Comparison of SMOS, modelled and in situ long-term soil moisture series in the northwest of Spain

Figures & data

Figure 1. Location of the REMEDHUS area representing soil moisture stations, weather stations and DGG centres of SMOS L2.

Table 1. REMEDHUS representative stations (topsoil properties). CV: coefficient of variation.

ID	Soil texture (%)				Organic matter (%)	Main land use (2010–2013)	Soil moisture (m^3 m^−3) (2010–2013)
	Class	Sand	Silt	Clay			Mean	Min/Max	CV (%)
K10	Sandy	91	6	3	0.27	Rainfed cereal	0.054	0.000–0.310	75
K4	Sandy	87	9	4	0.27	Vineyard	0.040	0.004–0.149	55
O7	Loamy sand	79	13	8	0.45	Rainfed cereal	0.115	0.011–0.341	57
H13	Sandy loam	70	11	18	0.66	Rainfed cereal	0.139	0.030–0.395	37
N9	Sandy clay loam	62	17	21	0.95	Rainfed cereal	0.185	0.055–0.449	44
M9	Sandy clay loam	50	25	25	1.42	Rainfed cereal	0.190	0.073–0.439	34
L7	Sandy clay loam	47	21	32	3.31	Rainfed cereal	0.211	0.072–0.429	41
H9	Silty clay loam	20	45	35	5.84	Pasture and forest	0.286	0.092–0.600	49

Table 2. Annual rainfall and aridity index (AI) during the calibration and validation periods.

Period	Annual rainfall (mm)					AI
	Cañizal	Granja	Carrizal	Villamor	Average	Cañizal	Granja	Carrizal	Villamor	Average
2008	378	391	–	491	420	0.36	0.39	–	0.52	0.42
2009	323	274	–	399	332	0.27	0.24	–	0.37	0.29
2008–2009	351	333	–	445	376	0.31	0.31	–	0.44	0.35
2010	480	414	556	591	510	0.43	0.41	0.53	0.60	0.49
2011	297	229	315	319	290	0.25	0.22	0.32	0.30	0.27
2012	337	278	373	438	357	0.29	0.27	0.37	0.42	0.34
2013	449	373	467	501	448	0.40	0.38	0.51	0.51	0.45
2010–2013	391	324	428	462	401	0.34	0.32	0.43	0.45	0.38
2008–2013	377	327	–	457	387	0.33	0.32	–	0.45	0.36

Table 3. Range of calibrated parameter values based on Rawls et al. (1982).

Calibrated parameters
ψb (mm)		Ks (mm/h)		λ		Kc
Min	Max	Min	Max	Min	Max	Min	Max
–72	–373	0.6	210	0.16	0.69	0.3	2.8

Table 4. Calibration and validation model results at the representative stations and for its application with averaged data. R: correlation coefficient; d: agreement index; RMSD: root mean square difference and bias in volumetric units (m³ m⁻³). All the correlations are significant at a 95% confidence level.

ID	Calibration				Validation
	R	d	RMSD (m^3 m^−3)	bias (m^3 m^−3)	R	d	RMSD (m^3 m^−3)	bias (m^3 m^−3)
K10	0.90	0.95	0.02	0.000	0.73	0.84	0.03	0.011
K4	0.84	0.91	0.01	0.000	0.73	0.80	0.02	0.008
O7	0.93	0.96	0.03	0.003	0.90	0.94	0.03	0.013
H13	0.85	0.92	0.03	0.001	0.89	0.93	0.03	0.009
N9	0.87	0.93	0.04	0.008	0.88	0.91	0.05	0.028
M9	0.95	0.97	0.02	0.002	0.93	0.94	0.03	0.022
L7	0.95	0.98	0.03	0.003	0.95	0.97	0.03	–0.009
H9	0.85	0.92	0.08	0.002	0.86	0.92	0.08	0.014
Average	0.90	0.95	0.03	–0.002	0.86	0.95	0.03	0.000

Figure 2. Modelled soil moisture (SWBM) vs in situ soil moisture (in situ) in the calibration (Cal) and validation periods (Val) for the M9, O7 and H13 stations and for the simulations with averaged data. The rainfall series of the La Granja and Cañizal weather stations and the average rainfall of the four weather stations are also shown.

Figure 3. Modelled soil moisture (SWBM) vs in situ observed soil moisture (in situ) in the calibration (Cal) and validation periods (Val) for the H9 and K10 stations and the rainfall series of the Cañizal and La Granja weather stations.

Table 5. Validation results of ascending (A) and descending (D) SMOS L2 series and the corresponding normalized SMOS series by linear regression (SMOS_REG) and by CDF matching (SMOS_CDF) vs in situ observations and vs the average of in situ observations within the 1913 DGG cell, and validation results of the averaged SMOS series vs the averaged in situ series of all the selected stations. N obs: number of observations; R: correlation coefficient; RMSD: root mean square difference and bias, both in volumetric units (m³ m⁻³). All the correlations are significant at a 95% confidence level.

ID	DGG cell	N obs	SMOS L2			SMOSREG		SMOSCDF
			R	RMSD (m^3 m^−3)	bias (m^3 m^−3)	R	RMSD (m^3 m^−3)	R	RMSD (m^3 m^−3)
K10	1913A	583	0.63	0.07	–0.05	0.63	0.03	0.64	0.03
	1913D	602	0.62	0.08	–0.06	0.62	0.03	0.62	0.03
K4	1400A	600	0.73	0.08	–0.06	0.73	0.02	0.73	0.02
	1400D	623	0.66	0.09	–0.07	0.66	0.02	0.66	0.02
O7	1914A	538	0.74	0.05	0.02	0.74	0.05	0.76	0.05
	1914D	518	0.73	0.05	0.02	0.73	0.04	0.74	0.04
H13	2425A	600	0.73	0.06	0.03	0.73	0.04	0.74	0.04
	2425D	626	0.63	0.06	0.03	0.63	0.04	0.63	0.04
N9	1913A	587	0.67	0.10	0.08	0.67	0.06	0.69	0.06
	1913D	600	0.66	0.10	0.08	0.66	0.06	0.66	0.06
M9	1913A	580	0.71	0.11	0.09	0.71	0.05	0.73	0.05
	1913D	593	0.66	0.10	0.09	0.66	0.05	0.68	0.05
L7	1913A	588	0.71	0.12	0.11	0.71	0.06	0.74	0.06
	1913D	604	0.68	0.13	0.11	0.68	0.06	0.71	0.06
H9	1912A	494	0.60	0.21	0.18	0.60	0.11	0.60	0.12
	1912D	518	0.57	0.21	0.18	0.57	0.11	0.57	0.13
K10, L7, M9, N9	1913A	560	0.72	0.08	0.06	0.72	0.04	0.75	0.05
	1913D	574	0.70	0.07	0.06	0.70	0.04	0.72	0.05
Average	Averaged A	694	0.77	0.06	0.05	0.77	0.04	0.79	0.04
	Averaged D	736	0.74	0.06	0.04	0.74	0.04	0.77	0.04

Figure 4. Ascending (A) vs descending (D) SMOS L2 series of the DGG cells: 1400 (K4), 1912 (H9), 1913 (K10, L7, M9 and N9), 1914 (O7) and 2425 (H13).

Figure 5. Time series of in situ (in situ) and SMOS ascending (SMOS) for the H9, M9, O7, H13 and K10 stations. The rainfall from La Granja and Cañizal weather stations is also shown.

Figure 6. Time series of averaged in situ (in situ) and averaged SMOS ascending (SMOS) of the selected stations and the average rainfall.

Figure 7. Time series of in situ (in situ) and of normalized SMOS ascending by linear regression (SMOS_REG) and by CDF matching (SMOS_CDF) for the H9, M9, O7, H13 and K10 stations and for the average of the selected stations.

Table 6. Validation results of ascending (A) and descending (D) SMOS L2 series and the corresponding normalized SMOS series by linear regression (SMOS_REG) and by CDF matching (SMOS_CDF) vs modelled series and vs the averaged modelled series within the 1913 DGG cell, and validation results of averaged SMOS series vs modelled series using averaged data. N obs: number of observations; R: correlation coefficient; RMSD: root mean square difference and bias, in volumetric units (m³ m⁻³). All the correlations are significant at a 95% confidence level.

ID	DGG cell	N obs	SMOS L2			SMOSREG		SMOSCDF
			R	RMSD (m^3 m^−3)	bias (m^3 m^−3)	R	RMSD (m^3 m^−3)	R	RMSD (m^3 m^−3)
K10	1913A	593	0.82	0.07	–0.06	0.82	0.02	0.82	0.02
	1913D	610	0.83	0.08	–0.07	0.83	0.02	0.83	0.02
K4	1400A	604	0.79	0.09	–0.07	0.79	0.01	0.80	0.01
	1400D	624	0.78	0.09	–0.08	0.78	0.01	0.78	0.01
O7	1914A	592	0.77	0.05	0.01	0.77	0.04	0.81	0.04
	1914D	547	0.78	0.04	0.01	0.78	0.04	0.80	0.04
H13	2425A	607	0.77	0.05	0.02	0.77	0.03	0.77	0.03
	2425D	634	0.74	0.05	0.01	0.74	0.03	0.73	0.03
N9	1913A	593	0.77	0.09	0.07	0.77	0.04	0.79	0.04
	1913D	610	0.76	0.12	0.11	0.76	0.06	0.79	0.06
M9	1913A	593	0.77	0.09	0.07	0.77	0.04	0.79	0.04
	1913D	610	0.77	0.08	0.06	0.77	0.04	0.79	0.04
L7	1913A	593	0.72	0.14	0.13	0.72	0.07	0.75	0.07
	1913D	610	0.72	0.13	0.12	0.72	0.06	0.76	0.07
H9	1912A	602	0.73	0.22	0.19	0.73	0.10	0.75	0.11
	1912D	645	0.75	0.21	0.18	0.75	0.10	0.77	0.10
K10, L7, N9, M9	1913A	593	0.77	0.08	0.06	0.77	0.05	0.79	0.05
	1913D	610	0.77	0.07	0.06	0.77	0.04	0.80	0.04
Average	Averaged A	694	0.80	0.07	0.05	0.80	0.04	0.83	0.04
	Averaged D	736	0.79	0.06	0.04	0.79	0.04	0.81	0.04

Figure 8. Time series of modelled observations (SWBM) and SMOS ascending (SMOS) for the H9, M9, O7, H13 and K10 stations. The rainfall pattern of La Granja and Cañizal weather stations is also shown.

Figure 9. Time series of modelled observations using averaged data (SWBM) and of averaged SMOS ascending (SMOS) data and the average rainfall.

Figure 10. Time series of modelled (SWBM) and of normalized SMOS ascending by linear regression (SMOS_REG) and by CDF matching (SMOS_CDF) for the H9, M9, O7, H13 and K10 stations and for the average of the selected stations.

Rawls, W.J., Brakensiek, D.L. and Saxton, K.E., 1982. Estimation of soil water properties. Transaction of the ASAE, 25(5), 1316–1320.

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