Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [TP-3 OCEAN/COASTAL ZONE MONITORING]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: MONITORING THE OCEANS WITH SATELLITE ALTIMETRY TECHNIQUES. Demitris Delikaraoglou, Nicholas Christou and Mario Berube

Document type:: Multivolume work

Structure type:: Chapter

Figure 2 - Typical GEOS AT 5-day ground track coverage precision of a few centimeters along an exactly recurring satellite track (cf. Figure 2). Measurements of time- averaged currents, such as those produced by the general ocean circulation, require even more exact repeating. Particularly, they require a knowledge of the geoid over wavelengths of 200 to 10,000 km, of the measurement of the height of the satellite relative to the Earth’s centre of mass, and of the height of the altimeter above the instantaneous sea surface, all with an accuracy of less than 5 to 10 cm. Fortunately, technological developments in radar altimeter instrumentation have come a long way since the early GEOS-3 and SEASAT altimeters, as shown by the improved measurement precision of the GEOSAT altimeter and the projected precision of the future TOPEX-type altimeters (cf. Figure 3). The uncertainties in the knowledge of the geoid and of the satellite’s geocentric altitude variations, gained independently, to a level of accuracy comparable to the resolution of the altimetry measurements, remain as important unresolved problems. For the ERS-1 mission, precise laser ranging tracking and the experimental PRARE system will be used to provide this orbit information. In the future, the satellites of the Global Positioning System (GPS) and a few globally distributed fiducial tracking sites operating in concert with GPS receivers on the altimeter-carrying satellites will provide the required sub-decimeter accuracy in the determination of the satellite’s orbit. Within the framework of the aforementioned initiatives, the Geodetic Survey Division, Canada Centre for Surveying (CCS) works closely with other agencies in Canada and USA to develop and test algorithms to extract information from satellite altimetry measurements to monitor oceanic variability and to measure surface elevations of the ice- covered regions (which in itself is perhaps the most meaningful parameter to measure to monitor volumetric change of the ice sheets). To date, satellite altimetry data from the GEOSAT Exact Repeat Mission (ERM) have contributed to the improvement of our knowledge of the Canadian marine geoid. Operational software is being developed to carry out the pre-processing and crossover adjustment of GEOSAT data in order to obtain a precise approximation of the sea surface heights globally or, in regional solutions, for instance, of the North Atlantic and North Pacific oceans, Hudson Bay, etc. The methodologies used currently make use of altimetry data to: • determine the time-averaged long wavelength sea surface topography over periods of a year or more; • detect the large scale fluctuations of the world’s oceans over periods of a few weeks to several months; and • estimate the annual cycle in the sea level variations. Figure 4 illustrates the present GEOSAT data processing flow at CCS. The primary data include GEOSAT Geophysical Data Records (GDR) tapes received from the U.S. National Oceanic and Atmospheric Administration (NOAA) [Cheney et al., 1987] through the Canadian Marine Environmental Data Service (MEDS), Ottawa. GDRs include merged altimeter and timing data, atmospheric corrections data, and orbital information (accurate to 3-4 m level, which is relatively large compared with the meter-level precision of the SEASAT orbits) as generated for the GEOSAT operational needs by the U.S. Navy Astronautics Group using a GEM-10 gravity field model, Doppler tracking data from only the continental U.S. and Hawaiian tracking sites, and other auxiliary parameters. Improved GEOSAT satellite ephemerides are received (with a few months delay) from NASA’s Goddard Space Flight Centre (GSFC). They are generated using additional Doppler tracking data from TRANET tracking stations overseen by the French Space Agency (CNES), the Geological Survey of Canada (at Priddis, Alberta and Ottawa, Ontario) and the Royal Observatory of Belgium, and the GEM-T1 or GEM-T2 gravity field model (Marsh et Figure 3 - The evolution of satellite altimeter instrumentation precision 84 Figure 4 - GEOSAT Data Processing Flow at CCS

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