Bare soil moisture retrieval from multi-temporal X-band TerraSAR-X SAR images

IGARSS 2015, Milan, ITA, 26-/07/2015 - 31/07/2015International audienceThe aim of the present study is to analyze the sensitivity of X-band SAR (TerraSAR-X) signals as a function of different physical bare soil parameters (soil moisture, soil roughness), and to evaluate the accuracy of change detection approach proposed for soil moisture estimation. Firstly, we presented a brief description of our ground and satellite database. Secondly, we considered the main results of our statistical analysis of the relationships between radar and soil parameters: soil moisture and different roughness parameters (the rms height, Zs parameter, and a new roughness parameter Zg. Finally, we proposed an algorithm combing multi-temporal X-band SAR images (TerraSAR-X) with different continuous thetaprobe measurements for the retrieval of surface soil moisture at a high spatial resolution

Evolution of the vegetation cover in Ichkeul National Park (Tunisia)

Ichkeul wetland ecosystems are characterized by hygrophile vegetation. This later requires to be submerged by fresh water during a period of the year in order to fullfi l its vegetative cycle. Hydrologic constructions and dry years infl uence the evolution of wetland vegetation distribution in Ichkeul National Park. To follow up this evolution, we mapped the vegetation in 1994 and 2002. The analysis of all existing data concerning Ichkeul wetland vegetation since 1967 and our surveys between 1994 and 2005 allowed us to understand the evolution of wetland vegetation distribution and explain it. Until 2002, ecosystems suffered from intense salinisation, the drying-up showed by development of halophilous vegetation and the extension of occasionally inundated areas. At the beginning of the year 2003, fresh water infl ows were generated by exceptional rains and entered the park, provoking water stagnation during more than two months in Ichkeul marshes. These conditions led to a regression of the halophilous vegetation and its replacement by an hygrophilous one, based on sedges, rushes,... Ichkeul wetland ecosystems showed a good resilience: one year was suffi cient to regenerate hygrophilous vegetation after 15 years of water shortageLes écosysternes lagunaires de l'Ichkeul sont caractérisés par une végétation hygrophile exigeant la submersion en eau douce pendant une période de l'année pour accomplir leur cycle végétatif. Les constructions hydrologiques et les années de sécheresses influencent l'évolution et la répartition de la végétation des marais du Parc national de l'Ichkeul. Pour suivre cette évolution, nous avons cartographié la végétation en 1994 et 2002. L'analyse des données publiées au sujet de la végétation des marais de l'Ichkeul depuis 1967 et de nos observations réalisées entre 1994 et 2005 nous a permis de comprendre l'évolution de la répartition de la végétation des marais et de l'expliquer. Jusqu'en 2002, les écosystèmes ont souffert d'une salinisation et d'une sécheresse intenses qui se sont traduites par le développement d'une végétation halophile et la réduction des superficies inondables. Au début de l'année 2003, des apports d'eau douce ont été produits par les pluies exceptionnelles et ont alimenté le parc, provoquant la stagnation de l'eau durant plus de deux mois dans les marais de l'Ichkeul. Ces conditions ont provoqué une dégradation de la végétation halophile au profit de la régénération de la végétation hygrophile à base de scirpes, de joncs, de carex... Les écosystèmes lagunaires de l'Ichkeul ont fait preuve d'une bonne résilience : une année favorable s'est avérée suffisante pour régénérer la végétation hygrophile après 15 ans de manque d'eau

Analysis of soil texture using terrasar x-band sar

International audienceIn this paper, it is proposed to use TERRASAR-X data for analysis and estimation of soil surface texture. Our study is based on experimental campaigns carried out over a semi-arid area in North Africa. Simultaneously to TERRASAR-X radar acquisitions, ground measurements (texture, soil moisture and roughness) were made on different test fields. A strong correlation is observed between soil texture and a processed signal from two radar images, the first acquired just after a rain event and the second corresponding to dry soil conditions, acquired three weeks later. An empirical relationship is proposed for the retrieval from radar signals of clay content percent. Soil texture mapping is proposed over the study site, which includes bare soils and olive groves

Soil surface moisture estimation over a semi-arid region using ENVISAT ASAR radar data for soil evaporation evaluation

The present paper proposes a method for the evaluation of soil evaporation, using soil moisture estimations based on radar satellite measurements. We present firstly an approach for the estimation and monitoring of soil moisture in a semi-arid region in North Africa, using ENVISAT ASAR images, over two types of vegetation covers. The first mapping process is dedicated solely to the monitoring of moisture variability related to rainfall events, over areas in the "non-irrigated olive tree" class of land use. The developed approach is based on a simple linear relationship between soil moisture and the backscattered radar signal normalised at a reference incidence angle. The second process is proposed over wheat fields, using an analysis of moisture variability due to both rainfall and irrigation. A semi-empirical model, based on the water-cloud model for vegetation correction, is used to retrieve soil moisture from the radar signal. Moisture mapping is carried out over wheat fields, showing high variability between irrigated and non-irrigated wheat covers. This analysis is based on a large database, including both ENVISAT ASAR and simultaneously acquired ground-truth measurements (moisture, vegetation, roughness), during the 2008–2009 vegetation cycle. Finally, a semi-empirical approach is proposed in order to relate surface moisture to the difference between soil evaporation and the climate demand, as defined by the potential evaporation. Mapping of the soil evaporation is proposed

Soil texture estimation over a semiarid area using TerraSAR-X radar data

In this letter, it is proposed to use TerraSAR-X data for analysis and estimation of soil surface texture. Our study is based on experimental campaigns carried out over a semiarid area in North Africa. Simultaneously with TerraSAR-X radar acquisitions, ground measurements (texture, soil moisture, and roughness) were made on different test fields. A strong correlation is observed between soil texture and a processed signal from two radar images, with the first acquired just after a rain event and the second corresponding to dry soil conditions, acquired three weeks later. An empirical relationship is proposed for the retrieval from radar signals of clay content percent. Soil texture mapping is proposed over the study site, which includes bare soils and olive groves

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

Evapotranspiration and evaporation/transpiration partitioning with dual source energy balance models in agricultural lands

EvapoTranspiration (ET) is an important component of the water cycle, especially in semi-arid lands. Its quantification is crucial for a sustainable management of scarce water resources. A way to quantify ET is to exploit the available surface temperature data from remote sensing as a signature of the surface energy balance, including the latent heat flux. Remotely sensed energy balance models enable to estimate stress levels and, in turn, the water status of most continental surfaces. The evaporation and transpiration components of ET are also just as important in agricultural water management and ecosystem health monitoring. Single temperatures can be used with dual source energy balance models but rely on specific assumptions on raw levels of plant water stress to get both components out of a single source of information. Additional information from remote sensing data are thus required, either something specifically related to evaporation (such as surface water content) or transpiration (such as PRI or fluorescence). This works evaluates the SPARSE dual source energy balance model ability to compute not only total ET, but also water stress and transpiration/evaporation components. First, the theoretical limits of the ET component retrieval are assessed through a simulation experiment using both retrieval and prescribed modes of SPARSE with the sole surface temperature. A similar work is performed with an additional constraint, the topsoil surface soil moisture level, showing the significant improvement on the retrieval. Then, a flux dataset acquired over rainfed wheat is used to check the robustness of both stress levels and ET retrievals. In particular, retrieval of the evaporation and transpiration components is assessed in both conditions (forcing by the sole temperature or the combination of temperature and soil moisture). In our example, there is no significant difference in the performance of the total ET retrieval, since the evaporation rate retrieved from the sole surface temperature is already fairly close to the one we can reconstruct from observed surface soil moisture time series, but current work is underway to test it over other plots.</p

Évolution de la couverture végétale du Parc national de l’Ichkeul (Tunisie)

Evolution of the vegetation cover in Ichkeul National Park (Tunisia). — Ichkeul wetland ecosystems are characterized by hygrophile vegetation. This later requires to be submerged by fresh water during a period of the year in order to fullfil its vegetative cycle. Hydrologic constructions and dry years influence the evolution of wetland vegetation distribution in Ichkeul National Park. To follow up this evolution, we mapped the vegetation in 1994 and 2002. The analysis of all existing data concerning Ichkeul wetland vegetation since 1967 and our surveys between 1994 and 2005 allowed us to understand the evolution of wetland vegetation distribution and explain it. Until 2002, ecosystems suffered from intense salinisation, the drying-up showed by development of halophilous vegetation and the extension of occasionally inundated areas. At the beginning of the year 2003, fresh water inflows were generated by exceptional rains and entered the park, provoking water stagnation during more than two months in Ichkeul marshes. These conditions led to a regression of the halophilous vegetation and its replacement by an hygrophilous one, based on sedges, rushes,... Ichkeul wetland ecosystems showed a good resilience : one year was sufficient to regenerate hygrophilous vegetation after 15 years of water shortage.Les écosystèmes lagunaires de l’Ichkeul sont caractérisés par une végétation hygrophile exigeant la submersion en eau douce pendant une période de l’année pour accomplir leur cycle végétatif. Les constructions hydrologiques et les années de sécheresses influencent l’évolution et la répartition de la végétation des marais du Parc national de l’Ichkeul. Pour suivre cette évolution, nous avons cartographié la végétation en 1994 et 2002. L’analyse des données publiées au sujet de la végétation des marais de l’Ichkeul depuis 1967 et de nos observations réalisées entre 1994 et 2005 nous a permis de comprendre l’évolution de la répartition de la végétation des marais et de l’expliquer. Jusqu’en 2002, les écosystèmes ont souffert d’une salinisation et d’une sécheresse intenses qui se sont traduites par le développement d’une végétation halophile et la réduction des superficies inondables. Au début de l’année 2003, des apports d’eau douce ont été produits par les pluies exceptionnelles et ont alimenté le parc, provoquant la stagnation de l’eau durant plus de deux mois dans les marais de l’Ichkeul. Ces conditions ont provoqué une dégradation de la végétation halophile au profit de la régénération de la végétation hygrophile à base de scirpes, de joncs, de carex... Les écosystèmes lagunaires de l’Ichkeul ont fait preuve d’une bonne résilience : une année favorable s’est avérée suffisante pour régénérer la végétation hygrophile après 15 ans de manque d’eau.Ghrabi Gammar Zeineb, Lili Chabaane Z., Zouaghi M. Évolution de la couverture végétale du Parc national de l’Ichkeul (Tunisie). In: Revue d'Écologie (La Terre et La Vie), tome 61, n°4, 2006. pp. 317-326

The Photochemical Reflectance Index (PRI) and the vegetation temperature as indicators of water stress and transpiration in Mediterranean olive grove

M2GARSS.Mediterranean and Middle-East Geoscience and Remote Sensing Symposium, Tunis, TUN, 09-/03/2020 - 09/03/2020To increase the olive tree water use efficiency, an early tracking of water stress is crucial. Several indices based on the near-infrared (the vegetation temperature) and the visible (The photochemical reflectance index (PRI)) spectral bands have shown to be useful to remotely assess the tree eco-physiological functioning status. First, at plant scale, we analyzed the relations between close-range remote sensing measurements (PRI, vegetation temperature) and the plant water stress measurements (plant available water (PAW), the transpiration, the water stress index...). The vegetation temperature was closely associated with the transpiration and the plant water stress indicator. However, the PRI, which was promising as an indicator of the water functioning of the plant, was not able to detect water stress over complex crown of isolated tree due to its high sensitivity to the structure