Surface Deformation Of The Whole Netherlands After PSI Analysis

Being a coastal country with low topography, the Netherlands is seriously threatened by the risk of being flooded. Improving our knowledge of the deformation signals affecting the country is therefore a need. Dutch authorities carry out periodic leveling measurements to monitor surface heights. A major country wide campain happens every 20 years, but if we take into account not only first order network campaigns but also higher order ones, heights are measured every 5 to 10 years, area dependent. However, the knowledge we obtain from these observations is very limited because the reduce density of benchmarks, around 1 every 10 km, (area dependent) and the low temporal sampling. A more thorough analysis can be performed with other geodetical techniques, in particular, time-series InSAR. These methods are able to provide with a density of reliable measurements of about 100 per km2, although this is case dependent. Furthermore, the archive of the European space Agency (ESA) provide us with an observation every 35 days for the Netherlands, with one year data gap in 1994 and 3 years gap from 2001-2004. To estimate land deformation over the whole of the Netherlands we need to combine InSAR estimates obtained for different tracks (satellite foot-prints), but this operation is not trivial. First, to capture large scale deformation we need to take into account that radar images are usually affected by orbital errors and atmosphere. Second, since InSAR produce deformation maps relative to an area (or pixel) that is part of the observed track, data combination requires to change these relative measurements to a common area or reference point. In this contribution we explore a method for data combination to produce a velocity map of the whole Netherlands that reflect the average rates of the period 1992- 2010). We combine all InSAR tracks available over the country for this period, plus leveling and GPS. These last two techniques help to better constrain the long- wavelength deformation signal and remove ramps produce by atmosphere or orbital errors that affects InSAR measurements.