Space-based synthetic aperture radar observations for monitoring of earth surface displacement

Abstract

Space-based observations with a state-of-art of earth observations satellites have been widely used to monitor environmental change which has been continuously occurring on our earth. The remotely sensed imagery from the space can be utilized for various applications such as cartography, security & surveillance, natural disaster monitoring, weather, geology, oceanography, agriculture, and environmental monitoring, etc. Since synthetic aperture radar (SAR) with microwave spectrum which can see the earth's surface without the limitation of the sun-light and weather condition, it can be very useful to monitor surface's change from natural disasters like flood, earthquakes or volcanos. Especially the SAR observations provide both the backscatter coefficients (amplitude) and time (phase) from target measured from the SAR system, so that we can apply interferometric SAR (InSAR) technique to calculate ground deformation due to earthquake or volcano and subsidence very accurately. In order to monitor a time-series of earth surface's displacement, sophisticated InSAR techniques have been proposed. Both the persistent scatterer interferometry (PSI) (Ferretti et al. 2000) and small baseline subset (SBAS) (Berardino et al. 2002) approaches use a large number (>20 images) of SAR observations to calculate a time-series of displacement very accurately. Numerous studies using these techniques have shown the SAR observations are one of great resources to monitor the ground deformation including subsidence. Recently we developed a small temporal baseline subset (STBAS) to reduce the decorrelation effects by large temporal baseline, which enables to calculate a time-series of displacements over quickly varying surfaces like wetland or ice sheet, etc. Although the terrestrial observations like GPS measurements can provide a high temporal resolution data of ground deformation, their relatively poor spatial resolution prevent from understanding of the earth's structure. The high spatial resolution of surface's displacement maps from the InSAR observations provide enhanced understanding the earth. Moreover it can be a great constraints to model the terrain's internal structure. The radar wavelength of the SAR observations is one of important parameters to acquire coherent interferometric signals over the earth surfaces. Generally longer wavelength such as the L-band can maintain higher coherence, because the short wavelength like the X-band is more sensitive to the decorrelation effects. However the longer wavelength SAR observations provide relatively coarse resolution. Thus we need to select carefully the acquisition parameters considering the earth surface's condition.