Philippe Schaeffer

Philippe Schaeffer
Collecte Localisation Satellites | CLS · Space Oceanography Group

R&D Engineer

About

38
Publications
7,122
Reads
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1,151
Citations
Citations since 2017
3 Research Items
347 Citations
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2017201820192020202120222023020406080
2017201820192020202120222023020406080
2017201820192020202120222023020406080

Publications

Publications (38)
Article
Full-text available
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and mo...
Article
Full-text available
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and mo...
Article
This paper presents an assessment and comparison of recent mean sea surface (MSS) models. Using a new approach and independent altimeter data sets, we quantify the major improvement of the CNES_CLS15 and the DTU15 models. We observe a reduction in the amplitude of omission errors thanks to the use of new geodetic altimeter data sets (i.e., Cryosat-...
Article
Precise orbit prediction requires a forecast of the atmospheric drag force with a high degree of accuracy. Artificial neural networks are universal approximators derived from artificial intelligence and are widely used for prediction. This paper presents a method of artificial neural networking for prediction of the thermosphere density by forecast...
Article
The ageing of Jason-1, the risk of losing control of the satellite, and the collision risk with TOPEX/Poseidon (still in orbit, and no longer maneuverable) initiated a reflectionon a so-called “Extension of Life phase” (EoL) phase that would involve moving Jason-1 to a new orbit to mitigate collision risks while optimizing its science return.This p...
Article
This article focuses on the determination and the validation of the new Mean Sea Surface from the CNES/CLS. This new model merges multiple satellite altimeters over 16 years of observations. Particular attention was paid on the analysis of the oceanic variability. Then a novel method was applied to remove this variability and to take into account d...
Article
At the end of 2011, the CNES/CLS Analysis Center has entirely re-processed the whole DORIS data set for orbit determination and tracking station coordinate estimation. In addition to SPOT-2, -3, -4, -5, Topex/Poseidon and Envisat, the DORIS/DGXX measurements of Jason-2 and Cryosat-2 are included in the products delivered to the IDS (combined multi-...
Article
Accurate knowledge of the ocean Mean Dynamic Topography at all spatial scales is mandatory for the full exploitation of altimetric data including their assimilation into operational ocean forecasting systems. In preparation for future GOCE data, whose resolution will allow to estimate the ocean MDT with centimetric accuray at 100km scales, a new gl...
Article
New marine gravity data have been integrated in the SHOM processing tools to improve the knowledge of the geoid. The studied area is covering the continental margin west of France up to Kingstrough structure. This paper presents the collocation method applied to compute the geoid from marine gravity data. An evaluation of the first results are show...
Article
The remote-sensing satellite ERS-1, launched in 1991 to study the Earth's environment, was placed on a geodetic (168-day repeat) orbit between 1994 April and 1995 March to map, through altimetric measurements, the gravity field over the whole oceanic domain with a resolution of 8 km at the equator in both along-track and cross-track directions. We...
Chapter
Full-text available
Initially, existing mean dynamic topography (MDT) models were collected and reviewed. The models were corrected for the differences in averaging period using the annual anomalies computed from satellite altimetry. Then a composite MDT was derived as the mean value in each grid node together with a standard deviation to represent its error. A new sy...
Article
Full-text available
Two approaches of ocean color data merging were tested and compared in the North and Equatorial Atlantic Basin: the weighted averaging and the objective analysis. The datasets used were the daily level-3 binned data of chlorophyll-a from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Moderate Resolution Imaging Spectroradiometer on the Aqu...
Conference Paper
Full-text available
The contribution of a recent geoid model derived from GRACE data (EIGEN-GRACE03S) for estimating the ocean Mean Dynamic Topography is investigated for global and regional studies. The recent EIGEN-GRACE03S geoid model allows to greatly improved the estimate of the ocean Mean Dynamic Topography (hereafter GR3-400 MDT) at scales larger than 400 km. A...
Article
The use of gravity field and steady state Ocean Circulation Explorer (GOCE) for operation oceanography is discussed. One of the main objectives of GOCE is to provide a sufficiently accurate geoid model to allow a precise estimation of absolute dynamic topography from altimetry. MERCATOR, the French initiative, is developing an operational capacity...
Article
Full-text available
In order to create high-resolution gravity maps in oceanic areas, all type of data have to be used and merged to preserve each specific knowledge. For this purpose, we use marine gravity data and satellite altimetric data. Each type of measurements gives information on a specific bandwidth of the gravity spectrum. The problem of mixing such heterog...
Article
The ERS-1 satellite, launched in 1991, has provided altimetric observations of the Greenland Ice Sheet and 80 per cent of the Antarctica Ice Sheet north of 82°S. It was placed in a geodetic (168-day repeat) orbit between April 1994 and March 1995, yielding a 1.5 km across-track spacing at latitude 70° with a higher along-track sampling of 350 m. We...
Article
The ERS1 satellite provides a high-resolution radar altimeter measurement up to 81.5° latitude for polar cap studies. Here we examine one particular effect of the interaction between the radar wave and the snowpack surface on height measurements. Measurements from ascending and descending tracks show systematic differences as large as 1 m. Such an...
Article
Tide gauge measurements recorded between 1978 and 1993 indicate that the Caspian sea level (CSL) has been rising at an average rate of ~12cm/yr during this 15-yr time span. Decadal CSL changes are currently attributed to changes in river runoff and effective evaporation. We have analysed three and a half years (from January 1993 through August 1996...
Article
Tide gauge measurements recorded between 1978 and 1993 indicate that the Caspian sea level (CSL) has been rising at an average rate of ∼12 cm/yr during this 15-yr time span. Decadal CSL changes are currently attributed to changes in river runoff and effective evaporation. We have analysed three and a half years (from January 1993 through August 199...
Article
A short-arc orbit technique was developed, and a very precise and efficient tool for regional orbit determination with a rigorous error budget is proposed for analyzing the TOPEX/POSEIDON (T/P) and ERS 1 missions. The purpose is to be able to determine very accurately, in some conditions, the local orbit, with a very small error in the radial direc...

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Projects

Project (1)
Project
In collaboration with the CNES and NASA oceanographic projects (T/P and Jason 1), the OCA developed a verification site in Corsica since 1996 and LEGOS installed sites in Kerguelen in 1993 and at Vanuatu in 1999. CALibration/VALidation embraces a wide variety of activities, ranging from the interpretation of information from internal-calibration modes of the sensors to validation of the fully corrected estimates of the reflector heights, whether it is sea level or inland water stage using in situ data. Now, Corsica is, like the Harvest platform (NASA side), an operating calibration site able to support a continuous monitoring with a high level of accuracy: a ’point calibration’ which yields instantaneous bias estimates with a 10-day repeatability of around 30 mm (standard deviation) and mean errors of 3-4 mm (standard error). We intend to continue and ensure the experiments already conducted during the first part of the FOAM project (2008-2012) at various sites (Corsica, Vanuatu, Kerguelen, lakes and rivers…) where the local conditions are different from each others but where permanent instruments and infrastructures already exist and have to be reinforced. In order to increase statistically the sea surface bias estimation but also to cover larger areas, we suggest to extend the calibration opportunities by using, not only over-flying passes, but also satellite passes located far away from the CAL/VAL site (few hundreds kilometers). Due to the increasing need of altimetry to monitor inland waters and in preparation to future missions (e.g., SARAL/AltiKa, Sentinel-3, Jason 3, Jason CS, SWOT) we propose to integrate the calibration activities on the oceanic domain and those on different water bodies such as rivers and lakes. The main objectives of the FOAM project continuation is two-fold: (i) ensure the experiments already conducted during the first part of the FOAM project (2008-2012) and (ii) conduct new developments in terms of processing and technology (GNSS reflectometry (GNSS-R), GPS buoy design and processing, …).