Foto del docente

Susanna Zerbini

Alma Mater Honorary Professor

Alma Mater Studiorum - Università di Bologna

Adjunct professor

Department of Physics and Astronomy "Augusto Righi"

Adjunct professor

Department of Physics and Astronomy "Augusto Righi"

Research

Keywords: Space and terrestrial geodetic techniques Reference systems Geodesy Deformation of the Earth's crust

The main interests focus on the following research themes:

  1. Study of the deformations of the Earth crust by combining different space geodetic techniques such as GNSS (Global Navigation Satellite System) and InSAR (Interferometric Synthetic Aperture Radar). The aim of the study is to achieve a time- and space-continuous description of the deformation by taking advantage of the complementary strengths of each technique by overcoming the limitations inherent in each single technique alone;

  2. Study of gravity variations using the continuous records of the superconducting gravimeter located at Medicina and absolute gravity measurements performed every six months in various stations;

  3. Estimate of atmospheric parameters by means of a combined analysis of GPS and InSAR data;

  4. Study of sea-level variations by means of tide gauge and satellite radar altimetry data;

  5. Study on the combination of space geodetic data, in particular GNSS and SLR (Satellite Laser Ranging), in the realization of the ITRF (International Terrestrial Reference Frame).

Her research involves studies of the deformations of the Earth’s crust at regional and local scale by means of space geodetic techniques (see point 1 above). In particular, focus is given to the vertical land motions which, in the southern Po plain and along the northern Adriatic coast, are of special interest. In fact, in this region, subsidence which combines natural and anthropogenic components, is characterized by relevant rates and it is the source of several problems. Starting in 1996, she has established a network of five permanent GPS stations located at Bologna, Loiano Medicina Marina di Ravenna and Trieste.

She is involved in studies related to the interpretation of high-precision gravimetric data (see point 2 above). Since 1996, in the framework of collaboration with the Frankfurt BKG (Bundesamt fuer Kartographie und Geodaesie), she contributes to the continuous functionality of a superconducting gravimeter (SG) at the Medicina station. The SG records are analyzed to monitor and interpret the long-period (linear and non-linear) variations and the annual oscillations of gravity. These changes are due to variations of both height and Newtonian mass attraction. At Medicina, two permanent GPS receivers allow determining daily values of the station height. By comparing the gravity time series with that of the station vertical component, it is possible to identify, in the gravity record, the mass attraction contribution which then needs to be interpreted.

She is interested in the combination of different space geodetic techniques. Today’s application of interferometric SAR techniques is limited by the knowledge of the wet tropospheric path delay in microwave observations (see point 3 above). GPS-based estimates of tropospheric delays may help in obtaining better corrections which will enhance the coherence and will allow InSAR to contribute in a wider range of applications.

In the frame of two large EU-funded projects which she coordinated, she has started to study mean sea-level variations. Accurate knowledge of vertical land motion is desirable when studying sea-level variations by means of tide gauge data (see point 4 above). Tide gauges, in fact, measure the sea level elevation with respect to a geodetic reference benchmark located in close proximity of the recording gauge. Therefore, vertical land motions, being embodied in the tide gauge records, need to be removed from the sea-level data before estimating sea-level trends. Today, this task can be accomplished accurately and continuously by co-locating a GNSS system at tide gauge stations or by exploiting the combination of GNSS and InSAR data.

She is interested in studies regarding the establishment of a highly accurate and stable International Terrestrial Reference Frame (ITRF) which is a fundamental requirement for the study of the planet Earth as an integrated and interconnected system (point 5 above). Currently, the ITRF is determined by the data of four space geodetic techniques: SLR (Satellite Laser Ranging), VLBI (Very Long Baseline Interferometry), GPS/GNSS (Global Positioning System/Global Navigation Satellite System) and DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite). In the realization of the ITRF, frontier research is concerned with the possibility of co-locating these different geodetic techniques on-board the same satellite. At present, a mission proposal is being developed (GRASP) and is under consideration by the European Space Agency (ESA). The GRASP mission proposal is based on the co-location of the sensors of the techniques currently used to determine the ITRF on the same extremely well calibrated spacecraft. This concept will allow establishing very precise and stable ties between the different techniques used to define the ITRF thus allowing to reach the 1 mm accuracy in the realization of the ITRF.

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