Sensitivity of Sentinel-1 backscatter to characteristics of buildings

In this study, Sentinel-1 interferometric wide swath (IW) mode backscatter is analysed with respect to physical parameters of buildings in Tallinn, Estonia. Dependence on height, alignment, density, shape, and material is shown and discussed. Distribution of backscatter was estimated with respect to each of the parameters, and a correlation matrix of all physical parameters and backscatter values was computed. Height has the strongest effect on backscatter values for both polarization bands, while shape and alignment to orbit has weaker effect on the backscatter. Relationship of co-polarized and cross-polarized backscatter with how a building is aligned with respect to the satellite’s look angle indicates that double bounce from wall–ground interactions is still the dominant scattering mechanism detected by Sentinel-1 in IW mode with 20 m resolution. In order to establish possible detection problems related to specifically oriented buildings at different latitudes, dihedral backscatter is modelled for buildings of oblong and square shapes. Results from this study should be used to improve existing and develop new urban area detection methods based on Sentinel-1 data

Electric Solar Wind Sail Propulsion System Development

The electric solar wind sail (E-sail) was invented in 2006 and has thereafter been developed rapidly. This paper is a progress report of E-sail technical development as it stands in August 2011. We conclude that E-sail development is well underway, no major problems have been encountered so far and a revolutionary level of performance (1 N in nite Isp thrust from 100-200 kg package) seems realistic