Surface water dynamics in the Amazon Basin: Application of satellite radar altimetry

Abstract

[1] Satellite radar altimetry has the ability to monitor variations in surface water height (stage) for large wetlands, rivers, and associated floodplains. A clear advantage is the provision of data where traditional gauges are absent. As part of an international program, a complete altimetric analysis of the Amazon Basin is being undertaken. Here, an updated and more rigorous evaluation of the TOPEX/POSEIDON (T/P) data set is presented for the first $7.5 years of the mission. With an initial study group of 230 targets, height variability at many ungauged locations can be observed for 30-50%, the range reflecting the clarity of the variations in lieu of instrument limitations. An assessment of the instrument performance confirms that the minimum river width attainable is $1 km in the presence of some inundated floodplain. This constraint does allow observation of the main stem (Solimões/Amazon) and the larger tributaries, but rugged terrain in the vicinity of the target additionally places severe limitations on data retrieval. First-order validation exercises with the deduced 1992-1999 time series of stage fluctuations reveal accuracies ranging from tens of centimeters to several meters (mean $1.1 m rms). Altimetric water levels in the Solimões and Amazon are particularly well defined with amplitudes <13 m and variations in peak-level timing from May to July. The water-surface gradient of the main stem is found to vary both spatially and temporally, with values ranging from 1.5 cm/km downstream to 4.0 cm/km for more upstream reaches. In agreement with ground-based estimates, the seasonal variability of the gradients reveals that the hysteresis characteristic of the flood wave varies along the main stem and the derived altimetric velocity of this flood wave is estimated to be $0.35 m/s. Overall, the altimetric results demonstrate that the T/P mission is successfully monitoring the transient flood waves of this continental-scale river basin.

Floodplain water storage in the Negro River basin estimated from microwave remote sensing of inundation area and water levels

“…It represents a unique source of data for floodplain, as the in-situ data records are generally located on the river mainstream. Although the radar altimetric measurements are still suffering severe limitations (Birkett, 1998;Birkett et al, 2002), the capability to sample, from one cycle to another, both mainstream and floodplain is a clear advantage compared with traditional in-situ measurements. This aspect is essential because it has been shown that the water volume stored in floodplains cannot be inferred from the flood extent, nor the elevation of the flood by its extent.…”

“…1 : We explained and clarified the notions of water storage variation and water volume calculated from half peak flow integrated discharge in the additional paragraph 3.5. 2 : Many studies such as Birkett et al (2002) or Oliveira Campos et al (2003 showed the quality of water level derived from radar altimetry measurements. We added in figure 4 a comparison of the in-situ water levels at Manaus gauge station and the altimeter derived water level obtained 8.5 km upstream.…”

“…In addition, the potential of satellite radar altimetry for monitoring water levels of large rivers has already been demonstrated (Birkett, 1998 ;Oliveira Campos et al, 2001 ;Maheu et al, 2003). Birkett et al (2002) undertook an extensive validation study of water levels derived from Topex/Poseidon radar over the entire Amazon basin and used satellite radar altimetry to estimate elevation profiles and water surface gradients along the Amazon mainstream.…”

Interannual variability of surface water extent at the global scale, 1993–2004

“…Recent advances in remote sensing have demonstrated that some hydraulic variables can be measured reliably from satellites. For example, satellite altimetry (Topex/Poseidon (T/P), Jason-1, ERS, and Envisat missions) has been used for systematic monitoring of water levels of large rivers, lakes, and floodplains, now providing an ∼15 year long time series [Birkett, 1998;Birkett et al, 2002;Gennero et al, 2005].…”

Space‐based measurement of river runoff

“…Observations of river inundation areas, water levels, and flow variability from orbital sen sors have the potential to directly measure the runoff component of the Earth's hydrologic cycle [Birkett et al, 2002;Brakenridge et al, 1998;Sippel et al, 1994Sippel et al, ,1998Townsend, 2001 ]. A remote-sensing-based measurement strategy for rivers and streams is emerging: Surface water data can be collected, their accuracy evaluated, and the results disseminated with out regard to political boundaries.The results can be used to address a wide variety of ap plications.…”