For a particular pixel across multiple co-registered InSAR images, the amplitude value of the received echo may fluctuate from a mean value based on how sustained/changing is the scattering mechanism by the targets within such pixel over time. The selection of pixels as persistent scatterers candidates used for creating a deformation map through time series analysis of several acquisitions is primarily based upon the amplitude dispersion index thresholding at low values in order to properly estimate the phase stability/dispersion only when the Signal-to-Noise ratio is high enough for such pixels, according to the work of (Ferretti et al., 2001).
Source of the figure:
(PDF) Permanent scatterers in SAR interferometry. IEEE Trans Geosci Remot Sen (researchgate.net)
1) What is meant by phase stability in this case?
2) How is the phase's standard deviation across a time series affected by the amplitude dispersion?
3) How does the contribution of uncompensated propagation disturbances such as the atmospheric phase contribution and the satellite's orbital position inaccuracies besides other sources of noise affect the phase stability ?
Hi there,
1 - In this context, phase stability refers to the consistency of the phase values acquired by the InSAR system over time for a particular pixel. A pixel with high phase stability will have phase values that are consistent across multiple acquisitions, while a pixel with low phase stability will have phase values that vary significantly over time. Phase stability is an important factor in InSAR analysis as it directly affects the accuracy of the deformation measurement.
2 - The amplitude dispersion across a time series of InSAR images can affect the phase's standard deviation by introducing noise to the system. When the amplitude of the signal varies significantly over time, it can result in a loss of coherence between the two acquisitions being compared, leading to increased phase noise and decreased phase stability. The selection of persistent scatterers candidates (PSCs) based on low amplitude dispersion index thresholding is done to ensure that the selected pixels have high coherence, which in turn ensures higher phase stability.
3 - Uncompensated propagation disturbances such as atmospheric phase contribution and satellite orbital position inaccuracies can significantly affect the phase stability of InSAR images. The atmospheric phase contribution is particularly problematic, as it can introduce significant phase noise into the system. This noise can be mitigated using various techniques, such as using a weather model to correct for the atmospheric contribution, or by using differential InSAR techniques that cancel out the atmospheric phase contribution. Satellite position inaccuracies can also affect the phase stability, particularly if the satellite's orbit is not accurately known. This can result in phase errors that can be corrected using various techniques, such as using GPS data to refine the satellite orbit.
Mahdi Khoshlahjeh Azar
I am really grateful for you taking the time for answering my inquiry.
In terms of phase stability, Any changes of the scatterer's physical properties over time can either delay or haste the backscattered signal which will be received at a different phase value for each acquisition. Therefore, isn't the deformation itself cause phase instability over time for a certain pixel? I assume that the deformational phase difference primarily alters the coherence but, unlike the stochastic attenuations of the backscattered signal created by atmospheric noise for example which can cause huge variations of the phase difference between each consecutive acquisition, phase measurements due to deformation reflect regular and gradual LOS movements without apparent frequent spikes in the displacement/time chart like these.
Correct me if I am wrong if you wouldn't mind
- Badges
- Science topic
- Similar topics
- Mathematics