9.13.2011

Applying inSAR principles to detect surface deformation in Metro Manila

I have just attended an InSAR training  showing how to detect surface deformation through phase differences between SAR signals.

SAR satellite transmits microwave to earth and receives reflected microwave signals from earth surface. The intensity of received microwave indicates electromagnetic characteristics of objects, and phase indicates distance between aperture and object. Surface deformation is measured by the difference in two observed phases. The observed phase differences still contains errors that ought to be corrected along processing enumerated by the steps below.

  1. Getting SLC (Single-Look Complex)
  2. Co-registration (registration of Master and Slave images)
  3. Interferometry ( measuring phase differences)
  4. Corrections (Removal of Orbital and Topographic Fringe)
  5. Phase Unwrapping (integration of extracted to actual phase difference)
  6. Geocoding
  7. Visualization of Results in ENVI
  8. Analysis and Interpretation
With the use of ALOS Palsar images from two different instances in time, the InSAR processing flow is initiated in a LINUX environment with the use of SIGMA-SAR software. 

After a real image and an interferometric image is produced, these image files are then viewed, further processed and analysed in ENVI. 

Our study area is Metro Manila, Philippines. Two ALOS Palsar images were used (2011 and 2007 images).

The following images were produced. By linking displays, the suspected are of deformation is along the area enclosed by the ellipse.



This is a close-up view of the interferometric image and the deformation (subsidence) is approximately 9.2cm along Caloocan City, Metro Manila.

The issue on land subsidence within this area is beyond the scope of this post. Land subsidence , as suspected to be in Caloocan City, may be due to its soil type and its proximity to Manila Bay. The results should also be compared with a current surface deformation study such as the results of a differential GPS campaign.

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