A comparison of the performance of the ice and ocean tracking modes of the ERS‐1 radar altimeter over non‐ocean surfaces

Scott, Rachel; Baker, S. G.; Birkett, C. M.; Cudlip, W.; Laxon, Seymour W.; Mantripp, D. R.; Mansley, Justin A. D.; Morley, Jeremy; Rapley, C. G.; Ridley, Jeff; Strawbridge, Fiona; Wingham, D. J.

doi:10.1029/94gl00178

Cited by 28 publications

(26 citation statements)

References 9 publications

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“…The altimeter (1991 to present) possesses an ice-tracking mode facility which has enabled increased tracking performance over land [Scott et al, 1994]. The enviromnental satellite mission (ENVISAT, launch in approximately 1999) will also carry a modified radar alti•neter (known as RA 2) which will have "guar,-mteed continuity" performance, i.e., operation without the loss of surface lock, over nonocean surfaces [Resti, 1993].…”

Section: Altimeter Tracking Performancementioning

confidence: 99%

The contribution of TOPEX/POSEIDON to the global monitoring of climatically sensitive lakes

Birkett¹

1995

J. Geophys. Res.

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Remote sensing and long‐term monitoring of closed and climatically sensitive open lakes can provide useful information for the study of climatic change. Satellite radar altimetry offers the advantages of day/night and all‐weather capability in the production of relative lake level changes on a global scale. A simple technique which derives relative lake level changes is described with specific relevance to the TOPEX/POSEIDON geophysical data record data set. An assessment of the coverage and global tracking performance of both the NASA radar altimeter and the solid state altimeter over these lakes is discussed, and results are presented for the first 1.75 years of the mission. Lake level time series were acquired for 12 closed lakes, six open lakes, and three reservoirs, providing information in many cases where ground gauge data are unobtainable or the lake is inaccessible. The results, accurate to ∼4 cm rms, mark the beginning of a very accurate lake level data set, showing that TOPEX/POSEIDON can successfully contribute to the long‐term global program.

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Section: Altimeter Tracking Performancementioning

confidence: 99%

The contribution of TOPEX/POSEIDON to the global monitoring of climatically sensitive lakes

Birkett¹

1995

J. Geophys. Res.

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236

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“…Through a repeat cycle of 165 days, the ground track spacing at 79øS is 2 km, providing a high density of height measurements across the plateau. Through the application of corrections to the height estimate [Cudlip et al, 1994] and the best available orbit ephemeris [Scharroo et al, 1993], an individual height measurement over the plateau has a precision of 25 cm and an accuracy of about 1 m [Scott et al, 1994]. Two cycles of data, offset from each other by half the track separation, from the 165-day repeat mission (comprising 250,000 individual measurements) were averaged and interpolated across a 3-km grid to provide the data from which the detailed surface elevation map of the ice sheet above the radio-echo lines of Lake Vostok was made (Figure 1).…”

Section: Satellite Radar Altimetrymentioning

confidence: 99%

An analysis of the ice‐sheet surface and subsurface topography above the Vostok Station subglacial lake, central East Antarctica

Siegert

Ridley²

1998

J. Geophys. Res.

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Abstract. Radio-echo sounding (RES) and satellite radar-altimeter data were analyzed in order to identify the surface and subsurface topography around the largest known subglacial lake, at Vostok Station, East Antarctica (named here as Lake Vostok). In doing so, a data set was established from which a qualitative description of the flow of ice across the lake was developed. Patterns of ice flow were constructed through consideration of (1) the ice-sheet surface from the satellite altimeter and (2) internal layering from RES. It is concluded that Lake Vostok influences the dynamics of the overriding ice. Specifically, although the flow of ice across the lake is dominated by the general eastward flow of the grounded ice sheet, a southward velocity component, caused by an ice-shelf-type ice-flow mechanism, is also present over the subglacial lake. A further 67 smaller subglacial lakes exist within central regions of the Antarctic Ice Sheet, occupying 5-10% of the ice-sheet base. Subglacial lakes may therefore exert a significant control on ice dynamics within central Antarctica.

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“…Initial studies showed that during the ERS 1 ice mode operating periods, 64% of wetland/river surfaces were acquired [Scott et al, 1994]. Although both instruments are set in an orbit with a longer repeat period (35 days), their greater coverage of rivers/wetlands (theoretically, 3 times that of TOPEX/POSEIDON), with an along-track spacing of -330 m, offers the potential for more regions to be studied and the minimum river width limit to be narrowed.…”

Section: Conclusion and Future Researchmentioning

confidence: 99%

Contribution of the TOPEX NASA Radar Altimeter to the global monitoring of large rivers and wetlands

Birkett¹

1998

Water Resources Research

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Abstract. For certain major rivers and wetlands, hydrological information can often be difficult to obtain due to the inaccessibility of the region, the sparse distribution of gauge stations, or the slow dissemination of data. Satellite radar altimeters have the potential to monitor height variations over inland waters. Here, it is shown that the NASA radar altimeter (NRA), currently operating on board the TOPEX/POSEIDON satellite, can successfully track both large wetlands and rivers of > 1 km width. The coverage, performance, and limitations of the NRA altimeter are discussed with relevance to these regions, and the merits of utilizing the geophysical data records (GDRs) and the sensor data records (SDRs) are explored. Time series of relative water level variations, for the first -3.7 years of the mission, have been obtained for a selection of the world's largest rivers, and for major wetlands of international importance. Validation shows the results can be accurate to -11 cm rms, offering the potential to observe these regions as part of a long-term hydrological monitor!ng program. IntroductionMajor river systems are important topics of research covering a wide range of applications such as transport, flood hazards, water and food resource management, studies of the hydrological cycle, and addressing the impacts of land use and climate change [Leopoldo et al., 1985]. Wetlands (swamps, marshes, floodplains, internal deltas, etc.) cover 6% of the world's land surface. The extent of inundated area and depth of wetland water varies seasonally and annually according to inflow, precipitation, and evaporation rates. As their hydraulic response is relatively slow, they are good proxy indicators of local climate, but they are also important with regard to local environmental and economic concerns, being both a source of food and fresh water [Maltby, 1986].Although most major North American and European rivers are frequently (daily) and accurately (better than 1 cm at the point of measurement) monitored (with water level variations being converted to discharge rates and the data subsequently archived), water levels for many other regions can be difficult to obtain due to the inaccessibility of the region, the sparse distribution of gauge stations, or the slow dissemination of data. Although primarily aimed at ocean applications, satellite radar altimetry has demonstrated a potential to provide both lake and river/wetland height data. A radar altimeter emits a series of microwave pulses toward the surface, and by noting the two-way time delay between pulse emission and echo reception, estimates the altimetric range, that is, the distance between the antenna and the surface (see Rapley [1990] for full details on radar altimetry). In To summarize, some degree of success has been achieved in deriving altimetric water levels over rivers and wetlands. The limitations have been poor knowledge of the satellite orbit and instrumental inefficiencies in data gathering (variable according to each altimeter). As the radar echoes fr...

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A comparison of the performance of the ice and ocean tracking modes of the ERS‐1 radar altimeter over non‐ocean surfaces

Cited by 28 publications

References 9 publications

The contribution of TOPEX/POSEIDON to the global monitoring of climatically sensitive lakes

The contribution of TOPEX/POSEIDON to the global monitoring of climatically sensitive lakes

An analysis of the ice‐sheet surface and subsurface topography above the Vostok Station subglacial lake, central East Antarctica

Contribution of the TOPEX NASA Radar Altimeter to the global monitoring of large rivers and wetlands

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