Η συνεισφορά των ψηφιακών μοντέλων τοπογραφίας στον υπολογισμό αναγωγών σχετικών με το πεδίο βαρύτητας της Γης
Contribution of DTMs in the calculation of topographic reductions of the gravity field of Earth
Παπαγεωργίου, Πέτρος Τιμολέων
Η συνεισφορά των ψηφιακών μοντέλων τοπογραφίας στον υπολογισμό αναγωγών σχετικών με το πεδίο βαρύτητας της γης.
Products from satellite missions always give big benefits to countries all over the world that are using them. The Shuttle Radar Topographic Mission (SRTM) is one of them. Its product, a high resolution digital terrain model (DTM) of 3 arcsec (90 m), was a model that become available for Greece for various uses. Until today, the only high resolution DTMs that were available for Greece were produced by the Hellenic Military Geographic Service (HMGS). They have various resolutions but the finest of them, the one of the 100 m, is not yet available and it is only being used for military purposes. These DTMs are produced by digitizing topographic maps and therefore their accuracy may sometimes be unknown or not so reliable. The need of a very high resolution DTM is necessary when a high resolution, e.g., 0.5 – 1 arcmin geoid has to be computed. If this can not be done and a coarser DTM is used then the results of the topographic effects are likely to be aliased due to the insufficient topographic information used for the computations. Digital Terrain Models (DTMs) are very important in studies that have to do with gravity field, because they provide the high frequency content of the gravity field spectrum. These DTMs are nowadays widely available for geoid and gravity field approximation, due the continuous launch of new altimetric and gravity field satellite missions. In several countries around the world though, the DTMs are not widely available because they are produced by geodetic/cartographic agencies and are related to confidential issues. Moreover, the DTMs available are not homogeneous because they are derived by a merging of available height data. On the contrary, SRTM was launched on-board space shuttle Endeavour and collected data of the Earth’s topography in global scale and with homogeneous coverage. This had as result the distribution of a global 3" (roughly 90 m) SRTM DTM by NASA and the National Geospatial Intelligence Agency (NGA)
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