We offer 4-year PhD position at Tallinn University of Technology, Research Group of Geodesy and Road Engineering.
Proposed doctoral thesis topic: Development of improved Satellite Altimetry Retracker specifically for the Baltic Sea.
Supervisors: Professor Artu Ellmann and Dr. Nicole Delpeche-Ellmann
Modern satellite altimetry (SA) missions (Sentinel-3, Cryosat-2, Jason-2,3 etc.) have the potential for determining accurate sea surface heights (SSH). It is known however that SA data products over coastal areas contain certain limitations, e.g. due to under-examined wet tropospheric correction, land and calm water interference, heterogeneous atmospheric forcings, etc. This project focuses on improving the range estimation by applying specialized developed retracking schemes. Retracking is necessary for the methodology employed in processing the range. Retracking can be study area dependant. For instance, reflected radar pulses are usually recorded against time in waveforms. Over the open ocean, waveforms normally conform well to the Brown model by the least squares estimation. Fitting to this waveform usually yields the required measurements of range (from which SSH is deduced). It has been found that about 5-10 km off the coastline a significant portion of the radar waveforms depart from the Brown model (increasing toward the coast). The factors that influence this anomaly includes land contamination, 'bright targets' in the footprint (patches of very calm water in sheltered areas) etc. At coast it is influenced by archipelagos, areas of calm waters and many other processes (e.g upwelling jets, filaments etc.) that may influence the range that is calculated. Thus the necessity for a retracking methodology designed for the coastal area is required in order to obtain accurate SA-SSH estimates.
- The PhD candidate shall develop an improved Satellite Altimetry (SA) retracker designed specifically for the Baltic Sea area. This development requires examining the SSH from various satellite altimetry (SA) missions (Sentinel-3, Cryosat-2, Jason-2,3 etc.) using the raw measurements along with different retracking methods.
- Detailed examination of the altimeter radar echoes and corrections applied shall be performed.
- Validation of SA derived SSH with in-situ data (tide gauges, airborne laser scanner, GNSS) is expected using statistical techniques of the various data sets.
- From these results a specific algorithm shall be designed to fit radar signals from different satellite missions and under different sea state (e.g. waves, upwellings, fronts etc.).
- The candidate is expected to assist in project related field campaigns.
- This study is part of the Estonian Research Council supported research for developing an iterative approach for near-coast marine geoid modelling by using re-tracked satellite altimetry, in-situ and modelled data.
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