Dr. Elena Nikolaeva Profile

Dr. Elena Nikolaeva

at National Environmental Agency

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Publications (1)

Proceedings Article | 15 October 2015 Paper

Multi-temporal intensity and coherence analysis of SAR images for land cover change detection on the Island of Crete

E. Nikolaeva, O. Sykioti, P. Elias, C. Kontoes

Proceedings Volume 9642, 964208 (2015) https://doi.org/10.1117/12.2194320

KEYWORDS: Backscatter, Synthetic aperture radar, Vegetation, Radar, Dielectrics, Coherence (optics), Earth observing sensors, Satellites, MODIS, Image analysis

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This study presents the use of multi-temporal Synthetic Aperture Radar (SAR) images for detection of land cover changes in the eastern part of the Island of Crete (Greece). For this purpose, fourteen Envisat ASAR acquisitions from July 2004 to December 2006 were calibrated and registered.

We applied a temporal filter and spatial averaging to the backscatter intensity to reduce the noise. Furthermore, we used the concept that the changes between different backscatter intensity observations can show changes on the target dielectric properties. In order to detect changes due to geometrical characteristics of land cover types, we created coherence maps using twenty-seven interferometric pairs with proper spatial and temporal baselines. In all calculations, layover and shadow effects, as well as the sea, were masked by using information from the digital elevation model of the area. The observed changes in the coherence values were analyzed with respect to different decorrelation factors that can contribute to the loss of coherence.

Our results present the different backscatter values for several land cover types (farmland, olive groves, forests, etc.). In addition, some land cover types such as olive groves show variations of backscatter signal due to the density and height of trees. Furthermore, olive groves show good coherence in interferograms with short time intervals. All interferometric pairs have low coherence in farmland because of the rapid growth of plants. Finally, the maps of backscatter temporal changes and coherence changes were superimposed and compared to auxiliary data such as multi-temporal optical satellite imagery (i.e. Landsat/ETM, Terra/Aqua MODIS) and thematic land cover maps (Corinne 2000). We found that changes are mostly due to plant growth and man-made activity.

This ongoing study shows the potential of SAR in providing complementary information such as changes in dielectric and geometric properties to optical data in land cover dynamics monitoring.

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