As a result of development efforts that will ultimately provide the Arizona Department of Water (ADWR) with a system to monitor ground subsidence, Vexcel has produced and delivered a time-series of images that accentuates significant ground deformation in the Phoenix and surrounding area over an eight year period. Ground subsidence-sinking due, in this case, to the extraction of water from natural underground water storage aquifers-poses a costly threat to roads, bridges, dams and underground pipes; in excess of $125M per year, according to the National Research Council. Working with the ADWR and the Center for Space Research, UT-Austin, Vexcel is employing its interferometric synthetic aperture radar (INSAR) expertise to monitor the extent and rate of the problem.

INSAR enables the collection of measurements of ground displacement by comparing electromagnetic signals collected by a given SAR sensor at different times. The resulting measurements are highly accurate, spatially dense in scope, and yet significantly less expensive than one could expect through traditional surveying techniques. The utility of SAR in Phoenix was originally demonstrated by Sean Buckley of the University of Texas Center for Space Research. Funding was later provided by NASA as part of its goal to extend space technology to commercial applications.

"For this project, Vexcel acquired an entire archive of data captured over the Phoenix valley from 1992 to 2000 by the ERS1-2 sensors," explained David Cohen, Ph.D., Director of Special Programs at Vexcel. "This wealth of data-roughly 80 frames of a 3600 square mile area- allows us to track the evolution of the subsidence occurring during this particular period of time for which satellite imagery exists. The ADWR and local water resource community can now compare these data to aquifer pumping, weather patterns, urban development and other activities that occurred within this same time frame to better understand what factors are contributing to this subsidence. From this information, water management policies and city planning decisions can be developed that will assist in managing the problem."

Vexcel's final deliverable for this project will be a semi-automated system that, with training, will allow the ADWR to ingest SAR data and produce INSAR deformation maps for the Arizona water resource community. The system will eventually be extended to the broader water resource community.

Source: Vexcel, Jan. 26, 2004