Determinación de la emisividad y de la temperatura de la superficie del mar mediante radiometría térmica.

RESUMEN La medida de la temperatura de la superficie del mar (TSM) desde satélite parecía ser un problema resuelto mediante aproximaciones que partían de la homogeneidad para esta superficie. Sin embargo, en los últimos años han surgido nuevas exigencias en cuanto a la precisión en la determinación de esta magnitud clave para el estudio de los procesos de intercambio en la interfase océano-atmósfera. En esta Tesis Doctoral, y en el marco de la Misión Soil Moisture and Ocean Salinity (SMOS) de la Agencia Espacial Europea, se abordan dos temas pendientes en el campo del desarrollo de algoritmos para la determinación precisa de la TSM a partir de observaciones desde el espacio. Se propone, en primer lugar, una metodología operativa y autónoma para la medida de la TSM in situ, que pueda servir como referencia para el desarrollo y validación de dichos algoritmos. Para ello, muchos trabajos han considerado medidas realizadas mediante sondas contacto a cierta profundidad, sin embargo la estratificación térmica de la capa más superficial del océano hace que exista una discrepancia significativa y no simple entre ambas temperaturas, apuntando a la necesidad de la medida de la TSM mediante radiometría térmica. La metodología propuesta parte de un análisis de las magnitudes participantes en el modelo radiativo para la superficie del mar, con el objetivo de establecer la mejor estrategia de medida para la obtención de la TSM con la máxima precisión posible. Dicha metodología permitió la medida de la TSM con una precisión de ± 0,15 K durante las campañas WInd and Salinity Experiment (WISE) 2000 y 2001, desarrolladas en la fase experimental de la misión SMOS. En segundo lugar, la emisividad de la superficie del mar (ESM), magnitud necesaria para la determinación de la TSM a partir de observaciones radiométricas, presenta unas dependencias que, de no estar bien caracterizadas, comportarían errores importantes en dicha temperatura. Para ello, se llevaron a cabo medidas angulares de la ESM para diferentes estados de la rugosidad del mar, que permitieron estudiar sus dependencias y, además, analizar la validez de los modelos teóricos existentes para su determinación. La comparación de estos valores experimentales con el modelo de Masuda et al. (1988) demuestra que éste estima adecuadamente la ESM para ángulos de observación inferiores a 50º, pero la subestima para ángulos superiores. Sin embargo, el modelo de Wu y Smith (1997), incorporando el efecto de la emisión reflejada de la propia superficie, consigue reproducir con mayor exactitud la ESM para cualquier geometría de observación y rugosidad de ésta. Comprobada la bondad de este modelo, pero teniendo en cuenta su complejidad matemática, la cual dificulta una aplicación operativa del mismo, el paso final fue el desarrollo de una parametrización simple pero precisa para la determinación de la ESM en función del ángulo de observación y de la velocidad del viento en superficie, la cual consigue reproducir dicha emisividad con un error inferior a ± 0,0010. Además, se proporcionan los coeficientes necesarios para el uso de dicha parametrización asociada a las bandas térmicas de sensores actualmente a bordo de satélite con posible visión para ángulos elevados: AATSR-ENVISAT, AVHRR-NOAA, MODIS-EOS Aqua/Terra y SEVIRI-MSG. La inclusión de dicha parametrizacion en los algoritmos de determinación de la TSM desde satélite permitiría corregir el decrecimiento de la ESM con el ángulo de observación, además del efecto de la rugosidad, mejorando su precisión para visiones apartadas del nadir, tanto en algoritmos de tipo multicanal como multiangular. ____________________________________________________________________________________________________ SUMMARY Sea Surface Temperature (SST) measurement from satellite seems to be solved. However, a higher accuracy in the SST is required nowadays to study the interchange processes produced in the sea-atmosphere interface. This Thesis, in the framework of the Soil Moisture and Ocean Salinity (SMOS) Mission of the European Space Agency, deals with two pending issues in the development of algorithms for an accurate SST retrieval from space. First, an operational and autonomous methodology is proposed for the in situ SST measurement, which could be a reference for the development and validation of these algorithms. Most of the previous works have been using values measured by contact probes in depth, but there is a significant difference between both temperatures due to the surface thermal stratification and so a SST determination by thermal radiometry is required. The methodology development begins with an analysis of each term of the sea radiative model to establish the best measurement strategy to obtain the maximum SST accuracy. This methodology permitted us to determine SST with an uncertainty of ±0.15K during the WInd and Salinity Experiment (WISE) 2000 and 2001, carried out within the SMOS Mission. Secondly, the Sea Surface Emissivity (SSE), which is necessary for the SST retrieval from radiometric observations, shows physical dependences that need an accurate characterization. Thus, angular SSE measurements were carried out under a wide range of sea surface roughness conditions, which allowed us to study these dependences and to analyse the soundness of the theoretical models for SSE estimate. The model proposed by Masuda et al. (1988) works only for observation angles up to 50º, but the Wu and Smith model (1997) reproduces accurately SSE for any viewing geometry and surface roughness. Once the soundness of this last model was checked as well as its mathematical complexity, the final step was the development of a simple parametrization to obtain the SSE as a function of the observation angle and the surface wind speed. This operational algorithm is provided for several current satellite sensors: AATSR-ENVISAT, AVHRR-NOAA, MODIS-EOS Aqua/Terra and SEVIRI-MSG; and permits the SSE determination with an uncertainty lower than ±0.1%

Impact of Initial Soil Temperature Derived from Remote Sensing and Numerical Weather Prediction Datasets on the Simulation of Extreme Heat Events

Extreme heat weather events have received increasing attention and has become of special importance as they can remarkably affect sectors as diverse as public health, energy consumption, water resources, natural biodiversity and agricultural production. In this regard, summer temperatures have become a parameter of essential interest under a framework of a hypothetical increase in the number of intense-heat conditions. Thus, their forecast is a crucial aspect bearing in mind a mitigation of the effects and impacts that these intense-heat situations could produce. The current work tries to reach a better understanding of these sorts of situations that are really common over the Western Mediterranean coast. An extreme heat episode that took place in the Valencia Region in July 2009 is analysed, based on the simulations performed with the Regional Atmospheric Modeling System (RAMS). This event recorded maximum temperatures exceeding 40 °C amply extended over the region besides reaching minimum temperatures up to 25.92 °C. We examine the role of improved skin and soil temperature (ST) initial conditions in the forecast results by means of different modelling and satellite-derived products. The influence of incorporating the Land Surface Temperature (LST) into RAMS is not found to produce a meaningful impact on the simulation results, independently of the resolution of the dataset used in the initial conditions of the model. In contrast, the introduction of the ST in lower levels, not only the skin temperature, has a more marked decisive effect in the simulation. Additionally, we have evaluated the influence of increasing the number of soil levels to spread deeper underground. This sensitivity experiment has revealed that more soil levels do not produce any meaningful impact on the simulation compared to the original one. In any case, RAMS is able to properly capture the observed patterns in those cases where a Western advection is widely extended over the area of study. This region’s variability in orography and in distances to the sea promotes the development of sea-breeze circulations, thus producing a convergence of two opposite wind flows, a Western synoptic advection and a sea-breeze circulation. As a result, the RAMS skill in those cases where a sea breeze is well developed depends on the proper location of the boundary and convergence lines of these two flows.This work has been funded by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (FEDER) through the project CGL2015-64268-R (MINECO/FEDER, UE), by the Regional Government of Valencia through the project PROMETEOII/2014/086 and by the Spanish Ministerio de Economía y Competitividad through the project CGL2011-30433-C02-02 (MINECO)

Evapotranspiration Retrieval Using S-SEBI Model with Landsat-8 Split-Window Land Surface Temperature Products over Two European Agricultural Crops

Crop evapotranspiration (ET) is a key variable within the global hydrological cycle to account for the irrigation scheduling, water budgeting, and planning of the water resources associated with irrigation in croplands. Remote sensing techniques provide geophysical information at a large spatial scale and over a relatively long time series, and even make possible the retrieval of ET at high spatiotemporal resolutions. The present short study analyzed the daily ET maps generated with the S-SEBI model, adapted to Landsat-8 retrieved land surface temperatures and broadband albedos, at two different crop sites for two consecutive years (2017-2018). Maps of land surface temperatures were determined using Landsat-8 Collection 2 data, after applying the split-window (SW) algorithm proposed for the operational SW product, which will be implemented in the future Collection 3. Preliminary results showed a good agreement with ground reference data for the main surface energy balance fluxes Rn and LE, and for daily ET values, with RMSEs around 50 W/m2 and 0.9 mm/d, respectively, and high correlation coefficient (R2 = 0.72-0.91). The acceptable uncertainties observed when comparing with local ground data were reaffirmed after the regional (spatial resolution of 9 km) comparison with reanalysis data obtained from ERA5-Land model, showing a StDev of 0.9 mm/d, RMSE = 1.1 mm/d, MAE = 0.9 mm/d, and MBE = −0.3 mm/d. This short communication tries to show some preliminary findings in the framework of the ongoing Tool4Extreme research project, in which one of the main objectives is the understanding and characterization of the hydrological cycle in the Mediterranean region, since it is key to improve the management of water resources in the context of climate change effects

Spatial and temporal patterns of the stability and humidity terms in the Haines index to improve the estimate of forest fire risk in the Valencia region of Spain

Ponencia presentada en: IX Congreso de la Asociación Española de Climatología celebrado en Almería entre el 28 y el 30 de octubre de 2014.[EN]The assessment of risk index in the propagation and evolution of a hypothetical forest fire is commonly based on stability and moisture content at different atmospheric levels. The Haines Index combines these terms to determine the environmental potential for wildfire growth. In this study the environmental stability and humidity associated with the lower atmospheric layers in the Western Mediterranean Basin are investigated by analysing Haines Index calculations over a 29 year period.[ES]La evaluación del índice de riesgo en la propagación y evolución de un hipotético incendio forestal está basada habitualmente en la estabilidad y el contenido de humedad en los diferentes niveles atmosféricos. El Índice de Haines combina estos términos para determinar el potencial ambiental en el desarrollo de un incendio forestal. En este estudio la estabilidad ambiental y la humedad asociada a las capas atmosféricas más bajas de la cuenca del Mediterráneo occidental se investigan mediante el análisis del cálculo del Índice de Haines durante un período de 29 años.We thank NCEP/NCAR for supplying the data necessary for this study. This study was supported by the Spanish Ministry of Innovation and Science (projects CGL2010-16364, CGL2011-30433-C02 and GRACCIE Consolider-Ingeio 2010; and Dr. Niclòs "Ramón y Cajal"Research Contract) and Generalitat Valenciana (Prometeo/2009/006 FEEDBACKS project). The Instituto Universitario CEAM-UMH is partly supported by the Generalitat

RAMS-forecasts comparison of typical summer atmospheric conditions over the Western Mediterranean coast

The Regional Atmospheric Modeling System (RAMS) has been used in order to perform a high-resolution numerical simulation of two meteorological events related to the most common atmospheric environments during the summer over the Western Mediterranean coast: mesoscale circulations and western synoptic advections. In this regard, we take advantage of the operational RAMS configuration running within the real-time forecasting system environment already implemented over this Mediterranean area, precisely in the Valencia Region and nearby areas. The attention of this paper is especially focused on identifying the main features of both events and the ability of the model in resolving the associated characteristics as well as in performing a comprehensive evaluation of the model by means of diverse meteorological observations available within the selected periods over the area of study. Additionally, as this paper is centred in RAMS-based forecasts, two simulations are operated applying the most two recent versions of the RAMS model implemented in the above-mentioned system: RAMS 4.4 and RAMS 6.0. Therefore, a comparison among both versions of the model has been performed as well. Finally, it is our intention to contrast the RAMS forecasts for two completely different atmospheric conditions common with the area of study in the summer. A main difference between the simulation of both meteorological situations has been found in the humidity. In this sense, whilst the model underestimates this magnitude considering the mesoscale event, especially at night time, the model reproduces the daily humidity properly under the western synoptic advection

Land surface air temperature retrieval from EOS-MODIS images

The knowledge of the spatial and temporal patterns of Surface Air Temperature (SAT) is essential to monitor a region¿s climate and meteorology, quantify surface exchange processes, improve climatic and meteorological model results, and study health and economic impacts. This work analyzed correlations between SAT and geophysical land surface variables, Land Surface Temperature (LST) mainly, to establish operative techniques to obtain spatially-continuous land SAT maps from satellite data, unlike data provided by meteorological station networks. The correlations were analyzed by using EOS-MODIS images, meteorological station network data, and geographical variables. Linear regressions with MODIS-retrieved LST data gave SAT with uncertainties higher than ±2K during daytime and of ±1.8K at night-time. Nevertheless, SAT uncertainties decreased up to ±1.2K when other satellite-retrieved surface parameters, i.e. vegetation index and albedo, together with meteorological and geographical data were considered as terms of multivariable regressions. The equations finally proposed were shown to work properly for different land covers

Evaluation of the MOD16A2 evapotranspiration product in an agricultural area of Argentina, the Pampas region

The Pampas Region is a big plain of approximately 520,000 km2 in Argentina. It is essential to estimate evapotranspiration (ET) in this region since the primary productivity is directly linked to water availability. Information provided by satellite missions allows monitoring the spatial and temporal variability of ET. In the current study, we evaluated the version 006 of MOD16A2 product (MOD16A2.006) of Potential Evapotranspiration (ETp) and Actual Evapotranspiration (ETa) in Argentinian Pampas Region (APR). MOD16A2.006 product was compared with Crop Evapotranspiration (ETc), calculated with local measurements from the Oficina de Riesgo Agropecuario (ORA), and Crop Coefficient (Kc) data (function of Normalized Difference Vegetation Index (NDVI)) in seven stations in the APR from 2009 to 2018. We evaluated ETa at two temporal scales: accumulated values (mm) per growth stages (soybean crop), and 8-day accumulated values (mm8d−1). The results showed a systematic overestimation around 65% for ETp(MOD16A2.006) (found and eliminated by means of a linear function) and underestimation (in most stations) for ETa(MOD16A2.006) in accumulated values per growth stages. Respect to mm8d−1, no systematic error was observed, but the relationship ETa(ORA) − ETa(MOD16A2.006) for soybean crop behaves similarly throughout APR

Thermal-infrared spectral and angular characterization of crude oil and seawater emissivities for oil slick identification

Previous work has shown that crude oil emissivity is lower than that of seawater in the thermal-infrared (TIR) spectrum. Thus, oil slicks cause an emissivity decrease relative to seawater in that region. The aim of this paper was to carry out experimental measurements to characterize crude oil and seawater emissivity spectral and angular variations. The results showed that crude oil emissivity is lower than seawater emissivity and essentially flat in the 8 - 13 μm atmospheric window. Crude oil emissivity has a marked emissivity decrease with angle (from 0.956±0.005 at 15º to 0.873±0.007 at 65º), even higher than that of seawater, and thus the seawater-crude emissivity difference increases with angle (from +0.030±0.007 at close-to-nadir angles up to +0.068±0.010 in average at 65º). In addition, the experimental results were checked by using the dual-angle viewing capability of the ENVISAT-AATSR images (i.e., 0º-22º and 53º-55º for nadir and forward views respectively), with data acquired during the BP Deepwater Horizon oil slick in 2010. The objective was to explore the applicability to satellite observations. Nadir-forward emissivity differences of +0.028 and +0.017 were obtained for the oil slick and surrounding clean seawater respectively. Emissivity differences between the seawater and oil slick were +0.035 and +0.046 for nadir and forward views respectively, in agreement with the experimental data. The increase of seawater-crude emissivity difference with angle gives significant differences for off-nadir observation angles, showing a new chance of crude oil slick identification from satellite TIR data

Cálculo de la evapotranspiración real diaria en la zona norte de Finlandia empleando técnicas de teledetección

J. M. Sánchez Tomás ([email protected])Hasta hace poco tiempo el estudio de la evapotranspiración (LE), fundamental en la ecuación de balance de energía, excluía zonas forestales debido a las dificultades experimentales de la toma de medidas en estas regiones. La teledetección acabó con dichas dificultades, facilitando el estudio de la LE real dentro de estas zonas, que suponen en torno a un 30% de toda la superficie terrestre. En este trabajo se presenta un método operativo para determinar la LE real a partir de medidas de temperatura de la superficie realizadas desde satélite. Este estudio se llevó a cabo de abril a junio de 2002 en Sodankylä, una región de bosque boreal en el norte de Finlandia, dentro del proyecto SIFLEX-2002 (Solar Induced Fluorescence Experiment-2002). Se ha realizado una validación del método, comparándolo con otras técnicas, y se ha obtenido para la zona de estudio un valor medio de LE diaria (LEd) de 2,6±0,5 mm/día. Finalmente hemos aplicado el método a una imagen del satélite Landsat 7-ETM+ de la zona para obtener un mapa de LEd a escala regional

Evaluation of landsat-8 thermal bands to monitor land surface temperature

Ponencia presentada en: IX Congreso de la Asociación Española de Climatología celebrado en Almería entre el 28 y el 30 de octubre de 2014.[ES]El nuevo Thermal Infrared Sensor (TIRS) a bordo del Landsat-8 (L8) dispone de dos bandas térmicas, 10 (11.60-11.19 μm) y 11 (11.50-12.51 μm), con una resolución espacial de 100m, con el fin de proporcionar temperaturas de la superficie terrestre (LST) de una manera más precisa que su predecesor Landsat-7 ETM+. El L8 fue lanzado en febrero de 2013, comenzando su adquisición operativa a mediados de abril. Los primeros estudios realizados por el equipo de calibración de L8 mostraron errores sistemáticos significativos para el TIRS, y en febrero de 2014 el archivo de imágenes L8 TIRS fue reprocesado para corregir dichos errores. En este estudio, con el fin de comprobar la calibración del L8 TIRS, realizamos medidas de campo en una zona llana y térmicamente homogénea dedicada al cultivo del arroz. A partir de estas medidas de LST simulamos las radiancias y temperaturas de brillo a nivel del satélite y las comparamos con los datos TIRS. Tal y como apuntaba el equipo de L8, nuestros resultados muestran una sobreestimación para la banda 11. Sin embargo, el recalibrado aplicado por dicho equipo para ambas bandas ha resultado no ser satisfactorio en nuestra zona experimental, ya que proponen sustraer errores sistemáticos mayores a los requeridos.[EN]The new Landsat-8 (L8) Thermal Infrared Sensor (TIRS) has two thermal bands, 10 (11.60- 11.19 μm) and 11 (11.50-12.51 μm) at 100-m spatial resolution, aimed to provide more accurate Land Surface Temperatures (LST) than Landsat-7 ETM+. L8 was launched on February 2013, and operational acquisitions started in middle April 2013. The first studies by the L8 Calibration Team showed significant TIRS temperature offsets, and in February 2014 the L8 TIRS archive was reprocessed to remove these offsets. In this study, ground LST measurements were performed in a flat and thermally homogeneous area of rice-crop fields for checking the calibration of the L8 TIRS bands. At-sensor radiances and brightness temperatures were simulated from ground-measured LSTs and compared with TIRS values. A significant overestimation was observed for band 11, in agreement with the L8 Calibration Team results. However, their recalibration was shown unsatisfactory in our test site for both bands, since they proposed subtracting higher offsets than required.This study was supported by the Spanish Ministerio de Economía y Competitividad (projects CGL2010-16364, CGL2010-17577/CLI, CGL2011-13579-E, CGL2011-30433 and GRACCIE Consolider-Ingenio 2010; and Dr. Niclòs "Ramón y Cajal" Research Contract) and Generalitat Valenciana (PROMETEO/2009/006 and PROMETEO/2009/086 projects)