Ace: a New Global Digital Elevation Model Incorporating Satellite Altimeter Derived Heights

A new Global Digital Elevation Model is being generated at 30" resolution by combining the best available ground truth with a unique global database of satellite altimeter derived heights. This model, ACE (Altimeter Corrected Elevations) demonstrates radically improved spatial accuracy and resolution over large parts of the globe, in particular over Africa and South America. The independent altimeter based dataset, which contains over 100 million individual height estimates, has enabled the identification and correction of gross errors in individual ground truth datasets. Source data of low spatial resolution have been replaced with greatly improved altimeter generated surfaces. Additionally, the use of this satellite derived near-global dataset of very high vertical accuracy, referenced to a single datum, has allowed the identification, measurement and correction of the vertical offsets between adjacent tiles of DTED data, widely reported by users of previous models. The result is a model in which a significant proportion of the earth's land surface is represented by a completely new dataset: this is especially true of areas for which previous models have drawn on Digital Chart of the World. Adjoining ground based datasets of good quality have also been adjusted for vertical misplacement. The detailed assessment of dataset quality undertaken as part of the programme to create the ACE GDEM has allowed the inclusion of a unique additional information matrix: a data quality indicator is being constructed for every land pixel of ACE, together with detailed source information. This will allow the user, for the first time, to make an informed judgement on expected performance of the ACE GDEM for the desired application. The ACE GDEM is now in beta release, undergoing validation with selected end users prior to full release early in 2001.