The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat

Evapotranspiration is an important component of the water cycle, especially in semi-arid lands. A way to quantify the spatial distribution of evapotranspiration and water stress from remote-sensing data is to exploit the available surface temperature as a signature of the surface energy balance. Remotely sensed energy balance models enable one to estimate stress levels and, in turn, the water status of continental surfaces. Dual-source models are particularly useful since they allow derivation of a rough estimate of the water stress of the vegetation instead of that of a soil–vegetation composite. They either assume that the soil and the vegetation interact almost independently with the atmosphere (patch approach corresponding to a parallel resistance scheme) or are tightly coupled (layer approach corresponding to a series resistance scheme). The water status of both sources is solved simultaneously from a single surface temperature observation based on a realistic underlying assumption which states that, in most cases, the vegetation is unstressed, and that if the vegetation is stressed, evaporation is negligible. In the latter case, if the vegetation stress is not properly accounted for, the resulting evaporation will decrease to unrealistic levels (negative fluxes) in order to maintain the same total surface temperature. This work assesses the retrieval performances of total and component evapotranspiration as well as surface and plant water stress levels by (1) proposing a new dual-source model named Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) in two versions (parallel and series resistance networks) based on the TSEB (Two-Source Energy Balance model, Norman et al., 1995) model rationale as well as state-of-the-art formulations of turbulent and radiative exchange, (2) challenging the limits of the underlying hypothesis for those two versions through a synthetic retrieval test and (3) testing the water stress retrievals (vegetation water stress and moisture-limited soil evaporation) against in situ data over contrasted test sites (irrigated and rainfed wheat). We demonstrated with those two data sets that the SPARSE series model is more robust to component stress retrieval for this cover type, that its performance increases by using bounding relationships based on potential conditions (root mean square error lowered by up to 11 W m−2 from values of the order of 50–80 W m−2), and that soil evaporation retrieval is generally consistent with an independent estimate from observed soil moisture evolution

Influence of seasonality and vegetation type on suburban microclimates

Urbanization is responsible for some of the fastest rates of land-use change around the world, with important consequences for local, regional, and global climate. Vegetation, which represents a significant proportion of many urban and suburban landscapes, can modify climate by altering local exchanges of heat, water vapor, and CO2. To determine how distinct urban forest communities vary in their microclimate effects over time, we measured stand-level leaf area index, soil temperature, infrared surface temperature, and soil water content over a complete growing season at 29 sites representing the five most common vegetation types in a suburban neighborhood of Minneapolis–Saint Paul, Minnesota. We found that seasonal patterns of soil and surface temperatures were controlled more by differences in stand-level leaf area index and tree cover than by plant functional type. Across the growing season, sites with high leaf area index had soil temperatures that were 7°C lower and surface temperatures that were 6°C lower than sites with low leaf area index. Site differences in mid-season soil temperature and turfgrass ground cover were best explained by leaf area index, whereas differences in mid-season surface temperature were best explained by percent tree cover. The significant cooling effects of urban tree canopies on soil temperature imply that seasonal changes in leaf area index may also modulate CO2 efflux from urban soils, a highly temperature-dependent process, and that this should be considered in calculations of total CO2 efflux for urban carbon budgets. Field-based estimates of percent tree cover were found to better predict mid-season leaf area index than satellite-derived estimates and consequently offer an approach to scale up urban biophysical properties

Evil angels and forensic scientists : representations of law in popular culture

Professor Chase (1986: 527) suggests law would benefit if it recognised and gave serious study to \u27the impact of legal ideas conveyed through the\u27 institutions of popular culture\u27. In responding to his challenge I intend to address just one aspect of law\u27s representation in popular culture, the law/science nexus through its manifestation as forensic science. That area relates directly to the role and status of these intersecting discourses, and raises the question of whether the hierarchy of discourses which gives natural precedence to science adversely affects law. In other words, is justice a casualty in these encounters? In examining this proposition, I have selected two texts with contrasting representations of science\u27s role in law

"Play it again" : a radio documentary, 10 years of FM broadcasting at 6UVS-FM

Traces the history of 6UVS-FM using excerpts from interviews with those instrumental in the establishment of the station. Produced by Virginia Rivalland. First broadcast by 6UVS-FM on 1 April 1987. Original sound tape reels of interviews used to compile this documentary programme are held at Murdoch University Library. This sound recording is part of the History of Murdoch University Collection

Transpiration and CO₂ fluxes of a pine forest: modelling the undergrowth effect

A modelling study is performed in order to quantify the relative effect of allowing for the physiological properties of an undergrowth grass sward on total canopy water and carbon fluxes of the Le-Bray forest (Les-Landes, South-western France). The Le-Bray forest consists of maritime pine and an herbaceous undergrowth (purple moor-grass), which is characterised by a low stomatal control of transpiration, in contrast to maritime pine. A CO2-responsive land surface model is used that includes responses of woody and herbaceous species to water stress. An attempt is made to represent the properties of the undergrowth vegetation in the land surface model Interactions between Soil, Biosphere, and Atmosphere, CO2-responsive, ISBA-A-gs. The new adjustment allows for a fairly different environmental response between the forest canopy and the understory in a simple manner. The model's simulations are compared with long term (1997 and 1998) micro-meteorological measurements over the Le-Bray site. The fluxes of energy, water and CO2, are simulated with and without the improved representation of the undergrowth vegetation, and the two simulations are compared with the observations. Accounting for the undergrowth permits one to improve the model's scores. A simple sensitivity experiment shows the behaviour of the model in response to climate change conditions, and the understory effect on the water balance and carbon storage of the forest. Accounting for the distinct characteristics of the undergrowth has a substantial and positive effect on the model accuracy and leads to a different response to climate change scenarios

Quantifying uncertainties in land surface temperature due to atmospheric correction: Application to Landsat-7 data over a Mediterranean agricultural region

International audienceThe impact of using non-coincident radiosoundings to remove atmosphere effect from thermal radiances is analyzed here. We considered 27 Landsat-7 ETM+ images acquired over a Mediterranean agricultural region, benefiting from nearby radiosoundings launched almost 2 hours later, and from the availability of a network of ground stations deployed over different types of ecosystems. We observed that, in the conditions of our images, surface temperature estimates slightly improved when considering one atmospheric profile interpolated to our particular date, time and location, in comparison with the use of non-coincident radiosoundings. However, it may imply an error up to ±2.5 K for brightness temperatures (in particular for very high temperatures and during summer when the atmosphere was warmer and the vapor pressure was higher), leading to important errors in the derivation of surface energy fluxes. The characterization of the lowest atmosphere layer appeared to be essential to improve the estimates of brightness temperatures

Effects of high spatial and temporal resolution Earth observations on simulated hydrometeorological variables in a cropland (southwestern France)

Agricultural landscapes are often constituted by a patchwork of crop fields whose seasonal evolution is dependent on specific crop rotation patterns and phenologies. This temporal and spatial heterogeneity affects surface hydrometeorological processes and must be taken into account in simulations of land surface and distributed hydrological models. The Sentinel-2 mission allows for the monitoring of land cover and vegetation dynamics at unprecedented spatial resolutions and revisit frequencies (20 m and 5 days, respectively) that are fully compatible with such heterogeneous agricultural landscapes. Here, we evaluate the impact of Sentinel-2-like remote sensing data on the simulation of surface water and energy fluxes via the Interactions between the Surface Biosphere Atmosphere (ISBA) land surface model included in the EXternalized SURface (SURFEX) modeling platform. The study focuses on the effect of the leaf area index (LAI) spatial and temporal variability on these fluxes. We compare the use of the LAI climatology from ECOCLIMAP-II, used by default in SURFEX-ISBA, and time series of LAI derived from the high-resolution Formosat-2 satellite data (8 m). The study area is an agricultural zone in southwestern France covering 576 km2 (24 km  ×  24 km). An innovative plot-scale approach is used, in which each computational unit has a homogeneous vegetation type. Evaluation of the simulations quality is done by comparing model outputs with in situ eddy covariance measurements of latent heat flux (LE). Our results show that the use of LAI derived from high-resolution remote sensing significantly improves simulated evapotranspiration with respect to ECOCLIMAP-II, especially when the surface is covered with summer crops. The comparison with in situ measurements shows an improvement of roughly 0.3 in the correlation coefficient and a decrease of around 30 % of the root mean square error (RMSE) in the simulated evapotranspiration. This finding is attributable to a better description of LAI evolution processes with Formosat-2 data, which further modify soil water content and drainage of soil reservoirs. Effects on annual drainage patterns remain small but significant, i.e., an increase roughly equivalent to 4 % of annual precipitation levels with simulations using Formosat-2 data in comparison to the reference simulation values. This study illustrates the potential for the Sentinel-2 mission to better represent effects of crop management on water budgeting for large, anthropized river basins

Assessing gross primary production from solar-induced chlorophyll fluorescence: field results and integration into biogeophysical models

Geophysical Research Abstracts, Vol. 10, EGU2008-A-07911, 2008 SRef-ID: 1607-7962/gra/EGU2008-A-07911 EGU General Assembly 2008Light energy absorbed by photosynthetic antenna pigments is only partly used up in photochemical processes, the remainder being dissipated through heat production or chlorophyll fluorescence. The possibility to use remote sensing methods to measure fluorescence emitted by the plants under natural solar illumination (solar-induced fluorescence, SIF) paves the way for the remote assessment of electron transport and photosynthetic processes. Although less straightforward than for near-field pulsesaturated fluorescence, the interpretation of solar-induced fluorescence is advancing, through the development of novel models of variable detail. The family of Earth Explorer missions is the result of a strategy within the Living Planet Programme of the European Space Agency where missions are designed to address critical and specific issues raised by the scientific community whilst demonstrating breakthrough technology in observing techniques. Following the selection of the first six Explorer missions, currently under development and implementation, the Agency released in March 2005 a new Call for Ideas focused on key processes that are fundamental for improving our understanding of the changing Earth System. The proposals were reviewed by scientific teams and assessed technically and programmatically, leading to the selection of six candidates in May 2006 to enter dedicated assessment studies. Amongst these missions is the FLuorescence EXplorer – FLEX – a mission dedicated to observing and monitoring SIF globally together with additional complementary information on the vegetation cover and its environmental setting allowing a correct interpretation of the observed SIF signal. In the framework of the FLEX mission assessment phase dedicated airborne campaigns and study activities were initiated in order to proof the mission concept, to consolidate the mission requirements and to develop the appropriate data processing tools and the necessary methods for assimilating the SIF signal into biogeophysical models with explicit description of vegetation dynamics. An overview of the mission is presented, together with a summary of its main preliminary results.Peer reviewe

Evaluation of EVASPA, a tool for mapping evapotranspiration from space

International audienc