DEM Extraction from High Resolution Satellite Stereopairs to Investigate the Hydraulic Hazard of Areas Subjected to River Floods

As far as the monitoring of the hydraulic hazard of flat areas is concerned, a very important role is played by studies concerning the outflow of water after river floods or downpours. Such studies are based on complex forecasting hydraulic models, which need an accurate and detailed DEM as input together with planimetric and altimetric data regarding all the natural and anthropic objects, as riverbanks or roads in relief, which may interfere with the outflow of water.

The aim of this work is the evaluation of DEMs extracted from high resolution stereo pairs (both panchromatic and multi spectral) for their application in hydraulic hazard analysis. The advantages arising from the use of satellite images are mainly relative low costs and fast elaboration.

The investigation has been carried out on an in-track Ikonos stereopair acquired over the area of the town of Ferrara (Northeastern Italy, near the Po delta) on July 2004.

The best workflow to generate the DEM has been evaluated: the orientation has been performed both with the commercial software PCI Geomatics OrthoEngine v10.2 and with the scientific software SISAR, developed by La Sapienza University of Rome, and SAT-PP, developed by ETH Zurich and now delivered by 4DiXplorer.

Image matching and DEM extraction have been performed not only with PCI Geomatics and SAT-PP but also with the scientific software BLUH, developed by Leibniz University of Hannover.

The DEM accuracy has been evaluated by sample comparisons, based on a consistent number of Check Points (CPs), surveyed by kinematic GNSS with a mean 3D accuracy of about 0.3 m. Areas with different land cover have been selected, in order to identify critical zones with low mean accuracy which may introduce significant errors in hydraulic modeling.