Abstract
In a recent publication, Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021) claimed (see, in particular, the Discussion and Recommendation Section in their article) that the advanced differential SAR interferometry (InSAR) algorithms for surface deformation retrieval, based on the small baseline approach, are affected by systematic biases in the generated InSAR products. Therefore, to avoid such biases, they recommended a strategy primarily focused on excluding “the short temporal baseline interferograms and using long baselines to decrease the overall phase errors.” In particular, among various techniques, Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021) identified the solution presented by Manunta <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2019) as a small baseline advanced InSAR processing approach where the presence of the above-mentioned biases (referred to as a fading signal) compromises the accuracy of the retrieved InSAR deformation products. We show that the claim of Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021) is not correct (at least) for what concerns the mentioned approach discussed by Manunta <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2019). In particular, by processing the Sentinel-1 dataset relevant to the same area in Sicily (southern Italy) investigated by Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021), we demonstrate that the generated InSAR products do not show any significant bias.
Highlights
The “nonclosure behavior” of the multilook interferometric synthetic aperture radar (SAR) (InSAR) phase signals relevant to distributed scatterers (DSs) represents the starting point of the analysis presented by Ansari et al [1]
Wherein M is the number of the interferograms of the exploited triangulation, A is the incidence matrix of the oriented graph associated with the interferometric pairs, φ(P) is the vector of the unwrapped interferometric phases “regenerated” from the retrieved time series vector, say φTS(P)
We have shown in this Comment that, differently from what was claimed by Ansari et al [1], the advanced interferometric SAR (InSAR) processing approach presented by Manunta et al [2], based on the exploitation of small baseline interferograms and including the processing stage discussed in [9], can be effectively applied to generate InSAR products that do not present any significant bias
Summary
The “nonclosure behavior” of the multilook interferometric SAR (InSAR) phase signals relevant to distributed scatterers (DSs) represents the starting point of the analysis presented by Ansari et al [1] (see formula 1 and 2 of the article in question). This is a rather wellknown concept for the InSAR community that in the last twenty years has been using temporal sequences of multilook interferograms for the retrieval of surface deformation time series and the corresponding mean velocity maps.
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