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1、Fundamental for SAR Remote Sensing,Passive remote sensing Active remote sensing,Passive systemOptical sensors,Active systemradar sensors,RADAR=RAdio Detection And Ranging,radar=a ranging or distance measuring device with a transmitter,a receiver,an antenna,and an electronics system to process and re
2、cord the data.Transmitter generates successive short bursts(or pulses of microwave(A)at regular intervals which are focused by the antenna into a beam(B).The antenna receives a portion of the transmitted energy reflected(or backscattered)from various objects within the illuminated beam(C).,Radar and
3、 electromagnetic spectrum,Radar signal:amplitude and phase,SAR signal is a complex natureSAR=Amplitude+phaseSpeckle appears as a grainy salt and pepper texture in an image.This is caused by random constructive and destructive interference from the multiple scattering returns that will occur within e
4、ach resolution cell.,Homogeneous target,Constructive interferenceDestructive interferenceVarious level of interference(between constructive and destructive),Signal-Surface interactions and back-scattering,Microwave interaction with natural surfaces is a function of:SAR configurationincidence anglefr
5、equencypolarisationSurfaces physical and electrical propertiesroughnesssoil moisturevegetation parametersSurfaces geometryLocal and large scale,Signal-Surface interactions:Rayleigh criterion,Specular reflection(smooth surface)h/8cos Diffuse reflection(rough surface)h/8cos,Specular to diffuse,1-Backs
6、catter over a rough surface(1):=radar response due to backscattered signal2 Penetration in a dry soil(2):response depends upon subsurface layer3-Smooth surface or a super-saturated soil(3):Specular reflection=low radar responseNote:influence of radar wavelength and incidence angle,Interaction of the
7、 Radar Signal with the Soil,Reflection off forest canopy(1)Penetration into foliage(2)(volume scattering)Multiple reflections on trees and soil(3),Backscatter of Radar Signal over Forests,1-Low incidence angle and short wavelengths(1)=:no penetration into vegetation2-Strong incidence and large wavel
8、engths(2):=penetration into vegetation=information on moisture,soil and/or water3-Specific temporal behavior of certain crop types(e.g.rice),Backscatter behavior over vegetation,Radar signal-surface interactions,Free(liquid)water=smooth surface,Urban area=rough surface,Ploughed fields=rough surface,
9、Crop at early stage=smooth surface,dark,bright,dark,bright,SAR:Geometry of Illumination,Synthetic Aperture Principle,SAR spatial resolution,Range resolution,Azimuth resolution:determined by the angular width of the radiated microwave beam and the slant range distance,Radar Image distortion:Slant-ran
10、ge scale distortion,Radar=measure the distance to features in slant-range rather than the true horizontal distance along the ground.a varying image scale,moving from near to far range Targets A1 and B1:same size on the ground,Different apparent dimensions in slant range(A2 and B2)Targets in the near
11、 range to appear compressed relative to the far range.Using trigonometry,ground-range distance can be calculated from the slant-range distance and platform altitude to convert to the proper ground-range format,A,B,C,D,Image brightness,Effect of topography:-Shadows-Foreshortening-Layover(extreme case
12、 of foreshortening,topography is inverted)=SAR use limitations in relief area,Shadow,Use of DEMto correct,A=Smaller=foreshortening,RADAR Geometric Distortions:Foreshortening-Shadowing-Layover,Influence of systems configuration:polarization,Polarization effects,Polarization Refers to the orientation
13、of the electric field Transmit microwave radiation either horizontally polarized(H)or vertically polarized(V).Antenna receives either the horizontally or vertically polarized backscattered energy,and some radars can receive both.Four combinations:HH-for horizontal transmit and horizontal receive,VV-
14、for vertical transmit and vertical receive,HV-for horizontal transmit and vertical receive,VH-for vertical transmit and horizontal receive,Influence of systems configuration:polarization and wavelength,Polarization effects,C,L,Wavelength effects,Comparison of optical and SAR data,OPTICALBiological S
15、ensitivity(ex:photosynthesis)High ResolutionSpectral Resolution(several bands),RADARPhysical Sensitivity(ex:roughness and moisture)High ResolutionAll weather acquisition(cloud penetration),Image processing techniques of SAR data,Geometric correction and geocodingCalibrationSpeckle filteringCoherence
16、 imagesClassificationAmplitude and phase SAR information,Quantitative analysis of SAR data,Prerequisite:Calibration(documented by ESA)Measurement accuracyERS signal stability(+/-0.2 dB)Observation scale0=f(roughness)*f(soil moisture)*f(vegetation parameter)1 date(1 equation,several unknown parameter
17、s?)multi-date,synergy with other sensors,SIGPoor scientific knowledge“SAR signal interaction with natural surfaces”,SAR data:interesting information Difficulty to use or extract,Speckleaffecting photo-interpretationintroducing uncertainty in the backscattering coefficient measurementCombined influen
18、ce of different parameters on the backscattering coefficient measurement and especially roughness,biomass and moistureComplexity of the interaction phenomena between the SAR signal and natural surfaces which is not fully understoodGeometry of SAR systems,SAR radiometry correction:Speckle filtering a
19、nd radiometric enhancement,Often a prerequisite before flood mapping or before classificationSpatial filtering:Mean filterAdaptative filterGamma-MAPLee,frost etc Temporal filtering:-Annual summing-Seasonal summing Optimized temporal filtering:3 local parameters-Textural distance-Radiometric mean-Cor
20、relation,(Temporal filtering on S images),Optimized temporal filtering=take in account local mean,j=1,S.S=number of image in the time seriee,I=Intensity of the pixel(a,r),m=local mean of the neighbourhood of the pixel(a,r),ak=weighting coefficient of the image k with:,o,SAR radiometry correction:Spe
21、ckle filtering and radiometric enhancement,Comparison of methods,Gamma-MAP Filter(widow size=3x3),Simple temporal mean,based on a 7 images time serie,Optimized temporal filtering-I,SAR radiometry correction:Speckle filtering and radiometric enhancement,Radiometry correction:speckle filtering,Gamma M
22、AP filter,Radiometry correction:speckle filtering by temporal filtering,One ERS image,Result of ERS temporal summing,1 SAR Image,8 SAR images,Temporal fusion a tool for classification enhancement,Notion of Phase coherenceCoherence value is defined as:The degree of coherence for each pair(s1,s2)of co
23、-registered complex values s1,s2 is given by:represents an average,which is estimated by the spatial average over a finite-size windowPhase coherence is closely related to the local deviation of the phase differentialPhase coherence provides information on geophysical change of the observed target,P
24、hase difference and coherence,Phase difference notion:Two signal of the same wavelength but one is displaced The displacement between corresponding points of the signal are know as phase difference.Phase difference is processed to obtain height and/or motion information o the Earth surface.A source
25、for SEM generation,Phase coherence sensitivity,Coherence by land cover theme:High coherence:bare soil,built-up area,rocksModerate coherence:vegetated areas,cropsLow coherence:forested areasNo coherence:Water bodies,major change,Coherence is related toGeometry of the target Acquisition geometry(notio
26、n of baseline)Stability of the target between two successive acquisitionsNotion of successive is broad:can be simultaneous with two decaled antennas,or two days,revisit time,35 days for ERS,etc.,SAR coherence data:mutitemporal acquissition,Coherence,Amplitude,Amplitude Changein RGB,Multitemporal SAR
27、 coherence data and Multi-temporal land use classification,Microwave sensors history,1960s First airborne radar systems:SLAR1970s First airborne SAR systems1980s Spaceborne SAR systems:SEASAT,SIR-A,SIR-BDevelopment of Radargrammetry1990s Many radar satellites:JERS-1,ALMAZ for ResearchERS-1,ERS-2(Res
28、earch/Commercial),RADARSAT(Commercial)Highlights:Ocean and Land Surfaces applicationsCommercial applicationsDevelopment of Interferometry2000 ENVISAT(Research/Commercial)Near future:Japanese ALOS,Canadian Radarsat 2/3,Italian Cosmo Skymed,German Terra SAR,Chinese SAR,ERS-1/2,C Band,V V,23o incidence
29、 100 x 100 km image with 25m resolution Extensive global archive since 91,RADARSAT,C Band,HH,20o-49o incidence Range of viewing(20 beam positions)Range in image coverage(50 x 50 to 500 x 500km)Range in resolution(8-100m)Limited archive but good programming service,ENVISAT SAR,C Band,HH,VV,HV 20o-49o
30、 incidence Range of viewing(beam positions)37 different and mutually exclusive operating modes in high,medium(Wide Swath Mode),Wide swath coverage;405 km swath with 150 m or 1 km resolution.Resolution,30 m to 1 kmData transfert potential coupling with Artemis,ENVISAT SAR,ENVISAT SAR,Future VHR SAR S
31、ensors,RADARSAT 2(Near future launch scheduled for February 2002,April 2003 and November 2005)daily revisit VHR SAR mode 3mALOS:L band,Phase array Terra-SAR:constellation X band(potentially a second constellation L band)Cosmo-Skymed(2004-2006)4 satellites constellation=less than 12 hour revisit time
32、VHR SAR mode 1-3mChinese X band in 2006SAR VHR=More documented and accurate landscape description=Urban flood mapping=Less confusion between flooded area and neighbourhood,RADARSAT II,Standard mode:25*25m,Ultra Fine mode 3*3m,TERRA-SAR X,Launch scheduled for March 2005(10-02-04),TERRA-SAR X,TERRA-SA
33、R X,COSMO SKYMED,SAR system developed by Italian leadership in conjunction with the optical VHR French Pleiades=Orfeo constellationConstellation of 4 satellite launch schedule 2004-2006 With 4 satellite revisit time:12hBand X:Multi polarisation,HH,VV,HV or VH,Image modeOne selectable polarizationSPO
34、T_LIGHT:1m or less,10*10 km2H_ IMAGE:few meters,several tens km2WIDE_ REGION(ScanSAR):few tens of meters,hundreds of kmHUGE_REGION(ScanSAR):several tens of meters,hundred km2Two selectable polarizationPING PONG:few meters,several tens km2,Flood extent mapping based on VHR SAR sensor,VHR SAR 50 cm,IG
35、N 25 000e,Radarsat 12,5 m,VHR SAR 0.5 m,IGN 25 000e,Radarsat 12,5 m,Flood extent mapping based on VHR SAR sensor,More documented and accurate landscape description,VHR SAR 0.5 m,Radarsat 12,5 m,Flood extent mapping based on VHR SAR sensor,More documented and accurate landscape description,Radar 50 cm,IGN 25 000e,Radarsat 12,5 m,Flood extent mapping based on VHR SAR sensor,0.5 m,12.5 m,VHR SAR,0.5 m,IGN 25 000e,Radarsat 12,5 m,Flood extent mapping based on VHR SAR sensor,Very accurate flood extent mapping,Fundamental for SAR Remote Sensing,
