A technology based upon analyses of InSAR surveys of incremental deformations over an operating geothermal field is emerging that might serve to monitor steam cap migrations on a timescale of weeks. Based upon theory developed in Horowitz and Hornby (in prep.), one can compute a harmonic potential field that has dilatational sources and sinks from 3 component surface displacement increment surveys. In the context of a water-steam fluid in porous rocks, steam filled material will have significantly different bulk moduli from water-filled material. In the presence of a regional stress field, changes in the pore-filling will appear as dilatational sources or sinks. There are commercial InSAR satellites in operation (e.g. Canada's Radarsat-1 and Radarsat-2), and a research system (ALOS PALSAR from Japan) is in orbit with L-band capabilities that can penetrate vegetation canopies. Imaging geometries may be problematic for computing three component displacement surveys over any given area, but we have successfully solved for the 3-component field in the case of afterslip from the 2003 Bam, Iran earthquake. We believe that this technology might be a cost-effective and higher sampling rate alternative/supplement to microgravity surveying for monitoring the migration of steam caps in an operating geothermal field.

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