Authors / CoAuthors
Christensen, N.B. | Lawrie, K.
Abstract
The inversion analyses presented in our paper and now extended in this Reply were ultimately only one part of the AEM system selection process for the BHMAR project. Both Derivative and Inversion analyses are in their nature theoretical, and it is impossible, in a theoretical analysis, to capture all of the aspects relevant for real surveys with little margin for error in political time frames. In reality, neither the Derivative nor Inversion analysis provided the degree of certainty required (by the project manager and client) to ascertain whether any of the candidate AEM systems were able to map the key managed aquifer recharge targets recognized in the study area. Consequently, a decision was made to acquire data over a test line with the 2 systems (SkyTEM and TEMPEST) that performed best in the Derivative and Inversion analysis studies. This approach was vindicated with quite distinctive and very different performance observed between these two systems, especially when compared with borehole and ground geophysical and hydrogeological data over known targets. Data were inverted both with contractors' software and with reference software common to all systems and the results were compared. Ultimately, it was the test line, particularly in the near-surface (top 20metres), thatmade the SkyTEM system stand out as the best system for the particular targets in the project area. SkyTEM mapped the key multi-layered hydrostratigraphy and water quality variability in the key aquifer that defined the key MAR targets, although the TEMPEST system had a superior performance at depths exceeding 100metres. Importantly, the SkyTEM system also mapped numerous, subtle fault-offsets in the shallow near-surface. These structures were critical to mapping recharge and inter-aquifer leakage pathways. Further analysis has demonstrated that selection of the most appropriate AEM system and inversion can result in order of magnitude differences in estimates of potential groundwater resources. The acquisition of SkyTEM data was an outstanding success, demonstrating the capability of AEM systems to provide high-resolution data for the rapid mapping and assessment of groundwater and strategic aquifer storages in Australia's complex and highly salinized floodplain environments. The SkyTEM data were used successfully to identify 14 major new groundwater targets and multiple MAR targets, and these have been validated by an extensive drilling program (Lawrie et al., 2012a-e). Increasingly, the demand from clients for higher certainty in project decision making, and quantifying errors, will see development of new system comparative analysis approaches such as the Inversion analysis approach documented in our initial paper. Ultimately, system fly-offs are likely in high-profile projects where budgets permit.
Product Type
nonGeographicDataset
eCat Id
79065
Contact for the resource
Custodian
Owner
Custodian
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
-
- External PublicationScientific Journal Paper
- ( Theme )
-
- AEM
- ( Theme )
-
- Airborne Electromagnetics
- ( Theme )
-
- geophysics
- ( Theme )
-
- model
- Australian and New Zealand Standard Research Classification (ANZSRC)
-
- Geophysics
-
- Published_Internal
Publication Date
2014-01-01T00:00:00
Creation Date
Security Constraints
Legal Constraints
Status
Purpose
Maintenance Information
notPlanned
Topic Category
geoscientificInformation
Series Information
Lineage
Reply to comment on the paper: Christensen, N. and Lawrie, K., 2012, Resolution analyses for selecting an appropriate airborne electromagnetic (AEM) system: Exploration Geophysics, 43, 213 -227.
Parent Information
Extents
Reference System
Spatial Resolution
Service Information
Associations
Downloads and Links
Source Information
Source data not available.