Abstract: A subsurface reservoir may be characterized and/or monitored based on fluid injection. For example, fluid may be injected into the reservoir, and data (e.g., seismic data, geodetic data, pressure data) relating to the injected fluid in the reservoir may be used to identify characteristics of the reservoir and/or to monitor the injected fluid in the reservoir. In some aspects, air or another type of surrogate fluid is injected into the reservoir, and the reservoir's viability as a carbon dioxide sequestration site can be analyzed based on response data collected from the reservoir. In some aspects, carbon dioxide is sequestered in the subsurface reservoir, and three-dimensional geodetic response data is collected and used to monitor and/or facilitate quality control.