Swamp forest can be distinguished from agricultural land by its
brighter blue colour. Fig. 7 shows that HH and VV have similar
intensities in most parts of the image. The small arms of the
river at the right as well as settlements stick out because of a
higher reflectance in HH than in VV. Some smaller areas in the
larger river arms that are characterized by a higher
backscattering in VV than in HH are supposed to be covered by
flooded vegetation. Comparing these areas to K3 in Fig. 6
approves this hypothesis because those areas additionally show
a dominant double-bounce contribution attached to vegetation
standing in water (Brisco, 2011).
2.3 Difference Images
In order to enhance the temporal changes the Kennaugh
elements of both acquisitions are differentiated (Figs. 8-11).
Figure 9: Differential K0
change in intensity
Figure 8: Differential
Kennaugh elements QL
Figure 11: Diff. K4
HH / VV intensities
Figure 10: Diff. K3
double bounce / surface
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Fig. 8 depicts the quicklook of the differential Kennaugh
elements in the same colour coding as the single acquisitions
above. The change in the backscattering strength is captured in
Fig. 9. Blue stands for a decrease in the total intensity of about
3dB. Over open water surfaces this behaviour can be referred to
the influence of wind that roughens the surface and thus,
increases the backscattering during the first image acquisition.
The yellow coloured areas in Fig. 10 report an increase in the
relation of double bounce to surface scattering. This can be
caused by an increase of the double bounce component or a
decrease of the surface scattering. As these areas coincide with
the negative changes in the total intensity it is reasonable that
the dominant surface scattering — apparent in Fig. 6 as large
dark blue region — is slightly reduced and hence causes the
increase in K3. The relation between HH and VV intensities
only exhibits minor changes particularly attached to man-made
objects that probably have been moved in the meantime.
3. CONCLUSION
For the first time a closed formalism is presented that enables a
uniform description of (partial-) polarimetric SAR data for
single image acquisitions as well as for time series. Because of
the high sensitivity of the Kennaugh elements speckle filtering
is absolutely required, and is done by a multiscale approach —
called pyramidal multilooking that trades radiometric accuracy
against geometric resolution. Especially in the context of
wetland monitoring this approach reveals a high potential even
though the polarimetric interpretation still is subject to further
investigations. This methodology was designed to be the kernel
of the future polarimetry and change detection processor
implemented at the German Aerospace Center.
4. REFERENCES
Brisco, B., Schmitt, A., Murnaghan, K., Kaya, S. and Roth, A.,
2011. SAR Polarimetric Change Detection for Flooded
Vegetation. International Journal of Digital Earth.
Hess, L.L., Melack, JM. and Simonett D.S. 2000. Radar
detection of flooding beneath the forest canopy: a review.
International Journal of Remote Sensing, 11:7, 1313-1325.
Schmitt, A., Wessel, B., Roth, A., 2012. Curvelet Approach for
SAR Image Denoising, Structure Enhancement, and Change
Detection. In: The International Archives of the
Photogrammetry, Remote Sensing and Spatial Information
Sciences, Paris, France. Vol. XXXVIII, Part 3/W4.
Schmitt, A., 2012. Aenderungserkennung in multitemporalen
und multipolarisierten ^ Radaraufnahmen, Dissertation
Karlsruhe Institute of Technology. hitp://digbib.ubka.uni-
karlsruhe.de/volltexte/1000025955 (13 Apr. 2012)
Wendleder, A., Breunig, M., Martin K., Wessel, B. and Roth,
A., 2011. Water body detection from TanDEM-X data: concept
and first evaluation of an accurate water indication mask. In:
IEEE International Geoscience and Remote Sensing
Symposium. Vancouver, Canada.
RAMSAR - Convention on Wetlands, Ramsar, Iran, 1971,
http://www.ramsar.wetlands.org, last visited 04/13/2012.
5. ACKNOWLEDGEMENTS
TerraSAR-X images from proposal LAN1403 O DLR 2011
