SPECIAL STUDY GROUP 2.194:

“GPS WATER LEVEL MEASUREMENTS”

http://op.gfz-potsdam.de/altimetry/SSG_buoys

 

T. Schöne

 

 

Chairman: Gerry Mader (USA)

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

 

Introduction

 

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 as well as for connecting remote tide gauges to a global reference frame.

 

The GPS buoy technique is still very new. Different groups are using different types of buoys and concepts. One common design is a life-saver type of buoys. The concept is very straightforward 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 selected 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. In the past two years several campaigns using both type of GPS buoys were carried out. However, an intercomparison of both techniques still needs to be performed.

 

A web page was established for Special Study Group 2.194 "GPS Water Level Measurements" on the GFZ web server in Potsdam (http://op.gfz-potsdam.de/altimetry/SSG_buoys/). 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 more frequent updating.

 

 

Figure 1: Access statistics to the WEB server

 

 

 

Meetings with SSG 2.194 Participation

 

A meeting was held in 2000 during the EGS in Nice. Here, mostly colleagues from Europe attended the meeting. In total 5 presentations were given (for the full report see the SSG WEB-page at

http://op.gfz-potsdam.de/altimetry/SSG_buoys/ssg_meeting_nice.html).

 

During the Asia-Pacific Space Geodynamic Project (APSG) Sea Level Workshop held as part of the GLOSS GE7 Meeting in Honolulu, Hawaii (April 23 & 24, 2001) a special session of the SSG was held. In total 7 presentations (oral and poster) were given:

 

  1. T. Schöne, Ch. Reigber, A. Braun, M. Forberg, R. Galas: GPS Buoys for calibrating Radar Altimeters for the SEAL Project
  2. M. Bushnell, D. Martin, and J. Sprinke, M. Chin, S. Cofer, D. Crump, and G. Mader, Frank Aikman: Improved Design of the National Ocean Service (NOS) GPS Buoy System
  3. P. Bonnefond, P. Exertier, and Y. Menard: Radar altimeter calibration using a GPS-Buoy in Corsica
  4. P. Bonnefond, P. Exertier, and Y. Menard: Leveling the sea surface using a GPS Catamaran
  5. R. Coleman, C. Watson, N. White, J. Church and R. Govind: Absolute altimeter verification activities in Bass Strait, Australia
  6. X. Dong, P. Woodworth, P. Moore, and R. Bingley: Absolute calibration of TOPEX/POSEIDON and JASON-1 using UK tide gauges, GPS and local precise Geoid model
  7. M.Martinez-Garcia, J.J. Martinez-Benjamin, and M.A. Ortiz-Castellon: GPS buoys technology applied to the absolute calibration of space radar altimeters and to the regional mapping the sea surface topography

 

Abstracts of this meeting have been published by IOC (Intergovernmental Oceanographic Commission, Workshop Report No. 180, UNESCO, 2002) and are available via the SSG’s WEB page.

 

REPORTS provided by the MEMBERS

 

A. Geiger, H.-G. Kahle: Lightweight offshore buoys

 

New buoys have been designed based on previous experiences. The newly developed buoys have a displacement of 10 kg which is a significant weight reduction compared to the predecessor. With its 40 cm diameter it can easily be handled. The dimension “of the buoy, weight of battery, receiver, and antenna have optimally been chosen and designed in order to reach the exact floating balance. No ballast is needed to stabilize the buoy or to reach the foreseen floating line in the middle of the spherical buoy. The shell is fabricated from polycarbonate, which is transparent for the microwaves also. Therefore, the whole buoy can be waterproofed sealed containing the battery, receiver and antenna. For present buoy experiments two Novatel DL-4 have been installed. The new pinwheel antenna is used. The operation autonomy reaches about 20 hours. The measurement rate can be set to 0.5 sec sampling interval, producing about 5 MB data per hour. First tests where successfully completed. The buoys will be used to calibrated sea surface determination techniques such as airborne or satellite altimetry. The GGL group is also involved in the calibration of the Jason altimetry.

 

GeoForschungsZentrum Potsdam (GFZ), Germany

In the context of the German Helmholtz Association's strategic project SEAL (Sea Level Change: An Integrated Approach to its Quantification) the GFZ Potsdam has developed a ruggedized offshore GPS-buoy (Fig. 1), which is able to measure the instantaneous sea level with high accuracy. In May 2002 the buoy has been deployed at an intersection point where the actual RA missions TOPEX, JASON-1, ERS-2, ENVISAT, and GFO-1 intersect. The position is the only point in the German Bight that allows data transmission to a land station via an HF radio link.

 

 

          

 

Fig.1: The new buoy on test in a friendly sea

 

During the first deployment period till August 2002 in total 26 satellite passes has been acquired. Each data set comprises one hour of multi-sensor measurements centered at the satellite pass time. Differential GPS data is collected at 10Hz sampling rate both on the buoy and a reference station. A dynamic motion sensor monitors tilt angles as well as 3-axis accelerations. Thus, together with the dipping depth, which is collected by an underwater pressure sensor, the GPS antenna height can be reduced to the instantaneous sea surface height for every single GPS measurement. Additionally several meteorological sensors provide data every 10 minutes (e.g. air and water temperature, air pressure, wind direction and speed) and three moored tide gauge sensors in the vicinity and a wave tide recorder beneath the GPS-buoy allow to account for the sea surface slope and significant wave height, respectively.

 

 

Fig. 1: GFZ’s ruggedized GPS buoy

 

The resulting series of coincident measurements is used to derive a range bias for each radar altimeter; the envisaged long-term deployment will allow the monitoring of all missions. Additional information on: http://op.gfz-potsdam.de/seal/.

 

 

Institut d'Estudis Espacials de Catalunya (IEEC) & Institut de Ciències del Mar (ICM), Spain

The last activities of the IEEC (Institute for the Space Studies of Catalonia) and the ICM (Institut de Ciències del Mar) were measurements of the sea level with Light GPS buoys, campaigns GRAC-II. Light GPS buoys (2) were used along the Catalan coast (North West Mediterranean) between the months of April and October of 2002, obtaining a set of results that provided measurements of sea level with respect to the Reference Ellipsoid WGS84. The data is being used in order to calibrate ENVISAT RA-2 (altimeter).

 

45 measurements at 10 different points (approximately at 10 miles from the coast) corresponding to different ENVISAT tracks were performed. The buoys were left to drift freely around the nominal point within a radius of 1 mile. These GPS buoys recorded data during a period of 3 hours centered in the ENVISAT overpass time. Moreover, a reference GPS ground station placed in the coast close to the ENVISAT point was used to derive an estimate of the tropospheric delay. An example of the 45 reports generated is [1].

 

The principle of this technique is based in the precise geocentric positioning of a GPS antenna placed inside a life-safer. The time series of the antenna phase geocentric location can be translated using GIPSY software to sea level estimates, with single errors of few centimeters (1 Hz estimate) and averaged values of 1 cm uncertainty. During the resent EGS/EUG/AGU a poster was presented [2].

 

[1] GRAC-II - Preliminary results of 27-MAY-2002 experiment # 12. IEEC-CSIC Research Unit. May 2002. Contact Josep Torrobella, badia@ieec.fcr.es for GRAC-II reports.

[2] Light GPS Buoys used in the Calibration of ENVISAT ALTIMETER. Josep Torrobella & The Grac-II Team, poster presentation, EGS03, Nice, April 2003.

 

 

Fig. 1: The “bi-buoy” system of IEEC and ICM

 

The documents are available at ftp://ftp.ieec.fcr.es/ieec/gps/badia/EGS03, files: posterbuoys-egs032.pdf and report147.pdf.

 

Naval Oceanographic Office, USA

The Naval Oceanographic Office continues to pursue water level measurement using RTK GPS and moored buoy platforms. NAVOCEANO was able to build one buoy and to conduct two preliminary trials; one completed this past April. Data needs still to be analyzed.

 

Funding at NAVOCEANO for GPS water level determination terminated over a year ago. The existing buoy equipment was provided to hydrographers at NAVOCEANO who now are trying to develop ways to use the buoy in conjunction with small-boat surveys.

 

Additionally, work was done with the Naval Research Laboratory (NRL) to develop airborne altimetry for ocean circulation over the shelf and slope. We have not yet managed to employ the GPS buoy with the NRL airborne survey. Nevertheless, this remains a goal for both organizations.

 

Observatoire de la Côte d’Azur - CERGA Bonnefond, P., P. Exertier, O. Laurain, F. Barlier, Y. Ménard, E. Jeansou, A. Orsoni: Radar Altimeter Calibration using a GPS-buoy in Corsica

Observatoire de la Côte d’Azur - CERGA, avenue N. Copernic, F-06130 Grasse

Centre National d’Etudes Spatiales, avenue E. Belin, F-31055 Toulouse

 

The Absolute calibration site of Corsica is working operationally for calibrating TOPEX/Poseidon and Jason-1 altimeters, using comparisons with tide gauges data. Taking the advantage of this site, a new experiment has been performed to calibrate altimeters: it uses kinematic GPS technique to monitor sea level heights. A reference receiver is placed at a geodetic point (near the lighthouse) while the other is on the sea.

Since February 2000, for each overflight a GPS buoy is placed under the ground track about 10 km off-shore, whenever sea state conditions are not too harsh to ensure safe navigation. GPS and altimetric sea heights are then compared to deduce altimeter biases. Systematic controls are also performed using measurements above the three tide gauges before and after the overflight. Results in the altimeter bias determination is at the same level considering buoy or tide gauges, the GPS data (buoy) also providing an estimation of the wet tropospheric path delay and Significant Wave Height; these parameters are then compared to T/P and Jason-1 measurements. Kinematic GPS (with a Catamaran) has also been used to map the local geoid during two campaigns in 1998 and 1999.

 

Bonnefond, P., P. Exertier, O. Laurain, F. Barlier Y. Ménard, E. Jeansou, A. Orsoni, B. Haines, D.G. Kubitschek and G. Born, Leveling Sea Surface using a GPS-Catamaran, Marine Geodesy, submitted, 2003.

 

 

Fig. 1: Photo of the GPS-Catamaran at M2 tide gauge location.

 

Fig. 2: GPS buoy made from a life buoy.

 

 

 

 

 

 

 

 

 

Fig. 3: Jason–1 altimeter bias time series from tide gauges (diamonds) and GPS buoy (crosses). Error bars correspond to the standard errors deduced from the tide gauge determination averaging.

 

Fig. 4: Contour map of the gridded GPS sea surface heights (in meters). White lines represent data used to compute the surface.

 

 

Bonnefond, P., P. Exertier, O. Laurain, Y. Ménard, G. Jan, E. Jeansou, and A. Orsoni, Absolute Calibration of Jason-1 and TOPEX/Poseidon Altimeters in Corsica, Marine Geodesy, submitted, 2003.

 

Technische Universität Dresden, Institut für Planetare Geodäsie, Germany

A multisensoral measurement system for the determination of sea-level heights at oceanographic platforms was developed at the "Technische Universität Dresden" (Liebsch et. al. 2003). The system consists of a GPS receiver, tide gauges, inclinometers, an air pressure sensor and a data logger. The equipment was installed on two stations of the "Marine Environmental Monitoring Network" (MARNET) in the southern Baltic Sea. MARNET stations are operated by the "Baltic Research Institute Warnemünde" (IOW) on behalf of the "Federal Maritime and Hydrographic Agency" (BSH) of Germany. Since February 2003 both systems are in operation. The Federal Ministry of Education and Research of Germany funded the research project.

 

G. Liebsch, L. Eberlein and R. Dietrich: Realisation of a multisensoral observation system for the determination of offshore sea-level heights, Poster, EGS-AGU-EUG Joint Assembly, Nice, France, 06-11 April 2003

 

The Ohio State University (OSU), College of Engineering

GOM – OSU Project Communications

For several years, The Ohio State University (OSU) and Texas A&M University (TAMU) have been working to get access to an oil platform in the Gulf of Mexico (GOM) that is within several kilometers of the triple cover over point for Jason-1, ERS-2, and GPO-1. There were a number of set backs when the lease blocks were sold and new operators had to be contacted. However, that is now history and we can move forward.

 

Briefly, the project consists of establishing a Continuous Geodetic Reference Station (CGRS) and a tide station on an oil platform in the GOM. The CGRS and tide gauge sensor will be connected by differential levels so the water level time series can be referred to the GPS reference framework to assist with the calibration of the satellite altimeters. In addition to the CGRS and Tide station on an oil platform, we plan to install a GPS unit on a TAMU buoy in the vicinity of the platform. The attached conceptual drawing shows the communications system to be used to access the GPS and tide data and place it on the Internet for direct access by the scientific community.

 

OSU will do additional GPS buoy (life ring) surveys between the platform and the TAMU/GPS buoy to determine the geoid gradient in the area.

 

OSU/TAMU plan to conduct site reconnaissance surveys at the platform in the GOM during June 2003. GPS and Tide station installations will begin as soon as station designs are accepted by the platform operator.

 

The initial action will be to install a Continuous Geodetic Reference Station (CGRS) on the oil platform. The CGRS will require that an antenna be placed on a structurally stable high point with a clear 360º view to the horizon. The antenna will have to be connected to the receiver with low loss coaxial cable. The receiver will require 12 volt DC power supplied via a sealed gel cell battery. The battery will require a float charger operated by 120 volt AC power, or a solar panel, to maintain sufficient battery charge state. The receiver will communicate data to a laptop PC. The laptop PC will require 120 volt AC power. The PC will communicate the data via the digital microwave radio system.

 

 

Fig. 1: communications system for the GOM-OSU project

 

Future plans include the installation of a GPS unit on a TAMU TABS buoy located near the triple satellite crossover point, which is within 5 kilometers of the oil platform. This buoy will transmit data via spread spectrum radio modems to the laptop PC on the oil platform. From that point the data will be stored and transmitted in the same manner as the CGRS on the oil platform.

 

Universität der Bundeswehr München, Institut für Erdmessung und Navigation (IfEN), Germany

For more information about the IfEN activities within the ESA funded project “ENVISAT Radar Altimeter Calibration Using GPS in Buoys”, please refer to http://forschung.unibw-muenchen.de/ainfo.php?&id=529.

 

Universitat Politecnica de Catalunya UPC, Barcelona, Spain

A Spanish/French JASON-1 calibration campaign is being prepared for June 2003 in the area of Ibiza Island in the NW Mediterranean Sea. The main objective, is to map with a new designed, builded and calibrated GPS catamaran, the Mean Sea Surface MSS/local marine geoid gradient in the north area of Ibiza island at one crossing point of an ascending and descending satellite track. One part of a descending orbit in the SE of the island is also included. Two tide-gauges are installed and operating in the island, one located in San Antonio harbor is a CGPS, the GPS installed on April 7, 2003, the other is located in the Ibiza harbor. This campaign with its associated strategies is expected to have French support (CNES, LEGOS, CERGA and Noveltis) and is based in the experience obtained by three previous campaigns made in March 1999, July 2000 and August 2002 in the Cape of Begur/ Llafranc/ Palamos area. The second and third campaign used data from l'Estartit tide gauge.

 

Direct absolute altimeter calibration was made from direct overflights using GPS buoys with a toroidal design performed at the ICC based in the original design of the University of Colorado at Boulder. The TOPEX Alt-B bias was estimated processing altimeter and GPS data.

 

Other main objective of the campaigns was to map with GPS buoys along an ascending T/P ground track about 15-20 km from the NE Spain coast, using coastal tide gauge measurements. In this case indirect absolute altimeter calibration is possible for any other altimetric satellite crossing the MSS, with the only requirement that tide gauges are operational during the overflight. Two tide gauges were placed temporally in Llafranc harbor and was used the data from the permanent L'Estartit tide gauge.

 

 

Fig. 1: GPS buoy of UPC

 

 

University of Tasmania (UTas), Centre for Spatial Information Science, Australia

A short summary of the activities of the UTas group:

 

1.                   Our main activity was the work for Jason-1 and T/P RA calibration using GPS bouys. A paper was recently submitted to Marine Geodesy special vol. on Jason-1 cal/val activities.

 

2.                   other work involved the use of GPS buoys in the calibration of bottom-mounted and conventional tide gauges, at Davis (Antarctica), Macquarie Island and Burnie, Australia. This work is currently in preparation for journal publication and forms part of a PhD thesis (Chris Watson).

 

 

Fig. 1: The UTas GPS buoy

 

Fig. 2: The resulting height time series

 

 

Publications by the Members

 

Blaha, J., G. Born, N. Guinasso, J. Herring, G. Jacobs, F. Kelly, R. Leben, R. Martin, G. Mellor, P. Niiler, M. Parke, R. Patchen, K. Schaudt, W. Scheffner, C. Shum, C. Ohlmann, W. Sturges, G. Weatherly, D. Webb and H. White: Gulf of Mexico ocean monitoring system, Oceanography, 13(2), 2000.

 

Bonnefond, P., P. Exertier, O. Laurain, F. Barlier Y. Ménard, E. Jeansou, A. Orsoni, B. Haines, D.G. Kubitschek and G. Born, Leveling Sea Surface using a GPS-Catamaran, Marine Geodesy, submitted, 2003.

Bonnefond, P., P. Exertier, O. Laurain, Y. Ménard, G. Jan, E. Jeansou, and A. Orsoni, Absolute Calibration of Jason-1 and TOPEX/Poseidon Altimeters in Corsica, Marine Geodesy, submitted, 2003.

 

Calmant, S., C. Shum, K. Cheng, W. Scherer and M. Bevis: Earthquake-related offsets in sea levels recorded by Tide Gauges: 2 recent examples in Vanuatu, South West Pacific, Workshop on crustal motion and sea level change, Toulouse, France, September 17-19, 2002.

 

Calmant, S., K. Cheng, and C. Shum: Sea level series and GPS surveys along the ground tracks of satellite altimeters overflying the tide gauges of the MOTEVAS project, EGS-AGU-EUG Joint Assembly, Nice, France, April 6-11, 2003.

 

Calmant, S., K. Cheng, C. Shum and D. Martin: Radar altimeter absolute calibration using GPS buoy and tide gauges, Fall AGU Meeting, San Francisco, December 6-10, 2002.

 

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. Shum and S. Calmant: Radar altimeter absolute calibration using GPS buoy and tide gauges, Weikko A. Heiskanen Symposium In Geodesy: Celebrating 50 years in Geodetic Science at the Ohio State University, Ohio State University, Columbus, Ohio, 1-5 October 2002.

 

Cheng, K., C. Shum, S. Han, M. Parke, K. Snow, Y. Yi, J. Benjamin, D. Mader, and G. Martin: GPS-Buoy water level instrument: Applications for radar altimeter calibration, IAG International Symposium on Gravity, Geoid, and Geodynamics 2000, July 31-August 4, 2000.

 

Cheng, K., C. Shum, S. Han, Y. Yi, and D. Martin: Application of GPS-buoy water level instrument for radar altimeter calibration, IAG Symposium Series, 123, M. Sideris (eds), 367-372, Springer-Verlag Berlin Heidelberg, 2001.

 

Cheng, K., C. Shum, Y. Yi, S. Calmant and D. Martin: Radar altimeter absolute calibration using GPS water level measurements, International Association of Geodesy 2001 Scientific Assembly in Budapest, Hungary, September, 2001.

 

Cheng, K., C. Shum, Y. Yi, S. Calmant, and D. Martin: Absolute radar altimeter calibration using GPS water level measurements, APSG Sea Level Workshop/GLOSS GE7 Meeting, Univ. of Hawaii, Honolulu, Hawaii, April 23-27, 2001.

 

Cheng, K., S. Calmant and C. Shum: Absolute calibration of satellite radar altimeters in Lake Erie, and Vanuatu, South Pacific, 27th General Assembly of the EGS in Nice, France, April 21-26, 2002.

Cheng, K.: Absolute calibration of radar altimeters using GPS water level measurements, Master Thesis, Ohio State University, March, 2001.

 

Huff, Lloyd C., Benjamin W. Remondi: GPS Expedition To Tangier Island, Proceedings of the ION 2000 National Meeting; Navigating into the New Millennium, January 26-28, 2000, Anaheim, CA., pp. 323-332

 

IOC: Abstracts of Presentations at Workshops during the 7th Session of the IOC Group of Experts on the Global Sea Level Observing System (GLOSS), Honolulu, Hawaii, USA, 23-27 April 2001, 2002

 

Jekeli, C., and P. Dumrongchai: On monitoring vertical datums with satellite altimetry and tide gauge data on large lakes, International Association of Geodesy 2001 Scientific Assembly in Budapest, Hungary, September, 2001.

 

Jekeli, C., Heights, the Geopotential, and Vertical Datums, Technical Report, Department of Civil and Environmental Engineering and Geodetic Science, Ohio State University, November, 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.

 

Kuo, C., Y. Yi, K. Cheng, and C. Shum: Great Lakes monitoring using space geodetic technologies, Weikko A. Heiskanen Symposium In Geodesy: Celebrating 50 years in Geodetic Science at the Ohio State University, Ohio State University, Columbus, Ohio, 1-5 October 2002.

 

Kuo, C.: Procedure to compute absolute lake level using Topex/Poseidon altimeter data, Technical Memorandum, Laboratory of Space Geodesy and Remote Sensing Research, The Ohio State University, July 27, 2000.

 

Liebsch, G., K. Novotny, R. Dietrich, and C. Shum: Comparison of multimission altimetric sea-surface heights with tide gauge observations in the Southern Baltic Sea, Marine Geodesy, 25, 213-234, 2002.

 

Liebsch, G., L. Eberlein and R. Dietrich: Realisation of a multisensoral observation system for the determination of offshore sea-level heights, Poster, EGS-AGU-EUG Joint Assembly, Nice, France, 06-11 April 2003

 

Martinez-Benjamin, J., M. Martinez-Garcia, J. Garate, J. Martin-Davila, J. Ferrandiz, M. Vigo-Aguiar, M. Ortiz-Castellon, J. Talaya, B. Perez, G. Kruizinga, B. Haines, O. Colombo, B. Chao, C. Shum, M. Parke, S. Han, and K. Cheng: The T/P CATALA altimeter calibration campaign, Spring AGU Meeting, Washington D.C. May 30-June 3, 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, 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, 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-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-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., 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.

 

Moore, T., Close, G., Lee, C., Moore, R.: RiGHt on the Water: River Monitoring Using GPS Heighting, galileo's World, Autumn 2000, pp. 22-27

 

Moore, T., Close, G., Moore, R.: RiGHt: River Livel Monitoting using GPS Heighting, Proc ION GPS 2000, 13th International Technical Meeting of the Sattelite Division of the Institute of Navigation, 8 pages, Salt Lake City, USA, September 2000.

 

Moore, T., Zhang, K., Close, G., Moore, R.: Real Time River Level Monitoring using GPS Heighting, GPS Solutions, Vol 4, No 2, ISSN 1080-5370, pp 63 - 67, Fall 2000.

 

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

 

Schöne, T., A. Braun, C. Reiber, M. Rentsch, and C. Shum: Concept for using GPS-Buoys for RA drift monitoring, ERS-ENVISAT Symposium, Gothenbury, Sweden, 2000.

 

Schöne, T., A. Braun, C. Reigber: Altimetrie und Meeresspiegel - Möglichkeiten und Grenzen der Beobachtung, Zürich, GAIA 10 (2001) 3, 226-229

 

Schöne, T., A. Braun, Chr. Reigber: Kontinuierliche Überwachung von Pegelstationen und GPS Hochseebojen, Deutscher Hydrographentag 2001, Potsdam, 2001

 

Schöne, T., M. Forberg, R. Galas, C. Reigber: GPS-buoys for lifetime RA drift monitoring, AGU Fall Meeting 2002, EOS Trans. AGU, 83(47), Fall Meet. Suppl., Abstract OS52A-0189, 2002

 

Schueler, T., Zimmermann, B., B. Riedl, G. W. Hein: Radar Altimeter Calibration of the Envisat Satellite: An Autonomous System of High-Precision for Instantaneous Sea Surface Height Determination Proceedings of NTM 2003 – National Technical Meeting, 22-24 January 2003, Anaheim, CA, USA, in press

 

Shannon, B., D.M. Martin: Kinematic GPS observations to establish a mean lower low water dredging datum directly in a navigation channel, http://op.gfz-potsdam.de/altimetry/SSG_buoys/

 

Shum, C. K., C. Jekeli, C. Y. Kuo, and Y. Yi: Monitoring lake level changes using satellite altimetry and GPS-buoys, National Sea Grant College Program a Program Assessment Team (PAT) visit, Ohio State

 

Shum, C., C. Kuo, Y. Yi and C. Zhao: Long-term global sea level change observed by altimetry and tide gauges, International Association of Geodesy 2001 Scientific Assembly in Budapest, Hungary, September, 2001.

 

Shum, C., D. Brzezinska, B. Hazelton, J. Kwon and C. Zhao: The Ohio State University IGS LEO GPS Pilot Project and Associate Analysis Center, IGS LEO Pilot Project Meeting, GFZ, Potsdam, Germany, February 6-8, 2001.

 

Shum, C., D. Brzezinska, S. Ge, B. Hazelton, Y. Yi, C. Zhao, M. Bevis, K. Hocke, J. Wickert, G. Jeffress, D. Martin, and M. Szabados: The use of GPS for measuring water vapor and sea level, Fifth Symposium on Integrated Observing Systems, Albuquerque, New Mexico January 15-19, 2001.

 

Shum, C., K. Cheng, and J. Reutter: Great Lakes monitoring using space geodetic technologies, invited lecture, GLERL Advanced Technology Seminar, Ann Arbor, Michigan, July 9, 2002.

 

Snay, R., M. Chin, D. Coner, T. Soler, C. Zervas, J. Oyler, M. Craymer, S. Gutman, C. Shum , K. Cheng, and C. Kuo: Great Lakes continuous GPS (CGPS) network for geodynamics, meteorology and safe navigation, Weikko A. Heiskanen Symposium In Geodesy: Celebrating 50 years in Geodetic Science at the Ohio State University, Ohio State University, Columbus, Ohio, 1-5 October 2002.

 

Torrobella, Josep & The Grac-II Team: Light GPS Buoys used in the Calibration of ENVISAT ALTIMETER., Poster presentation, EGS03, Nice, April 2003.

 

Torrobella, Josep: GRAC-II - Preliminary results of 27-MAY-2002 experiment # 12. IEEC-CSIC Research Unit. May 2002. Contact Josep Torrobella, badia@ieec.fcr.es for GRAC-II reports.

 

Tseng, H., C. Shum, C. Zhao, and J. Lin: Absolute sea level measurements from tide gauges and adjacent geodetic station vertical motion solutions, 25th General Assembly of the EGS in Nice, France, April 24-29, 2000.

 

Watson, C., R. Coleman, N. White, J. Church, R. Govind: Absolute Calibration of TOPEX/Poseidon and JASON-1 using GPS Buoys in Bass Strait, Australia, submitted to Marine Geodesy, Special Volume, 2003

 

Watson, C.: '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., 1999

 

Yi, Y., A. Braun, C. Shum, K. Cheng and S. Calment: Envisat RA2 cal/val results, Envisat RA-2/MWR CCVT Sixth Plenary Meeting, ESA/ESRIN, Frascati, Italy, March 25-27, 2003.

 

Yi, Y., A. Braun, K. Cheng, C. Shum, and S. Calmant: Initial ENVISAT RA-2 Cal/Val results, ENVISAT RA-MWR CCVT Fourth Plenary Meeting, ESA/ESRIN, Frascati, Italy, 3-4 December 2002.

 

Yi, Y., C. Kuo, C. Shum and C. Jekeli: Long-term Great Lakes water level changes observed by tide gauges and altimetry, International Association of Geodesy 2001 Scientific Assembly in Budapest, Hungary, September, 2001.

 

Yi, Y., K. Cheng, C. Shum, A. Braun, and S. Calmant: ENVISAT RA-2 calibration/validation, Proc. EGS-AGU-EUG Joint Assembly, Nice, France, April 6-11, 2003.

 

Zhao. C., C. Shum, Y. Yi, P. Luk, J. Finkelstein, J. Lillibridge, J. McMillan, and M. Rau: GFO radar altimeter data product verifications and ocean circulation studies, IAG Scientific Assembly, Vistas for Geodesy in the New Millennium, Budapest, Hungary, September 2-7, 2001.

 

Zimmermann, B., T. Schueler, B. Riedl, G. W. Hein, R. J. Biberger: Radar Altimeter Calibration of the ENVISAT Satellite Using an Autonomous GPS-based System of Moored Buoys for Instantaneous Sea Surface Height Determination GNSS 2003 – Euro0pean Navigation Conference, 22-25 April 2003, Graz, Austria