Demo 16. Colisión pelota de baloncesto-pelota de tenis

Objetivo: La pelota de tenis rebota hasta una altura superior a aquella desde la que fue lanzada cuando lo hace rebotando sobre la de baloncesto (no así cuando rebota en el suelo). Este fenómeno se explica apelando a la conservación de momento y energía mecánica

Demo 6. Caída de cuerpos en ausencia de aire

Objetivo: Demostrar que, en ausencia de aire (vacío parcial de aire), el tiempo de caída de los cuerpos es independiente de su masa o forma

Demo 20. Plano inclinado

Objetivo: Demostrar que el coeficiente de rozamiento sólo depende de la naturaleza de las superficies en contacto. Poner de manifiesto la diferencia entre rozamiento estático y dinámico

Demo 53. Compresión adiabática

Objetivo: Comprobación del aumento de la temperatura en una compresión adiabática irreversible

Influence of soil water content on the thermal infrared emissivity of bare soils. Implication for land surface temperature determination.

The influence of soil water content in thermal infrared emissivity is a known fact but has been poorly studied in the past. A laboratory study for quantifying the dependence of emissivity on soil moisture was carried out. Six samples of surface horizons of different soil types were selected for the experiment. The gravimetric method was chosen for determining the soil moisture, whereas the emissivity was measured at different soil water contents using the two-lid variant of the box method. As a result, the study showed that emissivity increases from 1.7% to 16% when water content becomes higher, especially in sandy soils in the 8.29.2 mm range. Accordingly, a set of equations was derived to obtain emissivity from soil moisture at different spectral bands for the analyzed mineral soils. Moreover, results showed that the spectral ratio decreases with increasing soil water content. Finally, the study showed that systematic errors from 0.1 to 2 K can be caused by soil moisture influence on emissivity

Influencia del efecto de la humedad del suelo en la emisividad del infrarrojo térmico

La influencia del efecto de la humedad del suelo en la emisividad del infrarrojo térmico es un hecho conocido pero poco estudiado en el pasado. Se ha diseñado un experimento para calcular la dependencia de la emisividad respecto a la humedad del suelo. Han sido seleccionadas seis muestras de horizontes superficiales de diferentes tipos de suelos mediterráneos. Su emisividad se ha medido con diferentes contenidos de agua de suelo, utilizando la variante de dos tapas del método de caja, mientras que el método gravimétrico ha sido seleccionado para obtener la humedad del suelo. Como resultado de esto, el estudio muestra que la emisividad aumenta significativamente cuando el contenido de agua se vuelve más alto, especialmente en suelos arenosos en el rango 8.2-9.2 μm. Se han deducido una serie de ecuaciones para obtener la emisividad de la humedad del suelo a distintas bandas espectrales para los tipos de suelo [email protected]; [email protected]; [email protected]; [email protected]; [email protected]

Effect of Soil Moisture on the Angular Variation of Thermal Infrared Emissivity of Inorganic Soils

Emissivity is influenced by different factors. This study deals with the effect of the soil moisture (SM) content on the zenithal (θ) variation of ratio-to-nadir emissivity (εr), for a wide variety of inorganic bare soils. To retrieve εr, a goniometer assembly was used, together with two identical CIMEL Electronique CE312-2 radiometers working at six spectral bands within 7.7-14.3 μm, performing simultaneous radiance measurements at different combinations of zenith and azimuth angles. The results showed that the effect of SM upon εr(θ) is different depending on the spectral range and textural composition of the sample. Sandy soils showed a decrease of εr(θ) from nadir up to 0.132 for θ ≥ 40° at 8-9.4 μm under dry conditions, but this decrease was reduced to 0.093 with the increase of SM. Clayey samples did not present dependence of εr(θ) on SM. Loamy texture samples presented a more sharp decrease of εr(θ) with the increase of SM, reaching differences between nadir values and 70 ° up to 6%, at all spectral ranges studied. Finally, a parameterization of εr with SM and θ was derived allowing to obtain ratio-to-nadir emissivities with an accuracy of ± 0.011

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

Validation of Collection 6 MODIS land surface temperature product using in situ measurements

Land surface temperature (LST) is an important physical quantity at the land-atmosphere interface. Since 2016 the Collection 6 (C6) MODIS LST product is publicly available, which includes three refinements over bare soil surfaces compared to the Collection 5 (C5) MODIS LST product. To encourage the use of the C6 MODIS LST product in a wide range of applications, it is necessary to evaluate the accuracy of the C6 MODIS LST product. In this study, we validated the C6 MODIS LST product using temperature-based method over various land cover types, including grasslands, croplands, cropland/natural vegetation mosaic, open shrublands, woody savannas, and barren/sparsely vegetated. In situ measurements were collected from various sites under different atmospheric and surface conditions, including seven SURFRAD sites (BND, TBL, DRA, FPK, GCM, PSU, and SXF) in the United States, three KIT sites (EVO, KAL, and GBB) in Portugal and Namibia, and three HiWATER sites (GBZ, HZZ, and HMZ) in China. The spatial representativeness of the in situ measurements at each site was separately evaluated during daytime and nighttime using all available clear-sky ASTER LST products at 90m spatial resolution. Only six sites during daytime are selected as sufficiently homogeneous sites despite the usually high spatial thermal heterogeneity, whereas during nighttime most sites can be considered to be thermally homogeneous and have similar LST and air temperature. The C6 MODIS LST product was validated using in situ measurements from the selected homogeneous sites during daytime and nighttime: except for the GBB site, large RMSE values (> 2 K) were obtained during daytime. However, if only satellite LST with a high spatial thermal homogeneity on the MODIS pixel scale are used for LST validation, the best daytime accuracy (RMSE<1.3 K) for the C6 MODIS LST product is achieved over the BND and DRA sites. Except for the DRA site, the RMSE values during nighttime are<2 K at the selected homogeneous sites. Furthermore, the accuracy of the C6 MODIS LST product was compared with that of the C5 MODIS LST product during nighttime at the selected homogeneous sites. Except for the GBB site, there are only small differences (< 0.4 K) between the RMSE values for the C5 and C6 MODIS LST products