Fernando Paz Pellat

Correcciones atmosféricas relativas de imágenes de satélite: patrones invariantes y modelos atmosféricos

To use information obtained with satellite technology reliably, it is necessary to eliminate or reduce the disruptive effects associated with the spectral information captured by sensors on space platforms. In this paper we analyze the inversion of radiative models of the atmosphere, which consists in determining the additive and multiplicative constants in each spectral band to make the necessary atmospheric corrections. The methodology proposes the use of invariant patterns of soil lines and dense vegetation for the inversion of radiative models. The results showed that, without knowledge of the atmospheric model or the type of aerosol, soil line data were relatively insufficient (low correlation) to obtain the additive and multiplicative constants of the atmospheric inversions, with problems of multiple solutions in the inversion process. Under similar conditions, the same was found for additive constants with the dense vegetation line, but for the multiplicative constants the results were favorable (R2 > 0.9). In contrast, with the knowledge of the atmospheric model and the aerosol model, estimates of additive and multiplicative constants were highly satisfactory (R2 > 0.99) in both cases. For soil line inversions, only one constraint of the two available was used. In conclusion, the use of invariant soil-line patterns allows us to establish two basic relationships to invert the radiative simulations of the atmosphere, prior to functional compaction, and field measurements can be made so that the proposed atmospheric correction process in this work can be considered in absolute and not relative terms.

Experiencia mexicana en el diseño de seguros ganaderos paramétricos satelitales de tipo catastrófico: bases conceptuales y teóricas

The development of instruments for climate risk management allows implementation of actions to adapt to climate change as well to make eff icient use of f inancial resources to mitigate its impacts. In Mexico, the use of these instruments has not been documented. For this reason, this paper develops a conceptual-theoretical framework for instrumentation of remote sensing satellite parametric insurance to present its advantages and limitations in scope. To this end, the concept of risk unit, payment threshold and insurance-associated elements were applied to establish the climate risk associated with agricultural (livestock) activities, mainly drought. Under the critical requirement of a linear relationship between spectral index and the plant biomass without additive constant, an optimized NDVIcp spectral index was used, which resulted in the development of a technically sound insurance scheme that did not require historical information on livestock production. Moreover, it accurately reflects the reality in the f ield. Finally, the framework allowed setting the bases for designing catastrophic-type satellital parametric livestock insurance that is solid, transparent, and conceptually accessible to its users.

Validación del modelo expo-lineal precipitación-escurrimiento en un simulador de lluvia.

La necesidad de desarrollar metodos simplif icados, operativos y coherentes para modelar la relacion precipitacion-escurrimiento a escala de eventos, permanece como uno de los grandes retos en el campo de la hidrologia. Si bien existen propuestas simples de modelacion como el metodo del Numero de Curva o NC, sus bases teoricas no tienen fundamentos hidrologicos. La ventaja del metodo del NC es que solo requiere de un parametro, lo cual lo hace muy atractivo en las aplicaciones. En este trabajo se analizan las bases del metodo del NC. Los resultados muestran que estos intentos simplif icados de modelacion estan limitados. Por otro lado, el modelo expo-lineal de Paz (2013) es flexible en terminos empiricos. Las bases teoricas de este modelo son discutidas en terminos de la hidrologia de area variable, en un formato suf icientemente general para hacer solido su uso. El modelo se aplico a un experimento en un simulador de lluvias con lotes de escurrimiento con diferentes tipos de suelo y coberturas aereas de pastos. Los resultados mostraron un buen ajuste experimental a los datos, particularmente en terminos de parametrizar el modelo expo-lineal en forma similar al metodo del NC. De estos desarrollos, se presenta un esquema de estimacion de los parametros del modelo expo-lineal que se puede usar en forma equivalente, por su simplicidad al tener un solo parametro libre, al metodo del NC.

An alternative approach in hydrograph decomposition and separation of the baseflow

Abstract The identification of the moment when direct flow ends and baseflow begins is one of the biggest challenges of hydrological cycle modeling. The objectives of this research were: to characterize the recession curves (RC) and to separate the components of the hydrograph in a compact model. The RC were extracted from time series in three subwatersheds in Mexico. An expo-linear model was adapted and fitted to the master recession curves to find the transition point of the hydrograph and separate the baseflow. The model discriminated the RC in two decreasing ratios: one linear associated to the direct flow, and one exponential linked to the baseflow. The transition point between these two flows was obtained analytically by equaling both ratios. The derivation of a model parameter allowed to find the maximum points in the hydrometric time series, which were the criterion to separate the baseflow. The application of this model is recommended in the analysis of RC with different magnitudes from the flexibility and attachment to the fundaments of exhaustion of a reservoir.