Abstract
We investigate the properties of EM signals in several different response-parameter domains to identify calibration errors in helicopter electromagnetic (HEM) data. In particular, we define a dimensionless response parameter α, derived from frequency-domain data, that is numerically identical to the historic wire-loop response parameter, and is closely related to the thin-sheet and half-space response parameters. The arctangent of α is the phase ϕ of the secondary field. We further define a dimensionless amplitude response parameter β, calculated as the ratio between inductive limits estimated from the data and from system geometry. The inductive limit calculated from geometry provides an initial altitude correction to the data amplitudes. Additional data corrections further correct phase effects and altimeter variations. The amplitude and phase errors in calibration become independent differences between the data and the fitted model in the ϕβ domain. This investigation was undertaken in the response-parameter domain rather than in the data domain, allowing the analysis to be independent of absolute values of conductivity and system frequencies. Statistical analysis in the ϕβ domain of recently acquired data suggests that amplitude calibration errors in HEM data may cause fitted models to have systematic depth errors of 1 to 2 m for near-surface conductors; variable altitude measurement errors are about 1.5 m over seawater.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.