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Microwave Remote Sensing: Principles and Applications. Outline Introduction to RSL at the University of Kansas Introduction and History of Microwave Remote Sensing Active Microwave Sensors Radar Altimeter. Scatterometer. Imaging Radar. Applications of Active Sensors Sea ice. Glacial ice

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microwave remote sensing principles and applications
Microwave Remote Sensing: Principles and Applications
  • Outline
    • Introduction to RSL at the University of Kansas
    • Introduction and History of Microwave Remote Sensing
    • Active Microwave Sensors
      • Radar Altimeter.
      • Scatterometer.
      • Imaging Radar.
    • Applications of Active Sensors
      • Sea ice.
      • Glacial ice
      • Ocean winds.
      • Soil Moisture.
      • Snow.
      • Vegetation.
      • Precipitation.
      • Solid Earth.

University of Kansas

microwave remote sensing principles and applications1
Microwave Remote Sensing: Principles and Applications
  • Passive Microwave Sensors
    • Radiometers
      • Traditional
      • Interferometer
      • Polarimetric Radiometer
  • Application of Passive Microwave Sensors
      • Sea ice.
      • Glacial ice
      • Soil Moisture.
      • Atmospheric sounding
      • Snow.
      • Vegetation.
      • Precipitation

University of Kansas

radar systems and remote sensing laboratory
Radar Systems and Remote Sensing Laboratory

Windvector Measurements over the Ocean

Radar at 14 GHz.

Concept developed at KU.

USA, Europe and Japan are planning to launch satellites to obtain data continuously.

University of Kansas

radar systems and remote sensing laboratory1
Radar Systems and Remote Sensing Laboratory

Founded in 1964.

4 Faculty members, 20 Graduate students - Ph. D & M.S.

4-6 Undergraduate students, 2 Staff

Now satellites based on concepts developed at RSL are in operation.

NSCAT, QUICKSCAT- Radars to measure ocean surface winds.

ADEOS-2 (JAPAN), Europeans Met Office is planning to launch satellite to support operational applications.

ScanSAR-

Radarsat- Canadian satellite

Envisat - European

SRTM -Shuttle Radar Topography Mission.Radar Systems and Remote Sensing Laboratory

University of Kansas

radar systems and remote sensing laboratory2
Radar Systems and Remote Sensing Laboratory
  • Shuttle Radar Topography Mission (SRTM)
    • to collect three-dimensional measurements of the Earth\'s surface.
    • Acquired data to obtain the most complete near-global mapping of our planet\'s topography to date.
    • This would not have been possible without ScanSAR operation--- concept developed at KU.

University of Kansas

ittc information technology telecommunication center
ITTC– Information Technology & Telecommunication Center
  • Communications academic emphasis and research programs established in 1983.
  • Now RSL is a part of the Center
  • Graduated students
    • degrees in EE, CS, CoE, Math
  • 29 faculty, 15 staff researchers, 6 Center staff
  • Current student population ~ 130
    • ~ 13 Ph.D., ~81 M.S., ~37 B.S.

University of Kansas

em spectrum
EM Spectrum
  • Microwave region
      • 300 MHz – 30 GHz.

Millimeter wave

      • 30 GHz – 300 GHz.

IEEE uses a different definition

      • 300 MHz – 100 GHz

University of Kansas

microwave remote sensing principles and applications2
Microwave Remote Sensing: Principles and Applications.
  • Advantages
    • Day/night coverage.
    • All weather except during periods of heavy rain.
    • Complementary information to that in optical and IR regions.
  • Disadvantages
    • Data are difficult to interpret.
    • Coarse resolution except for SAR.

University of Kansas

microwave remote sensing history
Microwave Remote Sensing— history
  • US has a long history in Microwave Remote Sensing.
    • Clutter Measurement program after the WW-II.
      • Ohio State University collected a large data base of clutter on variety of targets.
    • Earnest studies for the remote sensing of the earth can be considered to have began 1960s.
      • In 1960s NASA initiated studies to investigate the use of microwave technology to earth observation.

University of Kansas

microwave remote sensing history1
Microwave Remote Sensing— history
  • The research NASA and other agencies initiated resulted in:
    • Development of ground-based and airborne sensors.
    • Measurement of emission and scattering characteristics of many natural targets.
    • Development of models to explain and understand measured data.
    • Space missions with microwave sensors.
      • NIMBUS
        • Radiometers.
      • SKYLAB
        • Radar and Radiometers

University of Kansas

microwave remote sensing
Microwave Remote Sensing
  • Radar
    • Radio Detection and Ranging.
    • Texts:
      • Skolnik, M. I., Introduction to Radar Systems, McGraw Hill, 1981.
      • Stimson, G. W., Introduction to Airborne Radar, SciTech Publishing, 1998.

Applications

Civilian

Navigation and tracking

Search and surveillance

Imaging & Mapping

Weather

Sounding

Probing

Remote sensing

Military

Navigation and tracking

Search and surveillance

Imaging & Mapping

Weather

Proximity fuses

Counter measures

University of Kansas

review em theory and antennas
Review – EM theory and Antennas
  • Propagation of EM waves is governed by Maxwell equations.
  • For time-harmonic variation we can write the above equations as

University of Kansas

em theory
EM Theory
  • Helmholtz Equation
    • From the four Maxwell equations, we can derive vector Helmholtz equations
    • For each component of E and H field we can write a scalar equation

University of Kansas

uniform plane wave
Uniform plane wave

Amplitude and phase are constant on planes perpendicular to the direction of propagation.

TEM case– no component in the direction of propagation.

For a TEM wave propagating in z direction Ez = 0 and Hz =0

Ex(z,t) = Eo e-αzCos(ωt-jβz)

University of Kansas

em theory1
EM theory
  • α and β are determined by material properties.
  • Materials are classified as insulators and conductors

University of Kansas

em theory2
EM Theory
  • Reflection and refraction
    • Whenever a wave impinges on a dielectric interface, part of the wave will be reflected and remaining will be transmitted into the lower medium.

θi

θr

θt

University of Kansas

em theory scattering
EM Theory--Scattering
  • Microwave Scattering from a distributed target depends on
    • Dielectric constant.
    • Surface roughness.
    • Internal structure.
      • Homogeneous
      • Inhomogeneous
    • Wavelength or Frequency.
    • Polarization.

University of Kansas

microwave scattering

θi

θr

Microwave Scattering
  • Surface scattering
    • A surface is classified as smooth or rough by comparing its surface height deviation with wavelength.
      • Smooth h < λ/32 cos(θ)
      • For example at 1.5 GHz and = 60 deg.,
      • h < 1.25 cm

Smooth surface

Moderately rough surface

Very rough surface

University of Kansas

microwave scattering1
Microwave Scattering
  • Rough surface scattering

University of Kansas

microwave scattering2
Microwave Scattering
  • Volume scattering
    • Material is inhomogeneous such as
      • Snow
      • Firn
      • Vegetation
      • Multiyear ice

University of Kansas

microwave scattering3
Microwave Scattering
  • Surface scattering models
    • Geometric optics model
      • Surface height standard deviation is large compared to the wavelength.
    • Small perturbation model
      • Surface height standard deviation is small compared to the wavelength.
    • Two-scale model
      • Developed to compute scattering from the ocean
        • Small ripples riding on large waves.

University of Kansas

antennas
Antennas
  • Antennas are used to couple electromagnetic waves into free space or capture electromagnetic waves from free space.
  • Type of antennas
    • Wire
      • Dipole
      • Loop antenna
    • Aperture
      • Parabolic dish
      • Horn

University of Kansas

antennas1
Antennas
  • Antennas are characterized by their:
    • Directivity
      • It is the ratio of maximum radiated power to that radiated by an isotropic antenna.
    • Efficiency
      • Efficiency defines how much of the power is the total power radiated by the antenna to that delivered to the antenna.
    • Gain
      • It is the product of efficiency and directivity
    • Beamwidth
      • Width of the main lobe at 3-dB points.

dipole

University of Kansas

antenna gain
Antenna gain

University of Kansas

antennas2
Antennas
  • An array of antennas is used whenever higher than directivity is needed.
    • Can be used to electronic scanning.
    • Most of the SAR antennas are arrays.

University of Kansas

antenna array
Antenna Array
  • Let us consider simple array consisting of isotropic radiators.

R1

Ro

d

q

P

University of Kansas

radar principles
Radar Principles
  • Radar classified according to the trasmit waveform.
    • Continuous
      • Doppler
      • Altimeter
      • Scatterometer
    • Pulse
      • Wide range of applications

University of Kansas

radar principles1
Radar Principles
  • Radar measures distance by measuring time delay between the transmit and received pulse.
    • 1 us = 150 m
    • 1 ns = 15 cm

Radar

University of Kansas

radar principle
Radar— principle
  • Unambiguous range and Pulse Repetition Frequency (PRF)
    • PRF also determines the maximum doppler we can measure with a radar— SAR.
    • PRF > 2 fdmax

University of Kansas

radar principle1
Radar equation

For a monostatic radar

GT = GR

Radar sensitivity is determined by the minimum detectable signal set by the receiver noise.

No = kTBF

F= noise figure

Signal-to-noise ratio

Radar—Principle

PT

GT

R

University of Kansas

microwave remote sensing1
Microwave Remote Sensing
  • Radar cross section characterizes the size of the object as seen by the radar.

Where

Es = scattering field

Ei = incident field

r

University of Kansas

radar equation
Radar Equation
  • A distributed target contains many scattering centers within the illuminated area. It is characterized by radar cross section per unit area, which is refereed to as scattering coefficient

be

ba

qo

R

University of Kansas

radar equation1
Radar Equation

For a distributed power received falls off as 1/R2

For a point target power received falls off as 1/R4

University of Kansas

antenna array1
Antenna Array
  • Let us consider simple array consisting of isotropic radiators.

R1

Ro

d

q

P

University of Kansas

antenna array2
Antenna Array
  • Let us consider simple array consisting of isotropic radiators.

R1

Ro

d

q

P

University of Kansas

microwave remote sensing principles and applications history
Microwave Remote Sensing: Principles and Applications— History
  • Active Microwave sensing
    • Studies related to active sensing of the earth beagn in 1960s.
      • Clutter studies
      • SkYLab – radar altimeter and scatterometer in 1960s
      • SEASAT in 1978
      • ERS-1, JERS-1, ERS-2, RADARSAT, GEOSAT, Topex-Posoidon

University of Kansas

active sensors radar altimeter
Active Sensors – Radar Altimeter
  • Radar altimeter is a short pulse radar used for accurate height measurements.
    • Ocean topography.
    • Glacial ice topography
    • Sea ice characteristics
      • Classification and ice edge
      • Vegetation
  • http://topex-www.jpl.nasa.gov/technology/images/P38232.jpg

University of Kansas

radar altimeter
MissionsRadar Altimeter

University of Kansas

radar altimeter waveform
Radar Altimeter— Waveform
  • Satellite altimeters operate in pulse-limited mode.

University of Kansas

radar altimeter1
Radar Altimeter
  • A short pulse radar
    • Uses pulse compression to obtain fine range resolution or height measurement.
    • Range measurement uncertainty of a pulse radar.

University of Kansas

radar altimeter2
Radar altimeter
  • Other sources of errors
    • Atmospheric delays
    • Troposheric delays.
    • EM bias
    • Pointing errors
    • Orbit errors
    • Accuracies of few cms are being achieved with new generation sensors.
      • Dual-frequency
      • Water vapor— radiometers
      • GPS – orbit determination
      • Calibration.

Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999

sigma=5.5 cm

University of Kansas

radar altimeter typical system
Radar Altimeter—typical system

Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999

University of Kansas

radar altimeter3
Radar Altimeter
  • Waveform analysis
    • Time delay is measured very accurately and converted into distance.
    • Spreading of the pulse is related to SWH.
    • Scattering coefficient can be obtained by determining the power.

Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999

University of Kansas

radar altimeter typical system1
Radar Altimeter- typical system
  • Block diagram of Envisat RA

Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999

University of Kansas

active sensors
Active sensors
  • Scatterometer
    • Scatter o Meter – A calibrated radar used to measure scattering coefficient.
    • They are used to measure radar backscatter as a function of incidence angle.
    • Ground and aircraft-based scatterometers are widely used.
        • Experimental data on variety of targets to support model and algorithm development activities.
          • Developing algorithms for extracting target characteristics from data.
          • Understanding the physics of scattering to develop empirical or theoretical models.
          • Developing target classification algorithms

University of Kansas

active sensors scatterometers
Active sensors— Scatterometers
  • Wide range of applications
    • Wind vector measurements
    • Sea and glacial ice
    • Snow extent.
    • Vegetation mapping
    • Soil moisture
      • Semi-arid or dry areas.

University of Kansas

microwave remote sensing atmosphere and precipitation
Microwave Remote Sensing— Atmosphere and Precipitation
  • Global precipitation mission
    • Will consist of a primary spacecraft and a constellation.
      • Primary Spacecraft
        • Dual-frequency radar.
          • 14 and 35 GHz.
        • Passive Microwave Radiometer
    • Constellation Spacecraft
      • Passive Microwave Radiometer

University of Kansas

imaging radars scatterometers
Imaging Radars & Scatterometers
  • Imaging Radars
    • Real Aperture Radar (RAR)
    • Synthetic Aperture Radar (SAR)
      • Widely used for military and civilian applications.
    • RAR
      • Thin long antenna mounted on the side of an aircraft.

University of Kansas

imaging radars
RAR

Resolution is determined by antenna beamwidth in the along track direction

Pulse width in the cross-track direction

RAR geometry

Imaging radars

University of Kansas

imaging radars1
Imaging radars
  • For a radar operating at f=10 GHz with a 3-m long antenna in the along track direction and 0.5 us pulse, resolution at 45 degree incidence and range of 10 km is given by
  • Assume k=0.8

University of Kansas

imaging radars rar
Resolution

RARs were used until 1990s.

They are replaced by SARs.

Resolution should 1/20 about the dimensions of the target we want to recognize

Imaging Radars: RAR

MRS: vol. II, Ulaby, Moore and Fung

University of Kansas

slide53
SAR
  • Synthetic Aperture Radar
    • Use the forward motion of an aircraft or a spacecraft to synthesize a long antenna.
    • Satellite SARs
      • ERS-1, ERS-2, RADARSAT, ENVISAT, JERS-1, SEASAT, SIR-A,B& C.
      • Applications
        • Ocean wave imaging
        • Oil slick monitoring
        • Sea ice classification and dynamics
        • Soil moisture
        • Vegetation
        • Glacial ice surface velocity

University of Kansas

slide54
SAR
  • We can use a small physical antenna
  • For focused SAR resolution is independent of
    • Wavelength
    • Range
    • Best possible resolution is L/2
      • Where L= length of the physical antenna

University of Kansas

rf spectrum
RF Spectrum

Microwave Radiometry covers a range of frequencies.

Soil

Moisture

1-3 GHz

Resolution /

aperture

Ocean Surface Wind

19, 22 GHz

Polarimetry

Atmospheric

Temperature

54, 118 GHz

Accuracy

Atmospheric

Water Vapor

22, 24, 92, 150,

183 GHz

Accuracy

Cloud Ice

325, 448, 643 GHz

High frequency

l

30 cm

3 cm

0.3 mm

3 mm

1000 GHz

100 GHz

10 GHz

1 GHz

Sea Surface Salinity

1-3 GHz

Receiver sensitivity/

stability

Sea Ice

37 GHz

Polar coverage

Precipitation

11, 31,37,89 GHz

Frequent global

coverage

Atmospheric

Chemistry

190, 240, 640,

2500 GHz

High frequency

Hartley, NASA

L band

S band

C band

X band

Ku/K/Ka band

Millimeter

Submillimeter

University of Kansas

microwave radiometers theory
Microwave Radiometers— theory
  • Planck’s Law of radiation
  • Where S(λ,T) =Intensity of radiation in w/m2
  • T = temperature in Kelvins
  • h = Planck’s constant, 6.625 × 10-34 J·s
  • c = velocity of propagation m/s
  • k = Boltzmann constant, 1.380 × 10-23 J/K
  • λ = wavelength, m

University of Kansas

microwave radiometer
Microwave Radiometer
  • At microwave frequencies radiation intensity is directly proportional to the temperature.
  • For gray bodies
    • Pa = kTb B
    • k =Boltzman constant, B = bandwidth, Hz.
    • Tb = Brightness temperature, K
    • Tb =e Tphy
    • e = Emissivity of the object or media

University of Kansas

microwave radiometer1
Microwave Radiometer

Two basic types of radiometers

    • Total power radiometer
      • Highest sensitivity
    • Switching-type radiometers and its variants.
  • Typical total power radiometer

University of Kansas

microwave radiometer2
Microwave Radiometer
  • Dicke or Switching-type radiometer
    • Any fluctuations in gain of the receiver will reduce radiometer sensitivity.
    • To eliminate system effects, Dicke developed switching type radiometer.
      • It consists of switch and a synchronous detector. The input is switched between the antenna and noise source. If the injected noise power is equal to input signal power, the effect of gain fluctuations is eliminated.

University of Kansas

microwave radiometer3
Microwave Radiometer
  • Typical Dicke-type radiometer

University of Kansas

rf radiometry characteristics
RF Radiometry Characteristics

Moden Radiometer

Digital processor

To eliminate down conversion process

Antenna

Receiver

multiplexer/

spectrometer

digital

processor/

correlator

detector/

digitizer

low noise

amplifier

mixer

LO

Hartley, NASA

scan

University of Kansas

microwave remote sensing2
Microwave Remote Sensing
  • Research and application of microwave technology to remote sensing of
    • Oceans and ice
    • Solid earth and Natural hazards..
    • Atmosphere and precipitation.
    • Vegetation and Soil moisture

University of Kansas

microwave remote sensing ocean and ice
Microwave Remote Sensing— Ocean and Ice
  • Winds
    • Scatterometer.
      • Quickscat, Seawinds
    • Polarimetric radiometer
  • Ocean topography
    • Radar altimeters
  • Ocean salinity
    • AQUARIUS
      • Radiometer and radar combination.
        • Radar to measure winds for correcting for the effect of surface roughness.

University of Kansas

ocean vector winds scatterometers
Ocean Vector Winds— Scatterometers

QuikScat

  • Replacement mission for NSCAT, following loss of ADEOS
  • Launch date: June 19, 1999

SeaWinds

  • EOS instrument flying on the Japanese ADEOS II Mission
  • Launch date: December 14, 2002 ????

Instrument Characteristics of QuikScat and SeaWinds

  • Instrument with 120 W peak (30% duty) transmitter at 13.4 GHz, 1 m near-circular antenna with two beams at 46o and 54o incidence angles

Scatterometers send microwave pulses to the

Earth\'s surface, and measure the power scattered

back. Backscattered power over the oceans

depends on the surface roughness, which in turn

depends on wind speed and direction.

SeaWinds

QuikScat

Advanced sensors– larger aperture antennas.Passive polarimetric sensors.

University of Kansas

Courtesy: Yunjin Kim, JPL

ocean topography missions
Ocean Topography Missions

TOPEX/Poseidon and Jason-1

  • Joint NASA-CNES Program
    • TOPEX/Poseidon launched on August 10, 1992
    • Jason-1 launched on December 7, 2001
  • Instrument Characteristics
    • Ku-band, C-band dual frequency altimeter
    • Microwave radiometer to measure water vapor
    • GPS, DORIS, and laser reflector for precise orbit determination
  • Sea-level measurement accuracy is 4.2 cm
  • TOPEX/Poseidon & Jason-1 tandem mission for high resolution ocean topography measurements

The most effective measurement of ocean currents

from space is ocean topography, the height of the sea

surface above a surface of uniform gravity, the geoid.

The priority is to continue the measurement

with TOPEX/Poseidon accuracy

on a long-term basis for climate studies. 

Courtesy: Yunjin Kim, JPL

TOPEX/Poseidon Ocean topography of the Pacific Ocean during El Niño and La Niña.

University of Kansas

slide66

Ocean Surface Topography Mission An Experimental Wide-Swath Altimeter

By adding an interferometric radar system to a conventional radar altimeter system, a swath of 200 km can be achieved, and eddies can be monitored over most of the oceans every 10 days. The design of such a system has progressed, funded by NASA’s Instrument Incubator Program. This experiment is proposed to the next mission, OSTM (Ocean Surface Topography Mission)

South America

Courtesy: Yunjin Kim, JPL

University of Kansas

slide67

1 week of salinity measurements from space

100 yrs of salinity measurements by ship

Global Ocean Salinity

  • Aquarius (JPL, GSFC, CONAE)
    • ESSP-3 mission in the risk mitigation phase
  • First instrument to measure global ocean salinity
    • Passive and active microwave instrument at L-band
    • Resolution
      • Baseline 100km, Minimum 200km
    • Global coverage in 8 days
    • Accuracy: 0.2 psu
    • Baseline mission life: 3 years

University of Kansas

Courtesy: Yunjin Kim, JPL

slide68

SRTM (Shuttle Radar Topography Mission)

  • C-band single pass interferometric SAR for topographic measurements using a 60m mast
  • DEM of 80% of the Earth’s surface in a single 11 day shuttle flight
    • 60 degrees north and 56 degrees south latitude
    • 57 degrees inclination
  • 225 km swath
  • WGS84 ellipsoid datum
  • JPL/NASA will deliver all the processed data to NIMA by January 2003
  • Absolute accuracy requirements
    • 20 m horizontal
    • 16 m vertical
  • The current best estimate of the SRTM accuracy is
    • 10 m horizontal and 8 m vertical
  • Partnership between NASA and NIMA (National Imagery and Mapping Agency)
  • X-band from German and Italian space agencies

Courtesy: Yunjin Kim, JPL

University of Kansas

slide69

L-band InSAR Technology

  • Interferometric Synthetic Aperture Radar (InSAR) can measure surface deformation (mm-cm scale) through repeated observations of an area
    • L-band is preferable due to longer correlation time due to longer wavelength (24cm)
  • Solid Earth Science Working Group recommended that
    • In the next 5 years, the new space mission of highest priority for solid-Earth science is a satellite dedicated to InSAR measurements of the land surface at L-band

Surface deformation due to Hector Mine

Earthquake using repeat-pass InSAR data

InSAR velocity difference indicates a 10%

increase in ice flow velocity from 1996 to

2000 on Pine Island Glacier

[Rignot et al., 2001]

University of Kansas

microwave remote sensing soil moisture
Microwave Remote Sensing— Soil Moisture.

RadarPol: VV, HH & HV

Res – 3 and 10 km

Radiometer

Pol: H, V

Res =40 km,

dT= 0.64º K

SGP’97

Courtesy: Tom Jackson, USDA

  • HRDROS
    • Back-up ESSP mission for global soil moisture.
      • L-band radiometer.
      • L-band radar.

University of Kansas

slide71

Microwave Remote Sensing— Atmosphere and Precipitation

CloudSAT

Salient Features

NASA ESSP mission

First 94 GHz radar space borne system

Co-manifested with CALIPSO on Delta launch vehicle

Flies Formation with the EOS Constellation

Current launch date: April 2004

Operational life: 2 years

Partnership with DoD (on-orbit ops), DoE (validation) and CSA (radar development)

Science

Measure the vertical structure of clouds and quantify their ice and water content

Improve weather prediction and clarify climatic processes.

Improve cloud information from other satellite systems, in particular those of Aqua

Investigate the way aerosols affect clouds and precipitation

Investigate the utility of 94 GHz radar to observe and quantify precipitation, in the context of cloud properties, from space

University of Kansas

Courtesy: Yunjin Kim, JPL

earth science and rf radiometery
Earth Science and RF Radiometery

Atmospheric chemistry

Precipitation

Microwave Radiometry Applications.

Sea surface temperature/

Sea surface salinity

Hartley, NASA

Ocean surface wind

Soil moisture

Atmospheric temperature, humidity, and clouds

University of Kansas

conclusions
Conclusions
  • A brief overview of microwave remote sensing principles and applications.
  • Opportunities for research and education.
    • Science
    • Technology

University of Kansas

sar principle
SAR—Principle
  • SAR can explained using the concept of a matched filter or antenna array.

Ro

University of Kansas

sar principle1
SAR— Principle
  • Unfocussed SAR
        • No phase corrections are made.

Ro

r

University of Kansas

sar principle2
SAR— Principle
  • Focussed SAR

x

Ro

University of Kansas

sar principle3
SAR— Principle
  • Resolution

University of Kansas

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