*3.3. DInSAR Results Analysis*

As seen from the coherence analysis, temporal decorrelation is the major challenge for conventional DInSAR applications in the AOI. A considerable coherence loss was observed, even in short-temporal baseline interferometric pairs. Concerning the interferometric pairs where sufficient coherence remains (Bt ≤ 18 days, no-flood period), the main source of error that influences their differential interferometric phase and degrades the accuracy of LOS displacement estimates is the APS effect.

According to [85–87], a phase error of *π* 2 is considered relatively strong atmospheric distortion. At C-band, a phase error of *π* 2 results in an error of 0.7 cm in the LOS displacement estimate. To obtain reliable displacement values with DInSAR the displacement signal should dominate over the error terms. In this study, the DIS approach was applied, to improve the ratio between the displacement signal and the APS error.

**Figure 9.** Wrapped differential interferograms: (**a**) 14 December 2018–20 December 2018 and (**b**) 14 November 2018–20 November 2018; their respective coherence images (**<sup>c</sup>**,**d**), and histograms (**e**).

**Figure 10.** Sentinel-1 GRD intensity (in dB) of (**a**) 6 January 2018, (**b**) 5 February 2018, (**c**) 16 October 2019, and (**d**) 21 November 2019. (**<sup>a</sup>**,**<sup>c</sup>**) Correspond to the images before the flood event, and (**b**,**d**) to the images during the floods.

The DIS approach allowed obtaining the average LOS displacement rate estimation for the 2018–2019 period (2 years). The average LOS displacement rates obtained using Sentinel-1 SLC images from ascending and descending orbital pass are presented in Figures 12 and 13, respectively. In the average LOS displacement maps from both orbital passes, four zones with a higher average LOS displacement rate (magnitude) can be identified. These zones (b–e) are framed in Figures 12 and 13; the close-up to these zones is also presented. The LOS displacement obtained for these zones indicates the deformation of the Earth's surface away from the satellite in the ascending and descending pass results; this similarity suggests that the observed LOS displacements may be interpreted as mostly reflecting land subsidence. In zone b, the maximum average LOS displacement rates (−6 cm/yr) were obtained in the town of Paraíso, especially north of this urban center, where the Dos Bocas oil refinery is located. In Comalcalco and the surrounding areas, maximum average LOS displacement rates of −3 cm/yr were obtained.

**Figure 11.** Areas affected by the flood events of (**a**) 5 February 2018 and (**b**) 21 November 2019. Permanent water bodies are shown. A digital globe image is used as a background, the background image was taken from QGIS XYZ Tiles (https://mt1.google.com/vt/, accessed on 8 August 2022).

**Figure 12.** Map of average LOS displacement rates (cm/yr) obtained through the DIS approach, using the Sentinel-1 SLC images of ascending orbital pass acquired in the 2018–2019 period. Negative values indicate a movement away the satellite, (**a**) full AOI map. Blue rectangles enclose the zones with a higher average LOS displacement rate. Close-ups of the (**b**) Paraíso and Comalcalco; (**c**) Villahermosa; (**d**) Batería Samaria and (**e**) Batería Cactus zones are presented. The location of hydrocarbon wells is also shown.

**Figure 13.** Map of the average LOS displacement rate (cm/yr) obtained through the DIS approach using the Sentinel-1 SLC images of the descending orbital pass acquired in 2018–2019 period. Negative values indicate a movement away the satellite. (**a**) Full AOI map. Blue rectangles enclose the zones with a higher average LOS displacement rate. Close-ups of the (**b**) Paraíso and Comalcalco, (**c**) Villahermosa, (**d**) Batería Samaria and (**e**) Batería Cactus zones are presented. The location of hydrocarbon wells is also shown.

In zone c, average LOS displacement rates of up to −4 cm/yr were obtained in the south limits of the Villahermosa urban area, with up to −6 cm/yr in Pomaca and Saloya 2nd located to the north of Villahermosa. In the west limits of the Villahermosa urban area, average LOS displacement rates of up to −3 cm/yr were obtained. This region is the closest urban area to oil-producing wells (Figures 12c and 13c). The center of Villahermosa city could be considered stable (±0.5 cm/yr).

In localities between Comalcalco and Villahermosa (such as Nacajuca, Soyateco, and Jalpa de Méndez), average LOS displacement rates of up to −2 cm/yr were obtained. The city of Cárdenas, one of the main urban centers of the area, did not present a displacement signal, except for a small region southwest of this town, with an average LOS displacement up to −1 cm/yr.

In zones d and e, the obtained average LOS displacement rates reached −3 cm/yr. There is a large number of hydrocarbon-producing wells, i.e., the Batería Samaría II and Batería Captus extraction zones, close to zones d and e, respectively, suggesting a relationship between the hydrocarbon extraction and surface deformation.
