Microwave Remote Sensing Principles and Applications Outline Introduction

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 • • 11/18/02 Sea ice. Glacial ice Ocean winds. Soil Moisture. Snow. Vegetation. Precipitation. Solid Earth. University of Kansas

Microwave Remote Sensing: Principles and Applications • Passive Microwave Sensors – Radiometers • Traditional • Interferometer • Polarimetric Radiometer • Application of Passive Microwave Sensors • • 11/18/02 Sea ice. Glacial ice Soil Moisture. Atmospheric sounding Snow. Vegetation. Precipitation University of Kansas

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. 11/18/02 University of Kansas

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. Scan. SARRadarsat- Canadian satellite Envisat - European SRTM -Shuttle Radar Topography Mission. Radar Systems and Remote Sensing Laboratory 11/18/02 University of Kansas

Radar Systems and Remote Sensing Laboratory • Shuttle Radar Topography Mission (SRTM) – to collect threedimensional 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 Scan. SAR operation--concept developed at KU. 11/18/02 University of Kansas

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, Co. E, Math • 29 faculty, 15 staff researchers, 6 Center staff • Current student population ~ 130 – ~ 13 Ph. D. , ~81 M. S. , ~37 B. S. 11/18/02 University of Kansas

EM Spectrum • Microwave region • 300 MHz – 30 GHz. Millimeter wave • 30 GHz – 300 GHz. IEEE uses a different definition • 300 MHz – 100 GHz 11/18/02 University of Kansas

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. 11/18/02 University of Kansas

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 1960 s. • In 1960 s NASA initiated studies to investigate the use of microwave technology to earth observation. 11/18/02 University of Kansas

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 11/18/02 University of Kansas

Microwave Remote Sensing • Radar Applications – Radio Detection and Ranging. – Texts: Civilian Navigation and tracking • Skolnik, M. I. , Introduction to Radar Systems, Mc. Graw Hill, 1981. • Stimson, G. W. , Introduction to Airborne Radar, Sci. Tech Publishing, 1998. Search and surveillance Imaging & Mapping Military Navigation and tracking Search and surveillance Weather Imaging & Mapping Sounding Weather Probing Remote sensing Proximity fuses Counter measures 11/18/02 University of Kansas

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 11/18/02 University of Kansas

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 11/18/02 University of Kansas

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) 11/18/02 University of Kansas

EM theory • α and β are determined by material properties. • Materials are classified as insulators and conductors – 11/18/02 University of Kansas

EM Theory • Reflection and refraction θi – Whenever a wave impinges on a dielectric interface, part of the wave will be reflected and remaining will be transmitted into the lower medium. 11/18/02 University of Kansas θr θt

EM Theory--Scattering • Microwave Scattering from a distributed target depends on – Dielectric constant. – Surface roughness. – Internal structure. • Homogeneous • Inhomogeneous – Wavelength or Frequency. – Polarization. 11/18/02 University of Kansas

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 11/18/02 University of Kansas θi θr Smooth surface Moderately rough surface Very rough surface

Microwave Scattering • Rough surface scattering 11/18/02 University of Kansas

Microwave Scattering • Volume scattering – Material is inhomogeneous such as • • 11/18/02 Snow Firn Vegetation Multiyear ice University of Kansas

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. 11/18/02 University of Kansas

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 11/18/02 University of Kansas

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 d. B points. 11/18/02 University of Kansas dipole

Antenna gain 11/18/02 University of Kansas

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. 11/18/02 University of Kansas

Antenna Array • Let us consider simple array consisting of isotropic radiators. R 1 Ro d q P 11/18/02 University of Kansas

Radar Principles • Radar classified according to the trasmit waveform. – Continuous • Doppler • Altimeter • Scatterometer – Pulse • Wide range of applications 11/18/02 University of Kansas

Radar Principles • Radar measures distance by measuring time delay between the transmit and received pulse. Radar – 1 us = 150 m – 1 ns = 15 cm 11/18/02 University of Kansas

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 11/18/02 University of Kansas

Radar—Principle • Radar equation PT GT • • • R • • • 11/18/02 For a monostatic radar GT = G R Radar sensitivity is determined by the minimum detectable signal set by the receiver noise. No = k. TBF F= noise figure Signal-to-noise ratio University of Kansas

Microwave Remote Sensing • Radar cross section characterizes the size of the object as seen by the radar. Where Es = scattering field Ei = incident field 11/18/02 University of Kansas r

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 11/18/02 be qo University of Kansas ba R

Radar Equation For a distributed power received falls off as 1/R 2 For a point target power received falls off as 1/R 4 11/18/02 University of Kansas

Antenna Array • Let us consider simple array consisting of isotropic radiators. R 1 Ro d q P 11/18/02 University of Kansas

Antenna Array • Let us consider simple array consisting of isotropic radiators. R 1 Ro d q P 11/18/02 University of Kansas

Microwave Remote Sensing: Principles and Applications— History • Active Microwave sensing – Studies related to active sensing of the earth beagn in 1960 s. • Clutter studies • Sk. YLab – radar altimeter and scatterometer in 1960 s • SEASAT in 1978 • ERS-1, JERS-1, ERS-2, RADARSAT, GEOSAT, Topex-Posoidon

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/P 38232. jpg 11/18/02 University of Kansas

Radar Altimeter • Missions Satellite Radar Altimeters Mission Frequency Accuracy 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 < 10 cm 1992 -1998 TOPEX C &Ku < 10 cm 1992 - ERS-2 Ku < 10 cm 1996 - GFO Ku <10 cm 1998 - ENVISAT Ku &S <10 CM 2001 - Jason-1 Ku &C <10 cm 2000 - CRYOSAT and other missions Ku Few cm 2003 - 11/18/02 University of Kansas Period

Radar Altimeter— Waveform • Satellite altimeters operate in pulse-limited mode. 11/18/02 University of Kansas

Radar Altimeter • A short pulse radar – Uses pulse compression to obtain fine range resolution or height measurement. – Range measurement uncertainty of a pulse radar. 11/18/02 University of Kansas

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. • • 11/18/02 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 University of Kansas

Radar Altimeter—typical system Resti et al, “The Envisat Altimeter System RA-2, ”ESA Bulletin 98, June 1999 11/18/02 University of Kansas

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 11/18/02 University of Kansas

Radar Altimeter- typical system • Block diagram of Envisat RA Resti et al, “The Envisat Altimeter System RA-2, ”ESA Bulletin 98, June 1999 11/18/02 University of Kansas

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 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 11/18/02 University of Kansas

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. 11/18/02 University of Kansas

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 11/18/02 University of Kansas

Microwave Remote Sensing—Active Sensors Imaging Radars

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. 11/18/02 University of Kansas

Imaging radars • RAR geometry – Resolution is determined by antenna beamwidth in the along track direction – Pulse width in the cross-track direction 11/18/02 University of Kansas

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 11/18/02 University of Kansas

Imaging Radars: RARs were used until 1990 s. 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 11/18/02 University of Kansas

SAR • Synthetic Aperture Radar • • Use the forward motion of an aircraft or a spacecraft to synthesize a long antenna. Satellite SARs • • 11/18/02 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 University of Kansas

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 11/18/02 University of Kansas

RF Spectrum Microwave Radiometry covers a range of frequencies. Soil Moisture 1 -3 GHz Resolution / aperture l 30 cm 3 cm 1 GHz 10 GHz Sea Surface Salinity 1 -3 GHz Receiver sensitivity/ stability Atmospheric Water Vapor 22, 24, 92, 150, 183 GHz Accuracy Atmospheric Temperature 54, 118 GHz Accuracy Ocean Surface Wind 19, 22 GHz Polarimetry Cloud Ice 325, 448, 643 GHz High frequency 0. 3 mm Atmospheric Chemistry 190, 240, 640, 2500 GHz High frequency Precipitation 11, 37, 89 GHz Frequent global coverage Sea Ice 37 GHz Polar coverage 1000 GHz 100 GHz Hartley, NASA L band 11/18/02 S band C band X band Ku/K/Ka band University of Kansas Millimeter Submillimeter

Microwave Radiometers— theory • Planck’s Law of radiation • Where S(λ, T) =Intensity of radiation in w/m 2 • 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 11/18/02 University of Kansas

Microwave Radiometer • At microwave frequencies radiation intensity is directly proportional to the temperature. • For gray bodies – – – 11/18/02 Pa = k. Tb B k =Boltzman constant, B = bandwidth, Hz. Tb = Brightness temperature, K Tb =e Tphy e = Emissivity of the object or media University of Kansas

Microwave Radiometer Two basic types of radiometers – Total power radiometer • Highest sensitivity – Switching-type radiometers and its variants. • Typical total power radiometer 11/18/02 University of Kansas

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. 11/18/02 University of Kansas

Microwave Radiometer • Typical Dicke-type radiometer 11/18/02 University of Kansas

RF Radiometry Characteristics Moden Radiometer Digital processor To eliminate down conversion process Antenna Receiver low noise amplifier mixer multiplexer/ spectrometer LO scan 11/18/02 University of Kansas detector/ digitizer Hartley, NASA digital processor/ correlator

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 11/18/02 University of Kansas

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. 11/18/02 University of Kansas

Ocean Vector Winds— Scatterometers send microwave pulses to the Earth's surface, and measure the power scattered back. Backscattered power over the oceans Quik. Scat depends on the surface roughness, which in turn Sea. Winds depends on wind speed and direction. Quik. Scat • Replacement mission for NSCAT, following loss of ADEOS • Launch date: June 19, 1999 Sea. Winds • EOS instrument flying on the Japanese ADEOS II Mission • Launch date: December 14, 2002 ? ? Instrument Characteristics of Quik. Scat and Sea. Winds • Instrument with 120 W peak (30% duty) transmitter at 13. 4 GHz, 1 m near-circular antenna with two beams at 46 o and 54 o incidence angles Advanced sensors– larger aperture antennas. Passive polarimetric sensors. 11/18/02 University of Kansas Courtesy: Yunjin Kim, JPL

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 – – • Instrument Characteristics – – – • • TOPEX/Poseidon launched on August 10, 1992 Jason-1 launched on December 7, 2001 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 11/18/02 University of Kansas TOPEX/Poseidon Ocean topography of the Pacific Ocean during El Niño and La Niña.

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 11/18/02 University of Kansas

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 100 km, Minimum 200 km – Global coverage in 8 days 1 week of salinity measurements from space – Accuracy: 0. 2 psu – Baseline mission life: 3 years 11/18/02 University of Kansas 100 yrs of salinity measurements by ship Courtesy: Yunjin Kim, JPL

SRTM (Shuttle Radar Topography Mission) • • • Partnership between NASA and NIMA (National Imagery and Mapping Agency) • X-band from German and Italian space agencies • • • Courtesy: Yunjin Kim, JPL 11/18/02 C-band single pass interferometric SAR for topographic measurements using a 60 m 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 WGS 84 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 University of Kansas

L-band In. SAR Technology • • Interferometric Synthetic Aperture Radar (In. SAR) 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 (24 cm) 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 In. SAR measurements of the land surface at L-band 11/18/02 Surface deformation due to Hector Mine Earthquake using repeat-pass In. SAR data In. SAR velocity difference indicates a 10% increase in ice flow velocity from 1996 to 2000 on Pine Island Glacier University of Kansas [Rignot et al. , 2001]

Microwave Remote Sensing— Soil Moisture. Radar Pol: VV, HH & HV Res – 3 and 10 km SGP’ 97 Radiometer Pol: H, V Res =40 km, d. T= 0. 64º K Courtesy: Tom Jackson, USDA • HRDROS – Back-up ESSP mission for global soil moisture. • L-band radiometer. • L-band radar. 11/18/02 University of Kansas

Microwave Remote Sensing— Atmosphere and Precipitation Cloud. SAT 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 Do. D (on-orbit ops), Do. E (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 11/18/02 University of Kansas Courtesy: Yunjin Kim, JPL

Earth Science and RF Radiometery Atmospheric chemistry Precipitation Microwave Radiometry Applications. Sea surface temperature/ Sea surface salinity Hartley, NASA Ocean surface wind 11/18/02 Atmospheric temperature, humidity, and clouds University of Kansas Soil moisture

Conclusions • A brief overview of microwave remote sensing principles and applications. • Opportunities for research and education. – Science – Technology 11/18/02 University of Kansas

SAR—Principle • SAR can explained using the concept of a matched filter or antenna array. Ro 11/18/02 University of Kansas

SAR— Principle • Unfocussed SAR • No phase corrections are made. Ro r 11/18/02 University of Kansas

SAR— Principle • Focussed SAR x Ro 11/18/02 University of Kansas

SAR— Principle • Resolution 11/18/02 University of Kansas