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Introduction to Microwave Remote Sensing


Dr. Sandra Cruz Pol Microwave Remote Sensing INEL 6069 Dept. of Electrical & Computer Engineering, UPRM, Mayag ez, PR Fall 2008 Outline What is radiometry? – PowerPoint PPT presentation

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Title: Introduction to Microwave Remote Sensing

Introduction to Microwave Remote Sensing
  • Dr. Sandra Cruz Pol
  • Microwave Remote Sensing INEL 6069
  • Dept. of Electrical Computer Engineering,
  • UPRM, Mayagüez, PR
  • Fall 2008

  • What is radiometry?
  • Importance of Microwaves
  • Radar vs. Radiometer
  • Brief history
  • Recent applications DCAS
  • Plane Waves
  • Antennas

What is radiometry?
  • All objects radiate EM energy.
  • Radiometry measures of natural EM radiation from
    objects earth, ice, plants...

Electromagnetic Spectrum
Why Microwaves?
  • Capability to penetrate clouds and, to some
    extent, rain.
  • Independence of the sun as a source of
  • Provides info about geometry and bulk-dielectric
    properties.(e.g. salinity)

3 stages of El Niño
Projects ex.
  • Estudio de contenido de vapor de agua en nubes
    tipo stratus (NASA - TCESS)
  • Estudio de detección de razón de lluvia usando
    radares banda S y W. (NASA)
  • Estudio de reflectividad de
    cristales de hielo que
    componen las nubes
    tipo cirrus. (NSF).

Active Rain Gauge with W and S-band
  • Measures rain rate using the difference in radar
    reflectivity between two frequencies.

Raindrop Terminal Velocity
Doppler radar is used to measure rain rate. The
Doppler frequency is related to the terminal
velocity of the raindrops. We can also estimate
from this the particle size distribution.
v(D)9.251-e(-6.8 4.88D)
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Different Clouds on the Atmosphere
Collaborative Adaptive Sensing of the Atmosphere
  • Earth curvature effects prevent 72 of the
    troposphere below 1 km from being observed

Why study Clouds?
  • Affect Earths radiation budget
  • Improve global climate models (GCM)
  • Improve reliability of forecasts

Transmitted (white)
Absorbed (blue area)
Atmospheric Windows
Why Microwaves?
  • Penetrate more deeply into vegetation than
    optical waves.
  • Penetrate into ground (more into dry than wet
  • Visible and IR sensors can sometimes be used to
    complement this information

Soil Penetration
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Snow microwave penetration
Microwave Radar Bands
BAND Designation Nominal Frequency Range SPECIFIC Bands
HF 3-30 MHz0
VHF 30-300 MHz 138-144 MHz 216-225
UHF 300-1000MHz 420-450 MHz 890-942
L 1-2 GHz 1.215-1.4 GHz
S 2-4 GHz 2.3-2.5 GHz 2.7-3.7gt
C 4-8 GHz 5.25-5.925 GHz
X 8-12 GHz 8.5-10.68 GHz
Ku 12-18 GHz 13.4-14.0 GHz 15.7-17.7
K 18-27 GHz 24.05-24.25 GHz
Ka 27-40 GHz 33.4-36.0 GHz
V 40-75 GHz 59-64 GHz
W 75-110 GHz 76-81 GHz 92-100
millimeter 110-300 GHz
Where does energy goes?
  • Energy (EM waves) received at the Earth from the
    Sun is
  • absorbed (atmosphere , clouds, earth, ocean)
  • scattered
  • transmitted
  • Absorbed energy is transformed
  • into thermal energy.
  • Thermodynamic balance
  • through emission, absorption,RT

Microwave Remote Sensing Sensors
  • Passive uses of radiometers to study the Earth
  • Passive sensors are called microwave radiometers,
    which receive and detect the radiation emitted
    from various objects on the earth
  • Active uses RADAR (RAdio Detection And Ranging)
    to study Earth
  • Active microwave remote sensor illuminates the
    ground with microwave radiation and then receives
    the back-scattered energy from the object. Some
    of the active microwave remote sensors are
  • Radars CW, Pulse, Doppler, FM
  • Side looking airborne radar (SLAR)
  • Synthetic aperture radar (SAR)
  • Wind scatterometer
  • Altimeter
  • Polarimeter

Microwave Radiometer (most of the time) (Arecibo
Observatory) Microwave Radar (Tropical
Rainfall Measuring Mission (TRMM) satellite)
Microwaves can see inside
History of Radars
  • Henry Hertz, 1886 1st radio experiment,
    reflections detected _at_200MHz, confirmed
    experimentally that an electric spark propagates
    electromagnetic waves into space.
  • 1890, Tesla illuminated a vacuum tube
    wirelesslyhaving transmitted energy through the
    air using a Tesla coil to change 60Hz into
  • 1895 Marconi patent for radio, 1986 in England,
    using 17 patents from Tesla.
  • 1925- Pulse radars to measure height of
  • 1930- unintentional detection of airplanes
  • 1943 the Supreme Court overturned Marconi's
    patent in in favor of Tesla.
  • WWII- detecting ships and aircraft. Used PPI
  • MIT- developed magnetron hi-power Tx and
    klystron Lo-power source
  • 1938 Altimeter airborne FM radars at 400MHz to
    measure altitude.
  • 1950 SLAR finer resolution cause antennas
    length up to 15 m fixed to fuselage. Airplane
    motion produced a scan.
Sea Ice and Iceberg Detection by SLAR
  • Light blue sea ice with open water displayed in

History of Radars
  • 1952- 54 SAR fine resolution Doppler, pixel
    dimension in the along track direction
    independent of distance from radar, and antenna
    could be much smaller. Complex processing to
    produce an image.
  • Scatterometer radar that measures scattering
    coefficient. (In ocean, scatter is proportional
    to wind speed.)
  • 1970 Doppler becomes major technique for

RADARSAT is a Synthetic Aperture Radar (SAR) at
C-band. Used for oceanic oil spill and ice sheet
monitoring. A target's position along the flight
path determines the Doppler frequency of its
echoes Targets ahead of the aircraft produce a
positive Doppler offset targets behind the
aircraft produce a negative offset. As the
aircraft flies a distance (the synthetic
aperture), echoes are resolved into a number of
Doppler frequencies. The target's Doppler
frequency determines its azimuth position.
History of Microwave Radiometers
  • 1930s- First radiometers used for radio-astronomy
  • 1950s- First radiometers used for terrestrial

Water absorption measurements
  • circa 1945
  • A Radiation Laboratory roof-top crew use
    microwave radiometer equipment pointed at the sun
    to measure water absorption by the atmosphere.
    Atop Building 20 (from left) Edward R. Beringer,
    Robert L. Kyhl, Arthur B. Vane, and Robert H.
    Dicke (Photo from Five Years at the Radiation

Why monitor WV?
  • Water vapor is one of the most significant
    constituents of the atmosphere since it is the
    means by which moisture and latent heat are
    transported to cause "weather".
  • Water vapor is also a greenhouse gas that plays a
    critical role in the global climate system. This
    role is not restricted to absorbing and radiating
    energy from the sun, but includes the effect it
    has on the formation of clouds and aerosols and
    the chemistry of the lower atmosphere.
  • Despite its importance to atmospheric processes
    over a wide range of spatial and temporal scales,
    it is one of the least understood and poorly
    described components of the Earth's atmosphere.

Temperature profiles
  • 1965
  • On location at the National Center for
    Atmospheric Research (NCAR) in Texas. A launch
    crew prepares a 60-GHz atmospheric sensing
    receiver. Once lofted airborne by balloon, the
    receiver remotely sensed the temperature profile
    at different altitudes.
  • These experiments evolved into the Nimbus series
    of NASA satellites, which later became part of
    the National Oceanic and Atmospheric
    Administration's (NOAA) satellite weather
    forecasting system, also used by NASA.

Atmospheric Imagers
  • 1977
  • Checking an instrument that is the direct
    forerunner of today's operational satellite
    microwave atmospheric imagers used by NOAA

Modern Microwave Water Radiometer (MWR)
  • Provides time-series measurements of
    column-integrated amounts of water vapor and
    liquid water.
  • The instrument itself is essentially a sensitive
    microwave receiver.
  • That is, it is tuned to measure the microwave
    emissions of the vapor and liquid water molecules
    in the atmosphere at specific frequencies. (22

Truck mounted radiometer
  • This truck-mounted microwave radiometer system
    measures surface soil moisture at
  • L, S and C bands.

Medical Applications
  • Microwave Radiometry can be used for the
    detection of different diseases.
  • Madison, WI- tumor-detection system exploits the
    large dielectric contrast between normal tissues
    and malignant tumors at microwave frequencies.
  • Clinical trials at Moscow oncological centers,
    conducted in over 1000 patients have shown that
    breast cancer detective ability of microwave
    radiometry is 90.
  • Microwave Radiation used for treatment.
  • The microwave procedure used a finely focused
    beam which heats up and kills tumour cells. The
    trial is being organised at two centres in the
    US, in Palm Beach, Florida, and the Harbor UCLA
    Medical Centre in California. www.whitak
Microwave Temperature Profiler
  • is a microwave radiometer that measures thermal
    emission from oxygen molecules along a line of
    sight that is scanned in elevation angle.
  • Knowledge gained in developing this radiometers
    are useful in developing radiometers for
    unstart-prevention systems in high-speed (up to
    mach 2.4) civil-transport aircrafts.

NASA Topex/Poseidon and Jason 1
Altimeter on board measures sea levels with
accuracy to better than 5 cm!
  • One of the contributions to the altimetric delay
    is the wet path delay caused by tropospheric
    water vapor in the altimetric signal path.
  • The wet path delay is the additional time that it
    takes for the signal to pass through the water
  • If this contribution is not subtracted from the
    measured altimetric delay, this additional time
    will introduce error to the measured sea surface

NASA Jason 1
  • A downward-looking water vapor radiometer onboard
    the altimeter satellite measures microwave
    radiation at several different frequencies, 18
    GHz, 21 GHz, and 37 GHz.
  • These frequencies were chosen because radiances
    at these frequencies are sensitive to atmospheric
    water vapor and liquid water.

El Niño as measured by T/P
Weather Applications radar
  • DCAS systems

Electromagnetic Plane Waves -Review
  • Maxwell Eqs.
  • Polarization
  • Propagation in lossy media
  • Poynting vector (power)
  • Incidence (reflection, transmission)
  • Brewster angle
  • http//

Antennas -review
  • Types
  • Pattern
  • Beamwidth
  • Solid Angle
  • Directivity, Gain
  • Effective Area
  • Friis equation
  • Far Field
  • Radiation Resistance
  • Radome
  • Antenna Arrays