DWR Airborne Electromagnetic (AEM) Surveys Data

#Statewide AEM Surveys Project Overview
The Department of Water Resources’ (DWR’s) Statewide Airborne Electromagnetic (AEM) Surveys Project is funded through California’s Proposition 68 and the General Fund. The goal of the project is to improve the understanding of groundwater aquifer structure to support the state and local goal of sustainable groundwater management and the implementation of the Sustainable Groundwater Management Act (SGMA). 

During an AEM survey, a helicopter tows electronic equipment that sends signals into the ground which bounce back. The data collected are used to create continuous images showing the distribution of electrical resistivity values of the subsurface materials that can be interpreted for lithologic properties. The resulting information will provide a standardized, statewide dataset that improves the understanding of large-scale aquifer structures and supports the development or refinement of hydrogeologic conceptual models and can help identify areas for recharging groundwater.

DWR collected AEM data in all of California’s high- and medium-priority groundwater basins, where data collection is feasible. Data were collected in a coarsely spaced grid, with a line spacing of approximately 2-miles by 8-miles. AEM data collection started in 2021 and was completed in 2023.  Additional information about the project can be found on the [Statewide AEM Survey website](https://water.ca.gov/Programs/SGMA/AEM "Statewide AEM Survey website"). See the publication below for an overview of the project and a preliminary analysis of the AEM data.

DWR continues to collect data and has developed tools to utilize the Statewide AEM Survey data under the [Basin Characterization Program](https://water.ca.gov/Programs/Groundwater-Management/Bulletin-118/Basin-Characterization "Basin Characterization Program"). Visit the [Basin Characterization Program Open Data Portal page](https://data.cnra.ca.gov/dataset/dwr-basin-characterization "Basin Characterization Program Open Data Portal page") to access tools, datasets, and resulting maps and models. 

## [California’s Statewide Airborne Electromagnetic Surveys and Preliminary Hydrogeologic Interpretations](https://www.conservation.ca.gov/cgs/documents/publications/california-geology-magazine/CG_2024-AEMsurveys.pdf "California’s Statewide Airborne Electromagnetic Surveys and Preliminary Hydrogeologic Interpretations")

# Survey Areas
AEM data are being collected in groups of groundwater basins, defined as a Survey Area. See Survey Area Map for groundwater subbasins within a [Survey Area](https://data.cnra.ca.gov/dataset/aem/resource/a6286b07-5597-49e6-9cac-6a3a98b904df "Survey Area"): 

+ Survey Area 1: 180/400 Foot Aquifer (partial), East Side (partial), Upper Valley, Forebay Aquifer, Paso Robles, Atascadero (limited), Adelaida (limited), Cuyama Valley.
+ Survey Area 2: Scott River Valley, Shasta Valley, Butte Valley, Tulelake, Fall River Valley (limited), Big Valley (Modoc/Lassen County).
+ Survey Area 3: Big Valley (Lake County), Ukiah Valley, Santa Rosa Plain, Petaluma Valley, Sonoma Valley.
+ Survey Area 4: White Wolf, Kern County, Tulare Lake, Tule, Kaweah.
+ Survey Area 5:  Pleasant Valley, Westside, Kings, Madera, Chowchilla, Merced, Turlock, Modesto, Delta-Mendota
+ Survey Area 6: Cosumnes, Tracy, Eastern San Joaquin, East Contra Costa, Solano, Livermore, South American, North American, Yolo, Sutter, South Yuba, North Yuba 
+ Survey Area 7: Colusa, Butte, Wyandotte Creek, Vina, Los Molinos, Corning, Red Bluff, Antelope, Bowman, Bend, Millville, South Battle Creek, Anderson, Enterprise, Eel River, Sierra Valley 
+ Survey Area 8: Seaside, Monterey, 180/400 (partially surveyed Summer 2021), Eastside (partially surveyed Summer 2021), Langley, Pajaro, Santa Cruz Mid-County, Santa Margarita, San Benito, and Llagas (partial).
+ Survey Area 9: Basin Characterization Pilot Study 1 - Madera and Kings. 
+ Survey Area 10: San Antonio Creek Valley, Arroyo Grande, Santa Maria, San Luis Obispo,  Los Osos Area, Warden Creek, Chorro Valley (limited), Morro Valley (limited)
+ Survey Area 11: Indian Wells Valley, Rose Valley, Owens Valley, Fish Slough, Indio, Mission Creek, West Salton Sea (limited), East Salton Sea (limited), Ocotillo-Clark Valley (limited), Imperial Valley (limited),Chocolate Valley (limited), Borrego Springs, and San Jacinto

# Data Reports
Data reports detail the AEM data collection, processing, inversion, interpretation, and uncertainty analyses methods and procedures. Data reports also describe additional datasets used to support the AEM surveys, including digitized lithology and geophysical logs. Multiple data reports may be provided for a single Survey Area, depending on the Survey Area coverage.

# Data Availability and Types
All data collected as a part of the Statewide AEM Surveys will be made publicly available, by survey area, approximately six to twelve months after individual surveys are complete (depending on survey area size). Datasets that will be publicly available include:

### AEM Datasets
+ Flown Survey Lines
+ Raw AEM Data 
+ Processed AEM Data
+ Inverted AEM Data 
+ Inverted AEM Data Uncertainty Analysis
+ Interpreted AEM Data (for coarse fraction)
+ Interpreted AEM Data Uncertainty Analysis

### Supporting Datasets
+ [Digitized Lithology and Geophysical Logs](https://data.cnra.ca.gov/dataset/aem/resource/ae1bd8fb-f644-488e-9706-2f3ea2a36d17 "Digitized Lithology and Geophysical Logs")

### [NEW! Summary of revisions to digitized lithology and geophysical logs (1/14/2026)](https://data.cnra.ca.gov/dataset/aem/resource/f511fbd7-1e7d-44e2-9b2a-00e32f4ad88a "NEW! Revisions to digitized lithology and geophysical logs (1/14/2026)")

#AEM Data Viewers
DWR has developed AEM Data Viewers to provides a quick and easy way to visualize the AEM electrical resistivity data and the AEM data interpretations (as texture) in a three-dimensional space. The most recent data available are shown, which my be the provisional data for some areas that are not yet finalized.  The Data Viewers can be accessed by direct link, below, or from the [Data Viewer Landing Page](https://data.cnra.ca.gov/dataset/aem/resource/29c4478d-fc34-44ab-a373-7d484afa38e8 "Data Viewer Landing Page").

+ [CalGW Subsurface Viewer](https://subsurfaceviewer.water.ca.gov/ "CalGW Subsurface Viewer"): Provides a map, 2D profile, and 3D view of the Statewide AEM Survey electrical resistivity and coarse fraction data, along with lithology logs. The map dynamically shows the exact location of AEM data displayed. 

+ [SGMA Data Viewer (Basin Characterization tab)](https://sgma.water.ca.gov/webgis/?appid=SGMADataViewer#basincharacter "SGMA Data Viewer (Basin Characterization tab)"): Displays AEM data profile images along flight lines and AEM data depth slices in map view.

+ [3D AEM Data Viewer](https://dwr.maps.arcgis.com/apps/instant/3dviewer/index.html?appid=f781b14f42ab45e5b72f32cf07af899c "3D AEM Data Viewer"): 
Displays the Statewide AEM Survey electrical resistivity and coarse fraction data, along with lithology logs, in a three-dimensional space.

#AEM Depth Slice and Shallow Subsurface Average Maps
As a part of DWR’s upcoming Basin Characterization Program, DWR will be publishing a series of maps and tools to support advanced data analyses. The first of these maps have now been published and provide analyses of the Statewide AEM Survey data to support the identification of potential recharge areas. The maps are located on the SGMA Data Viewer (under the Hydrogeologic Conceptual Model tab) and show the AEM electrical resistivity and AEM-derived texture data as the following:

+ Shallow Subsurface Average: Maps showing the average electrical resistivity and AEM-derived texture in the shallow subsurface (the top approximately 50 feet below ground surface). These maps support identification of potential recharge areas, where the top 50 feet is dominated by high resistivity or coarse-grained materials.  

+ Depth Slices: Depth slice automations showing changes in electrical resistivity and AEM-derived texture with depth. These maps aid in delineating the geometry of large-scale features (for example, incised valley fills). 

Shapefiles for the formatted AEM electrical resistivity data and AEM derived texture data as depth slices and the shallow subsurface average can be downloaded here:

+ [Electrical Resistivity Depth Slices and Shallow Subsurface Average Maps](https://data.cnra.ca.gov/dataset/aem/resource/7d115ac3-d7b8-47fa-ab8b-a078b2525bbe "Electrical Resistivity Depth Slices and Shallow Subsurface Average Maps")

+ [Texture Interpretation (Coarse Fraction) Depth Slices and Shallow Subsurface Average Maps](https://data.cnra.ca.gov/dataset/aem/resource/0952506a-1ad8-4c04-9372-ded45148e6a6 "Texture Interpretation (Coarse Fraction) Depth Slices and Shallow Subsurface Average Maps")

#Technical Memos
Technical memos are developed by DWR's consultant team (Ramboll Consulting) to describe research related to AEM survey planning or data collection. Research described in the technical memos may also be formally published in a journal publication.
 
+ [AEM Test Flights to Evaluate the Bias Signal Caused by Vineyard Trellises Containing Metal](https://data.cnra.ca.gov/dataset/aem/resource/42e5798e-c633-4a7a-8398-fc96c2afaced "AEM Test Flights to Evaluate the Bias Signal Caused by Vineyard Trellises Containing Metal")  

+ [SkyTEM Instrument Comparison for Airborne EM](https://data.cnra.ca.gov/dataset/aem/resource/d38f1284-71f3-45e3-9af5-676ebe22f61b "SkyTEM Instrument Comparison for Airborne EM")

#2018-2020 AEM Pilot Studies
[Three AEM pilot studies](https://data.cnra.ca.gov/dataset/aem-pilot-studies "Three AEM pilot studies") were conducted in California from 2018-2020 to support the development of the Statewide AEM Survey Project. The AEM Pilot Studies were conducted in the Sacramento Valley in Colusa and Butte county groundwater basins, the Salinas Valley in Paso Robles groundwater basin, and in the Indian Wells Valley groundwater basin. 

#Provisional Statement
Data Reports and datasets labeled as *provisional* may be incomplete and are subject to revision until they have been thoroughly reviewed and received final approval. *Provisional* data and reports may be inaccurate  and subsequent review may result in revisions to the data and reports. Data users are cautioned to consider carefully the provisional nature of the information before using it for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences.

Tags: aem, airborne-electromagnetic, california-department-of-water-resources, geophysics
Organization: State of California