Better Understanding of Natural Hazards with InSAR Technology
12 March 2010
"The challenges of measuring a few centimetres displacement from a satellite flying at 7km/s and 700 km above the ground are particularly difficult, while the equatorial region with its typical dense vegetation and mountainous terrain makes the task even harder"
Dr Emmanuel Christophe, Centre for Remote Imaging, Sensing and Processing
HARNESSING InSAR TECHNOLOGY: Director of the Centre for Remote Imaging, Sensing and Processing Mr Kwoh Leong Keong (left) and Dr Emmanuel Christophe
Researchers in Singapore have brought remote sensing to the next level with the Interferometric Synthetic Aperture Radar (InSAR). The Centre for Remote Imaging, Sensing and Processing (CRISP) of NUS is the only agency in the region after Japan to have successfully produced interferometric maps over equatorial regions.
"We use two or more synthetic aperture radar (SAR) images to generate maps of the ground, using differences in the phase of the waves returning to the satellite. SAR allows us to look at centimetre movement on the ground," explained Dr Emmanuel Christophe, a research scientist at CRISP. InSAR can also be used for the geophysical monitoring of natural hazards such as earthquakes and volcanoes.
In fact, using InSAR, researchers have successfully processed a series of satellite images of the recent Haiti earthquake that revealed Haitian land surface changes. The images from the Japanese satellite 'Alos-Palsar' suggest that the length of the rupture was shorter than the original estimation which spanned from Petit Goave to the south of Port-au-Prince. This implies that the other part of the fault is still under constraints and may break in the future.
On the advantages of InSAR as compared to the widely used Global Positioning System (GPS), Dr Christophe said: "It is hard to get the whole picture with GPS. Using InSAR, we can obtain the whole ground information, with more data points than GPS. The InSAR is also able to measure subtle changes."
Director of CRISP Mr Kwoh Leong Keong said that the Centre had tried using InSAR for about ten years but up till now, it did not work in tropical areas owing to thick vegetation and high concentration of water vapour in the air.
"The challenges of measuring a few centimetres displacement from a satellite flying at 7km/s and 700 km above the ground are particularly difficult, while the equatorial region with its typical dense vegetation and mountainous terrain makes the task even harder," added Dr Christophe. Responding to the question on how InSARcan be useful in the Singapore context, Mr Kwoh noted that it can help guide the building of infrastructures, such as not building on fault lines and designing buildings at the right angles.
Other than remote sensing using InSAR, CRISP's research is also focused on the processing and applications of very high spatial resolution imagery, hyperspectral data and multiple polarizations SAR. Among various natural disasters studied by CRISP are the West Java earthquake, Typhoon Fengshen in the Philippines and the earthquake in Sumatra.