Introduction to Microwave Remote Sensing Dr Sandra Cruz

Introduction to Microwave Remote Sensing Dr. Sandra Cruz Pol Microwave Remote Sensing INEL 6069 Dept. of Electrical & Computer Engineering, UPRM, Mayagüez, PR Fall 2008 1

Outline l l l l What is radiometry? Importance of Microwaves Radar vs. Radiometer Brief history Recent applications: DCAS Plane Waves Antennas 2

What is radiometry? l All objects radiate EM energy. l Radiometry measures of natural EM radiation from objects; earth, ice, plants. . . 3

Electromagnetic Spectrum http: //www. lbl. gov/Micro. Worlds/ALSTool/EMSpec 2. html 4

Why Microwaves? l Capability to penetrate clouds and, to some extent, rain. l Independence of the sun as a source of illumination. l Provides info about geometry and bulkdielectric properties. (e. g. salinity) 5 3 stages of El Niño

Projects ex. Estudio de contenido de vapor de agua en nubes tipo stratus (NASA - TCESS) l Estudio de detección de razón de lluvia usando radares banda S y W. (NASA) l Estudio de reflectividad de cristales de hielo que componen las nubes tipo cirrus. (NSF). l 6

Active Rain Gauge with W and S-band l Measures rain rate using the difference in radar reflectivity between two frequencies. 7

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. 2 +4. 88 D) (-6. 8 D v(D)=9. 25[1 -e ] 8

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Different Clouds on the Atmosphere 10

Collaborative Adaptive Sensing of the Atmosphere (CASA) Earth curvature effects prevent 72% of the troposphere below 1 km from being observed 11

Why study Clouds? … Affect Earth’s radiation budget l Improve global climate models (GCM) l Improve reliability of forecasts l Transmitted (white) Absorbed (blue area) Atmospheric Windows Ka W 12

Why Microwaves? Penetrate more deeply into vegetation than optical waves. l Penetrate into ground (more into dry than wet soil). l Visible and IR sensors can sometimes be used to complement this information 13

Soil Penetration [www. uni. edu/storm/rs/2001/vh 7. html] 14

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Snow – microwave penetration 16

Microwave Radar Bands BAND Designation Nominal Frequency Range SPECIFIC Bands HF 3 -30 MHz 0 VHF 30 -300 MHz 138 -144 MHz 216 -225 UHF 300 -1000 MHz 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. 7> 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 (millimeter) 17 www. serve. com/mahood/RCS/bands. htm

Where does energy goes? l Energy (EM waves) received at the Earth from the Sun is – absorbed (atmosphere , clouds, earth, ocean…) – scattered – transmitted l Absorbed energy is transformed – into thermal energy. l Thermodynamic balance – through emission, absorption, …RT 18

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 : l Radars: CW, Pulse, Doppler, FM l Side looking airborne radar (SLAR) l Synthetic aperture radar (SAR) l Wind scatterometer l Altimeter 19 l Polarimeter

Microwave Radiometer (most of the time) (Arecibo Observatory) Microwave Radar (Tropical Rainfall Measuring Mission (TRMM) satellite) 20

Microwaves can see inside… 21

History of Radars Henry Hertz, 1886 1 st radio experiment, reflections detected @200 MHz, confirmed experimentally that an electric spark propagates electromagnetic waves into space. Side Looking Aperture Radar ( l 1890, Tesla illuminated a vacuum tube wirelessly—having Range resolution =>pulse width transmitted energy through the air using a Tesla Azimuth coil to change resolution=> antenna si 60 Hz into hi-freq. l l l l l 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 –Lopower source 1938 Altimeter – airborne FM radars at 400 MHz to measure altitude. www. csr. utexas. edu/projects/rs/whatissar/rar. html 1950 – SLAR – finer resolution cause antennas length up to 15 22 m fixed || to fuselage. Airplane motion produced a scan.

Sea Ice and Iceberg Detection by SLAR l Light blue sea ice with open water displayed in green http: //www. etl. noaa. gov/technology/instruments/rads/ice. html 23

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. ] l Scatterometer – radar that measures scattering coefficient. (In ocean, scatter is proportional to wind speed. ) l 1970 – Doppler becomes major technique for meteorology. l 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. 24 http: //www. met. ed. ac. uk/~chris/RS 1 Web/sar 2 -2000/ppframe. htm

History of Microwave Radiometers l 1930 s- First radiometers used for radio-astronomy l 1950 s- First radiometers used for terrestrial observations 25

Water absorption measurements circa 1945 l A Radiation Laboratory rooftop 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 26

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". l 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. l 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. l 27

Temperature profiles 1965 l 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. l 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. 28

Atmospheric Imagers 1977 l Checking an instrument that is the direct forerunner of today's operational satellite microwave atmospheric imagers used by NOAA 29

Modern Microwave Water Radiometer (MWR) Provides time-series measurements of columnintegrated 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) l H 2 O 30

Truck mounted radiometer This truck-mounted microwave radiometer system measures surface soil moisture at L, S and C bands. http: //daac. gsfc. nasa. gov/CAMPAIGN_DOCS/SGP 97/slmr. html#100 31

Medical Applications l 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%. l 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. php www. whitaker. org/abstracts/jun 99/hagness. html 32

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. l Knowledge gained in developing this radiometers are useful in developing radiometers for unstart-prevention systems in high-speed (up to mach 2. 4) civiltransport aircrafts. 33

NASA Topex/Poseidon and Jason 1 Altimeter on board measures sea levels with accuracy to better than 5 cm! l l l One of the contributions to the altimetric delay is the wet path del The wet path delay is the additional time that it takes for the signa If this contribution is not subtracted from the measured altimetric 34

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. l These frequencies were chosen because radiances at these frequencies are sensitive to atmospheric water vapor and liquid water. l 35

El Niño as measured by T/P 36

Weather Applications: radar 37

CASA NSF-ERC l DCAS systems 38

Electromagnetic Plane Waves -Review l l l Maxwell Eqs. Polarization Propagation in lossy media Poynting vector (power) Incidence (reflection, transmission) Brewster angle http: //www. geo. mtu. edu/rs/back/spectrum 39

Antennas -review l l l Types Pattern Beamwidth Solid Angle Directivity, Gain Effective Area Friis equation Far Field Radiation Resistance Radome Antenna Arrays 40