Water level changes in a large Amazon lake measured with spaceborne radar interferometry and altimetry

We demonstrate that interferometric processing of JERS-1 SAR data over an Amazon lake containing similar to 1500 islands yields centimeter-scale changes in the height of the water surface from February 14 to March 30, 1997. For the method to work, we qualitatively find that inundation of about one or two leafless trees per 25 m(2) multi-look SAR pixel is sufficient to return the radar pulse to the side-looking antenna. Validation is provided by multi-temporal TOPEX-POSEIDON altimetry profiles, which directly measure surface heights relative to a fixed datum. Because SAR provides an image, the water height changes (similar to 12 cm) can be converted to a net volume measurement (280 million m(3)) over the 44 days separating the JERS-1 acquisitions. Compared to historical gauge records, removal of this volume from the lake required a similar to 50% greater flow.