Soil moisture and freeze-thaw map using GNSS reflectometer and SMAP radiometer for Qinghai-Xizang Plateau

doi:10.11947/j.AGCS.2025.20240360

Abstract

Abstract:

GNSS-R technology has been applied to monitor soil moisture (SM) and freeze-thaw (F/T) conditions. However, GNSS-R SM retrieval is currently blank in high altitude areas, and GNSS-R F/T results are only available for short time series. Therefore, a five-year GNSS-R SM and F/T record for the Xizang Plateau region was developed in this study. The grid-by-grid average root mean square error (RMSE) and correlation (R) of CYGNSS SM were 0.064 cm³/cm³ and 0.53, respectively. The grid-by-grid average detection accuracy of CYGNSS F/T was 85.5%. The validation results from independent stations show that the RMSE and R for CYGNSS SM are 0.059 cm³/cm³ and 0.56, respectively, and the classification accuracy for CYGNSS F/T is 83.8%. This is comparable to the accuracy of SM and F/T of SMAP in the same period. This study will fill the gap of GNSS-R SM and F/T records at high altitudes. It is worth noting that the number of available days for CYGNSS is significantly higher than that of SMAP. The number of available days for CYGNSS SM is 47.0% higher than that of SMAP SM, and the number of available days for CYGNSS F/T is 14.7% higher than that of SMAP F/T. Moreover, this study also developed an empirical fusion framework for CYGNSS and SMAP. The average RMSE of the fused CYGNSS and SMAP SM (i.e., the CYGNSS-SMAP SM) is 0.056 cm³/cm³, with an R of 0.60. This is an 18.8% improvement in accuracy and a 34.7% improvement in the number of available days compared to the existing SMAP SM. The average accuracy of the fused CYGNSS and SMAP F/T (i.e., CYGNSS-SMAP F/T) is 89.8%. This is a 10.0% improvement in accuracy and a 10.2% improvement in the number of available days over the existing SMAP F/T. Fusing the CYGNSS reflectometer and SMAP radiometer can provide higher accuracy and continuity of SM and F/T in the Xizang Plateau region. The study also demonstrates the fairly good monitoring capability of the spaceborne GNSS-R technique in the high-altitude region.

Key words: CYGNSS, SMAP, soil moisture, soil freeze-thaw, Qinghai-Xizang Plateau

CLC Number:

P228

Wentao YANG, Fei GUO, Xiaohong ZHANG, Zhiyu ZHANG, Yifan ZHU, Zheng LI, Ziheng WU. Soil moisture and freeze-thaw map using GNSS reflectometer and SMAP radiometer for Qinghai-Xizang Plateau[J]. Acta Geodaetica et Cartographica Sinica, 2025, 54(4): 725-735.

Figures/Tables 14

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测站	网络	纬度	经度	SM_CYGNSS		F/T_CYGNSS		SM_SMAP			F/T_SMAP
测站	网络	纬度	经度	R	RMSE/（cm³/cm³）	分类精度/（%）	天数	R	RMSE/（cm³/cm³）	天数	分类精度/（%）	天数
CST-03	MAQU	33.9°N	102.0°E	0.43	0.065	100	1573	0.56	0.061	1155	76.7	1523
CST-04	MAQU	33.8°N	101.7°E	0.78	0.034	90.8	1593	0.78	0.065	1094	80.1	1401
CST-05	MAQU	33.7°N	101.9°E	0.76	0.065	98.7	1593	0.77	0.089	1094	78.8	1401
NST-01	MAQU	33.9°N	102.1°E	0.61	0.075	73.0	1573	0.75	0.043	1155	73.5	1523
NST-05	MAQU	33.6°N	102.0°E	0.46	0.051	80.2	1536	0.55	0.069	1197	85.9	1392
NST-06	MAQU	34.0°N	102.3°E	0.51	0.034	81.8	1573	0.64	0.056	1155	78.5	1523
NST-25	MAQU	34.0°N	102.0°E	0.72	0.084	77.0	1573	0.72	0.098	1155	86.4	1523
NST-31	MAQU	33.7°N	101.9°E	0.52	0.073	72.9	1593	0.68	0.064	1094	80.8	1401
NST-32	MAQU	33.7°N	101.8°E	0.43	0.045	79.0	1593	0.55	0.085	1094	91.5	1401
ALI02	NGARI	33.5°N	79.6°E	0.41	0.064	84.9	1647	0.79	0.067	586	83.9	773
All				0.56	0.059	83.8	1585	0.68	0.069	1078	81.6	1386

测站	网络	纬度	经度	CYGNSS-SMAP SM			CYGNSS-SMAP F/T
测站	网络	纬度	经度	R	RMSE/（cm³/cm³）	天数	分类精度/（%）	天数
CST-03	MAQU	33.9°N	102.0°E	0.70	0.058	1447	95.3	1578
CST-04	MAQU	33.8°N	101.7°E	0.70	0.039	1460	84.5	1584
CST-05	MAQU	33.7°N	101.9°E	0.70	0.062	1460	83.9	1584
NST-01	MAQU	33.9°N	102.1°E	0.61	0.070	1447	83.8	1578
NST-05	MAQU	33.6°N	102.0°E	0.74	0.049	1424	93.0	1524
NST-06	MAQU	34.0°N	102.3°E	0.66	0.038	1447	92.5	1578
NST-25	MAQU	34.0°N	102.0°E	0.57	0.076	1447	90.0	1578
NST-31	MAQU	33.7°N	101.9°E	0.59	0.038	1460	85.4	1584
NST-32	MAQU	33.7°N	101.8°E	0.31	0.060	1460	94.8	1584
ALI02	NGARI	33.5°N	79.6°E	0.40	0.065	1468	94.7	1569
All				0.60	0.056	1452	89.8	1574