Lectures Remote Sensing

Transcription

1 Lectures Remote Sensing OPTICAL REMOTE SENSING dr.ir. Jan Clevers Centre of Geo-Information Environmental Sciences Wageningen UR

2 EM Spectrum and Windows reflection emission µm 1mm 1cm 1m 10m atmospheric transmittance blue green red UV VIS NIR MIR MIR TIR TIR blocking effect of atmosphere microwaves human eye (incl. SRF) lidar photography (AP,MSP, SRF) thermal scanners (TIRS) radar (SLAR, SAR) multispectral scanners (MSS) microwave radiometry µm 1mm 1cm 1m 10m optical window wavelength microwave window

3 Source of EM radiation 10 0 radiation (Wcm -2 µm -1 ) 10-1 curves for an average object on earth 10-2 reflected solar radiation emitted thermal radiation wavelength (µm) REFLECTION EMISSION

4 RS using reflected solar radiation: (PASSIVE) Active <-> Passive RS using radiation emitted by objects: (PASSIVE) ACTIVE RS:

5 Multilevel platforms Sensor at a distance EM energy Earth

6 Remote Sensing Instrumentation General concept telemetry Sensor Recorder Detector Collector IFOV= β*h (in Nadir!) Ground receiving station angular aperture H β IFOV Instanteneous field of view - ground resolution element Terrain objects

7 DN: digital number signal level AD Conversion digitization levels dots indicate digitization level of waveform time sampling intervals

8 AD Conversion 6 bits: 64 digitization levels 8 bits: 256 digitization levels 10 bits: 1024 digitization levels 12 bits: 4096 digitization levels Number 79: How many bit levels are significant? NOISE caused by: sensor/imaging system atmosphere variability terrain object

9 Resolution concepts Spectral resolution: band width in nm or Hz mid-value sensitivity curve sensitivity 1 ½ 0 λ Spectral range: number and position of bands 50% - width 0.3 µm 70 cm

10 WorldView-2 Spectral Bands

11 Resolutions Radiometric resolution: smallest measurable step Q noise level Q min saturation level Q max S max B S S S min A A Q min Q Q B Q max

12 Resolutions Spatial resolution: size IFOV or pixel size in terms of terrain size sensor β radiometer β = angular aperture (mrad) H D = β H at nadir β H at oblique viewing angles ground resolution element (resolution cell) D

13 Example spatial resolution

14 Resolutions Temporal Resolution: (usable) recording frequency = time lapse between two successive images of the same area ( time distance )

15 Resolutions Phenomenological Resolution: (regarding object) extent of the surroundings of an object (terrain detail) necessary for recognition of the relevant object relationship IFOV - terrain detail image sharpness image context

16 Example difference detectability - recognizability

17 Coat of Mozart

18 Principles imaging sensor systems analogue recording digital recording digital recording aerial image plane shutter scanning mirror imaging optics line array detector imaging optics point detector imaging optics Camera (aerial photography) Whiskbroom scanner Pushbroom scanner

19 The position of the spectral bands of some Remote Sensing sensor systems in the optical window Meteosat NOAA AVHRR Landsat TM SPOT HRG multispectral SPOT HRG Panchromatic Pan: IKONOS, Quickbird, GeoEye, WorldView Multispectral: IKONOS, Quickbird, GeoEye, WorldView reflectance (%) dry soil 20 wet soil infrared infrared vegetation water λ wavelength (µm) near- middle- blue green red

20 Some Sensor Specifications Altitude (km) FOV (km) Radiometric resolution (bits) Spatial resolution (m) nadir Meteosat 36,000 hemisphere /5000 NOAA- AVHRR 835 3, Landsat-TM /120 SPOT (P/XS) /20 SPOT- Vegetation IKONOS (P/MS) /4 QuickBird (P/MS) /2.4

21 New developments: The image cube

22 LIDAR