scholarly journals Modeling Vegetation Water Stress over the Forest from Space: Temperature Vegetation Water Stress Index (TVWSI)

2021 ◽  
Vol 13 (22) ◽  
pp. 4635
Author(s):  
Rakesh Chandra Joshi ◽  
Dongryeol Ryu ◽  
Gary J. Sheridan ◽  
Patrick N. J. Lane
Keyword(s):  
Soil Moisture ◽  
Water Stress ◽  
Water Content ◽  
Stress Index ◽  
Australian Water ◽  
Environmental Models ◽  
Water Stress Index ◽  
Vegetation Water ◽  
Canopy Water ◽  
Content Information

The conventional Land Surface Temperature (LST)–Normalized Difference Vegetation Index (NDVI) trapezoid model has been widely used to retrieve vegetation water stress. However, it has two inherent limitations: (1) its complex and computationally intensive parameterization for multi-temporal observations and (2) deficiency in canopy water content information. We tested the hypothesis that an improved water stress index could be constructed by the representation of canopy water content information to the LST–NDVI trapezoid model. Therefore, this study proposes a new index that combines three indicators associated with vegetation water stress: canopy temperature through LST, canopy water content through Surface Water Content Index (SWCI), and canopy fractional cover through NDVI in one temporally transferrable index. Firstly, a new optical space of SWCI–NDVI was conceptualized based on the linear physical relationship between shortwave infrared (SWIR) and soil moisture. Secondly, the SWCI–NDVI feature space was parameterized, and an index d(SWCI, NDVI) was computed based on the distribution of the observations in the SWCI–NDVI spectral space. Finally, standardized LST (LST/long term mean of LST) was combined to d(SWCI, NDVI) to give a new water stress index, Temperature Vegetation Water Stress Index (TVWSI). The modeled soil moisture from the Australian Water Resource Assessment—Landscape (AWRA-L) and Soil Water Fraction (SWF) from four FLUXNET sites across Victoria and New South Wales were used to evaluate TVWSI. The index TVWSI exhibited a high correlation with AWRA-L soil moisture (R2 of 0.71 with p < 0.001) and the ground-based SWF (R2 of 0.25–0.51 with p < 0.001). TVWSI predicted soil moisture more accurately with RMSE of 21.82 mm (AWRA-L) and 0.02–0.04 (SWF) compared to the RMSE ranging 28.98–36.68 mm (AWRA-L) and 0.03–0.05 (SWF) were obtained for some widely used water stress indices. The TVWSI could also be a useful input parameter for other environmental models.

A new Remote Sensing-based vegetation water stress index: -Temperature Vegetation Water Stress Index (TVWSI)

2020 ◽  
Author(s):  
Rakesh Chandra Joshi ◽  
Dongryeol Ryu ◽  
Gary J. Sheridan ◽  
Patrick N.J. Lane
Keyword(s):  
Water Stress ◽  
Water Status ◽  
Canopy Temperature ◽  
Stress Index ◽  
Spectral Space ◽  
Water Stress Index ◽  
Water Stress Condition ◽  
Forested Areas ◽  
Vegetation Water ◽  
Canopy Water

&lt;p&gt;Remote sensing techniques are widely used to evaluate the biophysical status of vegetation, including water stress caused by soil water deficit. Based on the nominal links between water stress condition, transpiration and canopy temperature in the vegetation, numerous studies have used a trapezoidal relationship between Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) over vegetated surfaces to develop the water stress metric, in which the level of stress could be identified by the spatial location of the pixels on the spectral space (Goetz and Goetz 1997; Lambin, Lambin, and Ehrlich 1996; Nemani et al. 1993; Nemani and Running 1989; Price 1990; Sandholt, Rasmussen, and Andersen 2002). However, the amount of change in canopy temperature could also vary spatially by the canopy water status at that time. Thus, LST-NDVI alone cannot construct an efficient metric to see the spatial patterns of water stress at ecosystem level unless they are coupled with water status of vegetation at that moment. This study hypothesizes that a metric which can combine LST-NDVI information with an indicator for canopy water status could give more accurate estimations of the real-time vegetation water stress. The remotely sensed plant canopy water status indicator (a metric based on canopy reflection in the Short-Wave Infrared region (SWIR)) could add the canopy water status information to the LST-NDVI based indices, which may better explain spatial/temporal water stress condition in the plants especially in densely forested areas where signal saturation is a major issue. In this study, the third-dimensional information of SWIR has been combined with LST-NDVI spectral space to create a new remotely sensed vegetation water stress index, TVWSI (Temperature Vegetation Water Stress Index) which seems to be more realistic to capture stress dynamics at large scale.&amp;#160;&lt;/p&gt;&lt;p&gt;Sixty grids (2 km X 2 km) each containing 16 pixels of daily MODIS-reflectance (band 1 &amp;#8211; band 7, 500 m spatial resolution) and 4 pixels of daily MODIS-LST (1 km spatial resolution) were chosen over forested areas in Victoria representing most of the bioregions as classified by the Interim Biogeographic Regionalisation for Australia (IBRA7). From 2002 to 2018 daily TVWSI values of each grid were evaluated against the modelled daily available soil moisture content in the top 1 m of the soil profile, and rainfall data, from the Australian Bureau of Meteorology (BOM). TVWSI performed better than other dryness indices mentioned in the literature. A high correlation was obtained between TVWSI vs. soil moisture and TVWSI vs. rainfall with a coefficient of determination value of 0.6 (p&lt;0.001) and 0.61 (p&lt;0.001) respectively when data were combined spatially and temporally. Even improved correlations ranging (0.4-0.7, p&lt;0.001) were obtained for individual grids over the mentioned period. While correlation ranging (0.15-0.48, p&lt;0.001) were obtained using dryness indices like Perpendicular Drought Index (PDI), Modified PDI (MPDI), Temperature Vegetation Dryness Index (TVDI) and Vegetation Supply Water Index (VSWI). The result shows that the TVWSI can capture real-time ecosystem water stress well and the metric could be an efficient input parameter for many hydrological, drought and fire prediction models.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

A method for canopy water content estimation for highly vegetated surfaces-shortwave infrared perpendicular water stress index

2007 ◽  
Vol 50 (9) ◽  
pp. 1359-1368 ◽  
Author(s):  
Abduwasit Ghulam ◽  
Zhao-Liang Li ◽  
QiMing Qin ◽  
QingXi Tong ◽  
JiHua Wang ◽  
...  
Keyword(s):  
Water Stress ◽  
Water Content ◽  
Stress Index ◽  
Water Stress Index ◽  
Shortwave Infrared ◽  
Canopy Water

Inferring the effects of surface canopy water on VOD estimation from L-band backscatter 

2021 ◽  
Author(s):  
Saeed Khabbazan ◽  
Paul.C. Vermunt ◽  
Susan.C. Steele Dunne ◽  
Ge Gao ◽  
Mariette Vreugdenhil ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Linear Relationship ◽  
Water Content ◽  
Growing Season ◽  
Empirical Parameter ◽  
Vegetation Water Content ◽  
L Band ◽  
Vegetation Water ◽  
Canopy Water ◽  
Effect Of Surface

&lt;p&gt;Quantification of vegetation parameters such as Vegetation Optical Depth (VOD) and Vegetation Water Content (VWC) can be used for better irrigation management, yield forecasting, and soil moisture estimation. Since VOD is directly related to vegetation water content and canopy structure, it can be used as an indicator for VWC. Over the past few decades, optical and passive microwave satellite data have mostly been used to monitor VWC. However, recent research is using active data to monitor VOD and VWC benefitting from their high spatial and temporal resolution.&lt;/p&gt;&lt;p&gt;Attenuation of the microwave signal through the vegetation layer is parametrized by the VOD. VOD is assumed to be linearly related to VWC with the proportionality constant being an empirical parameter b. For a given wavelength and polarization, b is assumed static and only parametrized as a function of vegetation type. The hypothesis of this study is that the VOD is not similar for dry and wet vegetation and the static linear relationship between attenuation and vegetation water content is a simplification of reality.&lt;/p&gt;&lt;p&gt;The aim of this research is to understand the effect of surface canopy water on VOD estimation and the relationship between VOD and vegetation water content during the growing season of a corn canopy. In addition to studying the dependence of VOD on bulk VWC for dry and wet vegetation, the effect of different factors, such as different growth stages and internal vegetation water content is investigated using time series analysis.&lt;/p&gt;&lt;p&gt;A field experiment was conducted in Florida, USA, for a full growing season of sweet corn. The corn field was scanned every 30 minutes with a truck-mounted, fully polarimetric, L-band radar. Pre-dawn vegetation water content was measured using destructive sampling three times a week for a full growing season. VWC could therefore be analyzed by constituent (leaf, stem, ear) or by height. Meteorological data, surface canopy water (dew or interception), and soil moisture were measured every 15 minutes for the entire growing season.&lt;/p&gt;&lt;p&gt;The methodology of Vreugdenhil et al.&amp;#160; [1], developed by TU Wien for ASCAT data, was adapted to present a new technique to estimate VOD from single-incidence angle backscatter data in each polarization. The results showed that the effect of surface canopy water on the VOD estimation increased by vegetation biomass accumulation and the effect was higher in the VOD estimated from the co-pol compared with the VOD estimated from the cross-pol.&amp;#160;Moreover, the surface canopy water considerably affected the regression coefficient values (b-factor) of the linear relationship between VOD and VWC from dry and wet vegetation. This finding suggests that considering a similar b-factor for the dry and the wet vegetation will introduce errors in soil moisture retrievals. Furthermore, it highlights the importance of considering canopy wetness conditions when using tau-omega.&lt;/p&gt;&lt;ul&gt;&lt;li&gt;[1] Vreugdenhil,W. A. Dorigo,W.Wagner, R. A. De Jeu, S. Hahn, andM. J. VanMarle, &amp;#8220;Analyzing the vegetation parameterization in the TU-Wien ASCAT soil moisture retrieval,&amp;#8221; IEEE Transactions on Geoscience and Remote Sensing, vol. 54, pp. 3513&amp;#8211;3531, 2016&lt;/li&gt; &lt;/ul&gt;

scholarly journals Estimating Soil Moisture Under Low Frequency Surface Irrigation Using Crop Water Stress Index

2003 ◽  
Vol 129 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Paul D. Colaizzi ◽  
Edward M. Barnes ◽  
Thomas R. Clarke ◽  
Christopher Y. Choi ◽  
Peter M. Waller
Keyword(s):  
Soil Moisture ◽  
Water Stress ◽  
Low Frequency ◽  
Stress Index ◽  
Crop Water ◽  
Surface Irrigation ◽  
Crop Water Stress Index ◽  
Water Stress Index ◽  
Crop Water Stress

scholarly journals Reconstructing Continuous Vegetation Water Content To Understand Sub-daily Backscatter Variations

2021 ◽  
Author(s):  
Paul C. Vermunt ◽  
Susan C. Steele-Dunne ◽  
Saeed Khabbazan ◽  
Jasmeet Judge ◽  
Nick C. van de Giesen
Keyword(s):  
Soil Moisture ◽  
Water Content ◽  
Water Cycle ◽  
Water Dynamics ◽  
High Temporal Resolution ◽  
Daily Variations ◽  
Vegetation Water Content ◽  
Dew Formation ◽  
Vegetation Water ◽  
Canopy Water

Abstract. Microwave observations are sensitive to vegetation water content (VWC). Consequently, the increasing temporal and spatial resolution of spaceborne microwave observations creates a unique opportunity to study vegetation water dynamics and its role in the diurnal water cycle. However, we currently have a limited understanding of sub-daily variations in VWC and how they affect passive and active microwave observations. This is partly due to the challenges associated with measuring internal VWC for validation, particularly non-destructively and at timescales of less than a day. In this study, we aimed to (1) use field sensors to reconstruct diurnal and continuous records of internal VWC of corn, and (2) use these records to interpret the sub-daily behaviour of a 10-day time series of polarimetric L-band backscatter with high temporal resolution. Sub-daily variations of internal VWC were calculated based on the cumulative difference between estimated transpiration and sap flow rates at the base of the stems. Destructive samples were used to constrain the estimates and for validation. The inclusion of continuous surface canopy water estimates (dew or interception) and surface soil moisture allowed us to attribute hour-to-hour backscatter dynamics to either internal VWC, surface canopy water or soil moisture variations. Our results showed that internal VWC varied with 10–20 % during the day in non-stressed conditions, and the effect on backscatter was significant. Diurnal variations of internal VWC and nocturnal dew formation affected vertically polarized backscatter most. Moreover, on a typical dry day, backscatter variations were 1.5 (HH-pol) to 3 (VV-pol) times more sensitive to VWC than to soil moisture. These results demonstrate that radar observations have the potential to provide unprecedented insight into the role of vegetation water dynamics in land-atmosphere interactions at sub-daily timescales.

Effects of sub-daily internal and external canopy water fluctuations on radar backscatter

2020 ◽  
Author(s):  
Paul Vermunt ◽  
Susan Steele-Dunne ◽  
Saeed Khabbazan ◽  
Jasmeet Judge ◽  
Leila Guerriero
Keyword(s):  
Soil Moisture ◽  
The Netherlands ◽  
Water Content ◽  
Growing Season ◽  
Agricultural Crop ◽  
Radar Backscatter ◽  
Vegetation Water Content ◽  
Vegetation Water ◽  
Canopy Water ◽  
Daily Patterns

&lt;p&gt;Radar observations of vegetated surfaces are highly affected by water in the soil and canopy. Consequently, radar has been used to monitor surface soil moisture for decades now. In addition, radar has been proven a useful tool for monitoring agricultural crop growth and development and forest fuel load estimation, as a result of the sensitivity of backscatter to vegetation water content (VWC). These current applications are based on satellite revisit periods of days to weeks. However, with future satellite constellations and geosynchronous radar missions, such as ESA&amp;#8217;s Earth Explorer candidate mission HydroTerra, we will be able to monitor soil and vegetation multiple times per day. This opens up opportunities for new applications.&lt;/p&gt;&lt;p&gt;Examples could be (1) early detection of water stress in vegetation through anomalies in daily cycles of VWC, and (2) spatio-temporal estimations of rainfall interception, an important part of the water balance. However, currently, we lack the knowledge to physically understand sub-daily patterns in backscatter. Hence, the aim of our research is to understand the effect of water-related factors on sub-daily patterns of radar backscatter of a growing corn canopy.&lt;/p&gt;&lt;p&gt;Two intensive field campaigns were conducted in Florida (2018) and The Netherlands (2019). During both campaigns, soil moisture, external canopy water (dew, interception), soil water potential, and weather conditions were monitored every 15 minutes for the entire growing season. In addition, regular destructive sampling was performed to measure seasonal and sub-daily variations of vegetation water content. In Florida, hourly field scans were made with a truck-mounted polarimetric L-band scatterometer. In The Netherlands, these measurements were extended with X- and C-band frequencies.&lt;/p&gt;&lt;p&gt;Here, results will be presented from both campaigns. Different periods in the growing season will be highlighted. In particular, we will elaborate on the effects of variations in internal and external canopy water, and soil moisture on diurnal backscatter patterns.&lt;/p&gt;

scholarly journals Developing a Water-stress Index for Potted Poinsettia Production

HortScience ◽  
2020 ◽  
Vol 55 (8) ◽  
pp. 1295-1302
Author(s):  
Lloyd L. Nackley ◽  
Elias Fernandes de Sousa ◽  
Bruno J.L. Pitton ◽  
Jared Sisneroz ◽  
Lorence R. Oki
Keyword(s):  
Soil Moisture ◽  
Water Stress ◽  
Irrigation Management ◽  
Limited Resource ◽  
Agricultural Runoff ◽  
The United States ◽  
Stress Index ◽  
Environmental Sensors ◽  
Water Stress Index ◽  
Intensively Managed

Potted poinsettia (Euphorbia pulcherrima) is an important commercial commodity for the U.S. floriculture industry. The production of poinsettia demands intensively managed light control, heat, fertilizer, and water; inhibiting elongation with plant growth regulators, and protecting plants from diseases and pests with pesticide applications. Excessive irrigation creates pollution, promotes disease, and is expensive. Sensor-based control systems can optimize irrigation schedules. Irrigation management is crucial in nursery production of poinsettias because water is a limited resource and agricultural runoff is monitored in many states across the United States. By pairing environmental sensors with sensors that continuously monitor plant transpiration, we can determine how plant water use and water stress fluctuate with environmental and physiological demands. We hypothesized that continual measurements of sap flow could be correlated with environmental sensors to develop a new water stress index (WSI), which can deliver the benefits of detecting water stress that might affect the quality of potted poinsettias. To test this hypothesis, rooted cuttings of poinsettia (E. pulcherrima cv. Prestige Red) were individually potted into twelve 11-L black plastic nursery pots. Potted plants were grown in a naturally illuminated temperature-controlled glasshouse. The 12 plants were randomly assigned one of three watering treatments: weekly, biweekly, and triweekly irrigation. From the data collected, we were able to create a WSI that correlated available soil moisture with the difference between the expected transpiration with actual transpiration rates. Our results suggest that the plants in the weekly treatment group did not experience water stress until 0.3 m3·m–3 volume water content indicated by <0.2 WSI. These results support previous research that found 0.1 to 0.3 m3·m–3 can be stressful soil moisture conditions for greenhouse-grown crops. Results also show that for substrates with similar substrates that irrigation set points can be reduced to 0.2 m3·m–3 for improved irrigation efficiency.

scholarly journals Canopy-Air Temperature Differences and Soil Water as Predictors of Water Stress of Apple Trees Grown in a Humid, Temperate Climate

1992 ◽  
Vol 117 (3) ◽  
pp. 453-458 ◽  
Author(s):  
Preston K. Andrews ◽  
David J. Chalmers ◽  
Mapasaka Moremong
Keyword(s):  
Soil Moisture ◽  
Water Stress ◽  
Soil Water ◽  
Stress Index ◽  
Temperate Climate ◽  
Full Irrigation ◽  
Plastic Mulch ◽  
Crop Water Stress Index ◽  
Water Stress Index ◽  
Floor System

Temperature differences between tree canopies and air (Tc - Ta) and between leaves and air (T1 - Ta) of apples (Malus domestics Borkh. `Royal Gala') grown in New Zealand were measured with infrared (IR) thermometry. Treatments included three orchard-floor management systems and irrigation withheld (WI) for part of the growing season. Measurements of soil moisture indicated that, under full irrigation (FI), an alfalfa orchard-floor system apparently had higher soil water content than herbicide-strip (H) or plastic-mulch systems, whereas under the drought stress of WI, the H system retained the most water. The Tc - Ta and T1 - Ta of the WI treatment were significantly greater than those of the FI treatment after a soil-moisture differential was established. Linear regression between Tc - Ta, or T1 - Ta, and vapor pressure deficit (VPD) exhibited variable responses among dates. A crop water stress index (CWSI) was calculated from environmental measurements. The calculated CWSIS were not related to soil-moisture measurements. Even 35 days after full irrigation had been reinstated on the WI plots, the Tc - Ta, T1 - Ta, and CWSI of the WI plots were still significantly greater than those of the FI plots. These discrepancies in IR thermometry-based water-stress indices may be due to increased errors in the calculation of minimum CWSI at low VPDS and to fluctuating solar radiation and evapotranspiration, which are prevalent in humid, temperate climates.

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