geod quiz 3 - Sheet1 Flashcards
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
what is atmospheric “noise” and what do the different parts represent
refraction of microwaves by water vapor. the static part can resemble topography and the turbulent part can represent deformaiton
what is decorrelation
changes in radar scattering properties of pixels. (ex. vegetation, snow, flooding, time passing). longer wavelengths are less susceptiple
what are some applications of InSAR?
constraining rheological properties of the fault and crust, detecting and quantifying changes in magma chambers and understanding volcano plumbing, slow-moving landslides, glacier mechanics, changes in glacier flow, impact of seasonal changes in aquifers, reservoir monitoring
what are the applciations of Sentinal 1 and 1B and what even is that?
InSAR satellites, applications: monitoring ice, oil spills, marine winds, waves, land deformation, emergency hazard responding
What are some other InSAR satellites from different countries?
JAXA (Japan- disaster moonitoring and regional observations), RADARSAT-2 (Canada - ice monitoring, disaster management), TerraSAR-X (DE - geology, climatology, DEM generation), COSMO-SkyMED (It- security, mapping , intelligence, risk management, geology), NASA-ISRO SAR (Ie. NISAR - USA & INDIA - WILL measure changing ecosystems, ice mass info, hazards, first radar of it’s kindto systemattically map Earth using L and S band radar frequencies
what does LiDAR stand for and what kinds are there
Light Detection adn Ranging. Spaceborne, High altitude, Airborne (ALS), Terrestrial (TLS)
what actually is LiDAR?
surveying method measuring distance to a target by illuminating the target with pulsed laser ligth and measuring the reflected pulses with a sensor. then a 3d model can be made
what does LiDAR record
time (transmits a pulse of lught and records the returned pulse of light
how is range measured
1) time of flight (time it takes for emiited pulse to reflect off object and return to scanner) 2) phase shift (measuring the phase shift of a pulse, then calculating distance
what are the advantages and disadvantages of time of flight and phase shift w respect to measuring range
TOF: higher range, lower accuracy, lower pts/s, slower and larger. PHASE SHIFT: lower range, higher accuracy, higher pts/s, noise in data
what are some applications of LiDAR
studying geopatterns of the earth’s surface, how landscapes influence and record climate and tectonics, transport laws governing the evolution of the earth’s surface, landscape ecosystem dynamics, volcano form and process
what are the benefits of terrestrial laser scanners?
provides a large density of geospatial info (point cloud), the scanner is controlled by a laptop used for both data aquisition and initial processing, and the combo of TLS with GNSS/ GPS gives full geospatially referenced data
what are some TLS research applications?
measuing tsunamis, scarp erosion, paleoseismology, forest fire erosion, scanning polar environments,
why did early gps signals have decreased acuracy?
because of selective availibility. may 1 200 this changed
what are the three segments of GNSS
space segment, control segment, user segment
what does the space segment of GNSS consist of?
broadcasting radio signal towards users on earth, recieving commands from the ground. it consists of GNSS satelites orbiting earth
what does the control segment of GNSS consist of?
monitoring the space segment and senign commands to satellites. consists of a global network that tracks the satellites, monitors them, performs analyses, and sends them commands. We have some control stations around the world and a master one in CO
what does the user segment of GNSS consist of?
recording signal from satellites, interpreting radio signals from the satellites . consists of the equipment used to apply GNSS info
what does the observable (aka range measurement) of GNSS positioning equation depend on?
XYZ coordinates (uses pythag theorem)
how do we interpret the position from GNSS
1) measure arrival times of GNSS signals from a bunch of satellites , decode the signals and figure out their times, convert this to satellite positions
what is the fundamental frequency
10.23 Mhz
what do we use from the fundamental frequency?
L1 and L2 (used to transmit timing info by the GPS satellites)
how is the GPS signal coded
binary values, pseudorandom nosie codes (PRN codes)
what are PRN codes and how do they relate to L1 and L2
they are pseudorandom noise codes, unique to each satellite. THE Course acuisition code (C/A) code corrresponds ONLY to L1. THE Precision (P) code corresponds to L1 and L2
what is the ephemerides
the calculated positions of the satellites at regular intervals
what is the navigation message of the GPS signal
ephemetides for all satellites, ionospheric correction parameters, system status, satellite clock offset and drift
what is the Radio frequency aspect of GPS signals
the part of the reciever that processing incoming signals (L1 only and L1 and L2 - dual frequency signals).
what are the phase measurements?
when a satellite is locked (at t0) the gnss reciever starts tracking the incoming phase. it cunds the number of phases as a funct of time. NAD HAS TO ACCOUNT FOR PROAGATION ERRORS
what are the five GPS observables
1) L1 and L2: phase observable on L1 and L2 frequencies, in cycles 2) C/A, P: pseudorange observable 3) Navigation message
what are key differences between LiDAR and SfM
LIDAR: expensive laser equipment, works in densely vegetated landscapes, use precise time of flight measurements. SFM: cheap camera, colored points, warping occurs but easily solved for
what is SIFT
scale invariant feature transform. it allows for corresponding features to be matched even with large variations in scale or changing illumination
what is the basic stero algorithim in SFM
comapre with every pixel on same line in image, pick pixel with minimum match cost
what is the stero as energy minimization in SFM
uses match quality and smoothness (if two pixels are near each other, they should move abt the same amount)
what are the steps in SFM
1) match corresponding features and measure distances between them 2) calculate individual camera positions in a step known as bundle adjustment 3) a dense point cloud is amde 4) georectification (converiting the point cloud into on ewith a geographic coord system 5) make products (DEM, for ex.)
what is the difference between traditional stero-photogrammetry and SFM
SP: needs a stable platform (satellite, or steady plane), photographs at known positions. SFM: photos with many angles and distances, unstructured image aquisition
what are some SFM applications?
characterizing hand samples or outcrops, paleoseismic trenching, coastal erosion, volcanic mapping, landslide mapping,
