# Decomposing DInSAR Time-Series into 3-D in Combination with GPS in the Case of Low Strain Rates: An Application to the Hyblean Plateau, Sicily, Italy

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## Abstract

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## 1. Introduction

#### 1.1. Techniques of Atmospheric Correction

#### 1.2. Techniques for Decomposing the DInSAR Signal into a 3-Dimensional Velocity Field

## 2. Method and Data Collection

#### 2.1. Study Area

#### 2.2. Data Collection & Processing

#### 2.2.1. DInSAR Processing

#### 2.2.2. Tropospheric Correction

#### 2.2.3. Spatial Enhancement

#### 2.2.4. GPS Data

#### 2.2.5. SISTEM Integration

## 3. Results & Discussion

#### 3.1. Tropospheric Correction

#### 3.2. Spatial Enhancement

#### 3.3. SISTEM Decomposition

#### 3.3.1. Vertical Component

#### 3.3.2. Horizontal Components

#### 3.4. The Velocity Field in Its Geological Context

#### 3.4.1. Northern Rim of the Hyblean Plateau

#### 3.4.2. Scicli-Ragusa Fault Belt

#### 3.4.3. Ionian Boundary of the Hyblean Plateau

#### 3.4.4. The Presence of Subsidence

## 4. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 3.**GPS velocity field: Horizontal (

**a**) and vertical (

**b**) velocities with respect to the NOTO reference station (NOTO). Black stations have been installed between 1993 and 1997, while red stations were installed after 2000. The velocity field was originally calculated by Angelica et al. 2013 [65]).

**Figure 4.**(

**a**–

**h**) Mean LOS velocities (upper row: ascending track; lower row: descending track): (

**a**,

**e**) corrected for orbital and DEM error; (

**b**,

**f**) tropospheric corrected datasets; (

**c**,

**g**) gap-filled dataset; (

**d**,

**h**) multi-directional Lee filtered dataset.

**Figure 5.**Decomposed velocity field in reference to the Noto GPS station (

**a**,

**a’**) North-South component and WLS error; (

**b**,

**b’**) East-West component and WLS error; (

**c**,

**c’**) Up-Down component (from blue to red) and WLS errors. The corresponding GPS directional velocities have been plotted over the SISTEM output. The colour scale reflects the absolute residual of the GPS component with respect to the SISTEM solution.

**Figure 6.**(

**a**–

**f**) Recalculation of the mean LOS velocities from the SISTEM output; upper row ascending track; lower row: descending track. (

**a**,

**d**) original LOS mean velocities; (

**b**,

**e**) predicted LOS mean velocities from the 3-dimensional SISTEM components; (

**c**,

**f**) residuals of the predicted mean LOS velocities with respect to the original LOS velocities.

**Figure 7.**Zoom-in on the (

**a**) north-south velocity field along the Scicli-Ragusa fault; and (

**b**) the east-west velocity field of the area around the Avola fault with the overlay of the earthquakes associated with 2011/2012 seismic swarm event [69].

**Table 1.**Accuracy of DInSAR results before and after tropospherical correction. RMSE of GPS velocities projected into the LOS against the DInSAR results is given (middle column) as well as the mean RMSE for all interferograms used in the LOS velocity inversion (right column).

Mean LOS vs. GPS (RMSE) | Mean RMSE of all IFGs | |
---|---|---|

non-corrected Stack (Ascending) | 3.4 mm/year | 3.9 rad |

Tropos. corrected stack (Ascending) | 2.8 mm/year | 3.5 rad |

Percentual Improvement | 17.6% | 10% |

non-corrected Stack (Descending) | 3.3 mm/year | 4.2 rad |

Tropos. corrected stack (Descending) | 2.8 mm/year | 3.8 rad |

Percentual Improvement | 15% | 9.5% |

© 2017 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Vollrath, A.; Zucca, F.; Bekaert, D.; Bonforte, A.; Guglielmino, F.; Hooper, A.J.; Stramondo, S. Decomposing DInSAR Time-Series into 3-D in Combination with GPS in the Case of Low Strain Rates: An Application to the Hyblean Plateau, Sicily, Italy. *Remote Sens.* **2017**, *9*, 33.
https://doi.org/10.3390/rs9010033

**AMA Style**

Vollrath A, Zucca F, Bekaert D, Bonforte A, Guglielmino F, Hooper AJ, Stramondo S. Decomposing DInSAR Time-Series into 3-D in Combination with GPS in the Case of Low Strain Rates: An Application to the Hyblean Plateau, Sicily, Italy. *Remote Sensing*. 2017; 9(1):33.
https://doi.org/10.3390/rs9010033

**Chicago/Turabian Style**

Vollrath, Andreas, Francesco Zucca, David Bekaert, Alessandro Bonforte, Francesco Guglielmino, Andrew J. Hooper, and Salvatore Stramondo. 2017. "Decomposing DInSAR Time-Series into 3-D in Combination with GPS in the Case of Low Strain Rates: An Application to the Hyblean Plateau, Sicily, Italy" *Remote Sensing* 9, no. 1: 33.
https://doi.org/10.3390/rs9010033