Microwave%20Remote%20Sensing:%20Principles%20and%20Applications

1
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.

2
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

3
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.

4
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

5
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.

6
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.

7
EM Spectrum

• Microwave region
• 300 MHz 30 GHz.
• Millimeter wave
• 30 GHz 300 GHz.
• IEEE uses a different definition
• 300 MHz 100 GHz

8
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.

9
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.

10
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

11
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 Proximit
y fuses Counter measures
12
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

13
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

14
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-az Cos(?t-jßz)

15
EM theory

• a and ß are determined by material
  properties.
• Materials are classified as insulators and
  conductors

16
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.

?i
?r
?t
17
EM Theory--Scattering

• Microwave Scattering from a distributed target
  depends on
• Dielectric constant.
• Surface roughness.
• Internal structure.
• Homogeneous
• Inhomogeneous
• Wavelength or Frequency.
• Polarization.

18
Microwave Scattering

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

Smooth surface
Moderately rough surface
Very rough surface
19
Microwave Scattering

• Rough surface scattering

20
Microwave Scattering

• Volume scattering
• Material is inhomogeneous such as
• Snow
• Firn
• Vegetation
• Multiyear ice

21
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.

22
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

23
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
24
Antenna gain
25
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.

26
Antenna Array

• Let us consider simple array consisting of
  isotropic radiators.

R1
Ro
d
q
P
27
Radar Principles

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

28
Radar Principles

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

Radar
29
Radar principle

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

30
RadarPrinciple

• 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

PT
GT
R
31
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
32
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
33
Radar Equation
For a distributed power received falls off as
1/R2 For a point target power received falls
off as 1/R4
34
Antenna Array

• Let us consider simple array consisting of
  isotropic radiators.

R1
Ro
d
q
P
35
Antenna Array

• Let us consider simple array consisting of
  isotropic radiators.

R1
Ro
d
q
P
36
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

37
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/P3
  8232.jpg

38
Radar Altimeter
Satellite Radar Altimeters Satellite Radar Altimeters Satellite Radar Altimeters Satellite Radar Altimeters
Mission Frequency Accuracy Period
SKYLAB Ku 10 m 1973
GEOS Ku 1-5 M 1976
SEASAT Ku 1 m 1978
GEOSAT Ku 10 CM 1985-1990
ERS-1 Ku lt 10 cm 1992-1998
TOPEX C Ku lt 10 cm 1992-
ERS-2 Ku lt 10 cm 1996-
GFO Ku lt10 cm 1998-
ENVISAT Ku S lt10 CM 2001-
Jason-1 Ku C lt10 cm 2000-
 CRYOSAT and other missions Ku Few cm 2003-

• Missions

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Radar Altimeter Waveform

• Satellite altimeters operate in pulse-limited
  mode.

40
Radar Altimeter

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

41
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
sigma5.5 cm
42
Radar Altimetertypical system
Resti et al, The Envisat Altimeter System
RA-2,ESA Bulletin 98, June 1999
43
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
44
Radar Altimeter- typical system

• Block diagram of Envisat RA

Resti et al, The Envisat Altimeter System
RA-2,ESA Bulletin 98, June 1999
45
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

46
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.

47
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

48
Microwave Remote SensingActive Sensors

• Imaging Radars

49
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.

50
Imaging radars

• RAR
• Resolution is determined by antenna beamwidth in
  the along track direction
• Pulse width in the cross-track direction

• RAR geometry

51
Imaging radars

• For a radar operating at f10 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 k0.8

52
Imaging Radars RAR

• RARs were used until 1990s.
• They are replaced by SARs.
• Resolution should 1/20 about the dimensions of
  the target we want to recognize

• Resolution

MRS vol. II, Ulaby, Moore and Fung
53
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

54
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

55
RF Spectrum

• Microwave Radiometry covers a range of
  frequencies.

Soil Moisture 1-3 GHz Resolution / aperture
Atmospheric Temperature 54, 118 GHz Accuracy
Atmospheric Water Vapor 22, 24, 92, 150, 183
GHz Accuracy
Ocean Surface Wind 19, 22 GHz Polarimetry
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
Precipitation 11, 31,37,89 GHz Frequent
global coverage
Atmospheric Chemistry 190, 240, 640, 2500
GHz High frequency
Sea Ice 37 GHz Polar coverage
Hartley, NASA
L band
S band
C band
X band
Ku/K/Ka band
Millimeter
Submillimeter
56
Microwave Radiometers theory

• Plancks Law of radiation
• Where S(?,T) Intensity of radiation in w/m2
• T temperature in Kelvins
• h Plancks constant, 6.625 10-34 Js
• c velocity of propagation m/s
• k Boltzmann constant, 1.380 10-23 J/K
• ? wavelength, m

57
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

58
Microwave Radiometer

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

59
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.

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Microwave Radiometer

• Typical Dicke-type radiometer

61
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
62
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

63
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.

64
Ocean Vector Winds Scatterometers
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

• 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

Advanced sensors larger aperture
antennas.Passive polarimetric sensors.
Courtesy Yunjin Kim, JPL
65
Ocean Topography Missions
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.

• 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 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.
66
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 NASAs Instrument Incubator Program.
This experiment is proposed to the next mission,
OSTM (Ocean Surface Topography Mission)
South America
Courtesy Yunjin Kim, JPL
67
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

Courtesy Yunjin Kim, JPL
68
SRTM (Shuttle Radar Topography Mission)

• C-band single pass interferometric SAR for
  topographic measurements using a 60m mast
• DEM of 80 of the Earths 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
69
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
70
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
SGP97
Courtesy Tom Jackson, USDA

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

71
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
Courtesy Yunjin Kim, JPL
72
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
73
Conclusions

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

74
SARPrinciple

• SAR can explained using the concept of a matched
  filter or antenna array.

Ro
75
SAR Principle

• Unfocussed SAR
• No phase corrections are made.

Ro
r
76
SAR Principle

• Focussed SAR

x
Ro
77
SAR Principle

• Resolution