D. Arabelos - Academia.edu (original) (raw)

Papers by D. Arabelos

Research paper thumbnail of Assessment of recent tidal models in the Mediterranean Sea

Ocean tides especially in closed sea areas can deviate considerably from the theoretical values d... more Ocean tides especially in closed sea areas can deviate considerably from the theoretical values due to unequal water depths and to the fact that the continents impede the movement of water. Satellite altimetry enabled the development of improved tidal models event in closed sea areas, by assimilating altimeter data into hydrodynamic models. The Mediterranean Sea due to its morphology is an ideal test field for the assessment of tidal models, based on this technique. An attempt to assess the recent tidal models TPXO.6, GOT00.2 and NAO.99b was based on (a) an inter-comparison of tidal heights computed from the three models at different time moments on the same 15 t × 15 t grid covering the Mediterranean and (b) on the comparison of the statistics of a crossover analysis of nearly 2.3 years of JASON-1 altimeter data (Cycle 1-86), before and after the tidal correction, using the three tidal models. The inter-comparison in terms of mean value and standard deviation of the differences between the tidal heights on the 15 ~ × 15 ~ grid resulted in mean values up to 3 mm and standard deviations ranging from 16 to 26 mm. However, maximum values of differences exceed several din. On the other hand, the statistics of the crossover analysis showed a 17% decrease of the standard deviation of the JASON-1 crossover differences after the tidal correction. These results show a good agreement between the three tidal models.

Research paper thumbnail of Scientific data processing algorithms - the spacewise approach

The software elements able to produce GOCE products using either Least Squares Collocation (LSC) ... more The software elements able to produce GOCE products using either Least Squares Collocation (LSC) or the Integration approach are described. The software should be made available using a distribution system and the quality standards developed in the EU project MANICORAL. A number of problems remain unsolved, and require further investigations and software development. Here are identified some of the numerical problems. Since the number of individual observations will be of the order 10 7 , normal point or area values will have to be formed, reducing the dataset to 160000 (corresponding to estimating the spherical harmonic coefficients up to degree 400). The normal values may be used in an integration procedure if the normal values are located on the same sphere. If methods like LSC are used, a system of equations with a full coefficient matrix must be solved. Here we expect that the use of preconditioning based on approximate kernels which are zero outside a certain radius will make ...

Research paper thumbnail of The 1-cm geoid after GOCE

International Association of Geodesy Symposia, 2001

The new satellite gravity missions (CHAMP, GRACE and GOCE) will all bring substantial improvement... more The new satellite gravity missions (CHAMP, GRACE and GOCE) will all bring substantial improvements to our knowledge of the gravity field and thereby of the (quasi-) geoid. One of the aims of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) is to determine the geoid to within 1 cm at wavelengths down to 100 km.

Research paper thumbnail of Wavelet analysis of the LF radio signals collected by the European VLF/LF network from July 2009 to April 2011

Annals of Geophysics, 2012

ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-... more ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-300 kHz) bands was developed by an Italian factory. The receiver can monitor 10 frequencies distributed in these bands, with the measurement for each of them of the electric field intensity. Since 2009, to date, six of these radio receivers have been installed throughout Europe to establish a 'European VLF/LF Network'. At present, two of these are into operation in Italy, and the remaining four are located in Greece, Turkey, Portugal and Romania. For the present study, the LF radio data collected over about two years were analysed. At first, the day-time data and the night-time data were separated for each radio signal. Taking into account that the LF signals are characterized by ground-wave and sky-wave propagation modes, the day-time data are related to the ground wave and the night-time data to the sky wave. In this framework, the effects of solar activity and storm activity were defined in the different trends. Then, the earthquakes with M ≥5.0 that occurred over the same period were selected, as those located in a 300-km radius around each receiver/transmitter and within the 5th Fresnel zone related to each transmitter-receiver path. Where possible, the wavelet analysis was applied on the time series of the radio signal intensity, and some anomalies related to previous earthquakes were revealed. Except for some doubt in one case, success appears to have been obtained in all of the cases related to the 300 km circles in for the ground waves and the sky waves. For the Fresnel cases, success in two cases and one failure were seen in analysing the sky waves. The failure occurred in August/September, and might be related to the disturbed conditions of the ionosphere in summer

Research paper thumbnail of Estimation of the Gravity Field and Sea Surface Heights from Heterogeneous Data in the Central Mediterranean

International Association of Geodesy Symposia, 1991

Research paper thumbnail of Estimation of the Disturbing Potential Components and Comparison with GPS and Astrogeodetic Data

International Association of Geodesy Symposia, 1991

Research paper thumbnail of Gravity and Geoid in the Mediterranean from a Common Adjustment of ERS-1 and TOPEX Altimeter Data

International Association of Geodesy Symposia, 1995

Research paper thumbnail of Sea Surface Height Determination in the Mediterranean Sea by Local Adjustment of GEOSAT Altimeter Data

International Association of Geodesy Symposia, 1990

Research paper thumbnail of Tidal changes of the barometric pressure in the area of Thessaloniki

The marginal presence of the frequencies 0.03629 and 0.073036 cycles per day in the power spectru... more The marginal presence of the frequencies 0.03629 and 0.073036 cycles per day in the power spectrum of the daily measurements series of barometric pressure, was detected during an investigation upon the influence of barometric pressure and earth tides on the shallow underground water level variations in the area of Volvi. These frequencies coincide with those of the Mm(period of 27.55 days) and Mf(period of 13.69 days) constituents of the earth tides indicating a possible influence of the earth tides upon the barometric pressure. In order to investigate the influence of the earth tides upon the barometric pressure we analyzed a sample of five years hourly measurements (43,056 values) of barometric pressure in the area of Thessaloniki. The accuracy of these measurements was estimated to be equal about ±0.1hPa. The tidal analysis showed that the signal to noise ratio varies from 9 to 23 for the long period waves (Ssa, Mm, Mf, Mtm). For the short period constituents the corresponding qu...

Research paper thumbnail of Analysis of Geosat Altimeter Data

International Association of Geodesy Symposia, 1991

Research paper thumbnail of Geoid Computations in Taiwan

International Association of Geodesy Symposia, 1995

Research paper thumbnail of Gravimetric Geoid Determination for the Area of Greece

Astrophysics and Space Science Library, 1982

Research paper thumbnail of Combination of spaceborne, airborne and in-situ gravity measurements in support of Ocean Arctic Sea-Ice and MDT-mapping

Research paper thumbnail of ARCGICE Combination of Spaceborne, Airborne and In-Situ Gravity Measurements in Support of Arctic Sea-Ice Thickness Mapping

Research paper thumbnail of The European Network for studying the radio precursors of earthquakes: the case of the May 19, 2011 Turkey earthquake (Mw=5.7)

Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers was put into operati... more Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers was put into operation in Europe in order to study the disturbances produced by the earthquakes on the propagation of these signals. In 2011 the network was formed by nine receivers located three in Italy and one in Austria, Greece, Portugal, Romania, Russia and Turkey. On May 19, 2001 an earthquake with Mw=5.7 occurred in western Turkey, that is inside the "sensitive" area of the network. The radio data collected during April-May 2011 were studied using three different methods of analysis which are the wavelet spectra, the principal component technique and the standard deviation trends. Clear anomalies were revealed both in the signals broadcasted by the TRT transmitter (180 kHz) located near Ankara and in some VLF signals coming from transmitters located in western Europe and collected by the receiver TUR of the network located in eastern Turkey. Evident precursors phases were pointed out. Some ...

Research paper thumbnail of Global grids of gravity anomalies and vertical gravity gradients at 10 km altitude from GOCE gradient data 2009-2011 and polar gravity

ABSTRACT The GOCE satellite measures gravity gradients which are filtered and transformed to grad... more ABSTRACT The GOCE satellite measures gravity gradients which are filtered and transformed to gradients into an Earth-referenced frame by the GOCE High Level processing Facility. More than 80000000 data with 6 components are available from the period 2009-2011. IAG Arctic gravity was used north of 83 deg., while data at the Antarctic was not used due to bureaucratic restrictions by the data-holders. Subsets of the data have been used to produce gridded values at 10 km altitude of gravity anomalies and vertical gravity gradients in 20 deg. x 20 deg. blocks with 10' spacing. Various combinations and densities of data were used to obtain values in areas with known gravity anomalies. The (marginally) best choice was vertical gravity gradients selected with an approximately 0.125 deg spacing. Using Least-Squares Collocation, error-estimates were computed and compared to the difference between the GOCE-grids and grids derived from EGM2008 to deg. 512. In general a good agreement was found, however with some inconsistencies in certain areas. The computation time on a usual server with 24 processors was typically 100 minutes for a block with generally 40000 GOCE vertical gradients as input. The computations will be updated with new Wiener-filtered data in the near future.

Research paper thumbnail of Gravity Field Mapping from a Combination of Satellite Altimetry and Sea Gravimetry in the Mediterranean Sea: By D. Arabelos, M. Vermeer

Research paper thumbnail of Anomalies Observed in VLF and LF Radio Signals on the Occasion of the Western Turkey Earthquake (M<sub>w</sub> = 5.7) on May 19, 2011

International Journal of Geosciences, 2012

Since 2009 a network of VLF (20 -60 kHz) and LF (150 -300 kHz) radio receivers is operating in Eu... more Since 2009 a network of VLF (20 -60 kHz) and LF (150 -300 kHz) radio receivers is operating in Europe in order to study the disturbances produced by the earthquakes on the propagation of these signals. In 2011 the network was formed by nine receivers, of which three are located in Italy and one is in

Research paper thumbnail of Wavelet analysis of the LF radio signals collected by the European VLF/LF network from July 2009 to April 2011

Annals of Geophysics, 2012

ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-... more ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-300 kHz) bands was developed by an Italian factory. The receiver can monitor 10 frequencies distributed in these bands, with the measurement for each of them of the electric field intensity. Since 2009, to date, six of these radio receivers have been installed throughout Europe to establish a &#39;European VLF/LF Network&#39;. At present, two of these are into operation in Italy, and the remaining four are located in Greece, Turkey, Portugal and Romania. For the present study, the LF radio data collected over about two years were analysed. At first, the day-time data and the night-time data were separated for each radio signal. Taking into account that the LF signals are characterized by ground-wave and sky-wave propagation modes, the day-time data are related to the ground wave and the night-time data to the sky wave. In this framework, the effects of solar activity and storm activity were defined in the different trends. Then, the earthquakes with M ≥5.0 that occurred over the same period were selected, as those located in a 300-km radius around each receiver/transmitter and within the 5th Fresnel zone related to each transmitter-receiver path. Where possible, the wavelet analysis was applied on the time series of the radio signal intensity, and some anomalies related to previous earthquakes were revealed. Except for some doubt in one case, success appears to have been obtained in all of the cases related to the 300 km circles in for the ground waves and the sky waves. For the Fresnel cases, success in two cases and one failure were seen in analysing the sky waves. The failure occurred in August/September, and might be related to the disturbed conditions of the ionosphere in summer

Research paper thumbnail of Calibration of GOCE gravity gradient data using smooth ground gravity

Terrestrial gravity anomalies selected from three extended continental areas having a smooth grav... more Terrestrial gravity anomalies selected from three extended continental areas having a smooth gravity field have been used to determine the appropriate size of the area for gravity data collection as well as the data-sampling required for an external calibration of the GOCE gravity gradient data. The gravity data and a global gravity field model (EGM96) were used as input to least- squares collocation (LSC) which was used to calculate the error of predicted gravity gradient components at points on a realistic orbit of a simulated data set. The mean error showed that gravity gradient components could be predicted with an error of 2-3 mE (i.e. much below the expected error in the measurement band-width) in the case of an optimal size of the collection area and of the optimum resolution of the data. These optimal conditions e.g. for a smooth area inside Australia, correspond to an 0 0 12

Research paper thumbnail of Assessment of recent tidal models in the Mediterranean Sea

Ocean tides especially in closed sea areas can deviate considerably from the theoretical values d... more Ocean tides especially in closed sea areas can deviate considerably from the theoretical values due to unequal water depths and to the fact that the continents impede the movement of water. Satellite altimetry enabled the development of improved tidal models event in closed sea areas, by assimilating altimeter data into hydrodynamic models. The Mediterranean Sea due to its morphology is an ideal test field for the assessment of tidal models, based on this technique. An attempt to assess the recent tidal models TPXO.6, GOT00.2 and NAO.99b was based on (a) an inter-comparison of tidal heights computed from the three models at different time moments on the same 15 t × 15 t grid covering the Mediterranean and (b) on the comparison of the statistics of a crossover analysis of nearly 2.3 years of JASON-1 altimeter data (Cycle 1-86), before and after the tidal correction, using the three tidal models. The inter-comparison in terms of mean value and standard deviation of the differences between the tidal heights on the 15 ~ × 15 ~ grid resulted in mean values up to 3 mm and standard deviations ranging from 16 to 26 mm. However, maximum values of differences exceed several din. On the other hand, the statistics of the crossover analysis showed a 17% decrease of the standard deviation of the JASON-1 crossover differences after the tidal correction. These results show a good agreement between the three tidal models.

Research paper thumbnail of Scientific data processing algorithms - the spacewise approach

The software elements able to produce GOCE products using either Least Squares Collocation (LSC) ... more The software elements able to produce GOCE products using either Least Squares Collocation (LSC) or the Integration approach are described. The software should be made available using a distribution system and the quality standards developed in the EU project MANICORAL. A number of problems remain unsolved, and require further investigations and software development. Here are identified some of the numerical problems. Since the number of individual observations will be of the order 10 7 , normal point or area values will have to be formed, reducing the dataset to 160000 (corresponding to estimating the spherical harmonic coefficients up to degree 400). The normal values may be used in an integration procedure if the normal values are located on the same sphere. If methods like LSC are used, a system of equations with a full coefficient matrix must be solved. Here we expect that the use of preconditioning based on approximate kernels which are zero outside a certain radius will make ...

Research paper thumbnail of The 1-cm geoid after GOCE

International Association of Geodesy Symposia, 2001

The new satellite gravity missions (CHAMP, GRACE and GOCE) will all bring substantial improvement... more The new satellite gravity missions (CHAMP, GRACE and GOCE) will all bring substantial improvements to our knowledge of the gravity field and thereby of the (quasi-) geoid. One of the aims of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) is to determine the geoid to within 1 cm at wavelengths down to 100 km.

Research paper thumbnail of Wavelet analysis of the LF radio signals collected by the European VLF/LF network from July 2009 to April 2011

Annals of Geophysics, 2012

ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-... more ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-300 kHz) bands was developed by an Italian factory. The receiver can monitor 10 frequencies distributed in these bands, with the measurement for each of them of the electric field intensity. Since 2009, to date, six of these radio receivers have been installed throughout Europe to establish a &#39;European VLF/LF Network&#39;. At present, two of these are into operation in Italy, and the remaining four are located in Greece, Turkey, Portugal and Romania. For the present study, the LF radio data collected over about two years were analysed. At first, the day-time data and the night-time data were separated for each radio signal. Taking into account that the LF signals are characterized by ground-wave and sky-wave propagation modes, the day-time data are related to the ground wave and the night-time data to the sky wave. In this framework, the effects of solar activity and storm activity were defined in the different trends. Then, the earthquakes with M ≥5.0 that occurred over the same period were selected, as those located in a 300-km radius around each receiver/transmitter and within the 5th Fresnel zone related to each transmitter-receiver path. Where possible, the wavelet analysis was applied on the time series of the radio signal intensity, and some anomalies related to previous earthquakes were revealed. Except for some doubt in one case, success appears to have been obtained in all of the cases related to the 300 km circles in for the ground waves and the sky waves. For the Fresnel cases, success in two cases and one failure were seen in analysing the sky waves. The failure occurred in August/September, and might be related to the disturbed conditions of the ionosphere in summer

Research paper thumbnail of Estimation of the Gravity Field and Sea Surface Heights from Heterogeneous Data in the Central Mediterranean

International Association of Geodesy Symposia, 1991

Research paper thumbnail of Estimation of the Disturbing Potential Components and Comparison with GPS and Astrogeodetic Data

International Association of Geodesy Symposia, 1991

Research paper thumbnail of Gravity and Geoid in the Mediterranean from a Common Adjustment of ERS-1 and TOPEX Altimeter Data

International Association of Geodesy Symposia, 1995

Research paper thumbnail of Sea Surface Height Determination in the Mediterranean Sea by Local Adjustment of GEOSAT Altimeter Data

International Association of Geodesy Symposia, 1990

Research paper thumbnail of Tidal changes of the barometric pressure in the area of Thessaloniki

The marginal presence of the frequencies 0.03629 and 0.073036 cycles per day in the power spectru... more The marginal presence of the frequencies 0.03629 and 0.073036 cycles per day in the power spectrum of the daily measurements series of barometric pressure, was detected during an investigation upon the influence of barometric pressure and earth tides on the shallow underground water level variations in the area of Volvi. These frequencies coincide with those of the Mm(period of 27.55 days) and Mf(period of 13.69 days) constituents of the earth tides indicating a possible influence of the earth tides upon the barometric pressure. In order to investigate the influence of the earth tides upon the barometric pressure we analyzed a sample of five years hourly measurements (43,056 values) of barometric pressure in the area of Thessaloniki. The accuracy of these measurements was estimated to be equal about ±0.1hPa. The tidal analysis showed that the signal to noise ratio varies from 9 to 23 for the long period waves (Ssa, Mm, Mf, Mtm). For the short period constituents the corresponding qu...

Research paper thumbnail of Analysis of Geosat Altimeter Data

International Association of Geodesy Symposia, 1991

Research paper thumbnail of Geoid Computations in Taiwan

International Association of Geodesy Symposia, 1995

Research paper thumbnail of Gravimetric Geoid Determination for the Area of Greece

Astrophysics and Space Science Library, 1982

Research paper thumbnail of Combination of spaceborne, airborne and in-situ gravity measurements in support of Ocean Arctic Sea-Ice and MDT-mapping

Research paper thumbnail of ARCGICE Combination of Spaceborne, Airborne and In-Situ Gravity Measurements in Support of Arctic Sea-Ice Thickness Mapping

Research paper thumbnail of The European Network for studying the radio precursors of earthquakes: the case of the May 19, 2011 Turkey earthquake (Mw=5.7)

Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers was put into operati... more Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers was put into operation in Europe in order to study the disturbances produced by the earthquakes on the propagation of these signals. In 2011 the network was formed by nine receivers located three in Italy and one in Austria, Greece, Portugal, Romania, Russia and Turkey. On May 19, 2001 an earthquake with Mw=5.7 occurred in western Turkey, that is inside the "sensitive" area of the network. The radio data collected during April-May 2011 were studied using three different methods of analysis which are the wavelet spectra, the principal component technique and the standard deviation trends. Clear anomalies were revealed both in the signals broadcasted by the TRT transmitter (180 kHz) located near Ankara and in some VLF signals coming from transmitters located in western Europe and collected by the receiver TUR of the network located in eastern Turkey. Evident precursors phases were pointed out. Some ...

Research paper thumbnail of Global grids of gravity anomalies and vertical gravity gradients at 10 km altitude from GOCE gradient data 2009-2011 and polar gravity

ABSTRACT The GOCE satellite measures gravity gradients which are filtered and transformed to grad... more ABSTRACT The GOCE satellite measures gravity gradients which are filtered and transformed to gradients into an Earth-referenced frame by the GOCE High Level processing Facility. More than 80000000 data with 6 components are available from the period 2009-2011. IAG Arctic gravity was used north of 83 deg., while data at the Antarctic was not used due to bureaucratic restrictions by the data-holders. Subsets of the data have been used to produce gridded values at 10 km altitude of gravity anomalies and vertical gravity gradients in 20 deg. x 20 deg. blocks with 10&#39; spacing. Various combinations and densities of data were used to obtain values in areas with known gravity anomalies. The (marginally) best choice was vertical gravity gradients selected with an approximately 0.125 deg spacing. Using Least-Squares Collocation, error-estimates were computed and compared to the difference between the GOCE-grids and grids derived from EGM2008 to deg. 512. In general a good agreement was found, however with some inconsistencies in certain areas. The computation time on a usual server with 24 processors was typically 100 minutes for a block with generally 40000 GOCE vertical gradients as input. The computations will be updated with new Wiener-filtered data in the near future.

Research paper thumbnail of Gravity Field Mapping from a Combination of Satellite Altimetry and Sea Gravimetry in the Mediterranean Sea: By D. Arabelos, M. Vermeer

Research paper thumbnail of Anomalies Observed in VLF and LF Radio Signals on the Occasion of the Western Turkey Earthquake (M<sub>w</sub> = 5.7) on May 19, 2011

International Journal of Geosciences, 2012

Since 2009 a network of VLF (20 -60 kHz) and LF (150 -300 kHz) radio receivers is operating in Eu... more Since 2009 a network of VLF (20 -60 kHz) and LF (150 -300 kHz) radio receivers is operating in Europe in order to study the disturbances produced by the earthquakes on the propagation of these signals. In 2011 the network was formed by nine receivers, of which three are located in Italy and one is in

Research paper thumbnail of Wavelet analysis of the LF radio signals collected by the European VLF/LF network from July 2009 to April 2011

Annals of Geophysics, 2012

ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-... more ABSTRACT In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-300 kHz) bands was developed by an Italian factory. The receiver can monitor 10 frequencies distributed in these bands, with the measurement for each of them of the electric field intensity. Since 2009, to date, six of these radio receivers have been installed throughout Europe to establish a &#39;European VLF/LF Network&#39;. At present, two of these are into operation in Italy, and the remaining four are located in Greece, Turkey, Portugal and Romania. For the present study, the LF radio data collected over about two years were analysed. At first, the day-time data and the night-time data were separated for each radio signal. Taking into account that the LF signals are characterized by ground-wave and sky-wave propagation modes, the day-time data are related to the ground wave and the night-time data to the sky wave. In this framework, the effects of solar activity and storm activity were defined in the different trends. Then, the earthquakes with M ≥5.0 that occurred over the same period were selected, as those located in a 300-km radius around each receiver/transmitter and within the 5th Fresnel zone related to each transmitter-receiver path. Where possible, the wavelet analysis was applied on the time series of the radio signal intensity, and some anomalies related to previous earthquakes were revealed. Except for some doubt in one case, success appears to have been obtained in all of the cases related to the 300 km circles in for the ground waves and the sky waves. For the Fresnel cases, success in two cases and one failure were seen in analysing the sky waves. The failure occurred in August/September, and might be related to the disturbed conditions of the ionosphere in summer

Research paper thumbnail of Calibration of GOCE gravity gradient data using smooth ground gravity

Terrestrial gravity anomalies selected from three extended continental areas having a smooth grav... more Terrestrial gravity anomalies selected from three extended continental areas having a smooth gravity field have been used to determine the appropriate size of the area for gravity data collection as well as the data-sampling required for an external calibration of the GOCE gravity gradient data. The gravity data and a global gravity field model (EGM96) were used as input to least- squares collocation (LSC) which was used to calculate the error of predicted gravity gradient components at points on a realistic orbit of a simulated data set. The mean error showed that gravity gradient components could be predicted with an error of 2-3 mE (i.e. much below the expected error in the measurement band-width) in the case of an optimal size of the collection area and of the optimum resolution of the data. These optimal conditions e.g. for a smooth area inside Australia, correspond to an 0 0 12

Research paper thumbnail of Validation of Sea Level Anomalies – comparison of satellite altimetry and tide-gauge data in the Eastern Mediterranean

Sea level changes in the Eastern Mediterranean Sea are examined through the use of alti-metric da... more Sea level changes in the Eastern Mediterranean Sea are examined through the use of alti-metric data (SSALTO/DUACS gridded DT MSLA (Mediterranean Sea)), as well as data from tide-gauge stations in our research area. Annual Sea Level Anomalies for the period between 1993 and 2013 were obtained by averaging weekly values of SSALTO/DUACS gridded Delayed-Time Map of Sea Level Anomalies for the Mediterranean Sea. The results showed a small increase of Sea Level Anomaly (SLA) over the period under study. SLA in the Eastern Mediterranean was minimum in 1993, while in 2010 was maximum. Annual Sea Level Anomalies were also computed at locations near tide gauge stations in the Eastern Mediterranean Sea. Annual Mean Sea Level data from the Permanent Service for Mean Sea Level (PSMSL) and Oceanography Center of Cyprus were used to validate these altimetric data. In most cases, altimetric data are in agreement with the data from 20 tide-gauge stations in our research area. The maximum absolute difference between alti-metric and tide-gauge data is below 7 cm, except for the Piraievs station, where it is 11.69 cm. Introduction Aim of this study is to examine sea level variations in the Eastern Mediterranean Sea (30 ≤ φ ≤ 41, 22 ≤ λ ≤ 37). For this reason, we used altimetric data (SSALTO/DUACS grid-ded DT MSLA (Mediterranean Sea)), as well as data from tide-gauge stations in our research area. DUACS is part of the CNES multi-mission ground segment (SSALTO). It processes data from all altimeter missions: Saral/AltiKa, Cryosat-2, OSTM/Jason-2, Jason-1, Topex/ Poseidon, Envisat, GFO, ERS-1&2 and even Geosat. DUACS provides a consistent and homogeneous catalogue of products for varied applications, both for near real time applications and offline studies. DUACS gridded products (level 4), resulting from optimal analysis, are available free of charge for scientific studies or non-profit projects only. SSALTO/DUACS gridded DT MSLA is available in two versions. We chose 'reference' dataset, which is based on only two missions at most, with the same groundtrack. Thus, it is homogeneous all along the available time period thanks to a stable sampling. These 21-year period data (between 14-10-1992 and 07-08-2013) have spatial resolution 1/8º and temporal resolution 7 days.

Research paper thumbnail of PISTACH products for monitoring sea level variations in the Eastern Mediterranean using different mean sea surface models

Sea level changes in the Eastern Mediterranean Sea are examined through the use of coastal altime... more Sea level changes in the Eastern Mediterranean Sea are examined through the use of coastal altimetry PISTACH products. This study involves ascending passes 7, 83, and 159 of Jason-2 mission, as well as descending passes 68, 170 and 246, which pass over our research area. Data from 199 cycles were used, covering the period from July 2008 to December 2013. Sea Level Anomalies (SLA) were computed using mean sea surface model CLS01 and were obtained by averaging the values for each cycle. The investigation resulted in a large increase of SLA of about 20-30 cm in the period between 31 July 2012 and 7 August 2012. From then, SLA remained at a higher level than before. PISTACH products are conceived as an experimental evolution of the Jason-2 level-2 products and therefore we cannot rely on them to come to the conclusion that SLA had such a large increase. SLA were also computed using mean sea surface model DNSC08. Comparison of the results showed differences of SLA up to 42 mm. Introduction Purpose of this study is to examine sea level changes in the Eastern Medi-terranean Sea (30 ≤ φ ≤ 41, 22 ≤ λ ≤ 37) using PISTACH products. Many crucial issues for science, society or the economy arise in coastal zones and near continental waters. However, altimeter and radiometer instrument observations are perturbed by emerged lands (50 km off the coasts for radiometers, about 10 km for altimeters). This leads to missing or degraded data in the distributed datasets, mostly meant for open ocean studies. However, the instruments do give measurements which contain useful information for areas between 50 km offshore and the coastline, over continental water bodies and over emerged land as well. This is why CNES funded the PISTACH project (Prototype Innovant de Système de Traitement pour les Applications Côtières et l'Hydrologie, or Innovative Processing System Prototype for Coastal and Hydrology Applications), as part of the Jason-2 Project, to improve satellite radar altimetry products over coastal areas and continental waters. Basically, PISTACH products are conceived as an experimental evolution of the Jason-2 level-2 products. This study involves ascending passes 7, 83, and 159 of Jason-2 mission, as well as descending passes 68, 170 and 246, which pass over our research area.