scholarly journals Synergy between in situ and altimetry data to observe and study the Northern Current variations (NW Mediterranean Sea)

2018 ◽  
Author(s):  
Alice Carret ◽  
Florence Birol ◽  
Claude Estournel ◽  
Bruno Zakardjian ◽  
Pierre Testor
Keyword(s):  
Satellite Altimetry ◽  
Regional Scale ◽  
Spatial Coherence ◽  
The Other ◽  
Circulation System ◽  
Altimetry Data ◽  
Spatial Continuity ◽  
Northern Current ◽  
Observing Techniques

Abstract. During the last 15 years, substantial progress has been achieved in altimetry data processing, providing now data with enough accuracy to illustrate the potential of these observations for coastal applications. In parallel, new altimetry techniques improve the data quality by reducing the land contamination and by enhancing the signal-to-noise ratio. Satellite altimetry provides ever more robust and accurate measurements ever closer to the coast and resolve ever shorter ocean signals. An important issue is now to learn how to use altimetry data in conjunction with the other coastal observing techniques. Here, we demonstrate the ability of satellite altimetry to observe part of the Northern Current variability. We cross-compare and combine the currents provided by large data sets of ship-mounted ADCPs, gliders, HF radars and altimetry. We analyze how the different available observing techniques capture the current variability at different time-scales. We also study the coherence/divergence/complementarity of the informations derived from the different instruments considered. Two generation of altimetry missions are used: Jason 2 (nadir Ku-band radar) and SARAL/AltiKa (nadir Ka-band altimetry); their performances are compared. In terms of mean speed of the Northern Current, a very good spatial continuity and coherence is observed at regional scale, showing the complementarity between all the types of current measurements. In terms of current variability, there is still a good spatial coherence but the amplitude of the seasonal variations is underestimated by ~ 50 % in altimetry, compared to both gliders and ADCPs, because of a too low spatial resolution. For individual dates this number varies a lot as a function of the distance to the coast and width of the Northern Current. Compared to Jason 2, the SARAL/AltiKa data tend to give estimations of the NC characteristics that are closer to in situ data in a number of cases. Satellite altimetry obviously provides a synoptic view of the Northern Current circulation system and variability which helps to interpret the other current observations. Its regular sampling allows the observation of many features that may be missed by in situ measurements.

scholarly journals Synergy between in situ and altimetry data to observe and study Northern Current variations (NW Mediterranean Sea)

Ocean Science ◽  
2019 ◽  
Vol 15 (2) ◽  
pp. 269-290 ◽  
Author(s):  
Alice Carret ◽  
Florence Birol ◽  
Claude Estournel ◽  
Bruno Zakardjian ◽  
Pierre Testor
Keyword(s):  
Satellite Altimetry ◽  
Hf Radar ◽  
The Other ◽  
High Rate ◽  
Altimeter Data ◽  
Altimetry Data ◽  
In Situ Data ◽  
Northern Current ◽  
Observing Techniques

Abstract. During the last 15 years, substantial progress has been achieved in altimetry data processing, now providing data with enough accuracy to illustrate the potential of these observations for coastal applications. In parallel, new altimetry techniques improve data quality by reducing land contamination and enhancing the signal-to-noise ratio. Satellite altimetry provides more robust and accurate measurements ever closer to the coast and resolve shorter ocean signals. An important issue is now to learn how to use altimetry data in conjunction with other coastal observing techniques. Here, we cross-compare and combine the coastal currents provided by large datasets of ship-mounted acoustic Doppler current profilers (ADCPs), gliders, high-frequency (HF) radars and altimetry. We analyze how the different available observing techniques, with a particular focus on altimetry, capture the Northern Current variability at different timescales. We also study the coherence, divergence and complementarity of the information derived from the different instruments considered. Two generations of altimetry missions and both 1 Hz and high-rate measurements are used: Jason-2 (nadir Ku-band radar) and SARAL/AltiKa (nadir Ka-band altimetry); their performances are compared. In terms of mean speed of the Northern Current, a very good spatial continuity and coherence is observed at regional scale, showing the complementarity among the types of current measurements. In terms of current variability, there is still a good spatial coherence but the Northern Current amplitudes derived from altimetry, glider, ADCP and HF radar data differ, mainly because of differences in their respective spatial and temporal resolutions. If we consider seasonal variations, 1 Hz altimetry captures ∼60 % and ∼55 % of the continental slope current amplitude observed by the gliders and by the ADCPs, respectively. For individual dates this number varies a lot as a function of the characteristics of the Northern Current on the corresponding date, with no clear seasonal tendency observed. Compared to Jason-2, the SARAL altimeter data tend to give estimations of the NC characteristics that are closer to in situ data in a number of cases. The much noisier high-rate altimetry data appear to be more difficult to analyze but they provide current estimates that are generally closer to the other types of current measurements. Thus, satellite altimetry provides a synoptic view of the Northern Current circulation system and variability, which helps to interpret the other observations. Its regular sampling allows for the observation of many features that may be missed by irregular in situ data.

scholarly journals Comparing satellite altimetry and tide gauges observations in the Mediterranean Sea within the framework of singular spectrum analysis

MAUSAM ◽  
2021 ◽  
Vol 71 (2) ◽  
pp. 187-198
Author(s):  
HADDAD MAHDI ◽  
TAIBI HEBIB ◽  
MOKRANE MOUSTAFA ◽  
HAMMOUMI HOUSSEYN
Keyword(s):  
Sea Level ◽  
Spectrum Analysis ◽  
Satellite Altimetry ◽  
Tide Gauge ◽  
Singular Spectrum Analysis ◽  
Altimetry Data ◽  
Tide Gauges ◽  
The Mediterranean ◽  
Satellite Altimetry Data

By considering time series from satellite altimetry and tide gauges that extend back to 1993, Singular Spectrum Analysis (SSA) is applied to investigate and compare the non linear trends of the sea level along the Mediterranean coasts. The major issue of this comparison is to show if the satellite altimetry data could be representative of the local sea level as observed by tide gauges.   The results indicate that the local trends estimated from an in-situ tide gauge and satellite altimetry data show nearly identical positive rates over the period from 1993 to 2017. The differences between the estimated rates of sea level change from in-situ tide gauge and satellite measurements vary, in absolute value, from 0.18 to 4.29 mm/year with an average of 1.55 mm/year.   This result is sufficient to admit, if necessary, on the one hand, the complementarily of the two measurement techniques (satellite altimetry and tide gauges) and, on the other hand, the rise in sea level near the Mediterranean coastal areas.

Observing Sea Level Changes Using Satellite Altimetry and In Situ Data

2020 ◽  
Author(s):  
Nikos Flokos ◽  
Maria Tsakiri
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Coastal Zone ◽  
Satellite Altimetry ◽  
Tide Gauge ◽  
Altimeter Data ◽  
Atmospheric Effects ◽  
Data Sets ◽  
Altimetry Data

<p>corresponding author: N.Flokos</p><p>[email protected]</p><p>ABSTRACT</p><p>Sea level change is one of the key indicators of climate change with numerous effects such as flooding, erosion of beaches, salt intrusion.  The detailed global picture of sea level and the monitoring of its spatial-temporal changes is performed by Satellite Altimetry (SA). Nowadays, SA data compare well with measurements from the global tide gauge network, but the aim of 0.3 mm/year accuracy in the altimeter derived rate of global mean sea level rise is still not fully met. </p><p>Whilst the precise determination of global and regional sea level rise from SA data is promising, there is however an observational gap in our knowledge regarding the coastal zone. While Tide Gauges (TG) are usually located at the coast, therefore providing coastal sea level measurements, altimeters have difficulties there. Filling this gap becomes important when considering that the impact of sea level rise can be devastating on the coast with effects on society and ecosystems. This makes it even more significant knowing that there are many stretches of the world’s coast that still do not possess in situ level measuring devices.  </p><p>This work aims to discuss the available data and methods that link the SA measurements of sea level rise with TG measurements. Whilst there is rich literature on relevant applications, it is important to have a clear and concise methodology on this.</p><p>Tide gauge data</p><p>Several post processing steps need to be applied to the raw TG data to enrich the raw Sea Surface Heights (SSH) values and make them comparable with SA data. There are several geophysical corrections, such as pressure and wind effects, which can be applied to TG data in order to deduce  Sea Level (SL) and be consistent with altimeter data. High frequency atmospheric effects on TG data are corrected using the Dynamic Atmospheric Correction (DAC) provided by AVISO. One other large uncertainty is the vertical stability of the TG benchmark over time. TG data must be corrected for the Vertical Land Motion (VLM) to enable the comparison of two sea level measurements (TG and SA) and their later integration within the surfaces of the absolute sea heights. The main VLM dataset can be obtained from SONEL database (SONEL 2016) which provides crustal velocities from the continuous GNSS measurements at sites collocated to the TG.</p><p>Satellite altimetry data</p><p>Whilst Satellite Altimetry over the open ocean is a mature discipline, global altimetry data collected over the coastal ocean remain still largely unexploited. This is because of intrinsic difficulties in the corrections and issues of land contamination in the footprint that have so far resulted in systematic flagging and rejection of these data. In this work, the relevant methodology to overcome these problems and extend the capabilities of current and future altimeters to the coastal zone (coastal altimetry) will be discussed and a number of coastal altimetry data sets will be used (eg SARvatore, X-TRACK, RADS etc). Finally, a practical example using real data sets over the Aegean Sea will be presented. </p><p> </p><p> </p>

scholarly journals A Method to Estimate Three-Dimensional Thermal Structure from Satellite Altimetry Data

2009 ◽  
Vol 26 (12) ◽  
pp. 2655-2664 ◽  
Author(s):  
Akiko Takano ◽  
Hidekatsu Yamazaki ◽  
Takeyoshi Nagai ◽  
Osamu Honda
Keyword(s):  
Satellite Altimetry ◽  
Thermal Structure ◽  
Three Dimensional ◽  
Empirical Method ◽  
Altimetry Data ◽  
Spatiotemporal Mapping ◽  
Strong Linear Correlation ◽  
Globally Distributed ◽  
Satellite Altimetry Data

Abstract A new empirical method to estimate mesoscale three-dimensional oceanic thermal structures from near-real-time satellite altimetry data is presented. The method uses a two-layer model with a novel set of empirical parameters for stratification. Empirical parameters, which are calculated from altimetry data and in situ temperature and salinity profiles obtained from globally distributed Argo floats, allowed for significant increases in the spatiotemporal mapping of mesoscale temperature distributions. The accuracy of the method was validated by comparing the estimated isothermal depths with in situ temperature data. Three case studies in different regions and seasons showed excellent agreement, with a strong linear correlation between the estimated and observed isothermal depths. The authors present the details of the method, discuss its limitations, and demonstrate the ecological relevance of the method for fisheries management by successfully predicting pelagic fish distributions.

A very rapid in situ Kikuchi technique to determine relative crystal misorientation

1988 ◽  
Vol 46 ◽  
pp. 830-831
Author(s):  
J. I. Bennetch
Keyword(s):  
Electron Beam ◽  
Analytical Techniques ◽  
Superplastic Forming ◽  
The Other ◽  
Kikuchi Pattern ◽  
Kikuchi Line ◽  
Line Analysis

In a recent study of the superplastic forming (SPF) behavior of certain Al-Li-X alloys, the relative misorientation between adjacent (sub)grains proved to be an important parameter. It is well established that the most accurate way to determine misorientation across boundaries is by Kikuchi line analysis. However, the SPF study required the characterization of a large number of (sub)grains in each sample to be statistically meaningful, a very time-consuming task even for comparatively rapid Kikuchi analytical techniques.In order to circumvent this problem, an alternate, even more rapid in-situ Kikuchi technique was devised, eliminating the need for the developing of negatives and any subsequent measurements on photographic plates. All that is required is a double tilt low backlash goniometer capable of tilting ± 45° in one axis and ± 30° in the other axis. The procedure is as follows. While viewing the microscope screen, one merely tilts the specimen until a standard recognizable reference Kikuchi pattern is centered, making sure, at the same time, that the focused electron beam remains on the (sub)grain in question.

scholarly journals Evaluating Machine Learning and Geostatistical Methods for Spatial Gap-filling of Monthly ESA CCI Soil Moisture in China

2021 ◽  
Vol 13 (14) ◽  
pp. 2848
Author(s):  
Hao Sun ◽  
Qian Xu
Keyword(s):  
Machine Learning ◽  
Soil Moisture ◽  
Water Resource Management ◽  
Large Scale ◽  
Gap Filling ◽  
Spatial Continuity ◽  
Study Results ◽  
Data Gaps

Obtaining large-scale, long-term, and spatial continuous soil moisture (SM) data is crucial for climate change, hydrology, and water resource management, etc. ESA CCI SM is such a large-scale and long-term SM (longer than 40 years until now). However, there exist data gaps, especially for the area of China, due to the limitations in remote sensing of SM such as complex topography, human-induced radio frequency interference (RFI), and vegetation disturbances, etc. The data gaps make the CCI SM data cannot achieve spatial continuity, which entails the study of gap-filling methods. In order to develop suitable methods to fill the gaps of CCI SM in the whole area of China, we compared typical Machine Learning (ML) methods, including Random Forest method (RF), Feedforward Neural Network method (FNN), and Generalized Linear Model (GLM) with a geostatistical method, i.e., Ordinary Kriging (OK) in this study. More than 30 years of passive–active combined CCI SM from 1982 to 2018 and other biophysical variables such as Normalized Difference Vegetation Index (NDVI), precipitation, air temperature, Digital Elevation Model (DEM), soil type, and in situ SM from International Soil Moisture Network (ISMN) were utilized in this study. Results indicated that: 1) the data gap of CCI SM is frequent in China, which is found not only in cold seasons and areas but also in warm seasons and areas. The ratio of gap pixel numbers to the whole pixel numbers can be greater than 80%, and its average is around 40%. 2) ML methods can fill the gaps of CCI SM all up. Among the ML methods, RF had the best performance in fitting the relationship between CCI SM and biophysical variables. 3) Over simulated gap areas, RF had a comparable performance with OK, and they outperformed the FNN and GLM methods greatly. 4) Over in situ SM networks, RF achieved better performance than the OK method. 5) We also explored various strategies for gap-filling CCI SM. Results demonstrated that the strategy of constructing a monthly model with one RF for simulating monthly average SM and another RF for simulating monthly SM disturbance achieved the best performance. Such strategy combining with the ML method such as the RF is suggested in this study for filling the gaps of CCI SM in China.

Extensive Enteric Leiomyolysis Due to Cytomegalovirus Enterocolitis in Vertically Acquired Human Immunodeficiency Virus Infection in Infants

2000 ◽  
Vol 3 (6) ◽  
pp. 591-596 ◽  
Author(s):  
Virpi V. Smith ◽  
Amanda J. Williams ◽  
Vas Novelli ◽  
Marian Malone
Keyword(s):  
Human Immunodeficiency Virus ◽  
Vascular Endothelium ◽  
Muscularis Propria ◽  
The Other ◽  
Muscularis Mucosae ◽  
Immunodeficiency Virus ◽  
Acquired Immunodeficiency ◽  
Immunodeficiency Syndrome ◽  
Viral Inclusions

We report two infants with the acquired immunodeficiency syndrome (AIDS) and rectal bleeding due to cytomegalovirus (CMV) ileitis and colitis with minimal focal mucosal ulceration but with extensive leiomyolysis of the muscularis propria. Immunostaining and in situ hybridization for CMV showed numerous viral inclusions in the myocytes of the muscularis propria and vascular endothelium/smooth muscle with only occasional inclusions present in the muscularis mucosae. Colectomy was curative in one patient; in the other the bowel was only examined at postmortem.

Did Ground Cover Change Over Geologic Time?

2000 ◽  
Vol 6 ◽  
pp. 171-182 ◽  
Author(s):  
Ben A. LePage ◽  
Hermann W. Pfefferkorn
Keyword(s):  
Fossil Record ◽  
Ground Cover ◽  
The Other ◽  
Detailed Account ◽  
Geologic Time ◽  
The Past ◽  
Other Hand ◽  
Plant Fossil

When one hears the term “ground cover,” one immediately thinks of “grasses.” This perception is so deep-seated that paleobotanists even have been overheard to proclaim that “there was no ground cover before grasses.” Today grasses are so predominant in many environments that this perception is perpetuated easily. On the other hand, it is difficult to imagine the absence or lack of ground cover prior to the mid-Tertiary. We tested the hypothesis that different forms of ground cover existed in the past against examples from the Recent and the fossil record (Table 1). The Recent data were obtained from a large number of sources including those in the ecological, horticultural, and microbiological literature. Other data were derived from our knowledge of Precambrian life, sedimentology and paleosols, and the plant fossil record, especially in situ floras and fossil “monocultures.” Some of the data are original observations, but many others are from the literature. A detailed account of these results will be presented elsewhere (Pfefferkorn and LePage, in preparation).

Reproductive performance of group-synchronized Merino d'Arles and Romanov crossbred ewes. 1. A note on the effects of lactation on fecundity

1977 ◽  
Vol 24 (1) ◽  
pp. 113-116 ◽  
Author(s):  
F. J. Galindez ◽  
M. Prud'hon ◽  
G. Reboul
Keyword(s):  
Treatment Group ◽  
Reproductive Performance ◽  
The Other ◽  
Fertility Level ◽  
Homogeneous Groups ◽  
Treatment Groups ◽  
Significant Superiority

SUMMARYFifty-six Merino d'Aries and 56 Romanov × Merino crossbred lactating ewes were divided into two treatment groups, one (T1) with a ewe-to-ram ratio of 48: 1 (24 Merino and 24 crossbred) and the other (T2) of 64: 1 (32 Merino and 32 crossbred).Intravaginal sponges with 40 mg FGA (Searle) were inserted in two subgroups at 8-day intervals and withdrawn after 12 and 16 days in situ, in four equal groups at 4-day intervals. A dose of 400 IU pregnant mare's serum gonadotrophin (PMSG) was applied at sponge withdrawal.Fertility after two oestrous cycles was equally satisfactory in both treatments, though it was lower in treatment group T2. This could be due to the significantly low (P<0·01) number of Merino ewes raddled by the T2 ram (0·33 Merino against 0·92 crossbred) suggesting preferential behaviour by the ram in this treatment.Comparisons between breeds show a slight superiority in the fertility of crossbred ewes and a highly significant superiority in prolificacy These results suggest that using the described method, 2% of rams seems more than adequate to mate with progestagen-synchronized ewes with a satisfactory fertility level. It is, however, recommended to use homogeneous groups of ewes.

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