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Inside the hydro-physics processes at the plunge point location: an analysis by satellite and in situ data
A. T. Assireu,E. Alcantara,E. M. L. M. Novo,F. Roland
Hydrology and Earth System Sciences Discussions , 2011, DOI: 10.5194/hessd-8-1193-2011
Abstract: The plunge point locates the main point of mixing between river and the epilimnion reservoir water. The plunge point monitoring is essential to understand how it will be the behavior of density currents and its implications for reservoir. The applicability of satellite imagery products from different sensors (Landsat TM band 6 thermal signatures and visible channel) for characterization of the river-reservoir transition zone is presented in this study. We demonstrate the feasibility of the Landsat TM band imagery to discern the subsurface river plumes and the plunge point. The spatial variability of the plunge point evident in the hydrologic data illustrates the advantages of synoptic satellite measurements over in situ point measurements alone to detect the river-reservoir transition zone. It is indicated that the river flowing as underflow contributes to the thermal stability of the water column during wet season (summer-autumn). During the dry season, when the river-reservoir water temperature differences vanish and the river circulation is characterized by interflow-overflow, the river water inserts into the reservoir upper layers, affecting water quality. The results indicate good agreement between hydrologic and satellite data and that the jointly use of thermal and visible channel, operational monitoring of plunge point is feasible. The deduced information about the density current from this product could potentially be assimilated for numerical modeling and hence be of significant interest for environmental and climatological research.
On the Orbits of Infalling Satellite Halos  [PDF]
Andrew R. Wetzel
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17877.x
Abstract: The orbital properties of infalling satellite halos set the initial conditions which control the subsequent evolution of subhalos and the galaxies that they host, with implications for mass stripping, star formation quenching, and merging. Using a high-resolution, cosmological N-body simulation, I examine the orbital parameters of satellite halos as they merge with larger host halos, focusing primarily on orbital circularity and pericenter. I explore in detail how these orbital parameters depend on mass and redshift. Satellite orbits become more radial and plunge deeper into their host halo at higher host halo mass, but they do not significantly depend on satellite halo mass. Additionally, satellite orbits become more radial and plunge deeper into their host halos at higher redshift. I also examine satellite velocities, finding that most satellites infall with less specific angular momentum than the host halo virial value, but that satellites are `hotter' than the host virial velocity. I discuss the implications of these results to the processes of galaxy formation and evolution, and I provide fitting formulas to the mass and redshift dependence of satellite orbital circularity and pericenter.
The retrieval of cloud microphysical properties using satellite measurements and an in situ database  [cached]
Christophe Poix,Guy Febvre,Anne Fouilloux,Howard Larsen
Annales Geophysicae (ANGEO) , 2003,
Abstract: By combining AVHRR data from the NOAA satellites with information from a database of in situ measurements, large-scale maps can be generated of the microphysical parameters most immediately significant for the modelling of global circulation and climate. From the satellite data, the clouds can be classified into cumuliform, stratiform and cirrus classes and then into further sub-classes by cloud top temperature. At the same time a database of in situ measurements made by research aircraft is classified into the same sub-classes and a statistical analysis is used to derive relationships between the sub-classes and the cloud microphysical properties. These two analyses are then linked to give estimates of the microphysical properties of the satellite observed clouds. Examples are given of the application of this technique to derive maps of the probability of occurrence of precipitating clouds and of precipitating water content derived from a case study within the International Cirrus Experiment (ICE) held in 1989 over the North Sea.
Fine-scale features on the sea surface in SAR satellite imagery – Part 1: Simultaneous in-situ measurements  [PDF]
A. Soloviev,C. Maingot,S. Matt,R. E. Dodge
Ocean Science Discussions (OSD) , 2012, DOI: 10.5194/osd-9-2885-2012
Abstract: This work is aimed at identifying the origin of fine-scale features on the sea surface in synthetic aperture radar (SAR) imagery with the help of in-situ measurements as well as numerical models (presented in a companion paper). We are interested in natural and artificial features starting from the horizontal scale of the upper ocean mixed layer, around 30–50 m. These features are often associated with three-dimensional upper ocean dynamics. We have conducted a number of studies involving in-situ observations in the Straits of Florida during SAR satellite overpass. The data include examples of sharp frontal interfaces, wakes of surface ships, internal wave signatures, as well as slicks of artificial and natural origin. Atmospheric processes, such as squall lines and rain cells, produced prominent signatures on the sea surface. This data has allowed us to test an approach for distinguishing between natural and artificial features and atmospheric influences in SAR images that is based on a co-polarized phase difference filter.
Towards a merged satellite and in situ fluorescence ocean chlorophyll product
H. Lavigne, F. D'Ortenzio, H. Claustre,A. Poteau
Biogeosciences (BG) & Discussions (BGD) , 2012,
Abstract: Understanding the ocean carbon cycle requires a precise assessment of phytoplankton biomass in the oceans. In terms of numbers of observations, satellite data represent the largest available data set. However, as they are limited to surface waters, they have to be merged with in situ observations. Amongst the in situ data, fluorescence profiles constitute the greatest data set available, because fluorometers have operated routinely on oceanographic cruises since the 1970s. Nevertheless, fluorescence is only a proxy of the total chlorophyll a concentration and a data calibration is required. Calibration issues are, however, sources of uncertainty, and they have prevented a systematic and wide range exploitation of the fluorescence data set. In particular, very few attempts to standardize the fluorescence databases have been made. Consequently, merged estimations with other data sources (e.g. satellite) are lacking. We propose a merging method to fill this gap. It consists firstly in adjusting the fluorescence profile to impose a zero chlorophyll a concentration at depth. Secondly, each point of the fluorescence profile is then multiplied by a correction coefficient, which forces the chlorophyll a integrated content measured on the fluorescence profile to be consistent with the concomitant ocean colour observation. The method is close to the approach proposed by Boss et al. (2008) to correct fluorescence data of a profiling float, although important differences do exist. To develop and test our approach, in situ data from three open ocean stations (BATS, HOT and DYFAMED) were used. Comparison of the so-called "satellite-corrected" fluorescence profiles with concomitant bottle-derived estimations of chlorophyll a concentration was performed to evaluate the final error (estimated at 31%). Comparison with the Boss et al. (2008) method, using a subset of the DYFAMED data set, demonstrated that the methods have similar accuracy. The method was applied to two different data sets to demonstrate its utility. Using fluorescence profiles at BATS, we show that the integration of "satellite-corrected" fluorescence profiles in chlorophyll a climatologies could improve both the statistical relevance of chlorophyll a averages and the vertical structure of the chlorophyll a field. We also show that our method could be efficiently used to process, within near-real time, profiles obtained by a fluorometer deployed on autonomous platforms, in our case a bio-optical profiling float. The application of the proposed method should provide a first step towards the generation of a merged satellite/fluorescence chlorophyll a product, as the "satellite-corrected" profiles should then be consistent with satellite observations. Improved climatologies with more consistent satellite and in situ data are likely to enhance the performance of present biogeochemical models.
Joint use of satellite and in-situ data for coastal monitoring  [PDF]
F. Gohin
Ocean Science Discussions (OSD) , 2011, DOI: 10.5194/osd-8-955-2011
Abstract: Sea surface Temperature, Chlorophyll and turbidity are three variables of the coastal environment commonly measured by monitoring networks. The observation networks are often based on coastal stations which do not provide a sufficient coverage to val-idate the model outputs or to be used in assimilation over the continental shelf. Conversely, the products derived from satellite reflectance show generally a decreasing quality shoreward and an accurate assessment of these data is required. In this text, we show that the satellite-derived chlorophyll products, obtained through a dedicated coastal algorithm, fulfil the first requirement of a monitoring system: the ability to represent correctly the mean annual cycle. The annual cycle, mean and percentile 90 of the chlorophyll concentration, derived from MERIS/ESA and MODIS/NASA, have been compared to in-situ observations at twenty six selected stations from the Mediterranean Sea to the North-Sea. Keeping in mind the validation, the forcing or the assimilation in hydrological, sediment-transport or ecological models, the non-algal Suspended Particulate Matter (SPM) is also a parameter which is expected from the satellite imagery. However, the monitoring networks measure essentially the turbidity and a consistency between chlorophyll, representative of the phytoplankton biomass, non-algal SPM, and turbidity is required. In this study, we derive the satellite turbidity from chlorophyll and non-algal SPM with a common formula applied to in-situ or satellite observations. The distribution of the satellite-derived turbidity shows the same main statistical characteristics that measured in-situ; which satisfies our first condition to monitor the long-term changes or the large-scale spatial variation over the continental shelf and along the shore. For the first time, maps of turbidity, so useful for the surveillance of the benthic habitats, are proposed operationally from space on areas as different as the Southern North-Sea or the Western Mediterranean Sea, with validation at coastal stations.
Evaluation of the ISBA-TRIP continental hydrologic system over the Niger basin using in situ and satellite derived datasets
V. Pedinotti, A. Boone, B. Decharme, J. F. Crétaux, N. Mognard, G. Panthou, F. Papa,B. A. Tanimoun
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2012,
Abstract: During the 1970s and 1980s, West Africa has faced extreme climate variations with extended drought conditions. Of particular importance is the Niger basin, since it traverses a large part of the Sahel and is thus a critical source of water for an ever-increasing local population in this semi arid region. However, the understanding of the hydrological processes over this basin is currently limited by the lack of spatially distributed surface water and discharge measurements. The purpose of this study is to evaluate the ability of the ISBA-TRIP continental hydrologic system to represent key processes related to the hydrological cycle of the Niger basin. ISBA-TRIP is currently used within a coupled global climate model, so that the scheme must represent the first order processes which are critical for representing the water cycle while retaining a limited number of parameters and a simple representation of the physics. To this end, the scheme uses first-order approximations to account explicitly for the surface river routing, the floodplain dynamics, and the water storage using a deep aquifer reservoir. In the current study, simulations are done at a 0.5 by 0.5° spatial resolution over the 2002–2007 period (in order to take advantage of the recent satellite record and data from the African Monsoon Multidisciplinary Analyses project, AMMA). Four configurations of the model are compared to evaluate the separate impacts of the flooding scheme and the aquifer on the water cycle. Moreover, the model is forced by two different rainfall datasets to consider the sensitivity of the model to rainfall input uncertainties. The model is evaluated using in situ discharge measurements as well as satellite derived flood extent, total continental water storage changes and river height changes. The basic analysis of in situ discharges confirms the impact of the inner delta area, known as a significant flooded area, on the discharge, characterized by a strong reduction of the streamflow after the delta compared to the streamflow before the delta. In the simulations, the flooding scheme leads to a non-negligible increase of evaporation over large flooded areas, which decreases the Niger river flow by 15% to 50% in the locations situated after the inner delta as a function of the input rainfall dataset used as forcing. This improves the simulation of the river discharge downstream of the delta, confirming the need for coupling the land surface scheme with the flood model. The deep aquifer reservoir improves Niger low flows and the recession law during the dry season. The comparison with 3 satellite products from the Gravity Recovery and Climated Experiment (GRACE) shows a non negligible contribution of the deeper soil layers to the total storage (34% for groundwater and aquifer). The simulations also show a non negligible sensitivity of the simulations to rain uncertainties especially concerning the discharge. Finally, sensitivity tests show that a good parameterization
Observed and simulated hydroclimatology using distributed hydrologic model from in-situ and multi-satellite remote sensing datasets in Lake Victoria region in East Africa
S. I. Khan,P. Adhikari,Y. Hong,H. Vergara
Hydrology and Earth System Sciences Discussions , 2010, DOI: 10.5194/hessd-7-4785-2010
Abstract: Floods and droughts are common, recurring natural hazards in East African nations. Studies of hydro-climatology at daily, seasonal, and annual time scale is an important in understanding and ultimately minimizing the impacts of such hazards. Using daily in-situ data over the last two decades combined with the recently available multiple-years satellite remote sensing data, we analyzed and simulated, with a distributed hydrologic model, the hydro-climatology in Nzoia, one of the major contributing sub-basins of Lake Victoria in the East African highlands. The basin, with a semi arid climate, has no sustained base flow contribution to Lake Victoria. The short spell of high discharge showed that rain is the prime cause of floods in the basin. There is only a marginal increase in annual mean discharge over the last 21 years. The 2-, 5- and 10-year peak discharges, for the entire study period showed that more years since the mid 1990's have had high peak discharges despite having relatively less annual rain. The study also presents the hydrologic model calibration and validation results over the Nzoia Basin. The spatiotemporal variability of the water cycle components were quantified using a physically-based, distributed hydrologic model, with in-situ and multi-satellite remote sensing datasets. Moreover, the hydrologic capability of remote sensing data such as TRMM-3B42V6 was tested in terms of reconstruction of the water cycle components. The spatial distribution and time series of modeling results for precipitation (P), evapotranspiration (ET), and change in storage (dS/dt) showed considerable agreement with the monthly model runoff estimates and gauge observations. Runoff values responded to precipitation events that occurred across the catchment during the wet season from March to early June. The hydrologic model captured the spatial variability of the soil moisture storage. The spatially distributed model inputs, states, and outputs, were found to be useful for understanding the hydrologic behavior at the catchment scale. Relatively high flows were experienced near the basin outlet from previous rainfall, with a new flood peak responding to the rainfall in the upper part of the basin. The monthly peak runoff was observed in the months of April, May and November. The analysis revealed a linear relationship between rainfall and runoff for both wet and dry seasons. The model was found to be useful in poorly gauged catchments using satellite forcing data and showed the potential to be used not only for the investigation of the catchment scale water balance
Satellite Imagery and In-situ Data Overlay Approach for Fishery Zonation
Khairul Munadi,Fardhi Adria
TELKOMNIKA , 2010,
Abstract: Remote sensing technology can be used to better understand the earth’s characteristics. SeaWiFS (sea-viewing wide field-of-view sensor) is one of remote sensors used to observe global ocean phenomena. Previous studies showed that the distribution of chlorophyll-a in the ocean indicates the presence of fish. However, only a few studies tried to directly relate the chlorophyll-a distribution obtained through interpretation of satellite imagery to in-situ data of fish distribution. This paper investigates the relation between chlorophyll-a distribution and fish-capturing points in Aceh Province sea waters using overlay image analysis. The results are then used to identify the potential fishing ground in Aceh. The profile of chlorophyll-a concentration is derived from SeaWIFS satellite imagery. Fish-capturing points data is obtained from the fisherman communities of Banda Aceh, starting from June to November 2008. The results showed that the chlorophyll-a profile derived from satellite imagery has a positive relationship to fish-capturing point data. The most potential fish-capturing zone in Aceh sea waters is identified at 5-8o north latitude (N) and 96-99o east longitude (E).
Towards a merged satellite and in situ fluorescence ocean chlorophyll product  [PDF]
H. Lavigne,F. D'Ortenzio,H. Claustre,A. Poteau
Biogeosciences Discussions , 2011, DOI: 10.5194/bgd-8-11899-2011
Abstract: Understanding the ocean carbon cycle requires a precise assessment of phytoplankton biomass in the oceans. In terms of numbers of observations, satellite data represents the largest available data set. However, as they are limited to surface waters, they have to be merged with in situ observations. Amongst the in situ data, fluorescence profiles constitute the greatest data set available, because fluorometers operate routinely on oceanographic cruise since the seventies. Nevertheless, fluorescence is only a proxy of the Total Chlorophyll-a concentration and a data calibration is required. Calibration issues are, however, source of uncertainty and they have prevented a systematic and wide range exploitation of the fluorescence data set. In particular, very few attempts to standardize the fluorescence data bases exist. Consequently, merged estimations with other data sources (i.e. satellite) are lacking. We propose a merging method to fill this gap. It consists firstly, in adjusting the fluorescence profile to impose a zero Chlorophyll-a concentration at depth. Secondly, each point of the fluorescence profile is then multiplied by a correction coefficient which forces the Chlorophyll-a integrated content measured on the fluorescence profile to be consistent with the concomitant ocean color observation. The method is close to the approach proposed by Boss et al. (2008) to calibrate fluorescence data of a profiling float, although important differences do exist. To develop and test our approach, in situ data from three open ocean stations (BATS, HOT and DYFAMED) were used. Comparison of the so-called "satellite-corrected" fluorescence profiles with concomitant bottle derived estimations of Chlorophyll-a concentration was performed to evaluate the final error, which resulted to be of about 31 %. Comparison with the Boss et al. (2008) method, carried out on a subset of the DYFAMED data set simulating a profiling float time series, demonstrated that the methods have similar accuracy. Applications of the method were then explored on two different data sets. Using fluorescence profiles at BATS, we show that the integration of "satellite-corrected" fluorescence profiles in Chlorophyll-a climatologies could improve both the statistical relevance of Chlorophyll-a averages and the vertical structure of the Chlorophyll-a field. We also show that our method could be efficiently used to process, within near-real time, profiles obtained by a fluorometer deployed on autonomous platforms, in our case a bio-optical profiling float. The wide application of the proposed meth
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