InSAR

InSAR
NASA/JPL-Caltech · Public domain · source
Name	Interferometric Synthetic Aperture Radar
Acronym	InSAR
First use	1970s
Applications	Surface deformation, volcanology, seismology, glaciology, subsidence
Platforms	Spaceborne, airborne, UAV

InSAR InSAR is a radar remote sensing technique that measures surface deformation by comparing phase information from coherent radar images. It combines concepts from Synthetic Aperture Radar, radar interferometry, remote sensing, geodesy, and signal processing to detect millimetre- to centimetre-scale changes over time. Developed through contributions from researchers at institutions like Jet Propulsion Laboratory, European Space Agency, and NASA, InSAR has been applied in studies linked to Mount Etna, Kashmir earthquake (2005), and San Andreas Fault investigations.

Introduction

InSAR originates from early experiments in Synthetic Aperture Radar by teams at Lincoln Laboratory, MIT, and later programs at NASA Jet Propulsion Laboratory and European Space Agency satellites such as ERS-1, ERS-2, Envisat, RADARSAT and Sentinel-1. The method exploits phase coherence between repeat-pass radar acquisitions to form an interferogram that records relative surface displacement, topography, and scattering changes. Major scientific communities using InSAR include researchers from US Geological Survey, National Oceanic and Atmospheric Administration, California Institute of Technology, University of Cambridge, and ETH Zurich.

Principles and Methods

The core principle compares complex SAR returns from two acquisitions to compute phase differences influenced by path length, topography, and displacement; foundational theory draws on work by Roger J. Phillips, Klaus D. Schwerdtfeger, and institutions like Jet Propulsion Laboratory and CEA. Interferometric phase φ depends on wavelength used by sensors such as C-band, L-band, and X-band radars deployed on platforms like ERS-1, ALOS, and TerraSAR-X. Methods include single-pass interferometry using systems like SRTM and repeat-pass interferometry used by Sentinel-1 and RADARSAT-2, along with advanced techniques such as Differential Interferometry, Persistent Scatterer Interferometry developed by groups at Graz University of Technology and Politecnico di Milano, and Small Baseline Subset (SBAS) approaches used by teams at Delft University of Technology.

Data Processing and Analysis

Processing pipelines incorporate coregistration, phase unwrapping, atmospheric correction, and time-series inversion by software developed at centers like European Space Agency, AIST, JAXA, CSIRO, and universities such as Stanford University and University of Leeds. Key algorithms include Goldstein phase filtering, SNAPHU unwrapping by Stanford University affiliates, and adaptive multilooking used in processing chains at NASA Jet Propulsion Laboratory and Gamma Remote Sensing. Ancillary datasets often employed include Digital Elevation Models from Shuttle Radar Topography Mission and geodetic constraints from Global Positioning System networks maintained by agencies like NOAA and IGS to validate displacement measurements. Statistical inversion and error estimation draw on methodologies from Bayesian statistics, least-squares adjustment, and time-series analysis techniques used in studies by California Institute of Technology and ETH Zurich.

Applications

InSAR has broad applications across hazard, geoscience, and infrastructure domains with high-profile case studies at Mount St. Helens, Kilauea, Eyjafjallajökull, and urban subsidence studies in Venice, Shanghai, and Mexico City. In seismology it has been applied to the 1999 Izmit earthquake, 2011 Tōhoku earthquake and tsunami, and 1992 Landers earthquake to map coseismic deformation and rupture models used by research groups at USGS, GFZ German Research Centre for Geosciences, and University of California, Berkeley. Volcanology applications include monitoring at Popocatépetl, Mount Merapi, and Mauna Loa by teams from UNAM, VSI, and USGS to infer magma chamber processes. Cryosphere studies leverage InSAR for glacier dynamics at Greenland, Antarctica, and Himalayan glaciers studied by British Antarctic Survey and ICIMOD. Engineering and infrastructure monitoring includes dam and tunnel projects overseen by Eiffage, China Railway, and municipal authorities in Los Angeles and Rome.

Limitations and Errors

Limitations arise from temporal decorrelation in vegetated or snow-covered regions observed in studies at Amazon Basin and Alps, geometric decorrelation related to perpendicular baselines exemplified in ERS baseline constraints, atmospheric delays from tropospheric and ionospheric variability affecting observations over Tropical Andes and Himalayas, and phase unwrapping ambiguities encountered in complex ruptures such as Sumatra–Andaman earthquake (2004). Mitigation strategies from groups at European Space Agency, JAXA, and NASA include using longer wavelengths on ALOS L-band sensors, adopting persistent scatterer methods pioneered by Politecnico di Milano, integrating GNSS time series from IGS stations, and employing weather models from ECMWF for atmospheric correction. Systematic errors also stem from orbit inaccuracies tackled using precise orbit products from ISO and POD services used by ESA and JPL.

Instrumentation and Platforms

InSAR-capable missions and platforms span government programs and commercial operators: spaceborne missions include ERS-1, ERS-2, Envisat, RADARSAT-2, TerraSAR-X, TanDEM-X, ALOS-2, Sentinel-1A, Sentinel-1B, and planned missions by NASA and ESA. Airborne InSAR systems have been developed by NASA Jet Propulsion Laboratory, DLR, and companies such as Airbus Defence and Space and MDA for campaigns over sites like Yellowstone National Park and Campi Flegrei. Emerging platforms include UAV-based SAR systems tested by MIT Lincoln Laboratory and university groups at University of Tokyo and Carnegie Mellon University. Instrumentation components such as high-stability oscillators, dual-frequency transmitters, and phase-coherent receivers are engineered by manufacturers including Rohde & Schwarz, Thales Alenia Space, and Honeywell Aerospace.

Category:Remote sensing