Chairman: Gerry Mader (USA)

Co-chairs: Doug Martin (USA) & Tilo Schöne (Germany)



The SSG acts as a forum to exchange information about using GPS-buoys primarily for measuring the instantaneous sea level. Originally the establishment of the SSG was a request of the community to calibrate and monitor the satellite radar altimetry (RA) measurements of recent and forthcoming RA missions. Beside this, members of the group are using the techniques also for river or lake level monitoring.

The GPS buoy technique is very new and not yet well established. Different groups are using different types of buoys and concepts. Members from the US (OSU/Ohio or JPL) and the colleagues from Spain are using life-saver types of buoys. The concept is very straight forward and gives good results. Another concept is using ruggedized types of buoys, which are more suitable for harsh conditions and long-term deployment. Unfortunately this concept is very expensive. For example, for the absolute calibration campaign of ENVISAT, the European Space Agency ESA favorite a dual concept: ruggedized buoys for the long-term measurements and using life-saver types of buoys in a leapfrog scenario to get more calibration values, if the weather permits operations.

WEB Server


A web page was established for Special Study Group 2.194 "GPS Water Level Measurements" on the GFZ web server in Potsdam. In addition to the Terms of reference for SSG 2.194, the web site provides a list of the members with contact information, information activities and news of pending conferences and workshops, an electronic library, and an opportunity for members to submit a Technical Note on research and development activities to create a forum for discussing technical issues related to GPS water level measurements. Unfortunately, this feature has not been as active as the Chairs had hoped. The electronic library is widely used but needs updating


Figure1: Access Statistics


A meeting was held at the EGS in Nice (April 2000). Here, mostly colleagues from Europe attended the meeting. In total 5 presentations were given (for the full report, see the SSG WEB-page: http://op.gfz-potsdam.de/altimetry/SSG_buoys/ssg_meeting_nice.html).


1Tilo Schöne reported about the planned GPS-buoy activities at GFZ. Within a larger project, which now founded, a ruggedized buoy will be deployed in the North Sea. A triple crossover is selected, for which a crossover of ERS-2/ENVISAT intersects with a GFO and Topex/JASON-1 track. The lifetime of the buoy will be several years in order to monitor a bias and drift of the respective radar altimeter. The buoy will be equipped with additional sensors (e.g. wind speed, air pressure, etc.) and may serve as a basis for additional studies. The internal accelerometers and the wind speed sensor will be used for calibrating the respective altimeter measurements. To account for the sea surface slope, several water level recorders will be deployed in the surroundings.

1Etienne Favey reported about a project at lake Lac Leman. A special buoy design (Plexiglas ball, which protects batteries, receiver and antenna) was deployed and the results were compared to a airborne laser profiling. Three time series were acquired, which have a good agreement with the laser profiles. A second campaign was carried out in Greece, using the same setup. A third campaign was to profile the river Rhine. A Trimble 4600 LS was used, which is water proof and can be put to water without protection.

1Juan José Martinez-Benjamin reported about a campaign for TOPEX (TP239, 18.3.1999). The campaign (near Begur Cape, Llafrance) has successfully used 2 GPS reference stations, 2 tide gauges and compared it to a lightweight buoy. A similar campaign will repeated in near future.

1Antonio Rius reported about the GRAC campaign. 3 lightweight buoys were deployed, keeping the distance between the buoys as constant as possible. GIPSY was used for GPS processing, problems occurred with the tropospheric influence to the GPS data.

1C.K. Shum reported about campaigns at Lake Michigan for GFO-1 and TOPEX calibration.





The Ohio State University (OSU), College of Engineering

The OSU floater buoy consists of a choke ring mounted on a standard 30" life ring with a plexiglas dome for protection. Over the past several years the buoy has been used to look at problems ranging from altimeter calibration to mapping regional sea level. It has also been used in conjunction with tide gauge and altimeter data to collect data to look at problems associated with sea level mapping, positioning of tide gauges, waves, combining GPS measurements with bathymetry and other traditional hydrographic measurements, combining GPS water level measurements with numerical models, and studying GPS sampling requirements. Much of this data is still being analyzed and will hopefully be useful in designing future experiments. This summer it is hoped to return to Lake Michigan to look at regional water level mapping combining GPS, tide gauge, and altimetry. It is planned to position tide gauges along the coast of the Gulf of Mexico for use with calibrating aircraft altimetric measurements.

National Oceanic and Atmospheric Administration, National Ocean Service (NOS)

Precise orbits, improved antenna and receiver design, antenna phase center models, and more robust kinematic software all contribute to obtaining centimeter-level precision in the vertical component of GPS measurements from floating platforms (buoys, barges, or ships). This new high level of precision makes it possible to obtain GPS-derived water level time series suitable for the determination of tidal datums to support hydrographic surveys and maintenance dredging projects, mapping sea surface topography, satellite altimeter calibration, and the determination of boundary conditions for numerical models and model verification.

NOS, in general, relies on "buoys of opportunity" to conduct GPS buoy applied research activities. Partnering primarily with the US Coast Guard (USCG) and at least one time with the National Data Buoy Center. The USCG buoys were existing navigation buoys located in the Upper Chesapeake Bay, San Francisco Bay, and Lake Huron. NOS used the USCG batteries and solar panels for power and installed a GPS chokering antenna, a radio antenna and a radio modem on the buoys to retrieve the GPS data in real-time. There was no attempt obtain an absolute GPS-derived water level time series for determining tidal datums for harmonic constituents during the Upper Chesapeake Bay and Lake Huron deployments. The objectives of these deployments were to investigate power consumption, communication links, and baseline lengths for future projects. The antenna height relative to the plane of floatation of the San Francisco buoy was measured and the vertical component of the GPS kinematic solutions was adjusted to plane of floatation of the buoy and averaged into a 6 minute GPS-derived water level height. These data were subsequently processed to provide tidal datums and harmonic constituents for the San Francisco buoy.

NOS, in partnership with the USCG, is currently designing a new GPS Buoy System specifically to improve the boundary conditions for the NOS Coastal Forecast System and conduct model verification. The buoy will be deployed about 20 km off the East Coast of the US. In addition to the GPS and radio antenna, other components will be a tilt meter, a water level measurement system, and a micro controller to integrate the GPS data and ancillary sensor data into the radio transmission to shore.

NOS also working on the development of a small GPS buoy system to support NOS hydrographic survey and other missions in the US estuarine and coastal waters. The buoy will be able to measure water levels using precise DGPS to an accuracy of within 5 cm or better. Relative buoy motions should be properly compensated and sampling rate should be adequate to obtain the true averaged water level without aliasing. Averaged water level data are typically recorded at 6-minute intervals. The buoy data measuring system will be self-contained and operated up to 3 months with remote access of data from buoy via line-of-sight radio at convenient time intervals. This buoy system will be handled from a small survey vessel of approximately10 m length.

Navy Oceanographic Office

Summary of GPS Buoy Exercises for the Northern Gulf of Mexico Littoral Initiative (NGLI).

The Northern Gulf of Mexico Littoral Initiative (NGLI) was established to provide reliable, timely meteorological and oceanographic mesoscale models of the Gulf of Mexico littoral region through development and operation of a sustainable comprehensive nowcasting/forecasting system. In situ observations and remote sensing measurements such as turbidity, currents, sea surface height, temperature, salinity and optics will be collected for model validation via an extensive data collection network. The NGLI system is designed to sustain high-volume data availability, providing rapid access to information by a broad range of users.

The goal of NGLI is to become a sustained cooperative effort among federal and state agencies who will use in situ observations, remote sensing, and models to monitor and forecast ocean circulation, waves, sediment transport, and water properties. It is sponsored by the Department of Navy (CNMOC) and the Environmental Protection Agency/Gulf of Mexico Program (EPA/GOMP). The Naval Oceanographic Office (NAVOCEANO) has established a test bed in the Mississippi Bight, which is bordered on the west by the Mississippi River outflow and on the east by Mobile Bay. NGLI will initially support demonstrations in the littoral regions bordering the Northern Gulf of Mexico coastline, however, these demonstrations will ultimately be used to test, improve and validate models and capabilities in oceanographic regions likely to be encountered in overseas Navy operations. The NGLI can also provide the Army Corps of Engineers the capability to manage sediment transport and civil authorities the means to consider habitat loss and environmental impacts from increased pollution caused by amplified population, hotel and casino development, and industry.       

One of the primary shallow-water measurements required by the NGLI is sea surface elevation. Present day applications require in situ measurements of these quantities either by themselves or in conjunction with remotely sensed measurements. In particular, the increased use of ocean forecasting models by NAVOCEANO and numerical forecasting centers requires these measurement data in real-time or near real-time, either for boundary condition specification or data assimilation.

NGLI will develop a communication buoy as a platform for DGPS water level determination on satellite altimeter ground tracks. This buoy will be capable of supporting a GPS receiver for differential (DGPS) water level determination. GPS measurements will, in principle, aid in supporting forecasting of multiple circulation processes across the shelf. GPS measurements assist in enabling the buoy platform to support forecasting of multiple circulation processes across the shelf.

This effort will be presented in three phases:

The goal of Phase 1 is to determine the processing, timing, and communication requirements for measuring water level using a buoy. A NAVO/WHOI buoy will be outfitted with an RTK Dual Frequency GPS receiver, a suite of buoy motion sensors, and a data acquisition/storage system. A "Reference Station" will record RTK GPS data simultaneously. This reference station data will be used to process the buoy GPS data and simulate "on-the-fly" RTK measurements of the GPS antenna position. The RTK corrected buoy antenna position will then be corrected for short-term, wave induced, buoy motion. The outcome will be a clearer understanding of the requirements for computing centimeter level antenna positions in real time, correcting the buoy antenna position for wave motion, and for supporting the RTK link needed between a reference station GPS and the buoy mounted RTK "rover" GPS.

The goal of Phase 2 is to prototype the buoy processing required to support "on-board" real time RTK processing of the antenna position and correct it for wave induced buoy motion. Through this effort "on board" algorithms for the buoy system will be developed. Once the processor and buoy sensor systems are developed sufficiently to support the prototype algorithms, a buoy system will be integrated to support short term and local testing. This will include integration of a communications link allowing the buoy RTK GPS to receive real time RTK corrections from the reference station. The outcome of this phase will be prototype buoy hardware and software for real time resolution of RTK GPS and wave motion and empirical data for comparison to known water level data for direct comparison and for optimizing buoy systems in preparation for offshore testing

The goal of Phase 3 is to deploy a buoy capable of measuring and reporting water level measurements. The expected deployment site is in Mississippi Sound between 88.48 W 29.56 N and -88.62 W 29.84 N, which are the GFO satellite track positions. The system will operate at-sea for 6-months, with the data being received through the communications link.

GeoForschungsZentrum Potsdam (GFZ)

Activities at GFZ are still in the development stage. The GFZ buoy program is in support of the large scale program SEAL of the German Helmholtz Association aiming at an integrated approach for quantifying sea level on various space and time scales. The project is based on new observing techniques and recent high resolution models of the processes governing the system ocean-ice-earth.

A ruggedized GPS equipped buoy will be developed and deployed in the North Sea. A toroid buoy was already selected and tested. This surface rider type of buoy will not only permit the observation of the instantaneous sea level during the satellite pass, but also an estimation of the significant wave height will be performed. In addition, the buoy will be equipped with supplementary sensors, like wind speed, humidity and air pressure sensors, allowing a broader use for calibration, e.g. of the backscatter / wind speed relationship. Meteo data may also be used by German Authorities in their forcasting models. The buoy will be deployed at a crossover location of ERS-2 (and ENVISAT). A nearby crossover with TOPEX and GFO (less than 5 km) makes this site even more suitable for multi-mission calibration. In addition, up to three bottom mounted tide gauges will be deployed to account for the sea surface slope between the crossovers. The lifetime of the buoy is expected to be several years. Based on this experience, a second buoy will be deployed in cooperation with OSU.

In the next month the integration will be done and first in-situ test with the fully equipped buoy will be starting right before the start of ENVISAT. In the first test phase high rate data of the GPS and the buoy motion sensors will be aquired. The data set will be tested in order to find a optimal sampling scenario.


Universitat Politècnica de Catalunya (Spain)

Experience in calibration campaigns has been obtained in the Cape of Begur area, NE Spain.The first campaign made on March 1999 consisted of two reference stations on shore and two GPS buoys underneath the TOPEX/POSEIDON groundtrack to get the instantaneous sea level. The GPS buoys were designed at the Cartographic Institute of Catalonia using GPS antennas placed inside floats of toroidal form following a design from the University of Colorado. Data from L'Estartit tide gauge has been used as data from two specific tidegauges, float and pressure, under supervision from Clima Maritimo-Puertos del Estado. It was performed the absolute calibration of Topex altimeter Side B.

A second campaign with an advanced GPS buoy has been made on July 2000 with an estimation of the altimeter bias that hints at the level of accuracy that might be achievable for JASON-1 and ENVISAT.One other objective has been to GPS map the Mean Sea Surface (MSS) and to lay the foundation for a general indirect calibration site which allows to calibrate altimeters from different satellites crossing the area. These and future campaigns could contribute to calibration of emerging global sea-level records from TOPEX/POSEIDON and its successors.

These campaigns and their data processing have been made under a CICYT (Comision Interministerial de Ciencia y Tecnologia) National Coordinated R+D Project in Space Research, ref: ESP97-1816-CO4, that includes several govermental/research Institutes and Universities from Spain with International participation of France and the United States.


GPS Buoy Activities in Indonesia

(Imam Mudita wrote): Starting from the research topic I have chosen for my doctoral study program, GPS observation for sea level measurement on a floating buoy is being investigated. During the investigation period, a GPS buoy sea level measurements were taken on an in-house project campaign, as part of the UPT Baruna Jaya research activities, in April in the Bay of Jakarta. Figure 1 shows the buoy while collecting data during the campaign.

The data set were 15 days of continuous GPS observation in 0.5 seconds interval. Coincident tides data during the campaign from a near tide gauges station of PERUM PELABUHAN II were also taken. The result shows that GPS could be used as a tool for sea level measurement if a careful correction applied in the data processing (see Figure 2. in yellow color)

Currently, we are trying to integrate GPS measurement with Motion Reference Unit (MRU-5) as attitude sensor of the GPS antenna movement. We will deploy this system in April 2001.

For the next stage, we are going to make the system in a real time mode of observation with a reliable radio data communication and a more sophisticated buoy construction.

Instituto de Ciencias del Espacio (CSIC), Institut d'Estudis Espacials de Catalunya (IEEC)

The recent GPS buoy acitivies carried out at the Institute for the Space Studies of Catalonia (IEEC) are the "GPS Radar Altimeter Calibration" campaigns GRAC99 and GRAC2000. They had been conducted in June 1999 and September 2000 on board a research vessel to follow different Radar Altimeter (RA) tracks where to perform GPS buoy and oceanographic measurements. The combined GPS and oceanographic measurements were though to calibrate the RA sea level estimates with the emphasis on the geostrophic currents observation application.

In GRAC99, the GPS observations were gathered through a three-buoy structure, specially designed for the campaign. Four time series of GPS buoy measurements were conduceted under the ERS-1, ERS-2 and TOPEX/POSEIDON tracks when these RA were over-flying the area. The description of this campaign and the results are published in [1].

In GRAC2000, a new buoy structure was constructed. It was a two-buoy system thought to allow for a double checking approach of the solution: on one hand the sea level form both antennas (after phase center corrections) should be the same. On the other hand, the distance between the buoys was constant, and its value should be recovered from the positioning of the antennas.

In terms of data processing, the main characteristic of such GRAC campaigns were the distance of the GPS observation from the Reference Ground Stations, more than 80 km. Dedicated strategies to accurately solve the vertical position were developed.

GRAC99 yielded a publication, while there is a internal-project report about GRAC2000:

[1] The Use of GPS buoys in the determination of oceanic variables, Cardellach, E., D.Behrend, G.Ruffini, A.Rius, Earth Planets and Space, Vol.52, pp 1113-1116, 2000.

[2] GRAC 2000 GPS Buoy Report, included in the GRAC Report, Cardellach, E., April 2001. Contact Jordi Font, jfont@icm.csic.es for GRAC reports.




Christopher Watson (CW), Richard Coleman (RC), Tony Sprent (AS)

Centre for Spatial Information Science, University of Tasmania

John Hunter (JH), John Church (JC), il White (NW)

Antarctic CRC, University of Tasmania


Sea Level work (CW, RC, JH)

The application of GPS to localised oceanographic and geodetic experiments has been investigated with the design and construction of a series of GPS buoys. The buoys have been deployed at Port Arthur on Tasmania's southeast coast as part of a long term sea level study. The GPS buoys have be used in the determination of a precise marine geoid and they have also been instrumental in understanding local oceanographic phenomena (seiching) acting within the Port Arthur bay. A 1-2 day experiment was undertaken using two GPS buoys, 6 pressure sensors and the Port Arthur tide gauge as a way of verifying the performance of the GPS buoys.


Buoy Design and Operation (CW, AS, RC)

The first buoy system was constructed for the Port Arthur experiment by Chris Watson (Watson, 1999) and the buoys were simple 'wave rider' designs similar to those developed by Kelecy et al. (1994) and Key et al. (1997). The buoys were designed to only support the GPS antenna and hence needed to operate close to shore or be tethered to a boat where the GPS receiver is stored and operated. The floating platform consisted of a section cut from a heavy-duty plastic drum, which was braced and partially filled with polystyrene foam for buoyancy. Leica AT202+GP antennas and custom-made perspex antenna domes were fitted to the buoys. The buoy design is shown in Figure 1.

Figure 1. The prototype buoy design


The buoys performed well, however were limited due to their restriction of being operated close to shore or from a boat. The design was also quite susceptible to small surface wave activity.


Following the success of the prototype buoy, a more ruggedised version was designed and constructed by Tony Sprent. The buoys were utilised for further experiments at the Port Arthur site and will be used for satellite altimeter verification experiments at the Burnie verification site (see later). As it was aimed to measure the instantaneous sea surface at high sampling frequencies, a wave-rider style of buoy was still required. This will allow measurement of wave spectra and current velocity with the ability to filter the results to obtain the mean sea surface.


The newer buoy system was designed as a self-contained unit, with battery power, a GPS receiver and a choke ring antenna. This removes the previous restriction of operating the GPS from a tethered boat or from land. The design remains readily transportable for use in local experiments, whilst rugged enough for ocean based experiments. The buoy consists of a central water tight, cylindrical vessel which contains all the GPS equipment and batteries. All pieces of hardware inside the vessel are centrally constrained to ensure the overall construction is balanced about the central vertical axis. A removable stainless steel frame with three Ø300mm polystyrene floats is used to support the GPS equipment. A plan view of the buoy design with the antenna dome removed is shown in Figure 2.

Figure 2. Plan view of the latest buoy design.


The overall radius of the buoy is 850mm. The larger weight and lower centre of mass prevents any high frequency oscillation caused by small wind induced surface waves. The buoy is shown in section in Figure 3.



Figure 3. The latest buoy design for the Tasmanian experiments.


The buoys have been designed to accommodate Leica CRS1000 receivers and choke ring antennas (AT504). The dome is custom made out of 3mm 'Sunloid KD' which is an acrylic polyvinyl chloride material. The receivers have 64 Mb of internal memory and allow sampling rates of up to 10 Hz allowing for most experiment scenarios.


Altimeter Calibration (JC, RC, NW, CW)

The buoys will also be deployed as part of the Jason-1 and ENVISAT altimeter calibration activities - as well as cross-calibration with T/P and ERS-2. Both GPS buoys will be utilised off the north west coast of Tasmania, in Bass Strait as part of work towards a southern hemisphere altimeter verification experiment (see White et al., 1994). The two buoys will be positioned between 12 and 40 km from three static GPS reference sites and an acoustic tide gauge site in Burnie harbour. The position of the antenna phase centre relative to the mean level surrounding the buoy is of fundamental importance for this experiment - requirement is for accuracies at the 1 cm level. The effect of the plastic antenna radomes needs to be further investigated as absolute height is required. Accuracy of kinematic processing over medium to long baselines remains the principal difficulty for these applications. Software development has been started which is aimed at developing algorithms specifically tuned to processing on a floating platform.


Kelecy, T., Born, G., Parke, M. and Rocken, C. (1994). 'Precise mean sea level measurements using the Global Positioning System', Journal of Geophysical Research, 99(C4), pp. 7951-7959.

Key, K., Parke, M. and Born, G. (1998). 'Mapping the Sea Surface Using a GPS Buoy', Marine Geodesy, 21, pp. 67-79.

Watson, C. (1999). 'A Contribution to Absolute Sea Level in Tasmania', Thesis for Bachelor of Surveying with Honours, Centre for Spaital Information Science (CenSIS), University of Tasmania, Hobart, p. 197.

White, N., Coleman, R., Church, J., Morgan, P. and Walker, S. (1994). 'A southern hemisphere verification for the TOPEX/POSEIDON satellite altimeter mission', Journal of Geophysical Research, 99(C12), pp. 24505-24516.


Publications by the Members

Cardellach, E., D. Behrend, G. Ruffini, A. Rius: The Use of GPS buoys in the determination of oceanic variables, Earth Planets and Space, Vol.52, pp 1113-1116, 2000.

Cardellach, E.: GRAC 2000 GPS Buoy Report, included in the GRAC Report, Cardellach, E., April 2001. Contact Jordi Font, jfont@icm.csic.es for GRAC reports.

Cheng, K., C.K. Shum, M. Parke, K. Snow, S.C. Han, J.J. Benjamin, D. Martin, G. Mader: "GPS-Buoy water level instrument:Applications for radar altimeter calibration", oral presentation, GGG2000, Canada, 2000.

Colombo, O.L., A.G. Evans, M.I. Vigo, J.M. Ferrandiz, J.J. Benjamin: "Long-baseline (>1000km), sub-decimeter kinematic positioning of buoys at sea, with potential application to deep-sea studies", oral presentation, ION GPS 2000, Salt Lake City, Utah, USA, 2000.

Kruizinga, G.L.H., B. Haines, J.J. Martinez-Benjamin, M. Martinez-Garcia, J. Talaya, M.A. Ortiz, B. Perez: "The CATALA experiment, preliminary results of ALT-B calibration using GPS buoys off the Catalonian Coast (Spain)", ALT-B Calibration Workshop, Goddard Space Flight Center, Greenbelt, Maryland, USA, 1999.

Martinez-Benjamin, J.J., M. Martinez-Garcia, G.L.H. Kruizinga, B. Haines, M.A. Ortiz, J. Talaya, B. Perez, E. Alvarez, J. Garate, J.M. Davila, J.M. Ferrandiz, M.I. Vigo-Aguiar: "The CATALA campaigns: indirect calibration technique for ENVISAT altimeter calibration", ERS-ENVISAT SYMPOSIUM, Gothenburg, Sweden, 2000.

Martinez-Benjamin, J.J., M. Martinez-Garcia, G.L.H. Kruizinga, B. Haines, M. Ortiz, J. Talaya, J. Garate, J. Davila, J. Ferrandiz, M. Vigo-Aguiar, B. Perez, E. Alvarez: "The CATALA Experiment: Absolute Calibration of TOPEX Altimeter-B using GPS buoys in the NW-Mediterranena sea", POSTER, The Ocean Observing System for Climate, OCEANOBS 99, St Raphael, France, 1999.

Martinez-Benjamin, J.J., M. Martinez-Garcia, M.A. Ortiz, J. Talaya, G.L.H. Kruizinga, B. Haines, J. Garate, M. Davila, JM. Ferrandiz, M.I. Vigo-Aguiar, B. Perez, E. Alvarez, O. Colombo, B. Chao, CK. Shum: "The TOPEX/POSEIDON CATALA Altimeter Calibration Campaign", POSTER, American Geophysical Union, AGU-2000 Spring meeting, Washington, USA, 2000.

Martinez-Benjamin, J.J., M. Martinez-Garcia, M.A. Ortiz: "Validation of TOPEX/POSEIDON GDR by independent techniques", POSTER, XXVI General Assembly of the European Geophysical Society (EGS), Nice, France, 2001.

Martinez-Benjamin, J.J., M. Martinez-Garcia, M. Ortiz, J. Talaya, J.Garate, J. Davila, J. Ferrandiz, M. Vigo-Aguiar, B. Perez, E. Alvarez: "The TOPEX/POSEIDON and JASON-1 Calibration Campaigns in the Cape of Begur and Ibiza Island Regions", POSTER, TOPEX/POSEIDON/Jason-1 Science Working Team Meeting, Miami, USA, 2000.

Martinez-Garcia, M., G.L.H. Kruizinga, B. Haines, J.J. Martinez-Benjamin, M.A. Ortiz, J. Talaya, J. Garate, M. Davila: "PRELIMINARY RESULTS OF THE GPS BUOYS DATA PROCESSING IN THE NORTH WESTERN MEDITERRANEAN SEA", POSTER, International Union of Geodesy and Geophysiscs, IUGG, 18-30 July 1999, Birmingham.

Martinez-Garcia, M., G.L.H. Kruizinga, J.J. Martinez-Benjamin, M.A. Ortiz, J. Talaya: "Preliminary experience and technical aspects on the JASON-1 validation and calibration radar altimeter by using GPS buoys", oral presentation, XXV General Assembly of the European Geophysical Society (EGS), Nice, France, 2000.

Martinez-Garcia, M., J.J. Martinez-Benjamin, M.A. Ortiz: "Analysis and Strategies applied to the GPS buoys data for the TOPEX ALT-B Absolute Calibration in the NW-Mediterranean", POSTER, TOPEX/POSEIDON/Jason-1 Science Working Team Meeting, Miami, USA, 2000.

Martinez-Garcia, M., J.J. Martinez-Benjamin, M.A. Ortiz: "Strategies with GPS for the navigation of buoys", POSTER, GNSS-2001, Sevilla, Spain, 2001.

Martinez-Garcia, M., J.J. Martinez-Benjamin, M.A. Ortiz-Castellon: "Calibration techniques applied to satellite altimeter", oral presentation, XXVI General Assembly of the European Geophysical Society (EGS), Nice, France, 2001.

Ortiz, M.A., M. Martinez-Garcia, J.J. Martinez-Benjamin: "GPS buoys for altimeter calibration campaigns", POSTER, GNSS-2001, Sevilla, Spain, 2001.

Watson, C. (1999). "A Contribution to Absolute Sea Level in Tasmania", Thesis for Bachelor of Surveying with Honours, Centre for Spaital Information Science (CenSIS), University of Tasmania, Hobart, p. 197.



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