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Multiple-aperture SAR interferometry (MAI) has demonstrated outstanding measurement accuracy of along-track displacement when compared to pixel-offset-tracking methods; however, measuring slow-moving (cm/year) surface displacement remains a challenge. Stacking of multi-temporal observations is a potential approach to reducing noise and increasing measurement accuracy, but it is difficult to achieve a significant improvement by applying traditional stacking methods to multi-temporal MAI interferograms. This paper proposes an efficient MAI stacking method, where multi-temporal forward- and backward-looking residual interferograms are individually stacked before the MAI interferogram is generated. We tested the performance of this method using ENVISAT data from Kīlauea Volcano, Hawai'i, where displacement on the order of several centimeters per year is common. By comparing results from the proposed stacking methods with displacements from GPS data, we documented measurement accuracies of about 1.03 and 1.07 cm/year for the descending and ascending tracks, respectively-an improvement of about a factor of two when compared with that from the conventional stacking approach. Three-dimensional surface-displacement maps can be constructed by combining stacked InSAR and MAI observations, which will contribute to a better understanding of a variety of geological phenomena. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) surface deformation is retrieved for the March 6–10, 2011 (UTC dates), Kamoamoa fissure eruption along the East Rift Zone of Kīlauea Volcano, Hawai'i, through the integration of multi-temporal synthetic aperture radar (SAR) interferometry (InSAR) and multiple-aperture interferometry (MAI) measurements from the COSMO-SkyMed X-band SAR. The measurement accuracies of 1) the individual and multi-stacked MAI interferograms and 2) the 3D deformation, which is measured from COSMO-SkyMed data, are assessed using continuous GPS stations. The root-mean-square (RMS) errors of individual MAI interferograms for descending and ascending data are 2.97 ± 0.6 cm and 3.20 ± 0.62 cm, respectively. The MAI interferograms stacked from multi-temporal observations can produce better results by emphasizing surface deformation signals, with the RMS errors of 1.06 and 1.24 cm for descending and ascending data, respectively. The empirical equations for measurement uncertainties are determined with respect to interferometric coherence for individual and stacked MAI interferograms. An assessment of the 3D components of deformation was performed as well, and RMS errors of 0.75, 0.83, and 0.68 cm were estimated in the east, north, and up directions. A performance test of magma source model parameter estimations was carried out by using the InSAR and 3D measurements. From the 3D deformation field, we found that the magma chamber source at the Kīlauea caldera should be modeled by the spheroid source rather than the simple point source. The performance comparison between the InSAR and 3D modeled results showed that the 3D deformation field allows for precise model parameter estimation. [ABSTRACT FROM AUTHOR]