利用GNSS反射计和SMAP辐射计反演青藏高原土壤湿度和冻融状态

doi:10.11947/j.AGCS.2025.20240360

摘要/Abstract

摘要：

全球导航卫星系统反射测量（GNSS-R）技术已被应用于监测土壤湿度（SM）和冻融（F/T）状态。然而，目前GNSS-R SM反演结果在高海拔地区尚属空白，GNSS-R F/T反演结果也仅有短时间序列。因此，本文利用Cyclone GNSS（CYGNSS）数据建立了青藏高原地区为期5年的GNSS-R SM和F/T记录。与SMAP参考值相比，CYGNSS SM的均方根误差（RMSE）和相关性（R）分别为0.064 cm³/cm³和0.53。CYGNSS F/T的分类准确率为85.5%。独立地面观测站的验证结果显示，CYGNSS SM的RMSE和R分别为0.059 cm³/cm³和0.56，CYGNSS F/T的分类准确率为83.8%，与同期SMAP的SM和F/T分类准确率相当。这项研究将提供高海拔地区长时间序列的GNSS-R SM和F/T记录。值得注意的是，CYGNSS的可用天数明显多于SMAP。CYGNSS SM的可用天数比SMAP SM高47.0%，CYGNSS F/T的可用天数比SMAP F/T高14.7%。此外，本文为CYGNSS和SMAP开发了一个经验融合框架。融合后的CYGNSS和SMAP SM（即CYGNSS-SMAP SM）的平均RMSE为0.056 cm³/cm³，R为0.60。与现有的SMAP SM相比，精度提高了18.8%，可用天数增加了34.7%。融合CYGNSS和SMAP F/T（即CYGNSS-SMAP F/T）的精度为89.8%。与现有的SMAP F/T相比，精度提高了10.0%，可用天数增加了10.2%。融合CYGNSS反射计和SMAP辐射计观测数据可在青藏高原地区提供更高精度和连续性的SM和F/T。本文也证明了星载GNSS-R技术在高海拔地区具有强大的监测能力。

关键词: CYGNSS, SMAP, 土壤湿度, 土壤冻融, 青藏高原

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

中图分类号:

P228

杨文涛, 郭斐, 张小红, 张治宇, 朱逸凡, 李政, 吴子恒. 利用GNSS反射计和SMAP辐射计反演青藏高原土壤湿度和冻融状态[J]. 测绘学报, 2025, 54(4): 725-735.

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.

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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