microwave remote sensing intro psd

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Published on January 22, 2008

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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. Microwave Remote Sensing: Principles and Applications:  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 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. Radar Systems and Remote Sensing Laboratory:  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 Radar Systems and Remote Sensing Laboratory:  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. 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. 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 Microwave Remote Sensing: Principles and Applications.:  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. 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. Microwave Remote Sensing— history:  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 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 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 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 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-αz Cos(ωt-jβz) EM theory:  EM theory α and β are determined by material properties. Materials are classified as insulators and conductors EM Theory:  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 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. Microwave Scattering:  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 Microwave Scattering:  Microwave Scattering Rough surface scattering Microwave Scattering:  Microwave Scattering Volume scattering Material is inhomogeneous such as Snow Firn Vegetation Multiyear ice Microwave Scattering:  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. 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 Antennas:  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 Antenna gain:  Antenna gain Antennas:  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. Antenna Array:  Antenna Array Let us consider simple array consisting of isotropic radiators. P Ro d R1 q Radar Principles:  Radar Principles Radar classified according to the trasmit waveform. Continuous Doppler Altimeter Scatterometer Pulse Wide range of applications Radar Principles:  Radar Principles Radar measures distance by measuring time delay between the transmit and received pulse. 1 us = 150 m 1 ns = 15 cm Radar 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 Radar—Principle:  Radar—Principle 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 Microwave Remote Sensing:  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 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 R qo ba Radar Equation:  Radar Equation For a distributed power received falls off as 1/R2 For a point target power received falls off as 1/R4 Antenna Array:  Antenna Array Let us consider simple array consisting of isotropic radiators. P Ro d R1 q Antenna Array:  Antenna Array Let us consider simple array consisting of isotropic radiators. P Ro d R1 q 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 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 Radar Altimeter:  Radar Altimeter Missions Radar Altimeter— Waveform:  Radar Altimeter— Waveform Satellite altimeters operate in pulse-limited mode. Radar Altimeter:  Radar Altimeter A short pulse radar Uses pulse compression to obtain fine range resolution or height measurement. Range measurement uncertainty of a pulse radar. Radar altimeter:  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 Radar Altimeter—typical system:  Radar Altimeter—typical system Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999 Radar Altimeter:  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 Radar Altimeter- typical system:  Radar Altimeter- typical system Block diagram of Envisat RA Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999 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 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. 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 Microwave Remote Sensing—Active Sensors:  Microwave Remote Sensing—Active Sensors Imaging Radars 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. Imaging radars:  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:  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 Imaging Radars: RAR:  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 MRS: vol. II, Ulaby, Moore and Fung SAR:  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 SAR:  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 RF Spectrum:  RF Spectrum Microwave Radiometry covers a range of frequencies. 1 GHz 10 GHz 100 GHz 1000 GHz Soil Moisture 1-3 GHz Resolution / aperture Atmospheric Temperature 54, 118 GHz Accuracy Atmospheric Water Vapor 22, 24, 92, 150, 183 GHz Accuracy 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 Ocean Surface Wind 19, 22 GHz Polarimetry Cloud Ice 325, 448, 643 GHz High frequency 30 cm 3 cm 3 mm 0.3 mm l  L band S band C band X band Ku/K/Ka band Millimeter Submillimeter Hartley, NASA 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 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 Microwave Radiometer:  Microwave Radiometer Two basic types of radiometers Total power radiometer Highest sensitivity Switching-type radiometers and its variants. Typical total power radiometer Microwave Radiometer:  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. Microwave Radiometer:  Microwave Radiometer Typical Dicke-type radiometer RF Radiometry Characteristics:  RF Radiometry Characteristics Moden Radiometer Digital processor To eliminate down conversion process digital processor/ correlator scan low noise amplifier multiplexer/ spectrometer detector/ digitizer mixer LO Receiver Antenna Hartley, NASA Microwave Remote Sensing :  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 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. 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. QuikScat SeaWinds Advanced sensors– larger aperture antennas.Passive polarimetric sensors. 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 TOPEX/Poseidon Ocean topography of the Pacific Ocean during El Niño and La Niña. 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 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 Slide67:  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 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 Slide69:  L-band InSAR Technology InSAR velocity difference indicates a 10% increase in ice flow velocity from 1996 to 2000 on Pine Island Glacier [Rignot et al., 2001] Surface deformation due to Hector Mine Earthquake using repeat-pass InSAR data 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 Microwave Remote Sensing— Soil Moisture.:  Microwave Remote Sensing— Soil Moisture. HRDROS Back-up ESSP mission for global soil moisture. L-band radiometer. L-band radar. Courtesy: Tom Jackson, USDA SGP’97 Radar Pol: VV, HH & HV Res – 3 and 10 km Radiometer Pol: H, V Res =40 km, dT= 0.64º K Slide71:  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 CloudSAT Microwave Remote Sensing— Atmosphere and Precipitation Courtesy: Yunjin Kim, JPL Earth Science and RF Radiometery:  Earth Science and RF Radiometery Microwave Radiometry Applications. Ocean surface wind Soil moisture Sea surface temperature/ Sea surface salinity Atmospheric temperature, humidity, and clouds Precipitation Atmospheric chemistry Hartley, NASA Conclusions:  Conclusions A brief overview of microwave remote sensing principles and applications. Opportunities for research and education. Science Technology SAR—Principle:  SAR—Principle SAR can explained using the concept of a matched filter or antenna array. Ro SAR— Principle:  SAR— Principle Unfocussed SAR No phase corrections are made. Ro r SAR— Principle:  SAR— Principle Focussed SAR Ro x SAR— Principle:  SAR— Principle Resolution

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