Identification and temporally-spatial quantification of geomorphic relevant changes by construction projects in loess landscapes: case study Lanzhou City, NW China

Figures & data

Table 1. Technical data of most prominent remote sensing missions.

	MODIS	Landsat	Sentinel-2
Continuity since	1999	1972	2015
Swath wide [km]	2330	185	290
Spatial resolution	250 m (bands 1–2) 500 m (bands 3–7) 1000 m (bands 8–36)	30 m (pan 15 m)	10 m (bands 2–4, 8) 20 m (bands 5–7, 11,12) 60 m (bands1, 9, 10)
Band numbers	36	7 TM, 8 ETM+, 11 LDCM	13
Repeat cycle [d]	16	16	10 (5)*

TM – Thematic mapper, ETM+ – Enhanced thematic mapper, LDCM – Landsat Data Continuity Mission; *Bisection of the repeat cycle is facilitated by acting of two Sentinel-2.

Figure 1. Project area depicting the generalized lithostratigraphic settings based on Geological Map (Gansu Bureau of Geology and Mineral Resources (GBGMR), 1987) with underlying shaded relief produced in 2012.

Figure 2. Classification steps of changed areas, illustrated on PC2 from image stack 2013–10-11 to 2015–10-10: a) Selected greyscale coded PC containing the changes; b) Binning statistics of the factor values with 2nd and 98th percentiles representing changes; c) Mapping of the changed areas according to the binning statistics.

Table 2. Landsat scenes included in the study.

Mission	Instrument	Scene id	Acquisition date
Landsat 5	TM	LT51310351994296BJC00	1994–10-23
Landsat 5	TM	LT51310352001299BJC00	2001–10-26
Landsat 5	TM	LT51310352004276BJC00	2004–10-18
Landsat 5	TM	LT51310352006281IKR00	2006–10-08
Landsat 5	TM	LT51310352009289IKR02	2009–10-16
Landsat 5	TM	LT51310352011279IKR02	2011–10-06
Landsat 8	OLI	LC81310352013284LGN00	2013–10-11
Landsat 8	OLI	LC81300352015283LGN00	2015–10-10

Figure 3. Analysis flow chart.

Table 3. Important PCs, eigenvalues, loadings of the eigenvector for corresponding six bands, importance, and contrast C; the utilized PCs are in bold.

PC	Eigenvalue	Vector components scene 1						Vector components scene 2						Importance [%]	C
		Blue	Green	Red	NIR	SWIR1	SWIR2	Blue	Green	Red	NIR	SWIR1	SWIR2
		1994–10-23						2001–10-26
PC1	3,455,444	0.05	0.11	0.16	0.25	0.41	0.39	0.07	0.13	0.19	0.29	0.47	0.46	89.0	0.24
PC2	160,658	0.35	0.38	0.38	0.32	0.17	0.25	0.15	0.11	0.05	−0.06	−0.42	−0.41	4.1	2.43
PC3	144,181	0.19	0.15	0.08	−0.08	−0.45	−0.37	0.36	0.42	0.45	0.23	0.02	0.15	3.7	2.11
PC4	59,702	−0.08	−0.09	−0.14	0.46	0.01	−0.29	−0.11	−0.10	−0.13	0.71	0.05	−0.34	1.5	0.21
		2001–10-26						2004–10-18
PC1	3,622,996	−0.06	−0.13	−0.18	−0.27	−0.46	−0.45	−0.09	−0.15	−0.20	−0.26	−0.39	−0.41	88.33	0.05
PC2	204,673	−0.22	−0.28	−0.31	−0.40	−0.24	−0.24	0.07	0.12	0.21	−0.03	0.40	0.53	4.99	2.98
PC3	127,301	0.34	0.37	0.37	−0.15	−0.29	−0.07	0.31	0.36	0.42	−0.26	−0.16	0.09	3.1	0.19
PC4	88,934	−0.06	−0.04	0.02	−0.37	0.27	0.45	−0.09	−0.14	−0.12	−0.73	−0.06	0.11	2.17	1.29
		2004–10-18						2006–10-08
PC1	3,515,889	−0.09	−0.16	−0.21	−0.26	−0.40	−0.42	−0.10	−0.17	−0.22	−0.26	−0.41	−0.44	89.58	0.05
PC2	145,954	0.10	0.10	0.17	−0.66	−0.07	0.20	0.10	0.12	0.20	−0.58	0.01	0.28	3.72	0.30
PC3	126,064	−0.23	−0.28	−0.29	−0.04	0.35	0.27	−0.32	−0.39	−0.44	−0.28	0.19	0.17	3.21	0.85
PC4	93,876	0.19	0.27	0.35	0.17	0.32	0.41	−0.05	−0.09	−0.12	−0.22	−0.42	−0.47	2.39	3.07
		2006–10-08						2009–10-16
PC1	2,859,574	0.11	0.19	0.24	0.29	0.45	0.48	0.06	0.11	0.14	0.26	0.38	0.35	84.6	0.46
PC2	232,268	0.01	−0.04	−0.09	0.00	−0.37	−0.46	0.28	0.33	0.41	0.26	0.25	0.40	6.9	2.88
PC3	132,511	0.28	0.33	0.42	−0.30	−0.09	0.15	0.21	0.22	0.28	−0.53	−0.25	0.07	3.9	0.79
PC4	102,582	0.19	0.26	0.27	0.63	−0.07	−0.22	0.07	0.09	0.07	0.27	−0.33	−0.41	3.0	1.30
		2009–10-16						2011–10-06
PC1	2,498,583	0.08	0.13	0.17	0.29	0.41	0.39	0.10	0.15	0.20	0.27	0.44	0.45	84.4	0.14
PC2	169,068	0.30	0.32	0.40	−0.33	−0.24	0.10	0.30	0.34	0.41	−0.23	−0.23	0.06	5.7	0.10
PC3	138,161	0.18	0.24	0.29	0.42	0.27	0.28	−0.05	−0.08	−0.14	0.14	−0.41	−0.54	4.7	2.76
PC4	99,603	0.01	0.03	0.00	0.32	−0.34	−0.48	0.12	0.22	0.26	0.64	0.01	−0.11	3.4	1.60
		2011–10-06						2013–10-11
PC1	2,767,680	0.09	0.13	0.18	0.25	0.41	0.42	0.12	0.16	0.22	0.29	0.43	0.41	82.7	0.15
PC2	255,650	0.12	0.19	0.25	0.21	0.40	0.46	−0.15	−0.22	−0.30	−0.26	−0.32	−0.37	7.6	3.25
PC3	156,001	0.30	0.36	0.44	−0.17	−0.25	0.02	0.29	0.36	0.40	−0.20	−0.30	−0.02	4.7	0.17
PC4	114,213	−0.04	−0.11	−0.10	−0.68	0.12	0.31	−0.02	−0.07	−0.03	−0.52	0.17	0.31	3.4	0.34
		2013–10-11						2015–10-10
PC1	3,846,825	0.10	0.14	0.19	0.25	0.37	0.35	0.15	0.21	0.27	0.31	0.44	0.44	87.1	0.42
PC2	224,850	0.23	0.31	0.37	0.32	0.30	0.39	−0.04	−0.09	−0.16	−0.11	−0.39	−0.42	5.1	3.13
PC3	165,268	0.21	0.28	0.31	−0.23	−0.38	−0.16	0.30	0.42	0.49	0.01	−0.20	−0.10	3.7	0.89
PC4	126,999	−0.04	−0.01	−0.07	0.49	−0.18	−0.32	−0.04	0.02	−0.03	0.73	−0.04	−0.28	2.9	0.49

Figure 4. Changed areas in time intervals and validation spots; depicted on the Sentinel-2 scene [11/01/2016] (Natural colors: RGB bands 4, 3, 2). The city area is excluded.

Figure 5. The proportion of the leveled and bulldozed area in the respective periods.

Figure 6. Taipingyang development zone, July 2017, a) leveling and b) terracing work to generate construction land.

Figure 7. a) Housing community in the Biguiyuan development zone, 27–04-2016, b) Commercial building district and housing community in the Jiuzhou development zone, 26–04-2016.

Figure 8. Example of a visual check with Google Earth, showing leveling activities in Biguiyuan development zone in 2002–2004: a) Factor values of the change detection between the scenes Oct 2001 – Oct 2004. b) The beginning phase of earthworks in 2002 [11/25/2002]; c) Shape of the development area in November 2004 [11/04/2004]. Differences in the brownish hues indicate the leveling area in the center of the picture.

Figure 9. Elevation difference classes on the validation spot Taipingyang a) elevation in 2012, b) elevation in 2016, c) cutting and filling difference classes depicted on a Sentinel-2 scene [11/01/2016] (Natural colors: RGB bands 4, 3, 2).

Gansu Bureau of Geology and Mineral Resources (GBGMR) (1987). Geoenvironmental exploration report of Lanzhou city (in Chinese), Technical Report, Volume 3, Gansu, Lanzhou, 131 p.

 Google Scholar

Data availability statement

Derived data supporting the findings of change detection study are available from the corresponding author on request. Restrictions are given for the compared elevation models due to contract.