Systematic assessment of atmospheric uncertainties for InSAR data at volcanic arcs using large-scale atmospheric models: Application to the Cascade volcanoes, United States

a r t i c l e i n f o Satellite Radar Interferometry (InSAR) is suited to monitoring ground deformation on the scale of volcanic arcs, providing insight into the eruptive cycle over both long and short time periods. However, these measurements are often contaminated with atmospheric artefacts caused by changes in the refractivity of the atmosphere. Here, we test the use of two large-scale atmospheric models, ERA-Interim (ERA-I) and North American Regional Reanalysis (NARR), to correct atmospheric uncertainties in InSAR data from the Cascades Volcanic Arc, United States. At Lassen Volcanic Center, we find that NARR reduces interferogram standard deviation in 79% of cases by an average of 22%. Using NARR, we develop a strategy to produce a priori estimates of atmospheric uncertainties on an arc-wide basis. We show that in the Cascades, the RMS variation in range change is dependent upon volcano topography and increases by 0.7 cm per kilometre of relief. We use this to estimate detection thresholds for long-term monitoring of small magnitude (1 cm/yr) deformation signals, and short-term monitoring of ground deformation associated with pre-eruptive unrest. This new approach of assessing atmospheric uncertainties a priori is widely applicable to other volcanic arcs, and provides realistic estimates of atmospheric uncertainties suitable for use in near-real-time analysis of InSAR data during periods of volcanic unrest. In the past two decades, Interferometic Synthetic Aperture Radar (InSAR) has changed the way in which volcanic ground deformation is studied. Unlike ground-based techniques such as levelling or GPS, InSAR uses pairs of satellite radar images to produce 2D maps of ground displacements known as interferograms (for a full description see The spatial extent of these measurements (100 s kms) enables surveys of ground deformation across whole volcanic arcs (e., rather than geodetic studies of individual edifices. In addition to being significant from a hazard monitoring perspective, this also allows us to better understand the role of regional tectonics in volcanism (e. However, despite advances in data acquisition, sources of noise continue to limit InSAR measurements of small magnitude ground deformation. The most significant of these is spatiotemporal variability in atmospheric refractivity between satellite acquisitions, resulting in atmospheric artefacts in interferograms that may mask or lead to false interpretations of ground deformation (e. Improving the accuracy of satellite-based measurements of volcano deformation is essential for regional and global volcano monitoring strategies, as ground deformation is shown to have strong evidential links …