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Introduction to Microwave Introduction to Microwave Remote SensingRemote Sensing

Dr. Sandra Cruz PolMicrowave Remote Sensing INEL 6069Dept. of Electrical & Computer Engineering,UPRM, Mayagüez, PR

Fall 2008

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OutlineOutline

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

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What is What is radiometry?radiometry?

All objects radiate EM energy.

Radiometry measures of natural EM radiation from objects; earth, ice, plants...

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Electromagnetic SpectrumElectromagnetic Spectrum

http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

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Why Microwaves?Why Microwaves?

Capability to penetrate clouds and, to some extent, rain.

Independence of the sun as a source of illumination.

Provides info about geometry and bulk-dielectric properties.(e.g. salinity)

3 stages of El Niño

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Projects ex.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).

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Active Rain Gauge Active Rain Gauge with W and S-band with W and S-band

Measures rain rate using the difference in radar reflectivity between two frequencies.

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v(D)=9.25[1-e(-6.8 +4.88D)]

Raindrop Terminal Raindrop Terminal VelocityVelocity

Doppler radar is used to measure rain rate. The Doppler frequencyis related to the terminal velocity of the raindrops. We can alsoestimate from this the particle size distribution.

D2

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Different Clouds on the Different Clouds on the AtmosphereAtmosphere

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Collaborative Adaptive Sensing Collaborative Adaptive Sensing of the Atmosphere (CASA)of the Atmosphere (CASA)

Earth curvature effects prevent 72% of the troposphere below 1 km from being observed

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Affect Earth’s radiation budget Improve global climate models (GCM) Improve reliability of forecasts

Why study Clouds?…Why study Clouds?…

Absorbed(blue area)

Transmitted(white)

W

KaAtmospheric Windows

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Why Microwaves?Why Microwaves?

Penetrate more deeply into vegetation than optical waves.

Penetrate into ground (more into dry than wet soil).

Visible and IR sensors can sometimes be used to complement this information

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Soil PenetrationSoil Penetration[[www.uni.edu/storm/rs/2001/vh7.html]www.uni.edu/storm/rs/2001/vh7.html]

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Snow – microwave Snow – microwave penetrationpenetration

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Microwave Radar BandsMicrowave Radar Bands

www.serve.com/mahood/RCS/bands.htm

BANDDesignatio

n

NominalFrequency

Range

SPECIFICBands

HF 3-30 MHz0

VHF 30-300 MHz138-144 MHz

216-225

UHF 300-1000MHz420-450 MHz

890-942

L 1-2 GHz 1.215-1.4 GHz

S 2-4 GHz2.3-2.5 GHz

2.7-3.7>

C 4-8 GHz5.25-5.925

GHz

X 8-12 GHz 8.5-10.68 GHz

Ku 12-18 GHz13.4-14.0 GHz

15.7-17.7

K 18-27 GHz24.05-24.25

GHz

Ka 27-40 GHz 33.4-36.0 GHz

V 40-75 GHz 59-64 GHz

W 75-110 GHz76-81 GHz

92-100

millimeter 110-300 GHz

(millimeter)

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Where does energy goes?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

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Microwave Remote Sensing Microwave Remote Sensing SensorsSensors

Passive– uses of radiometers to study the EarthPassive 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

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Microwave Radiometer (most of the time)

(Arecibo Observatory)

Microwave Radar

(Tropical Rainfall Measuring Mission (TRMM) satellite)

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Microwaves can see inside…Microwaves can see inside…

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History of RadarsHistory of Radars

Henry Hertz, 1886 1st radio experiment, reflections detected @200MHz, confirmed experimentally that an electric spark propagates electromagnetic waves into space.

1890, Tesla illuminated a vacuum tube wirelessly—having transmitted energy through the air using a Tesla coil to change 60Hz into hi-freq.

1895 Marconi patent for radio, 1986 in England, using 17 patents from Tesla.

1925- Pulse radars to measure height of ionosphere. 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 displays. 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.

www.csr.utexas.edu/projects/rs/whatissar/rar.html

Side Looking Aperture Radar (SLAR)Range resolution =>pulse widthAzimuth resolution=> antenna size

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Sea Ice and Iceberg Sea Ice and Iceberg Detection by SLARDetection by SLAR

Light blue sea ice with open water displayed in green

http://www.etl.noaa.gov/technology/instruments/rads/ice.html

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HistoryHistory of Radarsof 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 meteorology.

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.

http://www.met.ed.ac.uk/~chris/RS1Web/sar2-2000/ppframe.htm

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HistoryHistoryof Microwave of Microwave RadiometersRadiometers

1930s- First radiometers used for radio-astronomy

1950s- First radiometers used for terrestrial observations

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Water absorption measurementsWater 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 Laboratory)

http://rleweb.mit.edu/groups/g-radhst.HTM

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Why monitor WV?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.

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Temperature profilesTemperature 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.

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Atmospheric ImagersAtmospheric Imagers

1977 Checking an instrument

that is the direct forerunner of today's operational satellite microwave atmospheric imagers used by NOAA

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Modern Microwave Water Modern Microwave Water

Radiometer (MWR)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 GHz)

H2O

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Truck mounted radiometerTruck mounted radiometer

http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/SGP97/slmr.html#100

This truck-mounted microwave radiometer system measures surface soil moisture at

L, S and C bands.

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Medical ApplicationsMedical 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.resltd.ru/eng/company/r_history.phpwww.whitaker.org/abstracts/jun99/hagness.html

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Microwave Temperature ProfilerMicrowave 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.

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NASA Topex/Poseidon and Jason NASA Topex/Poseidon and Jason 11

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 vapor.

If this contribution is not subtracted from the measured altimetric delay, this additional time will introduce error to the measured sea surface height.

Altimeter on board measures sea levels with accuracy to better than 5 cm!

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NASA Jason 1NASA 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.

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El Niño as measured by T/PEl Niño as measured by T/P

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Weather Applications: Weather Applications: radarradar

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CASA NSF-ERCCASA NSF-ERCDCAS systems

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Electromagnetic Plane WavesElectromagnetic Plane Waves--ReviewReview

http://www.geo.mtu.edu/rs/back/spectrum

Maxwell Eqs. Polarization Propagation in lossy media Poynting vector (power) Incidence (reflection, transmission) Brewster angle

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