Microwave remote sensing. Rudi Gens Alaska Satellite Facility Remote Sensing Support Center

Transcription

1 Microwave remote sensing Alaska Satellite Facility Remote Sensing Support Center 1

2 Remote Sensing Fundamental The entire range of EM radiation constitute the EM Spectrum SAR sensors sense electromagnetic radiations in the microwave region of the EM Spectrum 2

3 Radar wavelengths 3

4 Radar geometry 4

5 Optical versus radar 5

6 Resolution Answers to the following question Given two very bright infinitesimally small scattering centers, what is the smallest distance at which you can separate them and observe two objects? Objects can be much smaller than the resolution and still be observable such as bright point objects like stars 6

7 Polarization EM radiation propagates as two orthogonal waves, with an electric and magnetic component, moving at right angles to the direction of wave propagation. 7

8 Radar wavelengths (3.2 cm) (5.7 cm) (23.0 cm) 8

9 Radar scattering 9

10 Real aperture radar cross-range resolution can be only improved smaller wavelength longer antenna all radiating parts in phase 10

11 Synthetic aperture radar many little antennas form an effectively long antenna all radiating elements in phase 11

12 Real versus Synthetic Aperture 12

13 Geometric distortions caused by the side looking geometry of radar foreshortening layover shadow 13

14 Foreshortening distance A-B on the slope is shortened to A'-B' in the SAR image bright pixel values 14

15 Layover distance A-B on the slope is shortened to A'-B' in the SAR image extreme case of foreshortening top of the mountain is closer to the sensor than the bottom bright pixel values 15

16 Shadow distance B-C on the slope does not appear in the SAR image top of the mountain high enough so that backslope is completely in the shadow dark pixel values 16

17 Geometric distortions 17

18 Distortions: Foreshortening JERS-1 Credits: JAXA Radarsat-1 Credits: CSA 18

19 Distortions: Layover Credits: CSA 19

20 Distortions: Shadow Ascending Credits: CSA Descending 20

21 Advantages of SAR Use day and night Active sensor Sees through clouds (mostly) wavelength of microwaves versus light Repeat coverage Good for physical feature detection Resolution 21

22 Disadvantages of SAR It is not a picture Calibration Interpretation Extensive computer processing Time delays Data quality issues Few platforms Continuity of data Competition for data Resolution 22

23 Why is radar side looking? 23

24 Image interpretation 24

25 SAR applications 25

26 Geomorphology Radarsat image of Anchorage depicting varied returns of urban area. 26

27 Geomorphology Radarsat Fine-1 image of Delta Junction. Agricultural fields are highlighted by SAR. 27

28 Geomorphology Radarsat Standard image of Dasht-E-Lut Desert, Iran. Linear yardangs formed by unidirectional winds over clay sediment. 28

29 Land Use / Land Change Freeze/thaw processes mapped in Interior Alaska from fused Landsat classification and JERS imagery. 29

30 Burn Scar Detection C-band image (ERS-2) highlights burn scar through sensitivity to soil moisture. Yellow line represents official Alaska Fire Service (AFS) burn scar perimeter for Parks Hwy fire. Anomaly in SE may indicate error in AFS perimeter. 30

31 Soil Moisture Measurement 31

32 Hydrology Flooding of Red River in North Dakota. Trees and water serve as corner reflectors. 32

33 Hydrology Open water maps derived from unsupervised clustering classification. 33

34 Hydrology JERS-1 Radar Backscatter Image JERS-1 Texture Analysis Image Texture analysis used to distinguish forest from open water in flooded Amazon. 34

35 Hydrology Radarsat image of Yukon River during Spring thaw. 35

36 Flood Mapping Credits: Pohl, ITC Multi-temporal SAR flood data fused with Optical data 36

37 Hydrology Discerning bathymetry from SAR backscatter 17 Jan Jan Ic e : m 26 Jan Ic e : m 2 0 M a r Ic e : m 2 9 M a r Ic e : m 9 D ec Ic e : m 0.5 k m 25 Feb M a r Ic e : m Surface Water Frozen T h r e s h o ld in g 29 Mar May 1992 I n t e r p o la t i o n & S m o o th in g C la s s if ic a t io n E q u a lly - s p a c e d is o b a t h s R a w is o b a t h s m D e p t h in t e r v a l f o r e q u a lly - s p a c e d is o b a t h s Frozen to lake bottom Credit: Martin Jeffries m

38 Mapping Radar map of Antarctic formed from mosaic of Oct 1997 Radarsat images. 38

39 DEM Generation 39

40 Volcanology Radarsat image of Hawaii showing three stages of shield volcano evolution. 40

41 Tectonics Interferogram and model of Landers earthquake, California Massonnet, D. et al The Displacement Field Of The Landers Earthquake Mapped By Radar Interferometry. Nature, 364(6433):

42 Subsidence Monitoring Credits: SARMAP, Switzerland Subsidence measured from on the Oued Rhir area (Algeria) well locations shown in blue 42

43 Ocean Monitoring Primary source of Ocean surface roughness: Gravity-capillary Waves Wind generated waves Wavelength - order of 1 cm Waves get modulated by: Changing wind speed Oil spill Other surfactants Upwelling Currents Bathymetry Close-up photo of Capillary Waves 43