EE 529 Remote Sensing Techniques Introduction
Course Contents Radar Imaging Sensors Imaging Sensors Imaging Algorithms Imaging Algorithms
Course Contents (Cont( Cont d) Simulated Raw Data y r Processing Simulated Images
Course Contents (Cont( Cont d) Radar Imaging Sensors Imaging Sensors Real Image Imaging Algorithms Imaging Algorithms Simulated Image Complex Scene Complex Scene
Course Contents (Cont( Cont d) y r Surface Scattering Surface Scattering Nonimaging Sensors
Course Contents (Cont( Cont d) Prerequisites Knowledge of DSP, EMT and MATLAB Books [1] Introduction to the Physics and Techniques of Remote Sensing by C. Elachi and J. J. van Zyl (Chapters 1, 2 and 6). [2] Scattering, Natural Surfaces, and Fractals by G. Franceschetti and D. Riccio (Chapters 1 and 2). [3] Digital Signal Processing Techniques and Applications in Radar Image Processing by B. Wang (Chapters 4, 5 and 6).
Introduction to Remote Sensing Definition - Acquisition of information remotely - Components: - Energy source - Interaction of energy with atmosphere - Interaction with object - Energy scattered Data storage by sensor - Transmission, reception and processing of data and display Source Source/Sensor Image Processor Object
Introduction to Remote Sensing (Cont d) Advantages - Large amount of area can be observed in a small time period - Data can be collected from locations that are difficult to access Measurable variables -Topography -Soil moisture -Velocity of ocean waves -Condition and behavior of snow, sea ice, etc.
Introduction to Remote Sensing (Cont d) Applications - Agricultural monitoring - Cartography - Coastal erosion - Disaster monitoring - Soil characterization - Urban mapping - Oceanography - Pollution monitoring, etc.
Remote Sensing Systems System types - Passive and Active - Optical and Microwave - Imaging and Nonimaging Passive systems - Detect naturally occurring radiation-uv, visible light, near infrared, infrared - Receiver only - No independent illumination source - Measure the amount of emitted radiation - Examples are: Microwave radiometry, infrared imagery, aerial photography, etc.
Remote Sensing Systems (Cont d) Active systems - Emit radiation and analyze reflections - Use transmitter(s) and receiver(s) - Measure the amount of emitted radiation and - The time of arrival made possible as the time of emitted radiation can be known - Examples are: radar (real aperture and synthetic aperture radars), altimetry, scatterometry, etc.
Remote Sensing Systems (Cont d) Optical systems - Started in the middle of nineteenth century with the advent of photography and used balloons, kites, etc. as platforms - Later on used with aeroplanes and satellites - Applications: - Geology - Hydrology - Disaster monitoring - Cartography - Study of crop types, etc.
Remote Sensing Systems (Cont d) Optical systems Some satellite based systems-ikonos, LANDSAT, etc. Advantages: - High resolution - Normal images - Comparatively inexpensive Disadvantages/Limitations: - No night capability - Limited by weather - Alternative: Microwave remote sensing
Remote Sensing Systems (Cont d) Microwave systems - Started with the development of radar - Applications: - Cartography - Identification and monitoring of crops - Change and damage detection - Monitoring of landslides - Detection of snow cover - Some examples are: - Airborne: ESAR, EMISAR, AIRSAR, etc. - Satellite: RADARSAT 1&2, TerraSAR-X, ERS, etc.
Remote Sensing Systems (Cont d) Microwave systems - Advantages: - Day and night capability - Independent of weather - Can give properties of conditions on and inside a surfaces - Disadvantages: - Different from optical images requires image interpretation - Resolution not better than optical sensors
Remote Sensing Systems (Cont d) Imaging systems Give information in form of images Examples: Aerial photography, Real Aperture Radar, Synthetic Aperture Radar, Radiometer, etc. Optical Image
Remote Sensing Systems (Cont d) Imaging systems Give information in form of images Examples: Aerial photography, Real Aperture Radar, Synthetic Aperture Radar, Radiometer, etc. Optical Image Nonimaging systems Give information such as backscattering, height, etc. Examples: Radiometer, Scatterometer, Altimeter, etc.
Remote Sensing Systems (Cont d) Low Resolution Optical Image High Resolution Optical Image Low resolution gives less information
Remote Sensing Systems (Cont d) Optical Passive system
Remote Sensing Systems (Cont d) Microwave Active system
Remote Sensing Systems (Cont d) Microwave Active system Optical Passive system
Remote Sensing Systems (Cont d)
Remote Sensing Systems (Cont d)
Remote Sensing Systems (Cont d) Active Microwave Imaging systems Real Aperture Radar (RAR), Synthetic Aperture Radar (SAR) Strip of ground parallel to and offset to the side of the platform is imaged, hence the name Side Looking Radar RAR Incoherent processing SAR Coherent processing, better resolution than RAR y (Azimuth) Sensor Low resolution: Large pixel size High resolution: Small pixel size r (Range)
Remote Sensing Systems (Cont d) Nonimaging systems Altimeter Measures height Scatterometer Measures backscattered energy as a function of incidence angle Altimeter Scatterometer ct/2
Microwave Remote Sensing Energy Source r E ( z,t) = E E E x y z = E = E = 0 0 x 0 y cos cos ( ωt kz δ ) x ( ωt kz δ ) y k = 2π λ Plane waves E: Electrical field M: Magnetic field
Microwave Remote Sensing (Cont d) r E ( z,t) E = E E x y z = E = E = 0 0 x 0 y cos cos ( ωt kz δ ) x ( ωt kz δ ) y k = 2π λ Polarization: Spatial orientation of the electrical oscillation plane Vertical or Horizontal Polarization Change of amplitude and polarization gives useful information
Microwave Remote Sensing (Cont d) Interaction with atmosphere -Scattering - Rayleigh: Particle size < wavelength - Mie: Particle size wavelength - Nonselective: Particle size > wavelength x = 2πr λ -Absorption - Blocking of transmission of energy by molecules in the atmosphere - Limits the use for remote sensing
Microwave Remote Sensing (Cont d) Available frequency bands Use limited by transparency of the Earth s atmosphere
Microwave Remote Sensing (Cont d) Interaction with object
Microwave Remote Sensing (Cont d) Interaction with object For a single wavelength, a surface appears smoother as the incidence angle increases. Horizontal smooth surfaces that reflect nearly all the incidence energy away from the radar are called specular reflectors. These surfaces, such as calm water or paved roads appear dark on radar images. Rough surfaces scatter incident microwave energy in many directions. This is known as diffuse reflection. Vegetated surfaces cause diffuse reflectance and result in a brighter tone on radar images.
Microwave Remote Sensing (Cont d) Interaction with object Smooth surface Specular reflection No return Intermediate roughness Moderate return Rough surface Diffuse scattering Strong return Surface Roughness is determined with respect to radar wavelength and incidence angle. Surfaces will appear to have a greater or lesser degree of roughness, depending on the radar bandwidth used for imaging. Surface roughness influences the reflectivity of microwave energy. On radar images, rough surfaces appear brighter than smoother surfaces composed of the same material.
Microwave Remote Sensing (Cont d) Frequency bands used for microwave remote sensing applications P L S C X K Q V W 0.39 1.55 3.90 5.75 10.9 36.0 46.0 56.0 f (GHz) 0.3 1.0 3.0 10.0 30.0 100.0 λ = c / f 100 30 10 3 1 0.3 λ (cm) f c BW f Different achievable spatial resolutions depending on bandwidth (BW)
Microwave Remote Sensing (Cont d) Resolution in two dimensions for different sensors 10m 3m 1m 10cm ENVISAT / ASAR ERS 1&2 RADARSAT 1 RADARSAT 2 ALOS SENTINEL-1 Cosmo-Skymed SAR-Lupe FGAN - PAMIR HJ-1-C TerraSAR-X ONERA - RAMSES ONERA - SETHI
Microwave Remote Sensing (Cont d) Radiation-Object Interaction P L S C X K Q V W 0.39 1.55 3.90 5.75 10.9 36.0 46.0 56.0 0.3 1.0 3.0 10.0 30.0 100.0 f (GHz) 100 30 10 3 1 0.3 λ (cm) Different sensitivity to geo-physical parameters (moisture, ) Different penetration depths into volumes
Microwave Remote Sensing (Cont d) L-Band Resolution: 5m
Microwave Remote Sensing (Cont d) X-Band Resolution: 2.5m
Microwave Remote Sensing (Cont d) Radiometry High Sensor measures the power of the reflected signal, which determines the brightness of each element (pixel) in the image. Different surface features exhibit different scattering characteristics: Urban areas: very strong backscatter Forest: medium backscatter Calm water: smooth surface, low backscatter Rough sea: increased backscatter due to wind and current effects Low
Microwave Remote Sensing (Cont d) Sensor Scattering by a scene
Microwave Remote Sensing (Cont d) Sensor Scattering by a scene Raw data contains amplitude and phase Processing/Imaging generates an image containing both amplitude and phase 200 400 600 800 18 17.5 17 16.5 1000 16 1200 50 100 150 200 250 300 15.5
Microwave Remote Sensing (Cont d) Optical Image SAR Image High Low
Microwave Remote Sensing (Cont d) Optical Image E-SAR Sensor Parameters Frequency: 1.3 GHz Bandwidth: 100MHz Scattering Mechanisms
Microwave Remote Sensing (Cont d) Optical Image Raw Data Acquistion Sensor
Microwave Remote Sensing (Cont d) Raw Data y Simulated raw data r Processing SAR Image
Microwave Remote Sensing (Cont d) Raw Data SAR Image 200 18 400 17.5 Processing 600 17 800 16.5 1000 16 1200 50 100 150 200 250 300 15.5
Microwave Remote Sensing (Cont d) Optical Image SAR Image 200 18 400 17.5 600 17 800 16.5 1000 16 1200 50 100 150 200 250 300 15.5
Summary Remote Sensing Types of remote sensing systems Microwave remote sensing-imaging and nonimaging Scattering mechanisms SAR images