First Measurement of Soil Freeze/Thaw Cycles in the Tibetan Plateau Using CYGNSS GNSS-R Data

The process of soil freezing and thawing refers to the alternating phase change of liquid water and solid water in the soil, accompanied by a large amount of latent heat exchange. It plays a vital role in the land water process and is an important indicator of climate change. The Tibetan Plateau in China is known as the “roof of the world”, and it is one of the most prominent physical characteristics is the freezing and thawing process of the soil. For the first time, this paper utilizes the spaceborne GNSS-R mission, i.e., CYGNSS (Cyclone Global Navigation Satellite System), to study the feasibility of monitoring the soil freeze-thaw (FT) cycles on the Tibetan Plateau. In the theoretical analysis part, model simulations show that there are abrupt changes in soil permittivities and surface reflectivities as the soil FT occurs. The CYGNSS reflectivities from January 2018 to January 2020 are compared with the SMAP FT state. The relationship between CYGNSS reflectivity and SMAP soil moisture within this time series is analyzed and compared. The results show that the effect of soil moisture on reflectivity is very small and can be ignored. The periodic oscillation change of CYGNSS reflectivity is almost the same as the changes in SMAP FT data. Freeze-thaw conversion is the main factor affecting CYGNSS reflectivity. The periodical change of CYGNSS reflectivity in the 2 years indicates that it is mainly caused by soil FT cycles. It is feasible to use CYGNSS to monitor the soil FT cycles in the Tibetan Plateau. This research expands the current application field of CYGNSS and opens a new chapter in the study of cryosphere using spaceborne GNSS-R with high spatial-temporal resolution.

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Sampling depth of L-band radiometer measurements of soil moisture and freeze-thaw dynamics on the Tibetan Plateau

Remote Sensing of Environment ◽

10.1016/j.rse.2019.03.029 ◽

2019 ◽

Vol 226 ◽

pp. 16-25 ◽

Cited By ~ 7

Author(s):

Donghai Zheng ◽

Xin Li ◽

Xin Wang ◽

Zuoliang Wang ◽

Jun Wen ◽

...

Keyword(s):

Soil Moisture ◽

Tibetan Plateau ◽

The Tibetan Plateau ◽

Sampling Depth ◽

Freeze Thaw ◽

L Band ◽

Band Radiometer

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Progress and Challenges in Studying Regional Permafrost in the Tibetan Plateau Using Satellite Remote Sensing and Models

Frontiers in Earth Science ◽

10.3389/feart.2020.560403 ◽

2020 ◽

Vol 8 ◽

Author(s):

Huiru Jiang ◽

Guanheng Zheng ◽

Yonghong Yi ◽

Deliang Chen ◽

Wenjiang Zhang ◽

...

Keyword(s):

Remote Sensing ◽

Soil Moisture ◽

Tibetan Plateau ◽

Satellite Remote Sensing ◽

Surface Deformation ◽

Microwave Remote Sensing ◽

Local Scale ◽

The Tibetan Plateau ◽

Freeze Thaw ◽

Plateau Area

Recent climate change has induced widespread soil thawing and permafrost degradation in the Tibetan Plateau. Significant advances have been made in better characterizing Tibetan Plateau soil freeze/thaw dynamics, and their interaction with local-scale ecohydrological processes. However, factors such as sparse networks of in-situ sites and short observational period still limit our understanding of the Tibetan Plateau permafrost. Satellite-based optical and infrared remote sensing can provide information on land surface conditions at high spatial resolution, allowing for better representation of spatial heterogeneity in the Tibetan Plateau and further infer the related permafrost states. Being able to operate at “all-weather” conditions, microwave remote sensing has been widely used to retrieve surface soil moisture, freeze/thaw state, and surface deformation, that are critical to understand the Tibetan Plateau permafrost state and changes. However, coarse resolution (>10 km) of current passive microwave sensors can add large uncertainties to the above retrievals in the Tibetan Plateau area with high topographic relief. In addition, current microwave remote sensing methods are limited to detections in the upper soil layer within a few centimetres. On the other hand, algorithms that can link surface properties and soil freeze/thaw indices to permafrost properties at regional scale still need improvements. For example, most methods using InSAR (interferometric synthetic aperture radar) derived surface deformation to estimate active layer thickness either ignore the effects of vertical variability of soil water content and soil properties, or use site-specific soil moisture profiles. This can introduce non-negligible errors when upscaled to the broader Tibetan Plateau area. Integrating satellite remote sensing retrievals with process models will allow for more accurate representation of Tibetan Plateau permafrost conditions. However, such applications are still limiting due to a number of factors, including large uncertainties in current satellite products in the Tibetan Plateau area, and mismatch between model input data needs and information provided by current satellite sensors. Novel approaches to combine diverse datasets with models through model initialization, parameterization and data assimilation are needed to address the above challenges. Finally, we call for expansion of local-scale observational network, to obtain more information on deep soil temperature and moisture, soil organic carbon content, and ground ice content.

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Spatial-Temporal Distribution and Change of Seasonally Frozen Ground on the Tibetan Plateau from 1960 to 2014

10.5194/egusphere-egu2020-4050 ◽

2020 ◽

Author(s):

Siqiong Luo

Keyword(s):

Tibetan Plateau ◽

Regional Scale ◽

Temporal Distribution ◽

Thermal Conditions ◽

The Tibetan Plateau ◽

Frozen Ground ◽

Important Indicator ◽

Freeze Thaw ◽

Start Date ◽

Geographical Factors

The change in spatial-temporal distribution of seasonally frozen ground (SFG) is an important indicator of climate change. Based on observed daily freeze depth of SFG from meteorological stations on the Tibetan Plateau (TP) from 1960 to 2014, the spatial-temporal characteristics and &#160;trends in SFG were analyzed, and the relationships between them and climatic and geographical factors were explored. Spatial-temporal distribution of SFG on a regional scale was assessed by multiple regression functions. Results showed multi-year mean maximum freeze depth, freeze-thaw duration, freeze start date, and thaw end date demonstrate obvious distribution characteristics of climatic zones. A decreasing trend in maximum freeze depth and freeze-thaw duration occurred on the TP from 1960 to 2014. The freeze start date has been later and the thaw end date has been significantly earlier. Warming and wetting conditions of the soil resulted in a decrease in the maximum freeze depth and freeze-thaw duration, both spatially and temporally. The spatial distribution of SFG has been altered significantly by soil thermal conditions on the TP and could be assessed by elevation and latitude or by air temperature and precipitation, due to their high correlations. The regional average of maximum freeze depth and freeze-thaw duration caused by climatic and geographical factors was larger than those averaged using meteorological station data because most stations are located at lower altitudes. Maximum freeze depth and freeze-thaw duration has decreased sharply since 2000 on the entire TP.

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Hydrothermal Effects of Freeze-Thaw in the Taklimakan Desert

Sustainability ◽

10.3390/su13031292 ◽

2021 ◽

Vol 13 (3) ◽

pp. 1292

Author(s):

Liu Xinchun ◽

Kang Yongde ◽

Chen Hongna ◽

Lu Hui

Keyword(s):

Soil Moisture ◽

Moisture Content ◽

Ambient Temperature ◽

Soil Temperature ◽

Soil Moisture Content ◽

Soil Freezing ◽

Taklimakan Desert ◽

Freezing And Thawing ◽

Freeze Thaw ◽

The Taklimakan Desert

The Taklimakan Desert, also known as the “Sea of Death”, is the largest desert in China and also the world’s second largest remote desert. The road crossing the Taklimakan Desert is the longest desert road in the world and has been the center of the Silk Road since ancient times. Based on field observation data (November 2013 to May 2014) collected from the Tazhong and Xiaotang stations, we studied the interannual and diurnal variations of soil temperature, soil moisture content, and surface heat fluxes during different freezing and thawing periods. The annual and daily changes of soil temperature, soil moisture content, and surface energy fluxes at different freezing and thawing stages were analyzed. We illustrated the coupling relationship between water and heat in freezing-thawing soil in the Taklimakan Desert. We established a coupling model of soil water and heat during freezing and thawing. During the soil freezing period, the soil temperatures at different depths generally trended downward. The temperature difference between the Tazhong station and the Xiaotang station was 4~8.5 °C. The freezing time of soil at 20 cm depth occurred about 11 days after that at 10 cm depth. The effect of ambient temperature on soil temperature gradually weakened with the increase of soil depth. With the occurrence of the soil freezing process, the initial soil moisture contents at 5 cm, 10 cm, 20 cm, and 40 cm depths at the Xiaotang station were 6%, 10%, 29%, and 59%, respectively, and those at the Tazhong station were 5%, 3.6%, 4.4%, and 5.8%, respectively. As the ambient temperature decreased, the freezing front continued to move downward and the liquid soil water content at each depth decreased. The desert highway is closely related to the economic development and prosperity of southern Xinjiang. Therefore, it is important to maintain and inspect the safety and applicability of freeze-thaw zones and avoid casualties from vehicles and personnel.

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L-band Radiometry Measurement in the Tibetan Plateau

10.5194/egusphere-egu2020-3978 ◽

2020 ◽

Author(s):

Jun Wen ◽

Zhongbo Su ◽

Donghai Zheng ◽

Xin Wang

Keyword(s):

Soil Moisture ◽

Tibetan Plateau ◽

Rain Gauge ◽

Observation Angle ◽

Profile Measurement ◽

The Tibetan Plateau ◽

Resistive Load ◽

Freeze Thaw ◽

Internal Calibration ◽

L Band

Surface soil moisture and freeze/thaw state monitoring is essential for quantifying water and heat exchanges in cold regions, e.g. the Tibetan Plateau. L-band (1.4 GHz, 21 cm) radiometry is recognized as one of the best suitable techniques for global monitoring of soil moisture and freeze-thaw dynamics. This study reports a long term ground-based L-band radiometry measurements conducted in a seasonally frozen grassland site located in the northeastern part of the Tibetan Plateau. The ESA funded ELBARA-III radiometer is deployed in a Tibetan meadow ecosystem where a well-instrumented in-situ soil moisture and soil temperature (SMST) monitoring network was developed. The network holds 20 SMST profile measurement stations, and each station records every 15-min readings of 5TM ECH2O probes installed at soil depths of 5, 10, 20, 40, and 80 cm. The ELBARA-III radiometer has been deployed in the center of the SMST network at the beginning of 2016. The L-band radiometer is mounted on a tower with a height of 4.8m, and the antenna beam waist is about 6.5m above the surface. Brightness temperature (TB) measurements with vertical and horizontal polarizations are performed every 30 min at observation angles of 40&#176; to 70&#176; in steps of 5&#176;. A sky measurement with an observation angle of 155&#176; is performed once per day for calibration purposes next to the internal calibration sequence performed as part of every measurement run. The internal calibration adopted to derive the TB&#160;from the raw data is based on a two-point calibration strategy using a resistive load (RL) and an active cold load (ACL). A vertically dense SMST measurement profile is installed next to the radiometer tower. Concurrent measurements of micrometeorological variables are also performed in vicinity of the radiometer tower, such as solar radiation, wind speed, air temperature, air pressure, and humidity. A rain gauge and eddy-covariance system are setup in the ELBARA-III field site at the end of 2016 providing precipitation and surface heat flux measurements. Preliminary analysis of the ELBARA-III TB&#160;measurements will be given in this study.

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Time-Series InSAR Monitoring of Permafrost Freeze-Thaw Seasonal Displacement over Qinghai–Tibetan Plateau Using Sentinel-1 Data

Remote Sensing ◽

10.3390/rs11091000 ◽

2019 ◽

Vol 11 (9) ◽

pp. 1000 ◽

Cited By ~ 10

Author(s):

Xuefei Zhang ◽

Hong Zhang ◽

Chao Wang ◽

Yixian Tang ◽

Bo Zhang ◽

...

Keyword(s):

Time Series ◽

Soil Moisture ◽

Tibetan Plateau ◽

Surface Temperature ◽

Surface Deformation ◽

Root Zone ◽

Sedimentary Basins ◽

Deformation Analysis ◽

The Tibetan Plateau ◽

Freeze Thaw

Permafrost is widely distributed in the Tibetan Plateau. Seasonal freeze–thaw cycles of permafrost result in upward and downward surface displacement. Multitemporal interferometric synthetic aperture radar (MT-InSAR) observations provide an effective method for monitoring permafrost displacement under difficult terrain and climatic conditions. In this study, a seasonal sinusoidal model-based new small baselines subset (NSBAS) chain was adopted to obtain a deformation time series. An experimental study was carried out using 33 scenes of Sentinel-1 data (S-1) from 28 November 2017 to 29 December 2018 with frequent revisit (12 days) observations. The spatial and temporal characteristics of the surface displacements variation combined with different types of surface land cover, elevation and surface temperature factors were analyzed. The results revealed that the seasonal changes observed in the time series of ground movements, induced by freeze–thaw cycles were observed on flat surfaces of sedimentary basins and mountainous areas with gentle slopes. The estimated seasonal oscillations ranged from 2 mm to 30 mm, which were smaller in Alpine deserts than in Alpine meadows. In particular, there were significant systematic differences in seasonal surface deformation between areas near mountains and sedimentary basins. It was also found that the time series of deformation was consistent with the variation of surface temperature. Based on soil moisture active/passive (SMAP) L4 surface and root zone soil moisture data, the deformation analysis influenced by soil moisture factors was also carried out. The comprehensive analysis of deformation results and auxiliary data (elevation, soil moisture and surface temperature et al.) provides important insights for the monitoring of the seasonal freeze-thaw cycles in the Tibetan Plateau.

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Seasonal persistence of soil moisture anomalies related to freeze–thaw over the Tibetan Plateau and prediction signal of summer precipitation in eastern China

Climate Dynamics ◽

10.1007/s00382-019-04867-1 ◽

2019 ◽

Vol 53 (3-4) ◽

pp. 2411-2424 ◽

Cited By ~ 5

Author(s):

Kai Yang ◽

Chenghai Wang

Keyword(s):

Soil Moisture ◽

Tibetan Plateau ◽

Eastern China ◽

Summer Precipitation ◽

The Tibetan Plateau ◽

Freeze Thaw

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Freeze–Thaw Changes of Seasonally Frozen Ground on the Tibetan Plateau from 1960 to 2014

Journal of Climate ◽

10.1175/jcli-d-19-0923.1 ◽

2020 ◽

Vol 33 (21) ◽

pp. 9427-9446

Author(s):

Siqiong Luo ◽

Jingyuan Wang ◽

John W. Pomeroy ◽

Shihua Lyu

Keyword(s):

Tibetan Plateau ◽

Regional Scale ◽

The Tibetan Plateau ◽

Hydrothermal Conditions ◽

Frozen Ground ◽

Important Indicator ◽

Freeze Thaw ◽

Start Date ◽

Temperature And Precipitation ◽

Geographical Factors

AbstractThe freeze–thaw changes of seasonally frozen ground (SFG) are an important indicator of climate change. Based on observed daily freeze depth of SFG from meteorological stations on the Tibetan Plateau (TP) from 1960 to 2014, the spatial–temporal characteristics and trends in SFG were analyzed, and the relationships between them and climatic and geographical factors were explored. Freeze–thaw changes of SFG on a regional scale were assessed by multiple regression functions. Results showed multiyear mean maximum freeze depth, freeze–thaw duration, freeze start date, and thaw end date that demonstrate obvious distribution characteristics of climatic zones. A decreasing trend in maximum freeze depth and freeze–thaw duration occurred on the TP from 1960 to 2014. The freeze start date has been later, and the thaw end date has been significantly earlier. The freeze–thaw changes of SFG significantly affected by soil hydrothermal conditions on the TP could be assessed by elevation and latitude or by air temperature and precipitation, due to their high correlations. The regional average of maximum freeze depth and freeze–thaw duration caused by climatic and geographical factors were larger than those averaged using meteorological station data because most stations are located at lower altitudes. Maximum freeze depth and freeze–thaw duration have decreased sharply since 2000 on the entire TP. Warming and wetting conditions of the soil resulted in a significant decrease in maximum freeze depth and freeze–thaw duration in the most area of the TP, while drying soil results in a slight increase of them in the southeast of the TP.

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