1. Sea ice remote sensing from space
Remote Sensing I
Lecture 10
Summer 2006

2. Sea ice remote sensing from space
Optical (e.g. MODIS)
High resolution (about 100 meters)
Can‘t „see“ through clouds; difficult to distinguish clouds and sea ice
Passive Microwave
Can differentiate between open water, first year and multiyear ice
Can „see“ through clouds
Low spatial resolution (several km)
Radar
Can look through clouds
High spatial resolution (< 1km)
Images difficult to interprete

3. MODIS - Antarctica 21 March 2005

4. Radar Image
ENVISAT ASAR
15 April 2005

5. Sea ice concentration from AMSR-E 89 GHz
09 July 2006
courtesy of Lars Kaleschke

6. Sea ice concentration from AMSR-E 89 GHz
23 April 2006
courtesy of Lars Kaleschke

7. 1. RADAR

8. Real Aperture Radar
Viewing angle θ h S
Opening angle β Xa Xr

9. Antenna beamwidth
The opening angle β (beamwidth) of an antenna with aperture D
at a wavelength of λ is given by:
The azimuth resolution for a real aperture radar is then

10. Azimuth resolution fro real aperture radar
Example: h=800km, λ=23cm, D=12m then Xa=16km
This is a coarse resolution!

11. Synthetic aperture radar: SchematicL
Radar
flight direction
Ground L

12. Synthetic aperture radar
Ground „footprint“ L given by:
Individual measurements can be combined, corresponding to a
Measurement with a virtual or synthetic aperture of size L.
The resolution for such a synthetica aperture radar (SAR) is then given by:

13. 2. Passive Microwave Sensors

14. Passive microwave remote sensing

15. Emissivity of Sea Ice vs. Frequency
Summer
First year Ice
Multiyear Ice
Emissivity
Water
Frequency [GHz]

16. Polarization Ratio (PR) and Spectral Gradient (GR)
Clouds

17. Sea ice concentration
The sea ice surface concentration C can then be calculated from the
contributions of the three base points for open water, first year ice,
and multi year ice.
The sum of the three concentrations must sum to unit:

18. MODIS
645, 555, 469 nm
AMSR-E
89 GHz
courtesy of Lars Kaleschke

19. Optical tick clouds are still transparent at 89 GHz
courtesy of Lars Kaleschke

20. courtesy of Lars Kaleschke