anomaly?
gf (free air anomaly) = gobs (measured value of gravity) - gn (g using reference earth model) + gf
what is the bouger correction?
this takes into account that it is typically
what is the equation for the bouger correction
gb = 2piG density * h (h = height above sea level)
what is the terrain correction?
it accounts for the fact that moauntains are not infitite planes of rocks (like the bouger correction states). accounts for the peaks and valleys in rocks
when is the bouger anomoly negative?
over a mountain range. it reflects low density crustal root
what do inverse correlations of bouger anomalies indicate?
isostatic compensation
what does GRACE consist of? and what does it stand for?
Grvaity Recovery and Climate Experiment. it consists of 2 identical spacecraft flying about 220 km apart in a polar orbit above earth
what does GRACE do?
map earth’s gravity field by making accurate measurements of the distance between two satellites (and it’s very cost effective)
what is TWS?
total water storage. over the ocean it’s interpreted as ocean bottom pressure. on land it’s the sum of groundwater, soil moisture, surface water, snow and ice
what can GRACE measurements reflect on longer timescales?
post glacial rebound
what drives ice flow variability?
1) the geometry of the glacier (width, ice thickness, bed topography) 2) bed conditions (hard bedrock, soft sediment, amt of water) 3) ocean conditions (amt of submarine melt at terminus) 40 atmosphere conditions (amt of meltwater that can get to the glacier bed)
what does InSAR stand for
Interferoetric Synthetic Aperture Radar (use wave interference, pretend you have a big radar antenna, emit microwaves, emasure echoes)
what is synthetic aperture radar (SAR)
a form of radar used to create two or three D images of objects (ex. landscapes)
how does SAR work
it uses the motion of the radar antenna over a target region to provide finer spatial resolution than normal bean-scanning radars
what is SAR normally mounted to?
a moving platform (like an aircraft or spacecraft)
how are SAR images created?
sucessive pulses of radio waves are transmitted to illuminate a taget scene and the echo of each pulse is recorded. electromagnetic waves are transmitted sequentially, the echoes are collected, and the system electronic digitize and store the data for processing
how does SAR work simply?
1) satellite emits radar pulse 2) radar is backscattered 3) amplitue and phase of echo recorded at satellite
do slopes facing towards SAR satellites show brigter or darker values?
bright
are SAR areas of vegetation rouch or smooth?
rough
can we use SAR technology in any weather
yes, and can do day or night
what are the applications fo SAR technology?
ship tracks, ice tracking, oil slicks, land-use changes, planetary
what is phase
a function of the distance from the satellite to the ground
how does insar work?
it uses 2+ synthetic aperture radar (SAR) images to generate maps of surface deformation or digital elevation, useing differences in the phase of the waves returning to the satellite or aircraft
