OF REMOTE SENSING TECHNIQUES FOR VALIDATING HEIGHTS AND DEPTHS
REPORT FOR SSG 3.184
have been held on an ad-hoc basis at conferences, supplemented by
on several different radar based techniques for remotely sensed height
determination is being carried out by members of this study group.
global scale assessment of current Global Digital Elevation Models has
been performed using an independently derived height dataset,
containing over 100 million points. These data were calculated from
satellite altimeter data from the ERS-1 Geodetic Mission. Models
evaluated include GLOBE v1., GTOPO30, JGP95E, TerrainBase and ETOPO5.
The results confirm the presence of substantial errors common to all
models tested. These errors have been attributed to reliance on a
common stock of a small number of data sources. The most consistent
agreement was obtained where data were sourced from DTED; poor results
were generally obtained where the source was Digital Chart of the
World or the International Map of the World.
these errors were found to be contaminating existing GDEMs very
significantly, it was decided to create a new GDEM, ACE (Altimeter
Corrected Elevations, produced at De Montfort University) by fusing
the best of the available ground truth with a DEM derived from the
satellite-based dataset.. The first release of this new GDEM has just
been made. Globally, 28% of values have been outright replaced with
new altimeter based data, and a further 17% corrected for vertical
misplacement. The new model is currently being evaluated by members of
this approach does not enable detailed mapping, nor mapping over
mountainous regions where altimeters to date have lost lock. Several
different techniques and missions have been deployed to create
accurate detailed DEM data on a global scale. The recently flown
Shuttle Topographic Mission created a huge dataset which is currently
being processed. Data post-processing has proved very complex,
resulting in some delays to the original schedule. However, results
should be released soon, enabling assessment of these vital new DEM
data to be carried out within the next two years. Additionally, work
on InSAR and stereo SAR derived DEMs continues, forming another
increasingly important datastream as the application of these
techniques to mapping becomes more widespread.
launch of Envisat within the next few months should further increase
the available data pool, both by providing an additional source of SAR
data and by deploying the RA-2, an altimeter configured with an
additional tracking mode to allow the instrument to remain in lock
over more extreme terrain.
indications are that within the life of this working group, a
considerable advance will have been made in the mapping of the
earths topographic surfaces.