Soil temperature estimation at different depths over the central Tibetan Plateau integrating multiple Digital Earth observations and geo-computing

Figures & data

Figure 1. Study area.

Figure 2. Temperature distribution at different depths (05, 10, 20, 40 cm).

Table 1. Bandwidth and spatial resolution of MODIS and Landsat corresponding bands.

	Bandwidth (μm)			Resolution (m)
	Landsat 7	Landsat 8	MODIS	Landsat 7	Landsat 8	MODIS
Blue	0.45 ∼ 0.52	0.45 ∼ 0.51	0.46 ∼ 0.48	30	30	500
Red	0.63 ∼ 0.69	0.64 ∼ 0.67	0.62 ∼ 0.67	30	30	250
NIR	0.77 ∼ 0.90	0.85 ∼ 0.88	0.84 ∼ 0.88	30	30	500
TIR	10.40 ∼ 12.50	10.60 ∼ 11.19	10.78 ∼ 11.28	60	100	1000

Figure 3. Flow chart of this study.

Table 2. R² of two approaches at different depths and scales.

	0.0005°		0.0025°		0.0125°
Approach	LW	Direct	LW	Direct	LW	Direct
5 cm	0.851		0.855		0.865
10 cm	0.839	0.847	0.842	0.849	0.855	0.865
20 cm	0.859	0.866	0.861	0.870	0.866	0.876
40 cm	0.836	0.846	0.837	0.846	0.843	0.859

Table 3. RMSE (${}^{\circ }\mathrm{C}$) of two approaches at different depths and scales.

	0.0005°		0.0025°		0.0125°
Approach	LW	Direct	LW	Direct	LW	Direct
5 cm	2.813		2.772		2.670
10 cm	2.933	2.738	2.752	2.591	2.649	2.437
20 cm	2.678	2.453	2.589	2.322	2.306	2.270
40 cm	2.660	2.449	2.457	2.219	2.273	2.139

Table 4. MAE (${}^{\circ }\mathrm{C}$) of two approaches at different depths and scales.

	0.0005°		0.0025°		0.0125°
Approach	LW	Direct	LW	Direct	LW	Direct
5 cm	2.152		2.101		2.024
10 cm	2.130	2.124	2.114	2.093	2.019	1.962
20 cm	1.803	1.745	1.785	1.714	1.878	1.843
40 cm	1.714	1.686	1.694	1.650	1.707	1.634

Figure 4. Comparisons between the observed and predicted ST. (a) Scatter plot between observed and predicted ST, and (b) histogram of bias for predicted ST.

Figure 5. Time series of predicted and observed ST at station MS3488.

Figure 6. (a) R², (b) RMSE, and (c) MAE for different months.

Figure 7. Spatial distribution of predicted annual mean ST at a depth of 5, 10, 20, and 40 cm in 2011, 2014, 2017, and 2020. (unit: ${}^{\circ }\mathrm{C}$).

Figure 8. Spatial distribution of estimated surface ST on July 24th, 2015, for three spatial resolutions (0.0125°, 0.0025°, and 0.0005°).

Figure 9. ST’s rising trend at 5, 10, 20, and 40 cm.

Data availability

The data that support the findings of this study are openly available in NASA MODIS Portal (https://modis.gsfc.nasa.gov/), USGS Landsat Portal (https://earthexplorer.usgs.gov/), the Global land surface satellite products (http://www.glass.umd.edu/index.html), the Tibetan Plateau Science Data Center, National Earth System Science Data Sharing Infrastructure, National Science & Technology Infrastructure of China (http://tibet.geodata.cn).