Studying Volcanoes With InSAR: Where Have We Been and Where Are We Going? Howard Zebker, Cody Wortham Stanford University

10 Years Ago: Where Were We? Anticipated several new space radar systems for monitoring and forecasting of volcanic events Developing inverse methods to reveal the details of faulting or pressure changes at depth, and better describe precise magma chamber geometries Beginning reliable interferometric imaging, m-scale resolution of mm-scale deformation over wide areas Proposed high-res stereo radar for 3-D topographic maps fast events, e.g. rapid dome growth Foresaw data collection over all of Earth’s 600 potentially active volcanoes weekly or even daily Designing satellite constellations in along-track interferometric formation to map flow velocities

Reality: What actually happened Anticipated several new space radar systems for monitoring and forecasting of volcanic events Developing inverse methods to reveal the details of faulting or pressure changes at depth, and better describe precise magma chamber geometries Beginning reliable interferometric imaging, m-scale resolution of mm-scale deformation over wide areas Proposed high-res stereo radar for 3-D topographic maps fast events, e.g. rapid dome growth Foresaw data collection over all of Earth’s 600 potentially active volcanoes weekly or even daily Designing satellite constellations in along-track interferometric formation to map flow velocities

Reliable imaging Technology has advanced to where we know how to do this Want long wavelength, high resolution, rapid repeat times Systems beginning to reflect community knowledge Still waiting for the “perfect” system

Longer wavelengths yield higher correlation ALOS Kilauea interferogram: 460 day separation, 1490 m baseline Wortham et al., 2010

Time series volcano observations Eyjafjallajokull PS deformation SBAS deformation Time series From Hooper, 2008

PS image of San Andreas Fault - ERS satellite PS spacing is ~1km PS performance RMS error ~1 mm/yr Precision of PS method

Higher resolution promotes time series analyses A coarse resolution cell Brightest scatterer A fine resolution cell Same brightest scatterer, much less background Pixel does not scintillate, is “persistent” Bright scatterer perhaps less than rest of background Pixel scintillates over time from background signal

New spaceborne systems Radar systems launched this decade have expanded the data modalities for InSAR New frequency bands and orbit repeat geometries ALOS PALSAR (Japan) launched 2006 TerraSAR-X (Germany) launched 2007, Tandem-X satellite launched 2010 Some commercial systems as well

ALOS/PALSAR ALOS satellite, PALSAR radar instrument L-band, wavelength 24 cm Repeat period 46 days Multipolarization m resolution Very high correlation Just ended successful mission

TerraSAR-X X-band, wavelength 3 cm Repeat period 11 days Multipolarization 1-20 m resolution Ideal for time- series observations

Current research … Most exciting area is time series analysis Modeling continues to advance Tandem satellites supersede previous desire for radar stereo New measurements and methods will yield new descriptors

Time series mimics GPS imaging From Lundgren et al.

Modeling of Yellowstone caldera Interferograms: C-band Interpretation: Inflating sill From Wicks et al., 2006

Modeling Uzon caldera, Kamchatka Radarsat measurements (a) Distributed opening model, (b) distributed crack model, (c) depth slice of model b Lundgren and Lu, 2006

Probabilistic modeling of Etna activity Predict eruptive activity from observed deformation and thermal flux Highest activity from coincident increases PDF derived from spaceborne data only From Patrick et al., 2006

Tandem observations for DEMs Higher resolution and accuracy than traditional stereo Could produce radar stereo, but this method is superior Mt. Merapi Digital Elevation Model from Tandem TerraSAR-X observations From DLR

New local measurements From C. Werner, Gamma Res.

… but some things still lacking Enabling technology is coverage, temporal and geographic Optimizing designs for InSAR – Orbits: poor north retrieval – System parameters – High resolution, long wavelength helps Future mission prospect good/bad/?

Vector deformation SBAS vector solution for average deformation rate at Kilauea, HI ALOS yields fairly high correlation over 2 year time span Near polar orbit results in poor northing component retrieval Wortham et al., 2010

Poor retrieval – northing component Kilauea: GPS – black line, InSAR – Red symbols Up North East Wortham et al., 2010

Multiple Aperture InSAR (MAI) Method N. Bechor, PhD Thesis (2006) SLCs formed from forward and backward squinted beams Beam filtered in Doppler Interferograms formed from each beam MAI phase gives along-track displacement from differencing forward/backward interferograms

Average north displacement using MAI North component of displacement averaged over all InSAR acquisitions

Coverage ALOS L-band yields high correlation over challenging volcanoes South America data show comprehensive coverage possible 46 day repeat is too long- misses many signals PALSAR data rate/volume too low to monitor 600 volcanoes From: Fournier et al., 2010

NASA DESDynI-R Mission Launch in 20XX L-band, potential 2 m resolution Free and open data policy Specifically designed for InSAR Volcano hazards one of the major science objectives Artist’s concept from JPL

Additional exciting missions ALOS-2 (Japan): L-band follow-on to ALOS, launch 2013?, 1-10 m resolution, 14 day repeat But likely will be commercially oriented with data hard to get Tandem-L (Germany): Similar in philosophy to Tandem-X, but companion to DESDynI, no money yet Sentinel-1 (ESA): C-band heir to Envisat, 12 day repeat, 5 m resolution, 201w? Launch There are others…

Summary and looking ahead InSAR continues to evolve better accuracy and temporal/spatial coverage Volcano hazard applications benefit Future satellites converging on ~12 day repeats and m-scale resolution Limiting factor is probably data policy- agencies still don’t get the science message and pursue commercialization If data are acquired, volcanologists will come