The relationship between intermittent coherence and precision of ISBAS InSAR ground motion velocities: ERS-1/2 case studies in the UK

Cigna, Francesca; Sowter, Andrew. 2017 The relationship between intermittent coherence and precision of ISBAS InSAR ground motion velocities: ERS-1/2 case studies in the UK. Remote Sensing of Environment, 202. 177-198.

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Retrieving ground motion information for non-urban and semi-vegetated areas using differential Interferometric Synthetic Aperture Radar (InSAR) and Small Baseline Subset (SBAS) approaches with C-band satellite radar imagery is challenging due to temporal decorrelation. By exploiting six stacks of medium resolution ERS-1/2 SAR images acquired between 1992 and 2000 over four regions of interest in the UK, this paper demonstrates the performance of the recently developed processing method Intermittent SBAS (ISBAS). This approach builds upon the conventional low-resolution SBAS method and, by relaxing the approach to selecting image pixels to process and accounting for the intermittent nature of non-urban targets, is capable to extend the coverage of motion results across the full range of land cover types, even those typically unfavourable for InSAR. On average, the new ISBAS implementation provides 4 to 26 times more coverage than SBAS for the processed regions, with the spatial coverage of ground motion solutions increasing from only 4–12% land pixels with SBAS, to 39–99% with ISBAS. Despite relying only on temporal subsets of the networks of small baseline interferograms, intermittently coherent pixels show velocity standard errors of 0.8–1.4 mm/year on average, hence retain sub-millimetre to millimetre precision. The empirical relationships between intermittent coherence and standard errors in the estimated ground motion velocity are computed for each of the six datasets, and confirm that errors are controlled by the number of independent observations used for each image pixel to extract the ISBAS solution. In particular, velocity standard errors εvel for the intermittently coherent pixels are inversely proportional to the square root of the number of best coherence interferograms used, ni, and can be modelled as mm/year on average for the six datasets. The established empirical relationship also allows informed decisions on the ISBAS threshold for ni to be made. This is achieved by setting the maximum acceptable error in the velocity estimate εMAX, and then computing the corresponding minimum ni to accept an intermittently coherent pixel that will guarantee the desired precision. In the present era of ‘big SAR data’ and their derived ‘big InSAR data’, we discuss perspectives on the use of huge datasets of thousands or even millions of ground deformation time series – such as those produced using ISBAS, with a particular focus on the veracity of big data and the need for a quality assessment check-point in the ‘big InSAR data’ cycle.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 00344257
Date made live: 18 Jan 2018 09:48 +0 (UTC)

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