An electromagnetic simulator for sentinel-3 sar altimeter waveforms over land part ii: forests

Forests play a crucial role in the climate change mitigation by acting as sinks for carbon and, consequently, reducing the CO2 concentration in the atmosphere and slowing global warming. For this reason, above ground biomass (AGB) estimation is essential for effectively monitoring forest health around the globe. Although remote sensing–based forest AGB quantification can be pursued in different ways, in this work we discuss a new technique for vegetation observation through the use of altimetry data that has been introduced by the ESA-funded ALtimetry for BIOMass (ALBIOM) project. ALBIOM investigates the possibility of retrieving forest biomass through Copernicus Sentinel-3 Synthetic Aperture Radar Altimeter (SRAL) measurements at Ku- and C-bands in low- and high-resolution mode. To reach this goal, a simulator able to reproduce the altimeter acquisition system and the scattering phenomena that occur in the interaction of the radar altimeter pulse with vegetated surfaces has been developed. The Tor Vergata Vegetation Scattering Model (TOVSM) developed at Tor Vergata University has been exploited to simulate the contribution from the vegetation volume via the modelling of the backscattering of forest canopy through a discrete scatterer representation. A modification of the SAVERS (Soil And Vegetation Reflection Simulator) simulator developed by the team for Global Navigation Satellite System Reflectometry over land has also been taken into account to simulate the soil contribution

Sentinel-3 Delay-Doppler altimetry over Antarctica

The launch of Sentinel-3A in February 2016 represented the beginning of a new long-term series of operational satellite radar altimeters, which will provide Delay-Doppler altimetry measurements over ice sheets for decades to come. Given the potential benefits that these satellites can offer to a range of glaciological applications, it is important to establish their capacity to monitor ice sheet elevation and elevation change. Here, we present the first analysis of Sentinel-3 Delay-Doppler altimetry over the Antarctic ice sheet, and assess the accuracy and precision of retrievals of ice sheet elevation across a range of topographic regimes. Over the low-slope regions of the ice sheet interior, we find that the instrument achieves both an accuracy and a precision of the order of 10 cm, with ∼98 % of the data validated being within 50 cm of co-located airborne measurements. Across the steeper and more complex topography of the ice sheet margin, the accuracy decreases, although analysis at two coastal sites with densely surveyed airborne campaigns shows that ∼60 %–85 % of validated data are still within 1 m of co-located airborne elevation measurements. We then explore the utility of the Sentinel-3A Delay-Doppler altimeter for mapping ice sheet elevation change. We show that with only 2 years of available data, it is possible to resolve known signals of ice dynamic imbalance and to detect evidence of subglacial lake drainage activity. Our analysis demonstrates a new, long-term source of measurements of ice sheet elevation and elevation change, and the early potential of this operational system for monitoring ice sheet imbalance for decades to come

Spatio-temporal dynamics of four species of staurastrum (meyen 1829, emend. Ralfs 1848) in a colombian eutrophic reservoir

Se estudió la dinámica de cuatro especies del género Staurastrum en el embalse Riogrande II (6º 35’ 57’’ y 6º 28’ 79’’N y los 75o 32’ 17’’ y 75º 25’ 85’’O), un embalse eutrófico colombiano, en las escalas espacial y temporal. Las estaciones de muestreo fueron cinco: Presa, Río Grande abajo, Río Chico abajo, Río Chico arriba y Quebrada Las Ánimas. Los muestreos se realizaron cada diez días entre julio de 2002 y julio de 2003. Staurastrum es una desmidia característica de ambientes oligotróficos con pH generalmente bajo; sin embargo, el embalse evaluado es eutrófico. La especie más abundante y más ampliamente distribuida fue S. paradoxum. Los resultados muestran que las cuatro especies fueron altamente dinámicas en el tiempo (CV > 100%) y se distribuyeron contagiosamente en el espacio hacia la estación de mayor eutrofia (Río Chico arriba), principalmente S. gracile (k medio = 2). S. paradoxum presentó un valor de similitud muy pequeño (0.18) con respecto al grupo formado por S. gracile, i>S. tetracerum y S. longipes. El CO2 libre (R = 0.83), la pluviosidad (R = 0.62) y la clorofila a (R = 0.58) incidieron positivamente en la ecología de las especies estudiadas; y negativamente el gradiente lumínico (R = - 0.68). Ninguna de las formas de nutrientes consideradas se asoció significativamente con las variaciones de sus densidades. El comportamiento de las especies se explica por la Teoría del no equilibrio de Harris (1978), donde la estocasticidad del ambiente hace menos severa la competencia entre ellas. La fuerza que dirige la dinámica de estos désmidos es la atelomixis parcial del embalse, que permite que estas microalgas permanezcan en suspensión en la columna de agua. Se constituyeron, dos grupos de especies con estrategias ecológicas combinadas de aprovechamiento del ambiente: el primero, S. gracile, se clasificó como un estratega de la forma transicional R-S, mejor adaptado a las estaciones más eutrofizadas (Río Chico y Río Grande), mientras que la tríada S. longipes-S. paradoxum-S. tetracerum se ajustó más a la estrategia transicional C-S.Dynamics of four species of Staurastrum (Meyen 1829, emend. Ralfs 1848) in Riogrande II reservoir (6 o 35 '57'' - 6 o 28' 79''N; 75 o 32 '17'' - 75 o 25' 85''W) in the spatial and temporal scales were carried out. Sampling stations were five: Dam, Río Grande downstream, Río Chico downstream, Río Chico upstream and Ánimas. Samples were taken every ten days between July 2002 and July 2003. Staurastrum is a characteristic desmid of oligotrophic environments with low pH; however, the reservoir evaluated is an eutrophic one. The most abundant and widely distributed was S. paradoxum. The results show that these four species were highly dynamic over time (CV> 100%) and contagiously distributed in space up to the most eutrophic station (Río Chico upstream), mainly S. gracile (k mean = 2). S. paradoxum showed a very small similarity value (0.18) with respect to the group formed by S. gracile, S. tetracerum and S. longipes. Free CO2 (R = 0.83), rainfall (R = 0.62) and chlorophyll a (R = 0.58) impacted positively on the ecology of the species studied; and negatively light gradient (R = - 0.68). None of the forms of nutrients considered was significantly associated with changes in their densities. The behavior of species is explained by Harris' non-equilibrium theory' where environmental stochasticity makes less severe the competition between them. The driving force behind the dynamics of these desmids is the partial atelomixis which allows these algae to stay suspended in the water column. They formed two groups of species with mixed ecological strategies to use the environment: first, S. gracile, was classified as a transitional form strategist R-S, better adapted to more eutrophic stations (Rio Chico and Rio Grande), while the triad S. longipes-S. paradoxum-S. tetracerum adjusted more to the C-S transitional strategy.Facultad de Ciencias Naturales y Muse

Spatio-temporal dynamics of four species of staurastrum (meyen 1829, emend. Ralfs 1848) in a colombian eutrophic reservoir

Se estudió la dinámica de cuatro especies del género Staurastrum en el embalse Riogrande II (6º 35’ 57’’ y 6º 28’ 79’’N y los 75o 32’ 17’’ y 75º 25’ 85’’O), un embalse eutrófico colombiano, en las escalas espacial y temporal. Las estaciones de muestreo fueron cinco: Presa, Río Grande abajo, Río Chico abajo, Río Chico arriba y Quebrada Las Ánimas. Los muestreos se realizaron cada diez días entre julio de 2002 y julio de 2003. Staurastrum es una desmidia característica de ambientes oligotróficos con pH generalmente bajo; sin embargo, el embalse evaluado es eutrófico. La especie más abundante y más ampliamente distribuida fue S. paradoxum. Los resultados muestran que las cuatro especies fueron altamente dinámicas en el tiempo (CV > 100%) y se distribuyeron contagiosamente en el espacio hacia la estación de mayor eutrofia (Río Chico arriba), principalmente S. gracile (k medio = 2). S. paradoxum presentó un valor de similitud muy pequeño (0.18) con respecto al grupo formado por S. gracile, i>S. tetracerum y S. longipes. El CO2 libre (R = 0.83), la pluviosidad (R = 0.62) y la clorofila a (R = 0.58) incidieron positivamente en la ecología de las especies estudiadas; y negativamente el gradiente lumínico (R = - 0.68). Ninguna de las formas de nutrientes consideradas se asoció significativamente con las variaciones de sus densidades. El comportamiento de las especies se explica por la Teoría del no equilibrio de Harris (1978), donde la estocasticidad del ambiente hace menos severa la competencia entre ellas. La fuerza que dirige la dinámica de estos désmidos es la atelomixis parcial del embalse, que permite que estas microalgas permanezcan en suspensión en la columna de agua. Se constituyeron, dos grupos de especies con estrategias ecológicas combinadas de aprovechamiento del ambiente: el primero, S. gracile, se clasificó como un estratega de la forma transicional R-S, mejor adaptado a las estaciones más eutrofizadas (Río Chico y Río Grande), mientras que la tríada S. longipes-S. paradoxum-S. tetracerum se ajustó más a la estrategia transicional C-S.Dynamics of four species of Staurastrum (Meyen 1829, emend. Ralfs 1848) in Riogrande II reservoir (6 o 35 '57'' - 6 o 28' 79''N; 75 o 32 '17'' - 75 o 25' 85''W) in the spatial and temporal scales were carried out. Sampling stations were five: Dam, Río Grande downstream, Río Chico downstream, Río Chico upstream and Ánimas. Samples were taken every ten days between July 2002 and July 2003. Staurastrum is a characteristic desmid of oligotrophic environments with low pH; however, the reservoir evaluated is an eutrophic one. The most abundant and widely distributed was S. paradoxum. The results show that these four species were highly dynamic over time (CV> 100%) and contagiously distributed in space up to the most eutrophic station (Río Chico upstream), mainly S. gracile (k mean = 2). S. paradoxum showed a very small similarity value (0.18) with respect to the group formed by S. gracile, S. tetracerum and S. longipes. Free CO2 (R = 0.83), rainfall (R = 0.62) and chlorophyll a (R = 0.58) impacted positively on the ecology of the species studied; and negatively light gradient (R = - 0.68). None of the forms of nutrients considered was significantly associated with changes in their densities. The behavior of species is explained by Harris' non-equilibrium theory' where environmental stochasticity makes less severe the competition between them. The driving force behind the dynamics of these desmids is the partial atelomixis which allows these algae to stay suspended in the water column. They formed two groups of species with mixed ecological strategies to use the environment: first, S. gracile, was classified as a transitional form strategist R-S, better adapted to more eutrophic stations (Rio Chico and Rio Grande), while the triad S. longipes-S. paradoxum-S. tetracerum adjusted more to the C-S transitional strategy.Facultad de Ciencias Naturales y Muse

Spatio-temporal dynamics of four species of staurastrum (meyen 1829, emend. Ralfs 1848) in a colombian eutrophic reservoir

Se estudió la dinámica de cuatro especies del género Staurastrum en el embalse Riogrande II (6º 35’ 57’’ y 6º 28’ 79’’N y los 75o 32’ 17’’ y 75º 25’ 85’’O), un embalse eutrófico colombiano, en las escalas espacial y temporal. Las estaciones de muestreo fueron cinco: Presa, Río Grande abajo, Río Chico abajo, Río Chico arriba y Quebrada Las Ánimas. Los muestreos se realizaron cada diez días entre julio de 2002 y julio de 2003. Staurastrum es una desmidia característica de ambientes oligotróficos con pH generalmente bajo; sin embargo, el embalse evaluado es eutrófico. La especie más abundante y más ampliamente distribuida fue S. paradoxum. Los resultados muestran que las cuatro especies fueron altamente dinámicas en el tiempo (CV > 100%) y se distribuyeron contagiosamente en el espacio hacia la estación de mayor eutrofia (Río Chico arriba), principalmente S. gracile (k medio = 2). S. paradoxum presentó un valor de similitud muy pequeño (0.18) con respecto al grupo formado por S. gracile, i>S. tetracerum y S. longipes. El CO2 libre (R = 0.83), la pluviosidad (R = 0.62) y la clorofila a (R = 0.58) incidieron positivamente en la ecología de las especies estudiadas; y negativamente el gradiente lumínico (R = - 0.68). Ninguna de las formas de nutrientes consideradas se asoció significativamente con las variaciones de sus densidades. El comportamiento de las especies se explica por la Teoría del no equilibrio de Harris (1978), donde la estocasticidad del ambiente hace menos severa la competencia entre ellas. La fuerza que dirige la dinámica de estos désmidos es la atelomixis parcial del embalse, que permite que estas microalgas permanezcan en suspensión en la columna de agua. Se constituyeron, dos grupos de especies con estrategias ecológicas combinadas de aprovechamiento del ambiente: el primero, S. gracile, se clasificó como un estratega de la forma transicional R-S, mejor adaptado a las estaciones más eutrofizadas (Río Chico y Río Grande), mientras que la tríada S. longipes-S. paradoxum-S. tetracerum se ajustó más a la estrategia transicional C-S.Dynamics of four species of Staurastrum (Meyen 1829, emend. Ralfs 1848) in Riogrande II reservoir (6 o 35 '57'' - 6 o 28' 79''N; 75 o 32 '17'' - 75 o 25' 85''W) in the spatial and temporal scales were carried out. Sampling stations were five: Dam, Río Grande downstream, Río Chico downstream, Río Chico upstream and Ánimas. Samples were taken every ten days between July 2002 and July 2003. Staurastrum is a characteristic desmid of oligotrophic environments with low pH; however, the reservoir evaluated is an eutrophic one. The most abundant and widely distributed was S. paradoxum. The results show that these four species were highly dynamic over time (CV> 100%) and contagiously distributed in space up to the most eutrophic station (Río Chico upstream), mainly S. gracile (k mean = 2). S. paradoxum showed a very small similarity value (0.18) with respect to the group formed by S. gracile, S. tetracerum and S. longipes. Free CO2 (R = 0.83), rainfall (R = 0.62) and chlorophyll a (R = 0.58) impacted positively on the ecology of the species studied; and negatively light gradient (R = - 0.68). None of the forms of nutrients considered was significantly associated with changes in their densities. The behavior of species is explained by Harris' non-equilibrium theory' where environmental stochasticity makes less severe the competition between them. The driving force behind the dynamics of these desmids is the partial atelomixis which allows these algae to stay suspended in the water column. They formed two groups of species with mixed ecological strategies to use the environment: first, S. gracile, was classified as a transitional form strategist R-S, better adapted to more eutrophic stations (Rio Chico and Rio Grande), while the triad S. longipes-S. paradoxum-S. tetracerum adjusted more to the C-S transitional strategy.Facultad de Ciencias Naturales y Muse

MAVEN IUVS observations of the aftermath of the Comet Siding Spring meteor shower on Mars

We report the detection of intense emission from magnesium and iron in Mars' atmosphere caused by a meteor shower following Comet Siding Spring's close encounter with Mars. The observations were made with the Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile EvolutioN spacecraft orbiting Mars. Ionized magnesium caused the brightest emission from the planet's atmosphere for many hours, resulting from resonant scattering of solar ultraviolet light. Modeling suggests a substantial fluence of low-density dust particles 1-100μm in size, with the large amount and small size contrary to predictions. The event created a temporary planet-wide ionospheric layer below Mars' main dayside ionosphere. The dramatic meteor shower response at Mars is starkly different from the case at Earth, where a steady state metal layer is always observable but perturbations caused by even the strongest meteor showers are challenging to detect

Sea level along the world’s coastlines can be measured by a network of virtual altimetry stations

For nearly 30 years, space-based radar altimetry has been routinely measuring changes in sea level at global and regional scales. But this technique designed for the open ocean does not provide reliable sea level data within 20 km to the coast, mostly due to land contamination within the radar echo in the vicinity of the coast. This problem can now be overcome through dedicated reprocessing, allowing the retrieval of valid sea level data in the 0-20 km band from the coast, and then the access to novel information on sea level change in the world coastal zones. Here we present sea level anomalies and associated coastal sea level trends at 756 altimetry-based virtual coastal stations located along the coasts of North and South America, Northeast Atlantic, Mediterranean Sea, Africa, North Indian Ocean, Asia and Australia. This new dataset, derived from the reprocessing of high-resolution (300 m) along-track altimetry data from the Jason-1, 2 and 3 missions from January 2002 to December 2019, allows the analysis of the decadal evolution of coastal sea level and fills the coastal gap where sparse sea level information is currently available