National Aeronautics and Space Administration

 

Centre National d’Etudes Spatiales

 

 

NRA-97-MTPE-09

TP2-J0-BC-580-MS-CNES

 

 

Role of the Error Propagation in the Altimetric Data Analysis: Orbit, SLR and DORIS Tracking Measurements, and Instrumental Calibration

 

 

Principal Investigator:

Pierre Exertier

UMR-6527, OCA-CERGA, av. N. Copernic, F-06130 Grasse, France

 

Co-Investigators:

P. Bonnefond, O. Laurain, Y. Boudon and F. Barlier

OCA-CERGA, av. N. Copernic,

06130 Grasse, France

Y. Ménard, E. Jeansou and A. Orsoni

CNES, av. Ed. Belin,

31055 Toulouse Cedex, France

 

 

F. Pierron

OCA-CERGA, Observatoire de Calern, Caussols,

06130 Grasse, France

B. Haines

JPL,

Pasadena CA 91109, US

 

 

 

J.J. Benjamin-Martinez

University of Catalugna,

Barcelogna, Spain


 

GROUPE DE TRAVAIL SCIENTIFIQUE JASON-1

I.       COVER LETTER

Page de garde des propositions

Annonce pour la Recherche NASA/CNES

N° 97-MTPE-XX, TP2-J0-BC-580-MS-CNES

 

 

Proposition n°.......................... (ne pas remplir, réservé NASA/CNES)

Titre : Role of the Error Propagation in the Altimetric Data Analysis: Orbit, SLR                and DORIS Tracking Measurements, and Instrumental Calibration    

Chercheur principal :

Nom : Exertier, Pierre ...............................................................................................

Département : UMR 6527 (CERGA) ........................................................................

Organisation : Observatoire de la Côte d’Azur .......................................................

Rue / B.P Avenue Nicolas Copernic..........................................................................

Ville : Grasse ........... Etat :...................................... Code postal : 06130...................

Pays : France............ Adresse e-mail : exertier@obs-azur.fr...................................

Téléphone : (33-4/04) 93-40-53-86 ......................... Fax : (33-4/04) 93-40-53-33......

 

 

Collaborateurs :

Nom

Organisation

Téléphone

Bonnefond, Pascal

UMR 6527 - OCA

(33-4/04) 93-40-53-63

Laurain, Olivier

UMR 6527 - OCA

(33-4/04) 93-40-53-45

Boudon, Yves

UMR 6527 - OCA

(33-4/04) 93-40-53-81

Barlier, François

UMR 6527 - OCA

(33-4/04) 93-40-53-46

Pierron, Francis

UMR 6527 - OCA

(33-4/04) 93-40-54-20

Ménard, Yves

CNES - ED/AL/JT

(33-5/05) 61-27-48-72

Jeansou, Eric

CNES - ED/AL/MA

 

Orsoni, Alain

CNES - ED/AL/MA

 

Haines, Bruce

JPL

 

Benjamin-Martinez, J.J.

University of Catalugna

 

 

 

Budget (pour investigateurs américains et français seulement) :

 

1ère année 80 KF................... 2ème année 350 KF.................. 3ème année 350 KF

 

Total : 780 KF......................

 

 

Autorisé par : François Mignard    CNRS - UMR 6527

                             (Nom)                         (Organisation)

II.       TABLE OF CONTENTS

I. COVER LETTER..........................................................................................................

II. TABLE OF CONTENTS.............................................................................................

III. IDENTIFYING INFORMATION.............................................................................

III.1. Title.......................................................................................................................

III.2. Principal Investigator..........................................................................................

III.3. Co-Investigators...................................................................................................

III.4. Cooperations........................................................................................................

IV. INVESTIGATION AND TECHNICAL PLAN.......................................................

IV.1. Summary..............................................................................................................

IV.2. Experimental Objectives.....................................................................................

IV.2.1. Orbitography...................................................................................................

Near-real time validation......................................................................................

Long term stability................................................................................................

IV.2.2. Error Analysis.................................................................................................

IV.2.3. Calibration Experiment..................................................................................

IV.2.4. Altimetry..........................................................................................................

IV.3. Approach..............................................................................................................

IV.3.1. Methods...........................................................................................................

Geometrical short-arc technique..........................................................................

Semi-analytical methods........................................................................................

IV.3.2. Experimental: Corsica-Capraia absolute calibration experiment.................

Site and instruments..............................................................................................

Methodology..........................................................................................................

IV.4. Experimental and Work Plan.............................................................................

IV.4.1. Prelaunch Phase.............................................................................................

Extended short-arc orbit technique.......................................................................

Semi-analytical methods......................................................................................

Improvement of the Corsica experiment configuration.......................................

IV.4.2. Validation Phase...........................................................................................

Precise orbit validation.......................................................................................

Absolute calibration experiment..........................................................................

IV.4.3. Whole Mission...............................................................................................

Long-term orbit precision stability.....................................................................

Periodical absolute calibration experiment........................................................

Mediterranean mean sea level variations...........................................................

IV.4.4. Summary of the Needed Products................................................................

IV.5. Anticipated Results and Significance of the Investigation.............................

IV.6. References...........................................................................................................

V. MANAGEMENT PLAN AND COST PLAN..........................................................

V.1. Management Plan................................................................................................

V.2. Cost plan..............................................................................................................

V.2.1. Cost categories................................................................................................

V.2.2. Detailed cost schedule.....................................................................................

VI. BIOGRAPHICAL INFORMATION OF THE P.I.................................................

III.       IDENTIFYING INFORMATION

III.1.       Title

Role of the Error Propagation in the Altimetric Data Analysis: Orbit, SLR and DORIS Tracking Measurements, and Instrumental Calibration

III.2.       Principal Investigator

Pierre Exertier

UMR-6527, OCA-CERGA, av. N. Copernic, F-06130 Grasse

Tel: 33.4.93.40.53.86, Fax: 33.4.93.40.53.33

E-mail: exertier@obs-azur.fr

III.3.       Co-Investigators

·         Related topics: the whole proposal

Pascal Bonnefond, Olivier Laurain, Yves Boudon and François Barlier

UMR-6527, OCA-CERGA, av. N. Copernic, F-06130 Grasse

Tel: 33.4.93.40.53.53, Fax: 33.4.93.40.53.33

E-mail: bonnefond@obs-azur.fr, laurain@obs-azur.fr, barlier@obs-azur.fr

 

·         Related topics: French Transportable Laser Ranging Station, absolute calibration

Francis Pierron

UMR-6527, OCA-CERGA, Observatoire de Calern, Caussols, F-06130 Grasse,

Tel: 33.4.93.40.54.20, Fax: 33.4.93.40.53.33

E-mail: pierron@obs-azur.fr

 

·         Related topics: absolute calibration

Yves Ménard (CNES), Eric Jeansou (SILOGIC) and A. Orsoni (IGN)

CNES, av. Ed. Belin, 31055 Toulouse Cedex

E-mail: Yves.Menard@cnes.fr, jeansou@thetis.cst.cnes.fr, Alain.Orsoni@cnes.fr

 

·         Related topics: absolute calibration

Bruce Haines

Jet Propulsion Laboratory, California Institute of Technology

Pasadena CA 91109, US

E-mail: bjh@cobra.jpl.nasa.gov

 

·         Related topics: collaboration for absolute calibration

Juan Jose Benjamin-Martinez

University of Catalugna, Department of Applied Physics

08034 Barcelogna, Spain

III.4.       Cooperations

Cooperations will be developed with other groups in France: C. Le Provost and A. Cazenave (GRGS/Toulouse), C. Boucher and P. Willis (IGN)

IV.       INVESTIGATION AND TECHNICAL PLAN

IV.1.       Summary

The primary objective of this investigation is related to space geodesy and consists to better understand the role of the error propagation into the altimetric data analysis. It is expected to establish a kind of data base related to the errors in the various aspects of modeling, methods and data editing scheme. The technical aspects of the investigation will include : (i) analysis of the orbit quality and improvement of the precise orbit determination at local and global space scales thanks to an extended short-arc technique, (ii) analysis of the tracking measurements - laser and DORIS - including the monitoring of their associated error budget and the role of the error propagation into the orbit and the terrestrial reference frame, (iii) an absolute calibration campaign of the radar altimeter, and (iv) the determination of mean sea surfaces as well as the estimation of their temporal variations at different space scales, in particular at very low frequencies.

The global analysis of error propagations which is proposed as a scientific objective must lead to better evaluate the limit under which the interpretation of the altimetric data should be corrupted.

During the prelaunch phase of the Jason mission, our investigation will include several aspects, though some of them have already been investigated or are going to be analyzed :

          - the determination of error budgets for laser tracking instruments involved in the TOPEX/Poseidon precise orbit during the period 92-97, and the comparison in term of orbit residuals per instrument with the laser tracking on LAGEOS satellites,

          - the analysis of DORIS orbit residuals during the same period, which are still at the level of 0.55 mm/sec, and the comparison with a semi-analytical a priori analysis of possible error sources (gravity field, reference frame, geophysical corrections, instrumental bias),

          - the development of an extended short-arc orbit technique, in view of controlling and improving the dynamic precise orbits of Jason‑1,

          - technological aspects, as the improvement of the French Transportable Laser Ranging System (detector, frequency, divergence and pulse width), the development of a regional geodetic network between Grasse and Corsica including laser, DORIS and GPS positioning and an absolute gravimetric campaign,

          - an absolute calibration campaign in Corsica of T/P altimeters in the same conditions than for the future validation phase of Jason‑1.

 

IV.2.       Experimental Objectives

The determination of mean sea level variations is a central question in the current debate on climate change and its impact on the environment including oceanic circulation features. To answer this, oceanography needs very accurate time series from satellite altimetry but also longer series from tide gauges data. In both cases, problems in geodesy are much more difficult to solve, taking into account the 1-cm overall accuracy objective for Jason‑1. From the space point of view, orbit quality is of particular importance but error budget on the altimetric measurements is also at the same level. From the terrestrial point of view, the geodetic link of tide gauges into the space reference frame defined by satellite altimetry is also one of the most important problem in geodesy. These aspects will lead us to develop ultra-precise validation and calibration techniques, including in-situ absolute calibration experiment.

These components - orbit, measurements and their calibrations - form the basis of all the error budgets published in the framework of the TOPEX/Poseidon (T/P) mission during both geophysical evaluation and scientific results phases [Bonnefond et al., 1995; Marshall et al., 1995]. They have permitted: (i) to constrain the results of the mission giving limits to the interpretation of altimetric signals, (ii) to indicate the possible improvement sources and (iii) to contribute to the development of new evaluation, validation and calibration methods [Nouël et al., 1994; Tapley et al., 1994].

In collaboration with other investigators of the T/P Extended Mission and Jason‑1 Mission Science Working Team working at understanding the coupling effect between climate and sea level global changes [Cazenave et al., 1997], our contribution will be dedicated to a large error analysis. Actually, we will focus on the analysis of Satellite Laser Ranging (SLR), DORIS tracking, and geodetic measurements, including tide gauges and collocations, for controlling and demonstrating the capability for the T/P, ERS-1/2 and Jason‑1 data to detect very fine changes in sea level.

IV.2.1.       Orbitography

Near-real time validation

Principally during the validation phase but also extended to the whole Jason‑1 mission, we intend to estimate the quality of the operational precise orbit. This estimation will be mainly based on orbit errors determination using a laser-based short-arc technique. In the framework of T/P such a technique has proved to be able to evaluate not only the precision but also the accuracy of dynamic orbits [Bonnefond et al., 1995; Bonnefond et al., 1997a]. However, it can only be done in specific area where a dense SLR data coverage is available, namely US and Europe. We will then also compare results with other independent methods such GPS-based reduced dynamic technique [Haines et al., 1995].

Long term stability

The validation process describes previously will be able to evaluate the « short-period » orbit errors (over a repeat cycle). However it is important to estimate the long-period stability of the orbit determination process in order to prevent any very low-frequency orbit errors which can induce not realistic sea level signals. This will be done using an orbit filtering technique and a semi-analytical theory of the mean orbital motion applied over long time period [Métris and Exertier, 1995].

IV.2.2.       Error Analysis

Error analyses, as scientific objective in space geodesy, are going to play an increasing role in space geodetic projects like altimetry. The improvement of the precise orbit determination and the estimation of its error budget in time and space have been undoubtedly great priorities in this field [Bonnefond et al., 1995; Marshall et al., 1995]. However, taking into account the new requirements of Jason, at the level of one centimeter, our objectives are to enlarge the study of the error propagation above the orbit determination. From a global point of view, by analyzing the laser and DORIS tracking measurements (precision and biases) associated to a given terrestrial reference frame and their « true » capability to control the orbit determination. From a regional and local point of view, by establishing and monitoring a dedicated geodetic network including laser, DORIS and GPS positioning and tide gauges measurements in order to be able to re-iterate at several occasions an absolute calibration campaign.

IV.2.3.       Calibration Experiment

During the last years, complementary altimetric missions have notably permitted to compare the instruments: relative calibrations have been achieved, global statistics and results show the power of such a technique [Benveniste, 1997]. However, recent problems have been discovered both in the algorithms and the instruments: the SPTR and USO drift corrections for ERS [Benveniste, 1997] and the oscillator drift corrections for TOPEX/Poseidon [AVISO, 1996]. This reinforces the interest of regular absolute calibration campaigns to detect such problems in near-real time. Beyond the calibration of the altimeters, the calibration sites also are very useful in assessing the various components of the altimetric systems, even if it is only a single-point verification. The calibration sites are often equipped with a complete system of in-situ instruments which have the capability of measuring very accurately the environmental parameters interfering in the altimetric measurement: sea state, sea level, troposphere and ionosphere effects, reference frame stability, etc. [Ménard et al., 1994].

Such work has begun notably with a probationary experiment which has been carried out between Grasse (France), Corsica (France) and Capraia (Italy), from October 96 to February 97 [Bonnefond et al., 1997b]. It has been conducted by OCA-CERGA, CNES and IGN. Results have been analyzed and show the different ways of possible improvements [Stoufs, 1997].  Thus, we propose to iterate this experiment in 1999, as a « campaign-0 » before the launch of Jason‑1 in order to make benefits of our last calibration campaign on the  same site. It is expected to assess the validity of new materials and choices which are under considerations here, taking into account requirements of the new mission. This will prepare the effective calibration of Jason‑1 in early 2000 as a « campaign-1 » to be performed during the validation phase of the mission.

IV.2.4.       Altimetry

In the framework of Jason‑1, we intend to continue our analysis on the mean sea level fluctuations over the Mediterranean area [Bonnefond et al., 1995]. This work is being conducted under contract with the European Community [SELF II, 1997] and in collaboration with A. Cazenave (GRGS/Toulouse, France). The contract will end at the beginning of 1998 but we will continue to increase altimetry time series, in order to better monitor the sea level variations and then to better separate interannual signals and secular trend. This work is linked to A. Cazenave proposal to Jason‑1 Science Working Team, as we are also Co-Investigators [Cazenave et al., 1997]: details for this study can be found in the A. Cazenave proposal.

IV.3.       Approach

IV.3.1.       Methods

Geometrical short-arc technique

The approach we use for the short-arc orbit determination strategy is to assume that a long-arc orbit is available covering several days (e.g., one repeat cycle) determined from a given global tracking data set (in practice, essentially SLR and DORIS data). We determine corrections to this dynamic orbit for short arcs that are typically of 10 to 15 min. duration and so of length up to about 4000 km. Let us note that the corrected tracks of the satellite are no longer exact solutions of the differential equation system for its motion. Instead of dynamically fitting short arcs, we determine, in fact, kinematic corrections representing local orbit errors as well as station coordinate errors or systematic errors in the tracking data. The values of these corrections to be applied to the input orbit are estimated in a least squares procedure from the intensive SLR tracking data that is assumed to be available along the short arcs. Moreover, criteria on the geometrical configuration - between the tracking network and the passes - have been determined and selected in order to guarantee a short-arc radial precision better than 2 cm [Bonnefond et al., 1995].

Semi-analytical methods

The technical aspects on which the error analysis is based concern a priori models and semi-analytical methods, and then a large investigation in the data, the laser and DORIS tracking data in our case. As an example, geographically correlated orbit errors have been evidenced by theoretical considerations [Exertier and Bonnefond, 1997a]; in addition they have been estimated by comparing different techniques and data [Bonnefond et al., 1997a; Haines et al., 1995; Tapley et al., 1994].

Figure 1.  Predicted radial velocity errors (mm/s), for a pseudo-DORIS Doppler signal, due to the difference in coefficients between the JGM-3 and GRIM4-S4 models for the T/P orbit. The circles correspond to projections of the DORIS station visibility cones.

However, for TOPEX/Poseidon, it is true that inadequate knowledge of the gravity field is no longer the dominant source of orbital error. As an example of developing theoretical methods which concern the propagation of error due to the gravity field in the orbit, we have demonstrated that this error in term of predicted DORIS residuals is at level of 0.2 mm/s (Figure 1) in average at the T/P altitude [Exertier et al., 1997b]. This work shows that DORIS in its present form, with measurement errors currently around 0.3 mm/s, can provide no more extra information, on average, on Earth's gravity field from the TOPEX/Poseidon orbital altitude. To improve the gravity field using DORIS tracking measurements, we need to progress toward 0.1 mm/s instrumentation in similar future missions, e.g. Jason‑1. We need to look elsewhere for the cause of the current 0.55 mm/s rms error.

IV.3.2.       Experimental: Corsica-Capraia absolute calibration experiment

Figure 2.  Configuration of the Corsica-Capraia experiment.

Site and instruments

Figure 3.  French Transportable Laser Ranging Station at Aspretto (Ajaccio, Corsica).

The choice of the site is of course very important for such an experiment because laser station and tide gauges have to be close to the altimetric measurements to be calibrated. If a small island is theoretically better in order to avoid altimeter problems during the overflight, it often requires complicated logistics. Near Corsica, the ERS and T/P ground tracks configuration as well as the implantation possibility have conducted to the choice of a double site (Figure 2). First, the island of Capraia (Italy) is very closed to T/P and ERS‑2 crossover points and benefits of an existing tide gauge. On the other hand, Ajaccio (Corsica) is a better site concerning the administrative authorizations and the geographical access; it allows to minimize the costs. The French Transportable Laser Ranging Station (FTLRS, CNES-IGN-CERGA) has been installed, on a small hill, at the Aspretto’s BAN (air and sea military base, located ~2 km from Ajaccio, Figure 3). This military base offers classical logistic infrastructure and has a small private port with relatively small traffic. A MORS tide gauge (EPSHOM, Brest) has been immersed at this place to be close to a descending ERS‑2 ground track (number 130). The closest T/P ground track is ascending (number 85) and located at 40 km south. An AANDERAA tide gauge (CNES, Toulouse) has been then immersed at the Senetosa cap, 1.5 km apart from the T/P sub-satellite track (number 85).

The FTLRS of course plays a dominating role in this experiment, concerning principally the operating and budget levels as well as the quality of the results. It is also the first operational experiment with this instrument permitting to demonstrate the laser ranging precision is of about 2 cm. Moreover, a collocation campaign with the DORIS tracking system has been realized. To this purpose, CNES and IGN have collaborated in installing the DORIS beacons and in positioning the reference points with GPS respectively. During this experiment, due to the proximity of the main DORIS beacon (Toulouse), it was necessary for the DORIS ground segment to use the Kourou site as main beacon.

Methodology

The approach we are going to use in this experimental investigation is based on the following aspects, already initiated during the last campaign:

·         Acquisition: observations of satellites passes with laser ranging and DORIS beacons.

·         Geodetic collocation: determination of SLR coordinates and comparison with DORIS/GPS solutions. Short-arc technique is used to reduce the orbit errors part in the total error budget, allowing to homogenize the reference system for a multi-satellites solution.

·         Geodetic links: A GPS survey tie has been established on one side between the SLR sites in Ajaccio and Grasse, and on the other side between the tide gauge leveling mark and Ajaccio. An optical leveling has been performed between the tide gauge leveling mark and the instrument reference, so that the tide gauge measurement could be linked to a global geodetic reference system through the Senetosa/Ajaccio (FTLRS station coordinates) baseline. International Terrestrial Reference Frame (ITRF) will be adopted.

·         Altimetric data analysis: 10 per second altimetric data were spatially filtered on 50 km, using a mean track computed with 3 years TOPEX/POSEIDON data.

·         Tide gauges data analysis: A pressure tide-gauge with a 5 min acquisition rate at Senetosa. A second pressure tide-gauge with a 2 min acquisition rate was settled near Ajaccio. The two time series showed a sufficient correlation so that data from Ajaccio can be used in place of those of Senetosa, a 2 months coincident period having permitted to compute the leveling bias between both sites (geoid effect).

·         Orbit: Short-arc orbit computation for calibration passes using SLR data from regional network and from FTLRS.

In this field, the development of a pseudo-permanent collocation and calibration site in the western Mediterranean area, in order first to estimate the radar altimeter bias, is an opportunity to have available a true experimental field where the different error sources could be clearly analyzed.

IV.4.       Experimental and Work Plan

IV.4.1.       Prelaunch Phase

Extended short-arc orbit technique

We are currently working on the improvement of a such technique in order to increase the overall accuracy to the 1 cm level required for Jason‑1. However, the main part of the overall error comes from SLR data and laser station coordinates and not from the method used. Then we are trying to improve data editing techniques in order to select automatically data/SLR sites with the required accuracy.

We are also working on the existing software (CALTIM, OCA-CERGA) to be almost fully automatic in order to be able to validate the precise orbit determination (CNES) in near-real time.

Semi-analytical methods

At the level of one centimeter, the role of the terrestrial reference frame and tracking measurements, in term of precision and accuracy, has to be evidenced and clearly estimated in view of the orbit determination at global, regional and local space scales. Thanks to orbit improvements realized during the current T/P altimetric mission, a posteriori error budgets have been published on these topics [Bonnefond et al., 1997a]. But it is expected in this investigation to a priori analyze the error propagation and to extend existing methods to improve the orbit accuracy and finally the altimetric products. As practical examples of possible error sources to be investigated, it is expected to study the effects of the geocenter motion, atmospheric pressure loading, long periodic tides, and instrumental accuracy stability.

Improvement of the Corsica experiment configuration

During the prelaunch phase of Jason‑1 we will focus our efforts concerning absolute calibration experiment on the following items, in order to achieve an optimal configuration before the launch:

·         Site configuration:

Additional local studies are planned to better apprehend geoid effects: two tide gauges (provided by CNES Jason‑1 Project) are planned to be installed at the beginning of 1998 on either side of T/P track at Senetosa. New GPS observations will be performed by IGN. A meteorological station will also be installed in the vicinity of the tide gauges.

Other sites will also considered with better land/sea configuration from the altimeter: GPS buoy (studied by CNES Jason‑1 Project) near Bastia for the same T/P ground track as observed at Senetosa (number 85, see Figure 2).

·         FTLRS improvement:

The actual precision and accuracy of the FTLRS is at the level of other good stations in the SLR network, allowing a great quality in the determination of station coordinates. However, improvements have to be done in two principal directions:

          - acquisition of SLR data on LAGEOS satellites,

          - better stability on the time biases and the calibration.

This is particularly important for using this SLR station for short-arc orbit determination in the altimeter calibration process. We have to underline that such improvements are in progress at CERGA (F. Pierron) in preparation of Jason-1 mission.

·         « Campaign-0 » in 1999:

The duration of joint laser and tide-gauge observations should be of at least 5 months in order to benefit from the diminution of geographically correlated error by the short arc technique.

Tide gauges measurements will be available at CNES (Jason‑1 Project team).

All other products (orbit, tracking data, altimetric data) are available through the T/P Extended Mission project, in which we are involved.

IV.4.2.       Validation Phase

Precise orbit validation

This validation will be performed using the extended short-arc orbit technique, based on SLR tracking measurements available at CDDIS. For this purpose the main product needed is Precise Orbit (DORIS level 1b will be also required).

Absolute calibration experiment

The effective calibration of Jason‑1 is proposed to be realized during the validation phase of the mission. The « campaign-1 » will be a reiteration of the previous « campaign-0 ». For this purpose the products needed are as follows:

- Preliminary Orbit and IGDR (at least for calibration passes, number 85 for T/P)

- Precise Orbit and GDR

- SGDR Altimetric: when needed

IV.4.3.       Whole Mission

Long-term orbit precision stability

The long-term accuracy stability of the orbit is of very great importance as Jason objective is to obtain a very accurate monitoring of mean sea level variations at very low frequency. As previously said, we intend to study long-term orbit errors using the semi-analytical method develop at CERGA [Métris and Exertier, 1995]. This study will require to use Precise Orbit product as input of the method.

Periodical absolute calibration experiment

We want to underline that a single absolute calibration experiment is not sufficient to insure the requirement of Jason‑1. Indeed, problems in the algorithms or instrumental drifts should be monitor. This leads us to propose to renew the calibration campaign periodically (about once per year). We have to define with the project how to program and fund such periodical experiment.

Mediterranean mean sea level variations

The study of the mean sea level variations in the Mediterranean area will be performed continuously from the beginning of Jason‑1 mission. We will increase the time series already obtained with TOPEX/Poseidon and then try to identify very accurately the interannual signals and the secular trend. Even if this study will be realize in collaboration with A. Cazenave team, we need to receive GDR independently in order to perform our own analyses which will then be compared to those of A. Cazenave.

IV.4.4.       Summary of the Needed Products

·         Precise Orbit and Preliminary Orbit

·         DORIS level 1b

·         IGDR and GDR

·         SGDR (only for calibration passes)

IV.5.       Anticipated Results and Significance of the Investigation

The present proposal is focused on some geodetic and metrological features of the Jason‑1 mission but it includes also some geophysical applications performed in a cooperative effort. It is based on the following concepts. An accurate metrology always requires a strong permanent effort towards quality measurements and quality control. Systematic errors can only be evidenced, estimated and controlled either by theoretical considerations or by comparing different techniques (principle of collocation of techniques). As soon as the effort of improvement of facilities, tools, softwares, is stopped or diminished, the global quality of the metrology is decreasing. From this point of view, the 1 cm challenge in precision and possibly in accuracy is a very good objective, although nobody knows what exactly will be reached in precision and in accuracy (see the T/P mission but this time the progress will not be so spectacular, taking into account the present status of the metrology quality).

According to this proposal a positive step is expected on the following points:

·         Laser network improvement: the Grasse station and the mobile laser station (FTLRS) stations should be upgraded in accuracy, stability of biases and reliability. It is true also for the EUROLAS network which undertakes a general improvement in terms of the new international laser service. From this point of view, we are currently studying long-term stability of laser ranging accuracy through correlation of laser residuals per station between several satellites (e.g., TOPEX/Poseidon, LAGEOS I and LAGEOS II). An example of such correlations and amplitudes of the long-term variations of accuracy is shown in Figure 4.

·         Collocation experiments will be carried out in Grasse and Corsica between DORIS, GPS and SLR techniques. From the Corsica campaign we have demonstrated that it is possible to determine FTLRS station coordinates using low satellites (800 to 1500 km) with a precision at the level of 1-2 cm, which was confirmed by results of the collocation [Stoufs, 1997]. But some improvements could be achieved, and it is the purpose of the future campaign to do it.

·         Local geodetic networks will be set up including the vertical components at Grasse and Ajaccio (Corsica), with absolute gravity measurements and tide gauges measurements. Local mean sea level with high space resolution will be determined (ERS‑1 and GEOSAT geodetic missions data). Other areas could be considered if funded (Tahiti, Baleares and Canaries islands for example).

·         A cooperative and coordinated action will be performed with other groups and other laboratories (JPL, B. Haines; University of Texas, C.K. Shum; University of Cadiz and Catalugna, M. Catalan and J.J. Benjamin-Martinez).

·         An orbit improvement will be performed by short-arc techniques, including an error budget to be compared to dynamical or reduced-dynamic orbits. The nominal precision of the DORIS beacons should be of the order of 0.1 mm/s for better results on coordinates adjustment as well as for other geophysical studies such as gravity field improvement [Exertier at al., 1997].

Mean orbits will also be determined also for comparison over several years with the dynamic orbits.

·         The absolute altimeter calibration will be performed on a permanent and/or regular basis in the Ajaccio area, including an error budget on the different factors and the way to improve them. As a preliminary calibration experiment, data collected during the Corsica-Capraia campaign provided 9 bias estimations with the ELFE dynamic orbits (SOD/CNES), the mean of which is +5.6 cm, with a 3.9 cm standard deviation (Figure 5). 5 short-arcs, of which 3 were constrained by Ajaccio LASER station (FTLRS), gave similar results, though not statistically representative. Our estimation of the mean precision being thus 3.9/√9=1.3 cm. Uncertainties for absolute bias determination are probably due to land proximity, lack of knowledge on the short-scale geoid and then additional local studies are planned to better apprehend geoid effects.

·         Geophysical applications will be developed in a cooperative effort concerning the monitoring of the mean sea level in different areas (Black Sea, Eastern and Western Mediterranean sea, Cadiz gulf, for example). Crustal deformation will also be analyzed in the Grasse-Ajaccio area, on the basis of permanent GPS-SLR network in cooperative effort with IGN (C. Boucher, P. Willis), Institute of Geodynamic (E. Calais) for all the problems concerning the various geodetic features.

 

Most of the previous items have been already initiated or developed for previous experiments such as TOPEX/Poseidon, ERS‑1/2.

Figure 4.  Laser Residuals correlation between T/P and LAGEOS I for Hestmonceux (7840), from September 1992 to may 1997. Crosses correspond to a smoothing using a window width of 182 days and a step of 24 days.

 

Figure 5.  TOPEX/Poseidon altimeter bias determination during the Corsica-Capraia experiment. The mean is +5.6 cm, with a 3.9 cm standard deviation.

IV.6.       References

Archiving, Validation, and Interpretation of Satellite data in Oceanography AVISO User Handbook, Merged TOPEX/POSEIDON Products (GDR-Ms), 3rd ed., Publ. AVI-NT-02-101-CN, Cent. Natl. d’Etudes Spatiales, Toulouse, France, 1996.

Benveniste, J. ERS‑2 Altimetry Calibration, in Proceedings of the 3rd ERS Symposium, in proceedings of the 3rd ERS symposium, in press, 1997.

Bonnefond, P., P. Exertier, F. Barlier, Geographically correlated orbit errors determined from a Laser-based Short-Arc Technique, Geophys. Res. Lett., submitted, 1997a.

Bonnefond, P., P. Exertier, Y. Ménard, E. Jeansou, G. Manzella, S. Sparnocchia, F. Barlier, Calibration of Radar Altimeters and Validation of Orbit Determination in the Corsica-Capraia Area, Proceedings of the 3rd ERS Symposium, Mar 17-21, Florence, Italy, in press, 1997b.

Bonnefond, P., P. Exertier, P. Schaeffer, S. Bruinsma and F. Barlier, Satellite Altimetry From a Short-Arc Orbit Technique: Application to the Mediterranean, J. Geophys. Res., 100 (C12), 25365-25382, 1995.

Cazenave, A., et al., Investigation on long term sea level changes from Topex-Poseidon, ERS-1/2 and Jason‑1 at global and regional scales, proposal to Jason‑1 Science Working Team, Joint Research Announcement, 1997

Exertier, P. and P. Bonnefond, Analytical solution of perturbed circular motion: application to satellite geodesy, Journal of Geodesy, 71: 149-159, 1997a.

Exertier, P., P. Bonnefond, S. Bruinsma, DORIS Sensitivity, AVISO News Letter 5, 12-14, 1997b.

Haines, B.J. et al., Observations of TOPEX/POSEIDON Orbit Errors Due to Gravitational and Tidal Modeling Errors using the Global Positioning System, IUGG general assembly, Boulder CO USA, July, 1995.

Marshall, J.A., N.P. Zelensky, S.M. Klosko, D.S. Chinn, S.B. Luthcke, K.E. Rachlin, The temporal and spatial characteristics of TOPEX/Poseidon radial orbit error, J. of Geophys. Res., 100(C12), 25331-25352, 1995.

Ménard, Y., E. Jeansou, and P. Vincent, Calibration of the TOPEX/POSEIDON altimeters at Lampedusa: Additional results at Harvest, J. Geophys. Res., 99 (C12), 24487-24504, 1994.

Métris, G. and P. Exertier, Semi-analytical Theory of the Mean Orbital Motion, Astronony and Astrophysics, Vol. 294, 278-286, 1995.

Nouël, F., et al., Precise Centre National d’Etudes Spatiales orbits for TOPEX/POSEIDON: Is reaching 2 cm still a challenge?, J. Geophys. Res., 99 (C12), 24405-24419, 1994.

Stoufs, H-G., Analyse des données de la station laser ultra-mobile (CERGA/CNES/IGN), Campagne d'Ajaccio, mémoire de soutenance pour le diplôme d'ingénieur de l’Ecole Nationale des Arts et Industrie de Strasbourg, 21 Octobre 1997.

Satellite Altimetry, SELF II annual report, Programme Environnement et Climat de la CEE, 1997.

Tapley, B.D., et al., Precision Orbit Determination for TOPEX/POSEIDON, J. Geophys. Res., 99 (C12), 24383-24404, 1994.

V.       MANAGEMENT PLAN AND COST PLAN

V.1.       Management Plan

*        1998:                                                                                                                                   80 KF

·         Improvement of the French Transportable Laser Ranging Station (new wavelength, new detector, ...):

- workers: in charge of OCA-CERGA

- material:                                                                                                25 KF

·         Installation of a coastal numerical tide gauge at Ajaccio (Aspretto BAN, Corsica):

- material: in charge of EPSHOM-Brest

- installation:                                                                                            45 KF

- technical support: air and sea base of Aspretto

- data and material support for several years: in charge of EPSHOM-Brest

- workers: OCA-CERGA/ EPSHOM-Brest

·         Installation of 3 AANDERAA tide gauges at Senetosa:

One of the tide gauges will be immersed at the same place than for the previous campaign, to insure link between previous and new sea level measurements.

The two others will be immersed on either sides of the T/P-Jason‑1 ground-tracks.

- material (tide gauges): in charge of CNES Jason‑1 Project

- installation:                                                                                            10 KF

·         Installation of a meteorological station at Senetosa:

- material: in charge of CNES Jason‑1 Project

- installation: during tide gauges installation

·         GPS campaign at Corsica and Grasse:

- material: in charge of IGN

- installation: in charge of IGN

*        1999:                                                                                                                       350 KF

·         Absolute calibration campaign (« campaign-0 ») on T/P using FTLRS (5 months, from Feb. to June):

- transportation of FTLRS and insurance:                                                                                                             10 KF

- costs per month: 60 KF (5 months)                                                                                                            300 KF

- missions: 35 KF

- travels: 6 KF

- local transportations: 7 KF

- consumables: 12 KF

- consumables of the FTLRS:                                                                                                             25 KF

- missions to Corsica/Toulouse (PI and CoI’s):                                                                                                             15 KF

·         Tide gauges support including data acquisition:

- AANDERAA tide gauges (Senetosa): in charge of CNES Jason‑1 Project

- coastal numerical tide gauge (Ajaccio): in charge of EPSHOM-Brest

*        2000:                                                                                                                                   350 KF

·         Absolute calibration campaign (« campaign-1 ») on Jason‑1 and T/P using FTLRS, 5 months (from 1 month before launch to 4 months after launch): same planning and cost than 1999 campaign.

V.2.       Cost plan

V.2.1.       Cost categories

 

Material

Travel

Detailed costs

FTLRS:

·         Various materials for FTLRS (detector, optical, ...): 25 KF

·         Consumables and transportation for the FTLRS during 1999 campaign: 95 KF

·         Consumables and transportation for the FTLRS during 2000 campaign: 95 KF

Ajaccio tide gauge:

·         Support for the installation by EPSHOM: 45 KF

Senetosa tide gauges:

·         Support for the installation: 10 KF (other costs will be supported by CNES Jason‑1 Project)

Corsica campaigns:

·         Total cost of the 1999 and 2000 campaigns (travel, local cost, ...) for workers in charge of the FTLRS tracking: 480 KF (48 KF per month)

·         PI and CoI’s travels to Corsica and Toulouse (1999 and 2000): 30 KF

Total

270 KF

510 KF

V.2.2.       Detailed cost schedule

 

Principal Investigator and scientific collaborators costs

Cost of field studies

1998

10 KF

70 KF

1999

15 KF

335 KF

2000

15 KF

335 KF

 

VI.       BIOGRAPHICAL INFORMATION OF THE P.I.

Pierre EXERTIER

Centre d’Etudes et de Recherche en Géodynamique et Astrométrie

OCA-CERGA, CNRS UMR-6527, Avenue N. Copernic F-06130 Grasse

Tel.: (33)4.93.40.53.86 - Fax: (33)4.93.40.53.33

Education:

Engineer - Surveying, Nat. School Engineer - E.N.S.A.I.S., Strasbourg, France     (1982)

3e Cycle Thesis in Astronomy - University/Obs. of Paris-Meudon, France              (1985)

Ph.D. Thesis - Space Mechanics and Geodynamics, Dir. F. Barlier-G. Balmino     (1988)

Position held:

CNES Engineer at the CNES/IS/MS/MO (Metrology-Orbit), Toulouse, France,

from 1987 to 1989.

CNRS Researcher, at OCA-CERGA, Grasse, France, from 1989 to present.

Co.I. of several missions : ERS-1, TOPEX/Poseidon, LAGEOS-2.

Publications:

Bruinsma, S., R. Biancale, P. Exertier, 1997, Assessment of New Satellite Total Density Data, Planetary and Space Science, Submitted

Bonnefond, P., P. Exertier, F. Barlier, 1997, Geographically correlated orbit errors determined from a Laser-based Short-Arc Technique, Geophys. Res. Lett., Submitted

Exertier, P. and P. Bonnefond, 1997, Analytical Solution of Perturbed Circular Motion: Application to Satellite Geodesy, Journal of Geodesy, 71, 149-159

Bonnefond, P., P. Exertier, P. Schaeffer, S.L. Bruinsma, F. Barlier, 1995, Satellite Altimetry from a Short-Arc Orbit Technique: Application to the Mediterranean, J. Geophys. Res., 100(C12), 25365-25382

Métris, G., P. Exertier, 1995, Semi-Analytical Theory of the Mean Orbital Motion, Astron. and Astrophys., 294, 278-286

Exertier, P., E. Bois, 1995, Analytical Solution of the Perturbed Circular Motion: An Extended Formulation for Various Perturbations, Planet. Space Sci., 43, 863-874

Exertier P., G. Métris, Y. Boudon, F. Barlier, 1994, Long Term Evolution of Mean Orbital Elements of Artificial Satellites,Geophysical Monograph - IUGG, 82, Vol. 17, 103-108

Métris, G., P. Exertier, Y. Boudon, F. Barlier, 1993, Long Periodic Variations of the Motion of the Artificial Satellite due to Tesseral Harmonics (Non-Resonant Part), Celestial Mechanics, 57, 175-188

Exertier, P., 1993, Geopotential From Space Techniques, Celestial Mechanics, 57, 137-153

Bonnefond, P., P. Exertier, 1993, Precise Orbit Determination with a Short-Arc Technique, Celestial Mechanics, 57, 405

Cazenave, A., P. Gegout, L. Soudarin and K. Dominh, F. Barlier, P. Exertier and Y. Boudon, 1993, Geodetic Results from Lageos-1 and Doris Satellite Data, AGU Geophysical Monograph, Geodynamics, 23, 81-98

Exertier, P., 1990, Precise determination of mean orbital elements from osculating elements by semi-analytical filtering, Manuscripta Geodaetica, 15, 115-123

Referee of Scientific Papers: Celestial Mechanics and Dynamical Astronomy, Journal of Geodesy.

Teaching: « Satellite Geodesy » at the Nat. School Engineer - E.N.S.A.I.S., Strasbourg, France.

Research Interest:

·          Geodesy, Satellite Geodesy, Celestial Mechanics. Research and Development of new methods and theories of perturbed orbital motions.

·          Development of the semi-analytical theory of mean orbital motions. Applications to the determination of the Gravity Field, and the determination of its Temporal Variations.

·          Analysis of Satellite Tracking Data, laser ranging and Doppler-DORIS tracking data for Precise Orbit Determination and Positioning.

·          Development of the precise short-arc orbit technique. Applications to Satellite Altimetry in the Mediterranean Area; with Seasat, Geosat, ERS-1 and TOPEX/Poseidon data.

·          Development and Monitoring of Geodetic Campaigns in view of calibration and collocation experiments.