Obtención de mapas verdad-terreno de LAI, FAPAR y cobertura vegetal a partir de imágenes del satélite chileno FASat-C y medidas in-situ en la zona agrícola de Chimbarongo, Chile, para la validación de productos de satélite

Revista oficial de la Asociación Española de Teledetección[EN] In remote sensing, validation exercises are essential to ensure the quality of the products originated from satellite Earth observations. To assess the measurement uncertainty derived from satellite products, several ground field data from different ecosystems must be available for use. In the same order of importance, it is necessary to define data sampling and up-scaling methodologies to allow a suitable comparison between the ground data and the pixel size of the product. This paper shows the applied methodology used in the FP7 ImagineS project (Implementing Multi-scale Agricultural Indicators Exploiting Sentinels) to validate 10-days global LAI, FAPAR and vegetation cover products at 1km spatial resolution using in-situ data. These global products are derived from PROBA-V observations in the Copernicus Global Land Service. In particular, this case study shows the results of the field-campaign carried out in January of 2015 in the agricultural area of Chimbarongo, Chile. The methodology to scale the ground data and to create ground-based maps using FASat-C Chilean satellite imagery with a 5,8 m spatial resolution using multivariate least squares regression is shown. Finally, the same methodology was used with a 30 m spatial resolution Landsat-8 image to analyze the effect of the field-data input on the ground-truth maps used to validate the results. Our results show the reliability on the presented methodology and the consistency of the method with regard to the input data. Better results and lower RMSE errors were obtained using FASat-C data. The comparison with satellite products at 1 km shows a good agreement with Copernicus Global Land products derived from PROBA-V observations, and systematic negative bias for the MODIS products.[ES] El proceso de validación es fundamental en teledetección para garantizar la calidad de los productos obte-nidos a partir de las observaciones de satélite. En el caso concreto de productos de vegetación, es necesario disponer de datos verdad-terreno de diferentes tipos de ecosistemas, y desarrollar estrategias de muestreo y escalado que permitan la caracterización de la superficie y la correcta relación del tamaño de pixel que se desea validar. En este caso práctico, se presenta la metodología aplicada en el contexto del proyecto FP7 ImagineS (Implementing Multi-scale Agricultural Indicators Exploiting Sentinels) para la validación a partir de datos in-situ de los productos globales de LAI, FAPAR y cobertura vegetal. Estos productos se generan de forma operativa a 1 km de resolución espacial y 10 días de frecuencia temporal a partir de las observaciones de PROBA-V en la componente global del servicio europeo Coperni-cus de superficie terrestre (Copernicus Global Land Service). En particular, se presentan los resultados de la campaña de campo realizada en enero de 2015 en la zona agrícola de Chimbarongo, Chile, donde se aplica la metodología de escalado de datos de campo y generación de mapas verdad-terreno a partir de las observaciones del satélite chileno FASat-C de 5,8 m de resolución espacial, y utilizando técnicas de regresión multivariada por mínimos cuadrados. Finalmente, se ha aplicado el método a una imagen Landsat-8 de 30 m de resolución para analizar la influencia de la imagen en los mapas verdad-terreno utilizados para validar. Los resultados demuestran la fiabilidad de la metodología empleada, y la consistencia del método respecto a la imagen de alta resolución utilizada, obteniéndose un menor RMSE en los mapas generados a partir de FASat-C de mayor resolución espacial. Los mapas verdad-terreno se han comparado con los productos generados a partir de PROBA-V a 1 km en Copernicus Global Land y con el producto de MODIS también de 1 km, mostrando PROBA-V muy buen acuerdo en la zona de estudio, mientras que MODIS presenta un bias negativo respecto a los mapas verdad-terreno en la zona de estudio.Este estudio está financiado por el proyecto FP7 ImagineS n° 311766 de la Comunidad Europea. La organización de la campaña de campo, junto a la adquisición de las imágenes del sistema satelital chileno FASat-C ha sido posible gracias al Laboratorio para el Análisis de la Biosfera de la Universidad de Chile (LAB), en el marco del proyecto Fondecyt Iniciación n°11130359 y la Fuerza Aérea de Chile (FACH) a través del Grupo de Operaciones Espaciales (GOE). Las imágenes Landsat-8 de alta resolución han sido proporcionadas por el servicio EarthExplorer de USGS y la NASALatorre-Sánchez, C.; Camacho, F.; Mattar, C.; Santamaría-Artigas, A.; Leiva-Büchi, N.; Lacaze, R. (2016). LAI, FAPAR and FCOVER ground-truth map creation from FASat-C satellite imagery and in-situ measurements in Chimbarongo, Chile, for satellite products validation. Revista de Teledetección. (47):51-64. https://doi.org/10.4995/raet.2016.5691SWORD516447Barber, C. B., Dobkin, D. P., & Huhdanpaa, H. (1996). The quickhull algorithm for convex hulls. ACM Transactions on Mathematical Software, 22(4), 469-483. doi:10.1145/235815.235821Camacho, F., Latorre, C., Lacaze, R., Baret, F., De la Cruz, F., Demarez, V., Di Bella, C., Fang, H., García-Haro, J., Gonzalez, M. P., Kussul, N., López- Baeza, E., Mattar, C., Nestola, E., Pattey, E., Piccard, I., Rudiger, C., Savin, I., Sanchez-Azofeifa, A., Boschetti, M., Bossio, D., Weiss, M., Castrignano, A., Zribi, M. 2014. A Network of Sites for Ground Biophysical Measurements in support of Copernicus Global Land Product Validation. Proceedings of the IV RAQRS conference, Torrent, 22-26 September 2014. ISBN: 978-84-370-9808-1Camacho, F., Cernicharo, J., Lacaze, R., Baret, F., & Weiss, M. (2013). GEOV1: LAI, FAPAR essential climate variables and FCOVER global time series capitalizing over existing products. Part 2: Validation and intercomparison with reference products. Remote Sensing of Environment, 137, 310-329. doi:10.1016/j.rse.2013.02.030Cawley, G. C., & Talbot, N. L. C. (2003). Efficient leave-one-out cross-validation of kernel fisher discriminant classifiers. Pattern Recognition, 36(11), 2585-2592. doi:10.1016/s0031-3203(03)00136-5Chander, G., Hewison, T. J., Fox, N., Wu, X., Xiong, X., & Blackwell, W. J. (2013). Overview of Intercalibration of Satellite Instruments. IEEE Transactions on Geoscience and Remote Sensing, 51(3), 1056-1080. doi:10.1109/tgrs.2012.2228654CIREN 2002. Estudio Agrológico IX Región. Descripciones de suelos: Materiales y símbolos. N°122, 360 pp.Garrigues, S., Lacaze, R., Baret, F., Morisette, J. T., Weiss, M., Nickeson, J. E., … Yang, W. (2008). Validation and intercomparison of global Leaf Area Index products derived from remote sensing data. Journal of Geophysical Research: Biogeosciences, 113(G2), n/a-n/a. doi:10.1029/2007jg000635Ifarraguerri, A., & Chang, C.-I. (1999). Multispectral and hyperspectral image analysis with convex cones. IEEE Transactions on Geoscience and Remote Sensing, 37(2), 756-770. doi:10.1109/36.75219

On Second-Order Monadic Monoidal and Groupoidal Quantifiers

We study logics defined in terms of second-order monadic monoidal and groupoidal quantifiers. These are generalized quantifiers defined by monoid and groupoid word-problems, equivalently, by regular and context-free languages. We give a computational classification of the expressive power of these logics over strings with varying built-in predicates. In particular, we show that ATIME(n) can be logically characterized in terms of second-order monadic monoidal quantifiers

A Class of Automata for the Verification of Infinite, Resource-Allocating Behaviours

Process calculi for service-oriented computing often feature generation of fresh resources. So-called nominal automata have been studied both as semantic models for such calculi, and as acceptors of languages of finite words over infinite alphabets. In this paper we investi-gate nominal automata that accept infinite words. These automata are a generalisation of deterministic Muller automata to the setting of nominal sets. We prove decidability of complement, union, intersection, emptiness and equivalence, and determinacy by ultimately periodic words. The key to obtain such results is to use finite representations of the (otherwise infinite-state) defined class of automata. The definition of such operations enables model checking of process calculi featuring infinite behaviours, and resource allocation, to be implemented using classical automata-theoretic methods

Influence of root and leaf traits on the uptake of nutrients in cover crops

Aims: Cover crops play an important role in soil fertility as they can accumulate large amounts of nutrients. This study aimed at understanding the nutrient uptake capacity of a wide range of cover crops and at assessing the relevance of acquisition strategies. Methods: A field experiment was conducted to characterize 20 species in terms of leaf and root traits. Plant traits were related to nutrient concentration and shoot biomass production with a redundancy analysis. Acquisition strategies were identified using a cluster analysis. Results: Root systems varied greatly among cover crop species. Five nutrient acquisition strategies were delineated. Significant amounts of nutrients (about 120 kg ha−1 of nitrogen, 30 kg ha−1 of phosphorus and 190 kg ha−1 of potassium) were accumulated by the species in a short period. Nutrient acquisition strategies related to high accumulations of nutrients consisted in either high shoot biomass and root mass and dense tissues, or high nutrient concentrations and root length densities. Species with high root length densities showed lower C/N ratios. Conclusions: The same amounts of nutrients were accumulated by groups with different acquisition strategies. However, their nutrient concentrations offer different perspectives in terms of nutrient release for the subsequent crop and nutrient cycling improvement

Recent visible light and metal free strategies in [2+2] and [4+2] photocycloadditions

When aiming to synthesize molecules with elevated molecular complexity starting from relatively simple starting materials, photochemical transformations represent an open avenue to circumvent analogous multistep procedures. Specifically, light-mediated cycloadditions remain as powerful tools to generate new bonds begotten from non-very intuitive disconnections, that alternative thermal protocols would not offer. In response to the current trend in both industrial and academic research pointing towards green and sustainable processes, several strategies that meet these requirements are currently available in the literature. This Minireview summarizes [2+2] and [4+2] photocycloadditions that do not require the use of metal photocatalysts by means of alternative strategies. It is segmented according to the cycloaddition type in order to give the reader a friendly approach and we primarily focus on the most recent developments in the field carried out using visible light, a general overview of the mechanism in each case is offered as wellFinancial support was provided by the European Research Council (ERC-CoG, Contract Number: 647550), the Spanish Government (RTI2018-095038-B-I00), the ‘Comunidad de Madrid’ and European Structural Funds (S2018/NMT-4367). R. I. R thanks Fundación Carolina for a graduate fellowshi

Investigation of liquid water in gas diffusion layers of polymer electrolyte fuel cells using X-ray tomographic microscopy

In polymer electrolyte fuel cells (PEFCs), condensation of water within the pore network of the gas diffusion layers (GDL) can influence the gas transport properties and thus reduce the electrochemical conversion rates. The use of X-ray tomographic microscopy (XTM), which allows for a resolution in the order of one micrometer is investigated for studying ex situ the local saturation in GDL's. The strength of XTM is the high spatial resolution with simultaneous contrast for water and carbon, allowing for non-destructive 3D-imaging of the solid and the contained water. The application of this method for imaging the ex situ water intrusion into the porous network of GDLs is explored using absorption and phase contrast methods. It is shown that the inhomogeneous filling behavior of GDL materials can indeed be visualized with sufficient resolution. For Toray paper TGP-H-060 the local saturation was measured as function of the water pressure. The results, evaluated in 1D, 2D and 3D show a liquid water retention effect at the denser layers near the surface. A comparison with established capillary pressure functions is presented. Altogether, the results show the potential of the XTM-method as a tool for studying the liquid water behavior in PEFC on a microscopic scale