slide 46

INSAR can measure both topography and displacement. The equation for topography phase is given, while displacement phase is simpler. INSAR is more sensitive to displacement than topography. Smaller wavelengths are more sensitive for both topography and displacement. X-band SAR images can generate high resolution DEM and surface displacement. However, smaller wavelengths are easily affected by vegetation. So, choose the right wavelength for your study region. We can compare the inside sensitivity to topography and displacement. The equation of topography phase is minus 4 pi times perpendicular baseline times h over lambda r times phi look angle. Phi displacement is 4 pi times displacement over lambda. Note that the displacement is in the direction of satellite ground. You can see INSAR is more sensitive to displacement. For the topography, it has a huge value r in the denominator. So h needs to be large enough to reflect on the INSAR phase. But for the displacement, just a small value can cause phase change in INSAR. We also can see smaller wavelengths have higher sensitivity of topography and displacement. Along with the high range resolution of smaller wavelengths, using such SAR images like X-band SAR images is capable of generating a high resolution and high sensitivity DEM and surface displacement. However, it doesn't mean SAR images with smaller wavelengths are better than those with longer wavelengths. Smaller wavelengths SAR images have less penetration. So their results are easily affected by vegetation. We have talked about this in previous slides. We should use the SAR data with right wavelengths based on what kind of study region you target.