Airborne electromagnetic and magnetic survey data, southeastern San Joaquin Valley near Cawelo, California, 2016: Resistivity models

Airborne electromagnetic (AEM) and magnetic survey data were collected during October 2016 over a total distance of 262 line kilometers in the southeastern San Joaquin Valley near Cawelo, California. These data were collected in support of groundwater salinity mapping and hydrogeologic framework development as part of the U.S. Geological Survey California Oil, Gas, and Groundwater program and the California State Water Resources Control Board’s Oil and Gas Regional Monitoring Program. Deterministic spatially constrained inversions of the processed AEM data were conducted using the AarhusINV code (Auken and others, 2015) implemented in Aarhus Workbench software (Aarhus Geosoftware, Aarhus, Denmark). Inversion parameters were selected by running a series of test models with varying starting model resistivity values, layer discretization, horizontal/lateral constraints, and other inversion parameters. A 30-layer fixed-depth smooth inversion model was developed with layer top depths ranging between 4 and 400 meters and layer thickness increasing with depth. Inversions were run with vertical and lateral constraints of values of 2.0 and 1.6, respectively, and a 30 ohm-meter homogeneous half-space starting model. Sensor altitude was treated as a free parameter after the 5th iteration. Depth of investigation was calculated with a minimum and maximum depth of 5 and 500 meters. The data provided include inverted resistivity models along all flight lines. Digital data are described in the data dictionary, additional details regarding data inversion are described in the metadata processing steps.