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SH-01 Abstract

Altimetric Remote Sensing of the Amazon: Contribution to Surface Water Dynamics

Marcos Costa — UFV - Universidade Federal de Viçosa (SA-PI)


This project will utilize satellite radar altimetry

to derive three surface water state variables; water level, water depth, and

extent of inundation, which will aid in several studies of Amazon Basin

hydrology and climatology. A 9-year time series, with a 10-day time step will be

constructed for these variables, enabling the monitoring of large-scale seasonal

to interannual variations of the main river, its floodplain and tributaries, and

inland wetland regions. In addition, the progression of peak flow flood waves

and the gradient of the main river stem will be deduced. The contribution of

altimetry to discharge estimates will also be examined.


Unhindered by time of day, weather, vegetation or

canopy cover, satellite radar altimeters can retrieve surface water height

information as the satellite orbits the Earth. All retrieved heights are

determined with respect to one common reference datum. Due to the repeat nature

of the satellite orbit, they are also capable of monitoring the level changes of

large lakes, rivers, inland seas and wetlands, during the lifetime of the

satellite. This capability has been applied in several recent test case studies,

including the Amazon Basin, with validated techniques.

Instruments and Potential Accuracies

Altimetric height accuracies, spatial density and

temporal resolution are instrument dependent. The best accuracy for rivers and

wetlands is ~10cm rms, from the currently operating TOPEX/Poseidon satellite

whose data has a temporal resolution of ~10days (Birkett, 1998). However, the

ERS missions provide the greatest coverage of the Amazon Basin, and potentially

can acquire rivers of ~0.5km width and larger. With combined results from the

1990's ERS-1, ERS-2, and TOPEX/Poseidon missions, and from the two new instruments,

Jason-1 and ENVISAT, an altimetric data set spanning a time period greater than

10 years can be constructed for the Amazon Basin. Altimetry can thus improve

systematic observation on both a regional and basin scale, attaining water level

knowledge for river and wetland regions where there is poor accessibility and/or

low gauge density.


In addition to directly addressing the LBA priority

topics 2.3 (Testing remote sensing algorithms for estimation of surface state

variables) and 2.5 (Provision of missing surface data for documentation of

regional water cycles), this study will contribute to priority topics 2.1, 2.2,

4.1 and 4.4, through the provision of additional or new data for calibration and

validation. Specific relevance will be to the following:

a) Regional to continental scale surface

hydrology, including stream discharge, runoff estimation, and river routing.

b) Surface energy and water balance, and land

atmosphere interactions.

c) Biogeochemical processes.

All derived results will be made accessible to

LBA participants via a maintained World Wide Web site and/or ftp database.


Relevant References

Birkett, C.M., Radar altimetry: A new concept in

monitoring lake level changes, EOS Trans. 75,  No.24, pp.273-275, 1994.

Birkett, C.M., The contribution of TOPEX/POSEIDON

to the global monitoring of climatically sensitive lakes, JGR-Oceans, Vol.100,

C12, pp.25,179-25, 204, 1995a.

Birkett, C.M., The contribution of the TOPEX

(NRA) radar altimeter to the global monitoring of large rivers and wetlands,

Water Resour. Res., 34, No.5, pp.1223-1240, 1998.

Birkett, C.M., Murtugudde, R. and T. Allan,

Indian Ocean climate event brings floods to East Africa's lakes and the Sudd

Marsh, In Press, Geoph. Res. Letters, 1999.

Cazenave, A., Bonnefond, P., Dominh, K., and

Schaeffer, P., Caspian sea level from Topex- Poseidon altimetry: Level now

falling, Geophy. Res. Letters, 24, No.8, pp.881-884, 1997.

Dalton, J.A., and Kite, G.W., A first look at

using the TOPEX/POSEIDON satellite radar altimeter for measuring lake levels,

In: Remote Sensing in Hydrology, Proc. Symp. No.14, NHRI, Saskatoon, Canada, ed.

G.W. Kite, A. Pietroniro and T.D. Pultz, pp.105-112, 1995.

Koblinsky, C.J., R.T. Clarke, A.C. Brenner, and

Frey, H., Measurement of river level variations with satellite altimetry, Water

Resour. Res., 29(6), 1839­1848, 1993.

Morris, C.S., and Gill, S.K., Variation of Great

Lakes water levels described from Geosat altimetry, Water Resources Research,

30, No.4, pp.1009-1017, 1994.

Rapley, C. G., Guzkowska, M.A.J., Cudlip, W.,

and Mason, I.M., An exploratory study of inland water and land altimetry using

Seasat data, ESA Report No. 6483/85/NL/BI, 1987.


The Figures below show radar altimetric results

from the currently operating TOPEX/Poseidon satellite. Time series of relative

river height variations have been derived for two satellite passes over the main

river branch, and are compared with standard river stage data from conventional


March 1999


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