EE 529 Remote Sensing Techniques. Introduction

Transcription

1 EE 529 Remote Sensing Techniques Introduction

2 Course Contents Radar Imaging Sensors Imaging Sensors Imaging Algorithms Imaging Algorithms

3 Course Contents (Cont( Cont d) Simulated Raw Data y r Processing Simulated Images

4 Course Contents (Cont( Cont d) Radar Imaging Sensors Imaging Sensors Real Image Imaging Algorithms Imaging Algorithms Simulated Image Complex Scene Complex Scene

5 Course Contents (Cont( Cont d) y r Surface Scattering Surface Scattering Nonimaging Sensors

6 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).

7 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

8 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.

9 Introduction to Remote Sensing (Cont d) Applications - Agricultural monitoring - Cartography - Coastal erosion - Disaster monitoring - Soil characterization - Urban mapping - Oceanography - Pollution monitoring, etc.

10 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.

11 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.

12 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.

13 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

14 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.

15 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

16 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

17 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.

18 Remote Sensing Systems (Cont d) Low Resolution Optical Image High Resolution Optical Image Low resolution gives less information

19 Remote Sensing Systems (Cont d) Optical Passive system

20 Remote Sensing Systems (Cont d) Microwave Active system

21 Remote Sensing Systems (Cont d) Microwave Active system Optical Passive system

22 Remote Sensing Systems (Cont d)

23 Remote Sensing Systems (Cont d)

24 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)

25 Remote Sensing Systems (Cont d) Nonimaging systems Altimeter Measures height Scatterometer Measures backscattered energy as a function of incidence angle Altimeter Scatterometer ct/2

26 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

27 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

28 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

29 Microwave Remote Sensing (Cont d) Available frequency bands Use limited by transparency of the Earth s atmosphere

30 Microwave Remote Sensing (Cont d) Interaction with object

31 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.

32 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.

33 Microwave Remote Sensing (Cont d) Frequency bands used for microwave remote sensing applications P L S C X K Q V W f (GHz) λ = c / f λ (cm) f c BW f Different achievable spatial resolutions depending on bandwidth (BW)

34 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

35 Microwave Remote Sensing (Cont d) Radiation-Object Interaction P L S C X K Q V W f (GHz) λ (cm) Different sensitivity to geo-physical parameters (moisture, ) Different penetration depths into volumes

36 Microwave Remote Sensing (Cont d) L-Band Resolution: 5m

37 Microwave Remote Sensing (Cont d) X-Band Resolution: 2.5m

38 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

39 Microwave Remote Sensing (Cont d) Sensor Scattering by a scene

40 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

41 Microwave Remote Sensing (Cont d) Optical Image SAR Image High Low

42 Microwave Remote Sensing (Cont d) Optical Image E-SAR Sensor Parameters Frequency: 1.3 GHz Bandwidth: 100MHz Scattering Mechanisms

43 Microwave Remote Sensing (Cont d) Optical Image Raw Data Acquistion Sensor

44 Microwave Remote Sensing (Cont d) Raw Data y Simulated raw data r Processing SAR Image

45 Microwave Remote Sensing (Cont d) Raw Data SAR Image Processing

46 Microwave Remote Sensing (Cont d) Optical Image SAR Image

47 Summary Remote Sensing Types of remote sensing systems Microwave remote sensing-imaging and nonimaging Scattering mechanisms SAR images