TITLE:
Estimation of Subsidence in Po Delta Area (Northern Italy) by Integration of GPS Data, High-Precision Leveling and Archival Orthometric Elevations
AUTHORS:
Massimo Fabris, Vladimiro Achilli, Andrea Menin
KEYWORDS:
Subsidence, Po Delta, Spirit Leveling, GPS, Local Geoid Modeling
JOURNAL NAME:
International Journal of Geosciences,
Vol.5 No.6,
May
6,
2014
ABSTRACT:
Subsidence
in a deformation area can be measured in various ways, examples being
conventional high-precision leveling, differential InSAR and multi-temporal GPS
surveys. Integration of methods can improve results, and is crucial to extract
high-precision data. In particular, orthometric and ellipsoid elevations,
surveyed at different moments in time, can be compared to yield information on
vertical movements when geoid anomalies are known. However, a data checking procedure
must be applied if archival orthometric elevations are used, because long-term
measurements for many historical benchmarks may have been lost and/or replaced
with other points, but at different elevations. This type of checking can be
carried out over an area without gravimetric anomalies by modeling geoid
undulations and vertical displacements in the time-span used for analysis,
excluding points with anomalous values. This procedure was tested and applied
in the Po Delta area (northern Italy), historically subject to high subsidence
rates: the leveling benchmarks of 1983 were measured with the GPS technique in
2008. After checking of archival data and transformation from ellipsoid to
orthometric elevations, comparisons of the same points and interpolations on
the study area provided a subsidence map for the 1983-2008 period.