ALOS Interferogram of the "Father's Day" Rift Event along the East Rift Zone of Kilauea, Hawaii: Vector Displacement and Cracks

David Myer, David Sandwell, Masanobu Shimada, and Benjamin A. Brooks - June 28, 2007 - Updated August 12, 2007 - Updated December 17, 2007



Rift Event Location Map
Between June 17  and June 20, 2007, the East Rift of Kilauea Volcano opened approximately 2 meters. See USGS site for details.  Crustal deformation of the rifting event was monitored in real time using GPS stations.  Here we report on two interferograms - ascending and descending - that were collected by the L-band synthetic aperture radar aboard the ALOS spacecraft that is operated by the Japanese Space Agency - JAXA.    We find that the L-band interferograms retain coherence better than interferograms made from C-band instruments.  The interferometric phase is completely unwrapped with a single seed point.  In addition, azimuthal offsets can be derived from the reference and repeat images.  The three components provide the full 3-component vector displacement for this event. These data will be used, together with precise GPS measurements, to constrain the models of dike opening and caldera deflation associated with this event.


Ascending Interferogram
Radar interferogram constructed from ALOS PALSAR acquisitions on May 5 and June 20.  This time period spans most of the "Father's Day" (June 17) rift event.  These data were acquired in the fine beam dual polarization mode (FBD-HH, 14 MHz).  Correlation is high even in forested areas and the phase has been unwrapped and scaled to line-of-sight millimeters (LOS).  The radar look direction is from the WSW and 34 degrees from vertical.  GPS receivers with continuous vector measurements are marked by red triangles.



Zoom of Interferogram
This radar interferogram is zoomed from the previous image.  Rift-flank uplifts are largely symmetrical while there is pronounced asymmetry in the rift opening component.  The Makaopuhi crater shows more than 40 mm of local inflation.  GPS receivers with continuous vector measurements are marked by red triangles.

Descending Interferogram
Radar interferogram constructed from ALOS PALSAR acquisitions on Feb 28 and July 16 (8:52 GMT). This time period spans the “Fathers Day” (June 17) rift event. These data were acquired two modes. The Feb 28 acquisition was FBD-HH (14 MHz) while the July 16 acquisition was FBS (28 MHz) the raw FDB data were interpolated to the higher FBS sampling rate. The radar look direction is from the ESE and 34˚ from vertical.GPS receivers with continuous vector measurements are marked by red triangles.

Comparison with GPS LOS Displacements
Comparisons of 3 components of deformation from  two interferograms with deformation vectors from 19 continuous GPS sites show rms line-of-site precision of 14 mm and an rms azimuth precision (flight direction) of 71 mm.  


Azimuth Offsets Compared with GPS
Crustal displacement in the flight direction from ALOS PALSAR acquisitions on May 5 and June 20.  Displacements are derived from cross correlation of image patches and are scaled to mm.  This component of displacement is perpendicular to the LOS displacement and also about 10 times less accurate.  GPS receivers with continuous vector measurements are marked by black triangles.  A displacement profile extracted along the line A-A' (shown in the PDF but not the thumbnail at right) shows excellent agreement with the baseline change between GPS sites NUPM and KTPM.


Small Cracks Observed in Phase Gradient Confirmed by Field Observations - Blind Test
Areas of high phase gradient appear as cracks along the Chain of Craters Road.  The large crack was discovered and repared after the Father's Day Event.  The location of the smaller cract was predicted from the ALOS phase gradient, coordinates were sent to Matt Patrick (mpatrick@usgs.gov) at the HVO and he examined the road for cracks.  Here is his assessment: "Anyway, I did find three cracks in the road in the general area.  One crack is exactly where your line of points crosses the road.  I have attached a few photos.   The crack consists of three, left stepping segments which cross the entire road.  South of this crack about 150 m is another crack (crack 1 in map), however it does not cross the entire road (I didn't take a photo of it).  Thirty meters north of crack 2 is crack 3, which spans the road and is wider, maybe approaching a centimeter."