HYDROLOGIC VALIDATION FOR SATELLITE WATER LEVEL OVER RIVER PO BASIN
Vittucci, C1; Napolitano, F2; Benveniste, J3
1ESA/ESRIN; 2Università degli Studi di Roma “La Sapienza”; 3ESA
“River Po-Emergency dry weather”: article appeared on 2007, July 17th Italian newspapers ‘La Repubblica’ and ‘Il Messaggero’ by APAT Scientific Committee water level forecasts:
[…] “Last year 40 km of river body became Adriatic sea and water level continues to decrease, soon its overall length will became shorter than 100 km maybe it will interrupts on Pontelagoscuro (Ferrara), where salty sea water will go up to the river.”
[…] “An ecosystem revolution is nearer than we expected, suggestive wooded landscapes and their air fauna that years ago made river Po sides a typically country background, will risk to die forever.”
[…] “In addition typical Italian belts and natural products will disappear because of desert advancing.”
Northern Italy economy depends on this basin, but its importance is growing also at a global level where, comparing its water level trends to hydrological analysis of other European basins, it became a useful indicator of climate changes.
A real time monitoring will be an ideal condition to forecast floods events whereas for most of earth gauged basins, like river Po, it is quite simple nowadays, while for un-gauged basins we need additional instruments to give us information about water level variation data and possibility discharge.
Thanks to progress in satellite remote sensing technologies and radar altimetry capability to estimate inland water levels, it is now possible to monitor from space every kind of water bodies.
Thus the work concernes the validation of ERS-RA and ENVISAT-RA2 data series by their correlation with daily ground time series data over a well known basin like river Po, in order to confirm water level trends (from1995 to 2005), and verify that this satellite approach is adequate to monitor other ungauged basins.
Such validation is conducted through correlation coefficients computation for each satellite water level measurement and the nearest terrestrial one (e.g. upstream the first and downstream the second and vice versa.) for both ERS and ENVISAT satellites.
For some comparisons, that with satellite and station very close together, good results are obtained. But for the most part of water level comparisons, correlation coefficients seem not good enough.
Difficultiese arise in retrieving water level from radar altimeter echoes, even with the ice mode tracking. Furthermore: the big dimension of the footprint with respect to the chosen target; large distances in the location between ground and satellite measurements; presence of one or more affluents, make the comparisons more difficult.
To overcome these difficulties we considered using discharge ground data instead of water level.
The aim is, after reconstructing a flow scale, to pre-process ground data using an ad hoc Muskingum model in order to recreate a model of discharge propagation.
This step is now in elaboration; the results of this improved method will be presented.