Comparative accuracy assessment of satellite (Sentinel-2, SMAP) and ground-based (TDR, PR2) sensors in soil moisture estimation

Document Type : Research/Original/Regular Article

Authors

1 Department of Hydrology, Soil Conservation and Watershed Management Institute, Tehran, Iran

2 Department of Hydrology, Soil Conservation, and Watershed Management Research Institute, Tehran, Iran

3 Faculty of Natural Resources and Environment, Birjand University, Birjand, Iran

4 Soil Conservation and Watershed Management Research Institute, Shafie Street, Asheri Street, Km 10 of Jadeh Makhsoos, Tehran, Iran

Abstract

Introduction

Although soil moisture represents a small fraction of the world's available freshwater, it plays a crucial role as an effective water storage component within the hydrological cycle and is fundamentally important in hydrological, biological, and biogeochemical processes. The most critical aspect of soil moisture is the depth of water stored within the soil. Consequently, understanding the factors that influence soil moisture and its effects is essential for predicting future performance and ultimately enhancing agricultural production and food security. This understanding is also vital for optimizing irrigation water management and improving water use efficiency in agricultural fields. Therefore, various devices and equipment have been employed over the past few decades to estimate soil moisture. Their application requires consideration of several factors, including the need for calibration, accuracy of results, repeatability, spatial resolution, usability, and cost. Despite the significance of soil moisture in modeling hydrological, biogeochemical, and related dynamic processes, accurately measuring its temporal and spatial variations on a local or watershed scale presents challenges and high costs due to substantial fluctuations. Conversely, remote sensing data has provided opportunities for continuous and cost-effective monitoring of soil moisture estimates with appropriate temporal and spatial distribution, which must be controlled and calibrated with ground-based data. This study investigates and evaluates point-based sensors, including time-domain reflectometry (TDR) and the PR2 neutron probe, alongside sensors that offer suitable temporal and spatial distribution, such as Sentinel 2 and Soil Moisture Active Passive (SMAP), using weighted soil moisture measurement data.

Materials and Methods

In this study, soil moisture measurement as a direct method and TDR, PR2, Sentinel-2, and SMAP satellite images as indirect methods of soil moisture estimation were investigated. To assess and evaluate soil moisture sensors at the watershed scale, a part of the Telo region called Deh Sayid in Lavasanat, Tehran province, with an area of 328 hectares, was selected. Initially, due to the difficulty and high cost of measuring soil moisture by direct methods, data obtained from this method were considered the criterion for evaluating TDR and PR2 sensors. For this purpose, seven stations were established across this region in different land uses, where soil moisture monitoring was conducted through soil sampling and weight measurements in the SCWMRI laboratory, alongside simultaneous soil moisture measurements using TDR and PR2 sensors. Initially, the simultaneous data from these two sensors were evaluated against direct gravimetric observation values. Additionally, soil moisture was monitored by TDR and PR2 sensors during the passage of the Sentinel-2 and SMAP satellites from October 2020 to April 2022. During this period, TDR was used to evaluate PR2, Sentinel-2, and SMAP using statistical criteria, including correlation coefficient and percent deviation. Furthermore, considering the spatial scale of SMAP, the average of the simultaneous data from the seven stations was used for its evaluation.



Results and Discussion

The correlation between TDR and PR2 related to gravimetric method measurements showed that their coefficient of determination (R2) was 0.91 and 0.92, respectively, which showed a high correlation with absolute moisture values. Also, their percentage deviation was 6 and 23 percent, respectively. Therefore, TDR measured absolute soil moisture with much higher accuracy than PR2. The correlation coefficient of PR2 data with TDR varied between 0.826 and 0.933 at the monitoring stations, indicating a high correlation between them. To evaluate the moisture index of Sentinel 2 and SMAP images, simultaneous data from TDR were used due to the high accuracy of the TDR sensor. The results of the correlation analysis of the normalized differential water index (NDWI) obtained from Sentinel 2 images with TDR showed that the range of the coefficient of determination (R2) between the data of these two sensors was very high. The R² values vary from 0.003 at station P7 to 0.814 at station P2. The correlation coefficient at other stations is 0.094, 0.132, 0.587 and 0.723 at stations P3, P4, P6 and P5 respectively. However, at three stations P7, P5 and P6 the correlation coefficient is significant at the 5% level, but at three stations P2, P3 and P4 there is no significant correlation between them. The correlation coefficient of simultaneous SMAP data with the average TDR data at seven stations is 0.455 and the slope of their correlation line is 0.833. Therefore, SMAP shows more accuracy than Sentinel in estimating soil moisture

Conclusion

The result of this research indicated that the correlation between each of the two sensors, TDR and PR2, with gravimetric method is very high and close to each other with values of 0.956 and 0.962, respectively. Additionally, their absolute deviation is 6 and 23 percent, respectively. Consequently, TDR provides a more accurate estimate of the absolute value of soil moisture compared to PR2. Therefore, TDR is superior to PR2 as an appropriate estimator in the absence of the soil moisture data from gravimetric method in this region. Other findings from the study reveal that the indices obtained from Sentinel2 at various points yield different estimates of soil moisture; in pasture land with dense vegetation cover, the accuracy is significant, whereas in areas with tree cover, it lacks significant accuracy. Furthermore, the results demonstrated that the accuracy of Sentinel2 moisture indices is low, while SMAP offers higher accuracy for estimating moisture despite its lower spatial scale. Moreover, based on the findings of this study, the estimated absolute amount of soil moisture derived from remotely sensed data does not yet possess the necessary accuracy for practical applications, and further research is required to combine and test with other indices to enhance the accuracy of soil moisture estimates.

Keywords

Main Subjects


منابع
بلابادی، حامد، افراسیاب، پیمان، دلبری، معصومه، و قائدی، سعید (1396). تأثیر بافت خاک و شوری و نسبت جذب سدیم آب آبیاری بر دقت اندازه گیری رطوبت خاک به‌وسیلة‌ی دستگاه تتاپروب. علوم و مهندسی آبیاری، 40 (4)، 17-30. doi: 10.22055/jise.2017.13337
پرهمت، جهانگیر، عبده کلاهچی، عبدالنبی، تاجبخش، سید محمد، و کریمی ظفرآبادی، فاطمه (1403). بررسی دقت روش‌های غیرمستقیم اندازه‌گیری محتوی آب خاک از استفاده از داده‌های مشاهده‌ای صحرایی. گزارش نهایی طرح تحقیقاتی، انتشارات پژوهشکده حفاظت خاک و آبخیزداری، شماره ثبت 67056 مورخ 26/12/1403، 56 صفحه.
حاجی ملکی، خالد، واعظی، علیرضا، سرمدیان، فریدون، کراو، وید، و بروکا، لوکا (1399). اعتبارسنجی داده‌های رطوبت خاک سطحی ماهواره SMAP در کاربری‌های مختلف در حوضه سیمینه-زرینه (بوکان). مجله تحقیقات آب و خاک، 51(5)، 1317-1329. doi: 10.22059/ijswr.2020.291430.668371
صبوری نوقابی، مسعود ، رجبی، محمد مهدی، و اسعدی اسکوئی، ابراهیم (1400). اعتبارسنجی و ریزمقیاس سازی داده های رطوبت خاک ماهواره SMAP به روش SMBDA با استفاده از محصولات رادار Sentinel1 و داده‌های زمینی در منطقه صالح آباد ایلام. تحقیقات منابع آب ایران، 17(4)، 144-160. doi: 20.1001.1.17352347.1400.17.4.9.6
عبده کلاهچی، عبدالنبی، میری، مرتضی، زند، مهران، و پرهمت، جهانگیر (1402). مقایسه ارزیـابی محصولات رطوبت خاک SM، CC، ESA، GLDAS، GLDAS و SMAP با اندازه‌گیری‌های میدانی (مطالعه موردی: استان لرستان). محیط زیست و مهندسی آب، 9(4)، 548-562. doi:10.22034/ewe.2023.367471.1819
میری، مرتضی، نوروزی، علی‌اکبر، عبده کلاهچی، عبدالنبی، و پرهمت، جهانگیر (1402). ارزیابی کارایی تصاویر ماهواره‌ای و شاخص‌های طیفی در برآورد رطوبت خاک منطقه تلو در استان تهران. پژوهشهای خاک، 73(4)، 747-754. doi: 10.22092/ijsr.2024.364072.730
 
 
References
Abdeh Kolahchi, A., Miri, M., Zand, M., & Porhemmat, J. (2023). Comparative Evaluation of GLDAS, ESA CCI SM and SMAP Soil Moisture with in situ Measurements (Case Study: Lorestan Province). Environment and Water Engineering, 9(4), 548-562. doi:10.22034/EWE.2023.367471.1819 [In Persian]
Altafi Dadgar, M., Nakhaei, M., Porhemmat, J., Biswas, A., & Rostami, M. (2018). Transient potential groundwater recharge under surface irrigation in semiarid environment: An experimental and numerical study. Hydrological Processes, 32, 3771-3783. doi: 10.1002/hyp.13287
Altafi Dadgar, M., Nakhaei, M., Porhemmat, J., Eliasi, B., & Biswas. A. (2020). Potential groundwater recharge from deep drainage of irrigation water. Science of The Total Environment, 716, 137105. doi: 10.1016/j.scitotenv.2020.137105
Amente, G., Baker, J.M., & Reece, C.F. (2000). Estimation of soil solution electrical conductivity from bulk soil electrical conductivity in sandy soils. Soil Science Society of America Journal, 64, 1931-1939. doi: 10.2136/sssaj2000.6461931x
Babaeian, E., Sadeghi, M., Franz, T.E., Jones, S. & Tuller, M. (2018). Mapping soil moisture with the Optical Trapezoid Model (OPTRAM) based on long-term MODIS observations. Remote Sensing Environment, 211, 425-440. doi:10.1016/j.rse.2018.04.029
Balabadi, H., Afrasiab, P., Delbari, M., & Ghaedi, S. (2018). Effect of soil texture, irrigation water salinity, and sodium adsorption ratio on the soil moisture measurements acuracy by Theta Probe device. Journal of Irrigation Sciences and Engineering (JISE), 40(4), 17-30. doi: 10.22055/jise.2017.13337 [In Persian]
Bindlish, R., Jackson, T.J., Gasiewski, A.J., Klein, M., & Njoku, E.G. (2006). Soil moisture mapping and AMSRE validation using the PSR in SMEX02. Remote Sensing of Environment, 103, 127-139. doi: 10.1016/j.rse.2005.02.003
Blank, D., Eicker, A., Jensen, L., & Güntner, A. (2023). A global analysis of water storage variations from remotely sensed soil moisture and daily satellite gravimetry. Hydrology and Earth System Sciences, 27, 2413–2435. doi:10.5194/hess-2022-398
Brocca, L., Ciabatta, L., Massari, C., Camici, S., & Tarpanelli, A. (2017). Soil moisture for hydrological applications: open questions and new opportunities. Water, 9 (2), 140. doi: 10.3390/w9020140
Chandler, D.G., Seyfried, M., Murdock, M., & McNamara, J.P. (2004). Field calibration of water content reflectometers. Soil Science Society of American Journal, 68(5), 1501-1507. doi: 10.2136/sssaj2004.1501
Chanasyk, D.S., & Naeth, M.A. (1996). Field measurement of soil moisture using neutron probes. Canadian Journal of Soil Science, 76, 317-323. doi:10.4141/cjss96-038
Chanzy, A., Tarussov, A., Bonn, F., & Judge, A. (1996). Soil water content determination using a digital ground-penetrating radar. Soil Science Society of America Journal, 60, 1318-1326. doi:10.13031/2013.13822
Chen, F.,Crow W.T., Bindlish R., Colliander A., Burgin M.S., Asanuma J., & Aida K., (2018). Global-scale evaluation of SMAP, SMOS and ASCAT soil moisture products using triple collocation. Remote Sensing of Environment, 214, 1-13. doi: 10.1016/j.rse.2018.05.008
Chen, X., Quan, Q., Zhang, K., & Wei, J. (2021a). Spatiotemporal characteristics and attribution of dfry/wet conditions in the Weihe River Basin within a typical monsoon transition zone of east Asia over the recent 547 years. Environmental Modelling and Software, 143, 105116. doi: 10.1016/j.envsoft.2021.105116
Chen, Y., Feng, X., & Fu, B. (2021b). An improved global remote-sensing-based surface soil moisture (RSSSM) dataset covering 2003–2018. Earth System Science Data. 13, 1–31. doi: 10.5194/essd-13-1-2021
Corradini, C. (2014). Soil moisture in the development of hydrological processes and its determination at different spatial scales. Journal of Hydrology, 516, 1-5. doi: 10.1016/j.jhydrol.2014.02.051
Dafny, E., & Šimůnek, J., (2016). Infiltration in layered loessial deposits: Revised numerical simulations and recharge assessment. Journal of Hydrology, 538, 339-354. doi: 10.1016/j.jhydrol.2016.04.029
Domínguez-Niño, J.M., Arbat, G., Raij-Hoffman, I., Kisekka, I., Girona, J., & Casadesús, J. (2020). Parameterization of soil hydraulic parameters for HYDRUS-3D simulation of soil water dynamics in a drip-irrigated orchard. Water, 12, 1858. doi: 10.3390/w12071858
Everson, C.S., Mengistu, M.G., & Vather, T. (2017). The validation of the variables (evaporation and soil water) in hydrometeorological models: Phase II, Application of cosmic ray probes for soil water measurement. Water Research Commission, WRC Report No. 2323/1/17, ISBN: 978-1-4312-0900-2, 77 pages.
Fang, K., & Shen, C. (2020). Near-real-time forecast of satellite-based soil moisture using long short-term memory with an adaptive data integration kernel. J. Hydrometeorology, 21 (3), 399-413. doi:10.1175/jhm-d-19-0169.1
Ferrara, G., & Flore, J.A. (2003). Comparison between different methods for measuring transpiration in potted Apple trees. Biologia Plantarum, 46, 41-47. doi:10.1023/a:1022301931508
Goit, J.B., Groenevelt, P.H., Kay, B.D., & Loch, J.G.P. (1978). The applicability of dual gamma scanning to freezing soils and the problem of stratification. Soil Science Society of America Journal, 42, 858-863. doi: 10.2136/sssaj1978.03615995004200060003x
Haji, maleki, K., Vaezi, A., Sarmadian, F., Crow, W., & brocca, L. (2020). Validation of SMAP Satellite-Based Soil Moisture in Different Land Uses of Simineh-Zarrineh (Bokan) Basin. Iranian Journal of Soil and Water Research, 51(5), 1317-1329. doi: 10.22059/ijswr.2020.291430.668371 [In Persian]
Hammecker, C., Antonino, A.C.D., Maeght, J.L., & Boivin, P. (2003). Experimental and numerical study of water flow in soil under irrigation in northern Senegal: evidence of air entrapment. European Journal of Soil Science, 54, 491-503. doi:10.1046/j.1365-2389.2003.00482.x
Houser, P.R., Shuttleworth, J., Famiglietti, J.S., Gupta, H.V., Syed, K.H. & Goodrich, D.C. (1998). Integration of soil moisture remote sensing and hydrologic modeling using data assimilation. Water Resour Research, 34(12),3405–3420. doi:10.1029/1998wr900001
Hu, W., & Si, B.C. (2013). Soil water content evaluation considering time-invariant spatial pattern and space-variant temporal change. Hydrology and Earth System Sciences, 10, 12829–12860. doi:10.5194/hessd-10-12829-2013
Huang, J., & Hartemink, A.E. (2020). Soil and environmental issues in sandy soils, Earth-Science Reviews, 208, 103295. doi: 10.1016/j.earscirev.2020.103295
Huisman, J.A., Sperl, C., Bouten, W., & Verstraten, J.M. (2001). Soil water content measurements at different scales: accuracy of time domain reflectometry and ground-penetrating radar. Journal of Hydrology, 245, 48-58. doi: 10.1016/S0022-1694(01)00336-5
IAEA. (2008). Field estimation of soil water content a practical guide to methods, instrumentation and sensor technology, training course. International Atomic Energy Agency, Vienna, 131Pages.
Jakobi, J., Huisman, J.A., Vereecken, H., Diekkrüger, B., & Bogena H.R. (2018). Cosmic Ray Neutron Sensing for Simultaneous Soil Water Content and Biomass Quantification in Drought. Water Resources Research, 10(54), 7383-7402. doi: 10.1029/2018WR022692
Jiménez-Martínez, J., Skaggs, T.H., van Genuchten, M.Th., & Candela, L. (2009). A root zone modelling approach to estimating groundwater recharge from irrigated areas. Journal of Hydrology, 367, 138-149. doi: 10.1016/j.jhydrol.2009.01.002
Kisekka, I., Migliaccio, K., Muñoz-Carpena, R., Schaffer, B., & Khare, Y. (2015). Modelling soil water dynamics considering measurement uncertainty. Hydrological Processes, 29, 692-711. doi:10.1002/hyp.10173
Lebon, E., Dumas, V., Pieri, P., & Schultz, H. (2003). Modelling the seasonal dynamics of the soil water balance of vineyards. Functional Plant Biology, 30, 699-710. doi:10.1071/FP02222
Liu, Y., Yang, Y., & Song J. (2023). Variations in Global Soil Moisture During the Past Decades: Climate or Human Causes? Water Resources Research, 59, e2023WR034915. doi: 10.1029/2023WR034915
Lück, E., Guillemoteau, J., Tronicke, J., Rummel, U., & Hierold, W. (2022). From point to field scale - indirect monitoring of soil moisture variations at the DWD test site in Falkenberg. Geoderma, 427(10),116134. doi: 10.1016/j.geoderma.2022.116134
Markovi´c, O.M., Koˇcar, M.M., Baraˇc, Z., Turalija, A., Atılgan, A., Jug, D., & Ravli´c N. (2024). Field Performance Evaluation of Low-Cost Soil Moisture Sensors in Irrigated. Agriculture, 14(8), 1239. doi: 10.3390/agriculture14081239
Mattikalli, N.M., Engman, E.T., Ahuja, L.R., & Jackson, T.J. (1998). Microwave remote sensing of soil moisture for estimation of profile soil property. International Journal of Remote Sensing, 19, 1751-1767. doi: 10.1080/014311698215234
McFeeters, S.K.,1996. The Use of the Normalized Difference Water Index (NDWI) in the Delineation of Open Water Features. International Journal of Remote Sensing, 17, 1425-1432. doi: 10.1080/01431169608948714
Miri, M., Noroozi, A.A., Abdeh Kolahchi, A, & Porhemmat, J. (2024). Performance Evaluation of Satellite Images and Spectral Indices in Estimating Soil Moisture in Telo Region, Tehran Province. Journal of Soil Research (IJSR), 37(4), 343-354. doi: 10.22092/ijsr.2024.364072.730 [In Persian]
Mittelbach, H., Lehner, I., & Seneviratne, S.I. (2012). Comparison of four soil moisture sensor types under field conditions in Switzerland. Journal of Hydrology, 430–431, 39–49. doi: 10.1016/j.jhydrol.2012.01.041
Mohseni, F., Jamali, S., Ghorbanian, A., & Mokhtarzade, M. (2023). Global soil moisture trend analysis using microwave remote sensing data and an automated polynomial-based algorithm. Global and Planetary Change, 231, 104310. doi: 10.1016/j.gloplacha.2023.104310
Neale, C.M.U., Geli, H.M.E., Kustas, W.P., Alfieri, J.G., Gowda, P.H., Evett, S.R., Prueger, J.H., Hipps, L.E., Dulaney, W.P., Chávez, J.L., French, A.N., & Howell, T. A. (2012). Soil water content estimation using a remote sensing based hybrid evapotranspiration modeling approach. Advances in Water Resources, 50, 152-161. doi: 10.1016/j.advwatres.2012.10.008
Njoku, E.G., Jackson, T.J., Lakshmi, V., Chan, T.K., & Nghiem, S.V. (2003). Soil moisture retrieval from AMSR-E. IEEE Transactions on Geoscience Remote Sensing, 41(2),215–229. doi:10.1109/TGRS.2002.808243
pires, L.F., Bacchi, O.O.S., & Reichardt, K. (2005). Soil water retention curve determined by gamma-ray beam attenuation. Soil and Tillage Research, 82, 89-97. doi: 10.1016/j.still.2004.06.003
Porhemmat, J., Nakhaei, M., Altafi Dadgar, M., & Biswas, A. (2018). Investigating the effects of irrigation methods on potential groundwater recharge: A case study of semiarid regions in Iran. Journal of Hydrology, 565, 455-466. doi:.10.1016/j.jhydrol.2018.08.036
Porhemmat, J., Tajbakhsh, S.M., Altafi Dadgar, M., & Abdeh Kolahchi, A. (2025a). LongTerm Modeling of Soil Moisture Dynamic in Response to Land-Use/ Cover Changes: A Case Study in the Telo Watershed of Tehran, Iran. ECOPERSIA, 13(2), 199-219. doi: 10.22034/ECOPERSIA.13.2.199
Porhemmat, J., Abdeh Kolahchi, A., Tajbakhsh, S.M., Altafi Dadgar, M., & Karimi ZafarAbadi, F. (2025b). Investigating accuracy of indirect soil water content estimating by using field observation data. Final report of research project, Soil Conservation and Watershed Management Research Institute, 56 pages. [In Persian]
Puma, M.J., Celia, M.A., Rodriguez-Iturbe, I., & Guswa, A.J. (2005). Functional relationship to describe temporal statistics of soil moisture averaged over different depths. Advances in Water Resources, 28, 553-566. doi: 10.1016/j.advwatres.2004.08.015
Rahimzadeh-Bajgiran, P., Berg, A.A., Champagne, C., & Omasa, K. (2013). Estimation of soil moisture using optical/thermal infrared remote sensing in the Canadian Prairies. ISPRS J. Photogramm. Remote Sensing, 2013, 83, 94–103. doi: 10.1016/j.isprsjprs.2013.06.004
Rasheed, M.W., Tang, J., Sarwar, A., Shah, S., Saddique, N., Usman Khan, M., Imran Khan, M., Nawaz, S., Shamshiri, R.R., Aziz, M., & Sultan, M. (2022). Soil moisture measuring techniques and factors affecting the moisture dynamics: A comprehensive review. Sustainability, 14(18), 11538. doi: 10.3390/su141811538
Reynolds, J.M. (2011). An Introduction to applied and environmental geophysics. 2nd Edition, John Wiley & Sons: 797Pages.
Saboori, Noghabi, M., Rajabi, M.M., & Oskouei, E.A. (2022). Validation and Downscaling of SMAP Satellite Soil Moisture Data by the SMBDA Method Using Sentinel 1 Radar Products and Ground Data in SalehAbad Region of Ilam. Journal of Iran-Water Resources Research, 17(4), 144-160. doi: 20.1001.1.17352347.1400.17.4.9.6 [In Persian]
Sakaki, T., Sugihara, K., Adachi, T., Nishida, K., & Lin, W. (1998). Application of time domain reflectometry to determination of volumetric water content in rock. Water Resources Research, 34, 2623-2631. doi: 10.1029/98WR02038
Schmugge, T.J., Jackson, T.J., & McKim, H.L. (1980). Survey of methods for soil moisture determination. Water Resources Research, 16. 961-979. doi: 10.1029/WR016i006p00961
Seneviratne, S.I., Corti, T., Davin, E.L., Hirschi, M., Jaeger, E. B., Lehner, I., Orlowsky, B., & Teuling, A.J. (2010). Investigating soil moisture-climate interactions in a changing climate: a review. Earth Science Reviews, 99, 125-161. doi: 10.1016/j.earscirev.2010.02.004
Serbin, G., & Or. D. (2004). Ground-penetrating radar measurement of soil water content dynamics using a suspended horn antenna. IEEE Transactions on Geoscience and Remote Sensing, 42, 1695-1705. doi: 10.1109/TGRS.2004.831693
Sharma, K., Irmak, S., & Kukal, M. (2021). Propagation of soil moisture sensing uncertainty into estimation of total soil water, evapotranspiration and irrigation decision-making. Agricultural Water Management, 243(7), 106454. doi: 10.1016/j.agwat.2020.106454
Stafford, J.V. (1988). Remote, non-contact and in-situ measurement of soil moisture content: a review. Journal of Agricultural Engineering Research, 41(3), 151-172. doi: 10.1016/0021-8634(88)90175-8
Teshome, F.T., Bayabil, H.B., Schaffer, B., Ampatzidis, Y, & Hoogenboom, G. (2024). Improving soil moisture prediction with deep learning and machine learning models. Computers and Electronics in Agriculture, 226, 109414. doi: 10.1016/j.compag.2024.109414
Tian, Z., Li, Z., Liu, G., Li, B., & Ren, T. (2016). Soil water content determination with cosmic-ray neutron sensor: Correcting aboveground hydrogen effects with thermal/fast neutron ratio. Journal of Hydrology, 540, 923-933. doi: 10.1016/j.jhydrol.2016.07.004
Tian, H., Huang, N., Niu, Z., Qin, Y., Pei, J., & Wang, J. (2019). Mapping winter crops in China with multi-source satellite imagery and phenology-based algorithm. Remote Sensing, 11(17), 820. doi: 10.3390/rs11070820
Tian, H., Wang, Y., Chen, T., Zhang, L., & Qin, Y. (2021) Early-season mapping of winter crops using sentinel-2 optical imagery. Remote Sensing, 13(19), 3822. doi: 10.3390/rs13193822
Vereecken, H., Huisman, J.A., Bogena, H., Vanderborght, J., Vrugt, J.A., & Hopmans, J.W. (2008). On the value of soil moisture measurements in vadose zone hydrology: a review. Water Resources Research, 44(4), 1-21. doi: 10.1002/2014WR016852
Vereecken, H., Huisman, J.A., Pachepsky, Y., Montzka, C., Van Der Kruk, J., Bogena, H., Weihermüller, L., Herbst, M., Martinez, G. & Vanderborght, J. (2014). On the spatio-temporal dynamics of soil moisture at the field scale. Journal of Hydrology, 516, 76–96. doi: 10.1016/j.jhydrol.2013.11.061
Wang, L., & Qu, J. (2009) Satellite remote sensing applications for surface soil moisture monitoring: A review. Frontiers of Earth Science in China, 3, 237-247. doi: 10.1007/s11707-009-0023-7
Western, A.W., Grayson, R.B., & Blöschl, G. (2002). Scaling of soil moisture: A hydrologic perspective. Annual Review of Earth and Planetary Sciences, 30, 149-180. doi: 10.1146/annurev.earth.30.091201.140434
Western, A.W., & Seyfried, M.S. (2005), A calibration and temperature correction procedure for the water-content reflectometer, Hydrological Processes, 19, 3785–3793. doi: 10.1002/hyp.6069
Wörsching, H., Becker, R., Schlaeger, S., Bieberstein A., & Kudella, P. (2006). Spatial-TDR moisture measurement in a large scale levee model made of loamy soil material. 3rd International Symposium on Time Domain Reflectometry for Innovative Soils Applications, September 17-20, 2006, TDR 2006, Purdue University, West Lafayette, Indiana, USA.
Xu, H. (2006). Modification of normalized difference water index (NDWI) to enhance open water features in remotely sensed imagery. International Journal of Remote Sensing, 27(14), 1425-1432. doi: 10.1080/01431160600589179
Zhao, T., Shi, J., Lv, L., Xu, H., Chen, D., Cui, Q., Jackson, T.J., Yan, G., Jia, L., Chen, L., Zhao, K., Zheng, X., Zhao, L., Zheng, C., Ji, D., Xiong, C., Wang, T., Li, R., Pan, J., Wen, J. et al. (2020a). Soil moisture experiment in the Luan River supporting new satellite mission opportunities. Remote Sensing of Environment, 240, 111680. doi: 10.1016/j.rse.2020.111680
Zhao, T., Shi, J., Entekhabi, D., Jackson, T.J., Hu, L., Peng, Z., Yao, P., Li, S., & Kang, C.S. (2021). Retrievals of soil moisture and vegetation optical depth using a multi-channel collaborative algorithm. Remote Sensing Environment, 2021, 257, 112321. doi: 10.1016/j.rse.2021.112321
Zhang, J., Zhou, Z., Yao, F., Yang, L., & Hao, C. (2015). Validating the modified perpendicular drought index in the north China region using in situ soil moisture measurement. IEEE Geoscience and Remote Sensing Letters, 12(3), 542–546. doi: 10.1109/LGRS.2014.2349957