CoAuthors

Laurent Linguet (UAG ESPACE-DEV, Guyane Française); Stephane Calmant (IRD LEGOS, France)

Ogoué river basin is one the last preserved tropical rain forest basin in the world. Results of a study conducted on wall-to wall forest cover map using Landsat images (Fichet et al., 2014) gave a net forest loss of 0,38% from 1990 and 2000 and sensibly the same loss rate between 2000 and 2010. However the river basin covers about 75% of Gabon, and the country launched recently an ambitious development plan, with communication infrastructure, agriculture and forestry as well as mining projects. Hydrological cycle response to changes may be expected, in both quantitative and qualitative aspects. Unfortunately monitoring gauging stations have stopped functioning in the seventies, and Gabon will then be unable to evaluate, mitigate and adapt adequately to these environmental challenges.
Nadir altimetry has proved to be efficient in monitoring ungauged basins. When historical record is needed, as it is the case to be able evaluating parts of climate and anthropic impact on changes, the best way available today is to couple data from ERS, ENVISAT RA2 and ALtiKa altimeter, along with Jason2 when tracks crossing are nearby. Some bias are to be expected between the different missions, that cannot be evaluated using in situ data. An innovative method base on extended Kalman filter will be presented, leveraging on the relatively dense spatial distribution of the sampling scheme (18 envisat tracks crossing and 3 Jason2) for about 200 000km2 basin