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Step 5: Acquire the AEM data

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Procedures for Notification Prior to Data Acquisition

An agency is advised to send advanced notice of the survey to residents through their usual channels of communication (e.g. email distribution, notices in the local paper, newsletter, radio, etc.) We suggest that notification that goes out prior to the earliest possible flight time but the wording should accommodate changes in schedule that can occur. It is very difficult to accurately predict the start date. We have produced an example of an announcement, along with a figure that compares the magnetic field associated with the data acquisition to that of household appliances. We also advise notifying the emergency responders in the area (e.g. police, fire department) as they might receive calls from concerned individuals.

Contractual Agreements and Pricing Structure

The contract for acquisition of geophysical data needs to include clear explanations of what will be done and the pricing structure. There needs to be an agreement as to which party will absorb the risk and costs associated with downtime due to weather, equipment malfunction, or for any other reason. There must be agreement early in the project planning on the payment schedule. It is typical for the AEM service company to request an advance payment to cover, for example, the booking of the helicopter, while most public agencies can only pay for services delivered.

The agreement with SkyTEM that was put in place for this project

SkyTEM agrees to forego the 40% advance payment and instead issue an invoice for 90% of the total project on the last day of flying. Payment is due 14 days from receipt of invoice. The final invoice of 10% will be issued upon delivery of the final report from SkyTEM. Given this payment schedule, it is crucial that all data be handed over to the group responsible for QA/QC oversight on a daily basis while the field operation takes place. SkyTEM will perform quality control checks as well. Those responsible for oversight will do a final approval of the data no later than the day before the first invoice is due (13 days after the last day of flying). This was an acceptable agreement as a majority of the services provided by SkyTEM were completed before the first invoice was due.

Guidelines and Standards for AEM Measurements, Processing, and Inversion

When the geophysical mapping of Denmark with the AEM method began, a collaboration was established between the HydroGeophysics Group at Aarhus University, Denmark and the Danish EPA. This group was responsible for providing oversight and training, and for conducting the applied research required to continually improve the application of the AEM method. A report was produced that documents the guidelines and standards for AEM measurements, processing and inversion. As described in this report and in this publication, a national test site was developed in Denmark that was used for calibration and validation purposes. The Danish EPA used the guidelines from the report as part of the tender process, requiring that consultants and AEM contractors follow the guidelines in order to be successful in the bidding process. DWR should establish a test-site; this would require a neutral party to maintain the test-site and develop the guidelines, as was done by the HydroGeophysics Group and the EPA in Denmark. Ideally other test sites would be established throughout California that would provide easier access. With only one DWR test-site, a ground-based system could be used and validated at the test-site and then used at a local site in order to calibrate and validate the AEM system.

Requirements for Delivery/Archiving of AEM Data

Two different forms of the AEM data should be provided: (a) raw data and (b) processed data. The processing steps applied between (a) and (b) must be provided, preferably using on-line documentation.