Champaign County HTEM Project (2022–2024) | HTEM Airborne Mapping

In 2022, ISGS received funding to conduct an aerial geophysical survey known as helicopter-based time-domain electromagnetics (HTEM) for Champaign County. This effort, called the Champaign County HTEM Project, was funded by the State of Illinois to characterize the distribution and character of the Mahomet aquifer in Champaign County.

The Champaign County HTEM Project contracted with SkyTEM Canada, Inc. to collect the HTEM data and flights were conducted in December, 2022. For this project, flight lines were collected across the county, with a spacing of 650 meters between lines, for a total of 3,144 km of data collected. Helicopter flights and data were collected from December 3 to December 12. Data from this flight undergone evaluation, error removal, and processing through 2023 with final processing to be completed in early 2024. Analysis and interpretation of the data will result in the identification of targeted mapping units. Interpretation is scheduled to be completed late in 2024 (Figure 1).

**Figure 1.** Champaign County HTEM profiles collected in 2022. Warmer (more red) colors indicate higher resistivity, which tends to correspond to sandier sediments or carbonate and sandstone bedrock deposits. Cooler (more blue) colors indicate lower resistivity, which tends to correspond to more claylike sediments or shale- and coal-like bedrock deposits.

The individual profiles are used to interpret the distribution of sediments and rocks along the transect and provide calculations of the resitivity from land surface to a depth of approximately 700 feet (213 meters) (Figure 2). This example profile shows the Mahomet aquifer undelying shallow glacial tills, and bedrock deposits that include folded bedrock associated with the LaSalle Anticline.

Figure 2. Example resistivity profile from the Champaign County HTEM Project. Warmer (more red) colors indicate higher resistivity, which tends to correspond to sandier sediments or carbonate bedrock deposits. Cooler (more blue) colors indicate lower resistivity, which tends to correspond to more claylike sediments or shale-like bedrock deposits.

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