In 2017, TRE Altamira, in collaboration with Dewberry on behalf of the National Geodetic Survey with NOAA (National Oceanic and Atmospheric Administration), used InSAR to study coastal subsidence over Hampton Roads in Virginia, USA (figure below), in order to explore the possible correlation between surface displacement and sea-level rise.
In the initial study, the AOI was observed to exhibit mild subsidence over the duration of the full analysis, with an average displacement rate of -1.0 mm/year (-0.04 inches/year). The data processed for this analysis was outstanding; it comprised 130 images acquired by Cosmo-SkyMed (CSK), covering a period of 6 years (2011-2017). The analysis identified over 4 million measurement points for a density of 1,082 pts/km² (2,802 pts/mi²).
This project was the first coastal monitoring analysis to capture subsidence with a sub-millimetric level of accuracy -with the average associated standard deviation value for all data points found to be ± 0.35 mm/year (±0.01 inches/year)- using our SqueeSAR® algorithm.
The study successfully highlighted the presence of coastal subsidence within areas that were identified as being at-risk in the event of further sea-level rise.
The figure below shows a comparison of the coastal subsidence detected by SqueeSAR® (top) with the modelled sea-level rise (bottom).
A common trend noted within the subsidence data was seasonal deformation patterns on the bridges. The West Norfolk Bridge (below) is one such example. The average time series of displacement that was produced over the midsection of the bridge (white polygon) is shown in the figure below. The InSAR measurements showed maximum subsidence during February and March of each year and maximum uplift in July and August.
This collaboration with Dewberry and NOAA demonstrated the value of integrating InSAR subsidence data with modelled projections of sea-level rise to help inform risk-mitigation strategies.