scholarly journals The influence of vegetation water dynamics on the ASCAT backscatter-incidence angle relationship in the Amazon

2021 ◽  
Author(s):  
Ashwini Petchiappan ◽  
Susan C. Steele-Dunne ◽  
Mariette Vreugdenhil ◽  
Sebastian Hahn ◽  
Wolfgang Wagner ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Incidence Angle ◽  
Water Dynamics ◽  
Plant Water ◽  
Vegetation Monitoring ◽  
Equivalent Water Thickness ◽  
Moisture Availability ◽  
Phenological Changes ◽  
Data Record ◽  
Vegetation Water

Abstract. Microwave observations are sensitive to plant water content and could therefore provide essential information on biomass and plant water status in ecological and agricultural applications. The combined data record of the C-band scatterometers on ERS 1/2, the Metop series and the planned Metop Second Generation satellites will span over 40 years, which would provide a long-term perspective on the role of vegetation in the climate system. Recent research has indicated that the unique viewing geometry of ASCAT could be exploited to observe vegetation water dynamics. The incidence angle dependence of backscatter can be described with a second order polynomial, the slope and curvature of which are related to vegetation. In a study limited to grasslands, seasonal cycles, spatial patterns and interannual variability in the slope and curvature were found to vary among grassland types and were attributed to differences in moisture availability, growing season length and phenological changes. To exploit ASCAT slope and curvature for global vegetation monitoring, their dynamics over a wider range of vegetation types needs to be quantified and explained in terms of vegetation water dynamics. Here, we compare ASCAT data with meteorological data and GRACE Equivalent Water Thickness (EWT) to explain the dynamics of ASCAT backscatter, slope and curvature in terms of moisture availability and demand. We consider differences in the seasonal cycle, diurnal differences, and the response to the 2010 and 2015 droughts across ecoregions in the Amazon basin and surroundings. Results show that spatial and temporal patterns in backscatter reflect moisture availability indicated by GRACE EWT. Slope and curvature dynamics vary considerably among the ecoregions. The evergreen forests, often used as a calibration target, exhibit very stable behaviour even under drought conditions. The limited seasonal variation follows changes in the radiation cycle, and may indicate phenological changes such as litterfall. In contrast, the diversity of land cover types within the Cerrado region results in considerable heterogeneity in terms of the seasonal cycle and the influence of drought on both slope and curvature. Seasonal flooding in forest and savanna areas also produced a distinctive signature in terms of the backscatter as a function of incidence angle. This improved understanding of the incidence angle behaviour of backscatter increases our ability to interpret and make optimal use of the ASCAT data record and VOD products for vegetation monitoring.

scholarly journals Estimation of vegetation water content at leaf and canopy level using dual-wavelength commercial terrestrial laser scanners

2018 ◽  
Vol 8 (2) ◽  
pp. 20170041 ◽  
Author(s):  
Ahmed Elsherif ◽  
Rachel Gaulton ◽  
Jon Mills
Keyword(s):  
Water Content ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Intensity Data ◽  
Infrared Wavelength ◽  
Vegetation Water Content ◽  
Equivalent Water Thickness ◽  
Vertical Heterogeneity ◽  
Vegetation Water ◽  
Shortwave Infrared

Vegetation water content, quantified as the leaf equivalent water thickness (EWT), can serve as an indicator of vegetation stress. The intensity data recorded by terrestrial laser scanning (TLS) instruments, operating at shortwave infrared wavelengths, can be used to estimate the three-dimensional distribution of EWT, after a full and rigorous calibration for the range and incidence angle effects. However, TLS instruments do not record the incidence angles automatically, making calibration challenging. In this study, intensity data from two commercially available TLS instruments (Leica P40, 1550 nm shortwave infrared wavelength, and Leica P20, 808 nm near-infrared wavelength) were combined in a normalized difference index (NDI). The NDI was found to minimize the incidence angle effects with no need for further calibration. A dry-down experiment was conducted using deciduous and conifer canopies. The NDI was found to be highly correlated to EWT at leaf level ( R 2 of 0.91 and 0.74) and at canopy level ( R 2 of 0.89 and 0.74) for the deciduous and conifer canopies, respectively. Three-dimensional distributions of EWT at canopy level were generated, which revealed some vertical heterogeneity.

Relating ASCAT backscatter and dynamic vegetation parameters to vegetation water dynamics in the Amazon

2020 ◽  
Author(s):  
Ashwini Petchiappan ◽  
Susan Steele-Dunne ◽  
Mariette Vreugdenhil ◽  
Sebastian Hahn ◽  
Wolfgang Wagner
Keyword(s):  
Water Stress ◽  
Source Monitoring ◽  
Carbon Sink ◽  
Incidence Angle ◽  
Amazon Region ◽  
Water Dynamics ◽  
Amazon Forest ◽  
Spatial And Temporal Patterns ◽  
Vegetation Parameters ◽  
Vegetation Water

<p>The Amazon rainforest is among the most vital ecosystems on earth, holding about a quarter of the global terrestrial carbon sink. Since 2005, three 100-year return period droughts have occurred, the likes of which have the potential to turn the forest from a carbon sink to a carbon source. Monitoring the Amazon is essential to understand the functioning of the various ecoregions and how they respond to water stress. </p><p>In this study, we investigate the ASCAT backscatter and dynamic vegetation parameters (DVP) over the Amazon region as a potential source of information about the vegetation. The dynamic vegetation parameters are slope and curvature of the second order Taylor polynomial used to represent the incidence angle dependence of backscatter. We looked for spatial and temporal patterns in the backscatter and DVP over Amazonia, and related them to climatic variables such as radiation and precipitation from the Princeton Global Meteorological Forcing Dataset, as well as variations in terrestrial water storage from GRACE. </p><p>Results will be presented from the first ten years of ASCAT observations over the Amazon region, including the Cerrado grasslands southeast of the Amazon forest. We found that spatial patterns of the backscatter and ASCAT DVP reflect the distribution of major land cover types in the region. Seasonal variations in the parameters match the seasonality of moisture demand and availability, and show an influence of vegetation phenology. Diurnal differences in backscatter between the morning (~10:00 AM) and evening overpasses (~10:00 PM) suggest that the backscatter is sensitive to vegetation water dynamics. Significant anomalies were observed during the Amazon droughts of 2010 and 2015, indicating that ASCAT could detect water stress and drought effects in the vegetation. Therefore, the ASCAT DVP show promise for long-term monitoring of the Amazon with respect to vegetation water dynamics and droughts. </p>

Plants, vital players in the terrestrial water cycle

2021 ◽  
Author(s):  
Marie-Claire ten Veldhuis ◽  
Tom van den Berg ◽  
Martine van der Ploeg ◽  
Elias Kaiser ◽  
Satadal Dutta ◽  
...  
Keyword(s):  
Water Transport ◽  
Water Cycle ◽  
Turgor Pressure ◽  
Water Dynamics ◽  
Plant Water ◽  
Flow Monitoring ◽  
Vital Functions ◽  
Main Challenge ◽  
Macro Scale ◽  
Terrestrial Water

<p>Plant transpiration accounts for about half of all terrestrial evaporation (Jasechko et al., 2013). Plants need water for many vital functions including nutrient uptake, growth, maintenance of cell turgor pressure and leaf cooling. Due to the regulation of water transport by stomata in the leaves, plants lose 97% of the water they take via their roots, to the atmosphere. They can be viewed as transpiration-powered pumps on the interface between the soil and atmosphere.</p><p>Measuring plant-water dynamics is essential to gain better insight into their role in the terrestrial water cycle and plant productivity. It can be measured at different levels of integration, from the single cell micro-scale to the ecosystem macro-scale, on time scales from minutes to months. In this contribution, we give an overview of state-of-the-art techniques for transpiration measurement and highlight several promising innovations for monitoring plant-water relations. Some of the techniques we will cover include stomata imaging by microscopy, gas exchange for stomatal conductance and transpiration monitoring, thermometry for water stress detection, sap flow monitoring, hyperspectral imaging, ultrasound spectroscopy, accelerometry, scintillometry and satellite-remote sensing.</p><p>Outlook: To fully assess water transport within the soil-plant-atmosphere continuum, a variety of techniques is required to monitor environmental variables in combination with biological responses at different scales. Yet this is not sufficient: to truly solve for spatial heterogeneity as well as temporal variability, dense network sampling is needed.</p><p>In PLANTENNA (https://www.4tu.nl/plantenna/en/) a team of electronics, precision and microsystems engineers together with plant and environmental scientists develop and implement innovative (3D-)sensor networks that measure plant and environmental parameters at high resolution and low cost. Our main challenge for in-situ sensor autonomy (“plug and forget”) is energy: we want the sensor nodes to be hyper-efficient and rely fully on (miniaturised) energy-harvesting.</p><p><strong>REFERENCES: </strong></p><p>Jasechko, S., Sharp, Z. D., Gibson, J. J., Birks, S. J., Yi, Y., & Fawcett, P. J. (2013). Terrestrial water fluxes dominated by transpiration. Nature, 496(7445), 347-350.<br>Plantenna: "Internet of Plants". (n.d.). https://www.4tu.nl/plantenna/en/</p><p> </p>

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.

scholarly journals Editorial: The Green Side of the Water Cycle: New Advances in the Study of Plant Water Dynamics

2020 ◽  
Vol 11 ◽  
Author(s):  
Juan Pedro Ferrio ◽  
Maren Dubbert ◽  
Cristina Máguas
Keyword(s):  
Water Cycle ◽  
Water Dynamics ◽  
Plant Water

Improved Geolocation and Earth Incidence Angle Information for a Fundamental Climate Data Record of the SSM/I Sensors

2013 ◽  
Vol 51 (3) ◽  
pp. 1504-1513 ◽  
Author(s):  
Wesley Berg ◽  
Mathew R. P. Sapiano ◽  
Jennifer Horsman ◽  
Christian Kummerow
Keyword(s):  
Incidence Angle ◽  
Climate Data ◽  
Data Record ◽  
Climate Data Record

scholarly journals Terrestrial Laser Scanning Intensity Captures Diurnal Variation in Leaf Water Potential

2020 ◽  
Author(s):  
Samuli Junttila ◽  
Teemu Hölttä ◽  
Eetu Puttonen ◽  
Masato Katoh ◽  
Mikko Vastaranta ◽  
...  
Keyword(s):  
Diurnal Variation ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Tree Species ◽  
Laser Scanning ◽  
Terrestrial Laser Scanning ◽  
Leaf Water ◽  
Water Dynamics ◽  
Plant Water ◽  
Plant Mortality

Drought-induced plant mortality has increased globally during the last decades and is forecasted to influence global vegetation dynamics. Timely information on plant water dynamics is essential for understanding and anticipating drought-induced plant mortality. The most common metric that has been used for decades for measuring water stress is leaf water potential (ΨL), which is measured destructively. To obtain information on water dynamics from trees and forested landscapes, remote sensing methods have been developed. However, the spatial and temporal resolution of the existing methods have limited our understanding of water dynamics and diurnal variation of ΨL within single trees. Thus, we investigated the capability of terrestrial laser scanning (TLS) intensity in observing diurnal variation in ΨL during a 50 hour monitoring period and aimed to improve understanding on how large part of the diurnal variation in ΨL can be captured using intensity observations. We found that TLS intensity at 905 nm wavelength was able to explain 78% of the variation in ΨL for three trees of two tree species with a root-mean square error of 0.137 MPa. Based on our experiment with three trees, time-series of TLS intensity measurements can be used in detecting changes in ΨL, and thus it is worthwhile to expand the investigations to cover a wider range of tree species and forests and further increase our understanding of plant water dynamics at wider spatial and temporal scales.

scholarly journals CAN SMOS SOIL MOISTURE DRY-DOWNS BE USEFUL TO DETECT FLOOD CONDITIONS OVER THE ARGENTINEAN PAMPAS PLAINS?

2020 ◽  
Vol XLII-3/W12-2020 ◽  
pp. 279-283
Author(s):  
L. Cappelletti ◽  
A. Sörensson ◽  
R. Ruscica ◽  
M. M. Salvia ◽  
E. Jobbágy ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Time Scales ◽  
Capillary Rise ◽  
Precipitation Anomaly ◽  
Water Dynamics ◽  
Atmospheric Conditions ◽  
Short Period ◽  
Dry Down ◽  
Spatio Temporal ◽  
Vegetation Water

Abstract. The process of soil drying following a single rainfall input offers an integrated perspective on soil-vegetation water dynamics in responses to atmospheric conditions during periods without rainfall. In this work, the soil moisture dry-down time scale events (τ) was calculated using surface soil moisture data from the SMOS mission, with the objective to explore if the spatio-temporal variability of τ could be used as a proxy for regional flooding and waterlogging characterization. Our working hypothesis is that soil moisture dries up more slowly under flooded conditions as a result of slower surface water elimination by infiltration and capillary rise of water from the saturated zone close to the surface. A clear difference precipitation-moisture coupling was detected between two regions with different flooding dynamics. In a region where flooding is triggered by precipitation excesses on weekly-to-monthly time scales and where the coupling between precipitation and evapotranspiration is strong, a positive correlation between dry-down and 6-month accumulated precipitation anomaly was found for all seasons except winter. By contrast, in the other region where flooding is largely de-coupled from precipitation and evapotranspiration, but rather coupled to ground water table dynamics on time scales from several months to years, no significant correlations were found. These results are based on a short period of data: March 2010 – November 2014.

scholarly journals Dryland ecohydrology and climate change: critical issues and technical advances

2012 ◽  
Vol 16 (8) ◽  
pp. 2585-2603 ◽  
Author(s):  
L. Wang ◽  
P. D'Odorico ◽  
J. P. Evans ◽  
D. J. Eldridge ◽  
M. F. McCabe ◽  
...  
Keyword(s):  
Climate Change ◽  
Land Surface ◽  
Net Primary Productivity ◽  
Water Security ◽  
Water Dynamics ◽  
Tight Coupling ◽  
Technological Advances ◽  
Critical Issues ◽  
Technical Advances ◽  
Vegetation Water

Abstract. Drylands cover about 40% of the terrestrial land surface and account for approximately 40% of global net primary productivity. Water is fundamental to the biophysical processes that sustain ecosystem function and food production, particularly in drylands where a tight coupling exists between ecosystem productivity, surface energy balance, biogeochemical cycles, and water resource availability. Currently, drylands support at least 2 billion people and comprise both natural and managed ecosystems. In this synthesis, we identify some current critical issues in the understanding of dryland systems and discuss how arid and semiarid environments are responding to the changes in climate and land use. The issues range from societal aspects such as rapid population growth, the resulting food and water security, and development issues, to natural aspects such as ecohydrological consequences of bush encroachment and the causes of desertification. To improve current understanding and inform upon the needed research efforts to address these critical issues, we identify some recent technical advances in terms of monitoring dryland water dynamics, water budget and vegetation water use, with a focus on the use of stable isotopes and remote sensing. These technological advances provide new tools that assist in addressing critical issues in dryland ecohydrology under climate change.

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