Potential landslides identification based on temporal and spatial filtering of SBAS-InSAR results

Figures & data

Figure 1. (a) Location of the Three Gorges reservoir area and Badong County. The star indicates the location indication of the study area in the Three Gorges reservoir area. (b) Badong County and ALOS-2 PALSAR-2 images coverage. (c) Shape location of the study area, and the distribution of landslides and water systems in the study area.

Table 1. ALOS-2 PALSAR-2 images schedule.

Data number	Date	Data number	Date
1	2020/4/11	8	2020/11/7
2	2020/5/23	9	2021/1/16
3	2020/6/20	10	2021/3/13
4	2020/7/4	11	2021/4/10
5	2020/8/1	12	2021/6/5
6	2020/9/12	13	2021/7/3
7	2020/10/10	14	2021/8/14

Figure 2. Landslide causative factors maps: (a) Elevation; (b) slope; (c) NDVI; (d) lithology groups; (e) TWI; (f) land use/land cover. The lithology groups are described as follows: I: Hard medium to thick-bedded massive dolomite metamorphic conglomerate rock group; II-1: Hard medium to thickly laminated quartz sandstone quartzite fine sandstone rock group; II-3: Hard harder medium to thick-bedded sandstone mud siltstone interbedded with shale coal seams and mudstone shale interbedded rock group; II-4: Harder to softer thinly to moderately thickly bedded shale sandstone mudstone rock group; II-5: Soft thin to medium-thick bedded muddy siltstone shale rock group; III-1: Hard medium to thick-bedded strongly karsted carbonate rock group; III-2: Harder harder medium to thickly bedded strongly to moderately karsted carbonate rock group; III-3: Harder thin to medium-thick bedded weakly karsted carbonate rock group.

Table 2. Values for each category of causative factors.

Factors	Class	Landslides	Frequency of landslide	Classification value
Elevation	0–200 m	81	37%	1
	200–400 m	105	48%	2
	400–600 m	19	9%	3
	>600 m	16	7%	4
Slope	0–10°	6	3%	1
	10–20°	56	25%	2
	20–30°	99	45%	3
	30–40°	50	23%	4
	>40°	10	5%	5
NDVI	<0.1	30	14%	1
	0.1–0.3	34	15%	2
	0.3–0.5	40	18%	3
	0.5–0.7	74	33%	4
	>0.7	43	19%	5
Lithology groups	I	0	0%	1
	II-1	0	0%	1
	II-3	4	2%	2
	II-4	3	1%	3
	II-5	113	51%	5
	III-1	33	15%	3
	III-2	6	3%	2
	III-3	62	28%	4
TWI	<4.5	8	4%	1
	4.5–5	44	20%	2
	5–5.5	95	43%	3
	5.5–6	50	23%	4
	6–6.5	19	9%	5
	>6.5	5	2%	6
Land use/land cover	Arable land	48	22%	1
	Urban	20	9%	2
	Rural	13	6%	3
	Waters	27	12%	4
	Woodland	113	51%	5
	Grassland	0	0%	6
	Others	0	0%	7

Figure 3. Flow chart for identifying potential landslides in Badong based on spatial and temporal filtering of SBAS-InSAR results.

Figure 4. Spatial and temporal baselines of SAR datasets.

Figure 5. (a) Annual average deformation rate along the radar line of sight direction. The negative value represents the displacement of the target feature away from the satellite direction, which is shown in red in the figure, and the positive value represents the displacement of the target feature close to the satellite direction, which is shown in blue in the figure. (b) Nuclear density map.

Figure 6. (a–c) The monthly rainfall distributions for April 2020, May 2020 and July 2021, respectively. (d–f) The monthly accumulate deformation for April 2020, May 2020 and July 2021, respectively. n = 10 represents the dates of 10 SAR images.

Figure 7. Correlation distribution map. The darker the colour, the higher the correlation between the deformation here and the monthly rainfall.

Figure 8. ROC curve for GBDT model.

Figure 9. Landslide susceptibility map.

Figure 10. The map of the results of deformation landslides identification.

Table 3. Identifying landslides information table.

Deformation no.	Landslide name	Susceptibility	Correlation	Latitude, longitude	Maximum LOS rate (mm/year)	Field validation description
2	Wujiayuanzi landslide	Very high	0.2–0.4	31°12′30.281″ N, 110°17′52.852″ E	−68	Debris had rolled down on the highway side of the site. After investigation, the landslide was in a less stable state in the middle of the road cut slope zone at the back edge. Debris had rolled down on the highway side of the site. GPS data showed that the monitoring point increased the accumulated displacement deformation by 0–3 mm in 2019. The horizontal accumulated deformation increased 0–35.9 mm in 2020. The landslide was currently in the peristaltic deformation stage.
6	Hulubao landslide	High	0.4–0.6	31°4′18.771″ N 110°21′8.551″ E	−48	The site was under construction. Many anti-slip piles could be seen, and the surface soil showed obvious signs of excavation, with a soil layer of about 6–8 m. The front of the house on the north side of the survey site slipped in April or May 2021. The original landslide (landslide body No. 5) was deformed in 2012. It threatened the main body of the station building under construction and the road below.
7	Pengjiawuchang landslide	Very high	0.6–0.8	31°5′3.030″ N 110°24′0.178″ E	−66	The front edge of the road, orange tree development under-seat cracks, direction 188°, about 8 m long, the maximum under-seat about 0.5 m, in a straight line, seam width 1–2 cm. There is a local collapse in the multi-stage dry masonry retaining wall. Every year, the soil layer has a downward deformation, with the largest place being about 0.5 m, according to the households. It posed a threat to the slope’s residents and the road.
8	Dugongci landslide (Shijiapo)	Very high	0.4–0.6	31°3′22.433″ N 110°18′52.963″ E	−113	The point was in the south slope of the topography of the near east-west wash trough. Under the influence of tectonics, the rock fissures were more developed and the rock is more broken.
10	Tangu landslide	Very high	0.4–0.6	31°2′26.941″ N 110°26′17.352″ E	−64	The site soil was soft and the trees were skewed.
11	Songjiawuchang landslide	Very high	0.6–0.8	31°1′54.426″ N 110°27′7.280″ E	−79	There were cracks on the road with a direction of 220°and a depth of about 40 cm. The road was repaired in 2018 and 2019 according to the occupants, but there was a new cracking. Soil would slip during the rainy season. It posed a threat to the nearby residents and the road.
12	Chapengzi landslide (new)	High	0.2–0.4	31°1′23.924″ N 110°25′21.891″ E	−39	There were landslide management grids at the site, but they have collapsed several times and caused damage to bridges. The landslide and the bridge were both repaired at the same time. Construction began in October 2020 and was completed around September 15, 2021.
15	Huangtupo landslide	Very high	0.4–0.6	31°2′20.728″ N 110°23′9.516″ E	−38	There were many settlement deformation cracks on the highway. The walls of abandoned buildings cracked. The deformation length of the road was about 10 m. Those road cracks occurred about 2–3 years ago.
16	Zhaoshuling landslide	Very high	0.2–0.4	31°2′42.249″ N 110°20′44.047″ E	−31	Landslide control grids were visible on-site and under construction.
19	Ziduanmai landslide (new)	Very high	0.4–0.6	31°0′4.550″ N 110°19′16.393″ E	−37	Collapse deposited on a large scale. The rock was soft and had a thickness of about 15–25 m and a length of about 150 m. Localized sliding and collapse could be seen at the site along the road.
23	Songjiazhuang landslide	Very high	0.4–0.6	31°0′42.626″ N 110°15′15.877″ E	−83	Roadbed collapsed because rocks in the slope body above crumbled and hit the roadbed and highway guardrail. We could see the airside of the slope. The rock was in an unstable state and may crumble down at any time.

Notes on the minimum, maximum and mean values of the annual average deformation rate: the negative value represents the displacement of the target feature away from the satellite direction, and the positive value represents the displacement of the target feature close to the satellite direction.

Figure 11. Songjiawuchang landslide deformation analysis figures. (a) The map of the whole landslide and the indication of the location of the A–A′ profile line; (b) the map of the Songjiawuchang landslide profile; (c–e) combined maps of GPS, InSAR, and rainfall; (f–h) geological investigation site maps.

Data availability statement

The data that support the findings of this study are available from the Hubei Geological Environment Station but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of the Hubei Geological Environment Station.