toimub neljapäeval, 2. jaanuaril 2014. a. algusega kell 16.15 TÜ Füüsika Instituudi saalis Riia 142, ruum 108
Ettekanne : Kaupo Voormansik
Tartu Observatory; University of Tartu
X-band Synthetic Aperture Radar Applications for Environmental Monitoring
( material of PhD Thesis)
X-laineala tehisava-radari rakendused keskkonna kaugseireks
The research, described in this thesis, has been carried out in Tartu University, Regio Ltd, German Aerospace Center (DLR) and Tartu Observatory between 2010 and 2013. The research focused on testing the capabilities of new generation high-resolution X-band SAR satellites like TerraSAR-X for environmental monitoring.
X-band SAR canopy penetration was found to be sufficient for effective flood mapping in North European temperate forest during leaf-off season. Due to flooding, backscatter increased 6.2, 3.2 and 4.0 dB in deciduous, mixed and coniferous forest respectively. First high-resolution remote sensing data based flood maps about the Alam-Pedja Nature Reserve were created. The flood maps could be used as basis for future ecological studies about the Nature Reserve.
The improvement of using X-band SAR HH-VV polarimetric channel instead of conventional HH for flood mapping in forest was measured. In deciduous forest flooding increased the backscatter in HH (HH-VV) polarimetric channel by 8.2 (9.8), 7.2 (8.4) and 5.7 dB (6.7 dB) for tree heights 5-7, 14-19 and 20-28 m respectively. In coniferous forest, flooding increased the backscatter in HH (HH-VV) polarimetric channel by 4.8 (5.0), 3.6 (5.0) and 2.3 dB (3.0 dB) for tree heights 7, 16-18 and 23-28 m respectively. The improvement of using HH-VV polarimetric channel over HH was 0.2-1.6 dB, being the highest (1.6 dB) for short 5-7 m deciduous forest and lowest (0.2 dB) in short 7 m coniferous forest. The corresponding polarimetric phase difference increase between HH and VV channels related to the flooding was measured. In deciduous forest, the phase difference increased from 59° to 87°, 60° to 83° and 62° to 74° for tree heights 5-7, 14-19 and 20-28 m respectively. In coniferous forest, the phase difference increased from 59° to 69°, 59° to 70° and 61° to 71° for tree heights 7, 16-18 and 23-28 m respectively. The results demonstrate the slight improvement of using HH-VV polarimetric channel for flood mapping in forest instead of conventional HH channel. However, one also needs to keep in mind that the resolution and/or swath width of dual pol. modes are usually inferior to the single channel modes of the same SAR system.
Dual polarimetric HH/VV X-band SAR performance for grasslands parameters retrieval was tested. No reliable correlation between the SAR measurements and grass height was observed. Still numerous SAR variables, most notably the dual polarimetric dominant scattering alpha angle, was sensitive to the cut grass lying on the ground. A characteristic dominant scattering alpha angle increase from 10° to 25° was observed when grass was cut and left lying on the ground. The alpha angle went back to 10° after the grass was collected. The observed phenomenon was well described by a particle cloud model for vegetation backscattering. Primarily horizontally oriented dipoles (cut grass lying on the ground) correspond to higher scattering alpha angles than primarily vertically oriented dipoles (growing grass).