Marine controlled-source electromagnetic survey for deep imaging of submarine groundwater systems
Author: Eric Attias
My research focus on utilizing state-of-the-art marine remote sensing electromagnetic ocean technologies to explore and image shallow and deep Earth structures.
The backbone of the surface-towed CSEM system used in this survey are the Porpoise electric field receivers. We used a 1 km array with 4 Porpoises; each named after a fish that starts with the letter P: Parrotfish, Pike, Pompano, and Perch.
Data loggers of the Porpoise surface-towed receivers, and their associated fish.
The packing & demobilization of the CSEM system took us 6 hours, primarily because of the extreme heat at the honokohau harbor.
Khaira disassembles the Porpoises.
CSEM system gear.
CSEM system packing & demobilization.
CSEM system demobilization.
CSEM system demobilization.
CSEM system demobilization.
With the help of Max, Brenden, Khaira and Keven, we got the CSEM system all packed before sunest, and even managed to celebrate the succesful completion of the survey at “thebar without a Poproise”.
Yes, there is actually a bar by that name in Kona.
Our last day of operation was dedicated for surveying 3 crosslines (perpendicular to the Kona coastline) situated in the northern section of the survey area, inline with the offshore trajectories of the Kiholo Bay and the Hualalai volcano. These crosslines will help us to (a) validate the data acquired from 7 inlines in this area, and (b) detect any localized submarine lava tubes that extend offshore from the Hualalai volcano.
This completes our successful survey! where we collected multiple datasets from ~250 km of towlines (total of 15 survey lines) encompassed within the boundaries of the Hualalai aquifer. This data will be utilized to detect, delineate, and understand both the spatial distribution and interconnectivity of deep submarine groundwater deposits, offshore Kona, the Island of Hawai’i.
Survey Area 1: North section of the Hualalai groundwater system. Includes 7 survey inlines and 3 crosslines. The color bar represents bathymetric depth that ranges from 10 m (red) to 100 m (blue).Survey Area 2: Middle section of the Hualalai groundwater system. Includes 2 survey inlines. The color bar represents bathymetric depth that ranges from 10 m (red) to 100 m (blue).Survey Area 3: South section of the Hualalai groundwater system. Includes 3 survey inlines. The color bar represents bathymetric depth that ranges from 10 m (red) to 100 m (blue).Total survey coverage along the Hualalai groundwater system. Total of 15 survey lines. The color bar represents bathymetric depth that ranges from 10 m (red) to 100 m (blue).Porpoise array alignment along crossline 1. Our chase boat is positioned at the end of the 1 km array of Porpoise E-field receivers.A failed attempt to take a photo of the Porpoise array through a pair of binoculars.The team before the last recovery of the Porpoise array.Quoting Brenden: “we’re blonde, we’re making science, nothing can stop us!”.Quoting Max: “Well, maybe just blonde “.Eric & Dallas in a moment of joy after the final recovery of the CSEM system.Crew group photo, from front to back: Khaira, Jake, Dallas, Max, Jason, and Eric.
As shown above, a family of dolphins escorted us during our last transit back to the Honokohau harbor at Kona, the island of Hawai’i.
Finally, I wish to thank all the wonderful people that made this marine project possible: Gwen Jacobs, Steve Constable, Dallas Sherman, Khaira Ismail, Kevin Kelly, Michelle Choe, Ellen Koppenheffer, Jake Perez, Chris Armerding, John Souders, Jacques Lemire, James Barry, Jason Magalen, Brendan Hunter, Patrick Anderson, Max Sudnovsky, Steve Kennedy, Jason Hasler, Emily Wilson, Keith Olsen, Jan C War, Dean Towle, Keven Rinkenbach.
Our survey operation is improving daily, where the time for deployment & recovery of the CSEM, MBES, and Magnetometer systems are getting shorter. Thus, we can cover more area in the 14 hours of daily operation. Yesterday and Today we are surveying the north section of our survey area, starting from the Kiholo Bay where previous studies measured a substantial influx of groundwater into this Bay.
Data collection coverage along the northern section of the survey area.Power spectrograms showing the E-Field signal as recorded by each one of the Porpoises in days 4 and 5 of the survey. Note the decade in the signal as a function of the offset from the CSEM transmitter and transmitted Amps. The distinctive bands represent the strongest harmonics of waveform-D (3 Hz, 7 Hz, 13 Hz) that is used in this survey.
Bathymetry data from the Kailua-Kona Bay.
Bathymetry data from the Kailua-Kona Bay.
Bathymetry data from the Kailua-Kona Bay.
Bathymetry data from the Kiholo Bay area.
Bathymetry data from the Kiholo Bay area.
The images in the mosaic above show some various examples of the unprocessed MBES data. Note the variability in seafloor bathymetry at the surveyed area.
Logging of multi-beam backscatter water column data using Hypack.Jason, Khaira, and Eric are discussing water column Multi-beam data, whereas Patrick is operating the G-882 magnetometer system.Recording of the magnetic data streamed from the G-882 magnetometer. The data is logged using Geometrics MagLog software.Our captain Max is enjoying the calm transit to Kiholo Bay.
In the last 2 days, we mainly surveyed south of the Honokohau Harbor to avoid the high swell generated by Hurrican Olivia that passes the island. In the first day, to transit from the Northern area of our survey to the Southern part, we had to cross parallel to the Honokohau Harbor, thus limiting the boat traffic coming in and out of the harbor. With the help of our survey boat, the transition went smoothly.
In the second day, we surveyed along Kailua-Kona (well sheltered from wind and swell) the 30m and 50m depth counter lines. Both days of the survey were successful! As all operated according to plan, and multiple datasets were collected. Today we decided to idle the operation due to the weather. Our survey operation will resume on the 13th.
A map showing the survey coverage to date. Survey tracks are illustrated by multi-beam data projection.A sample of unprocessed MBES data.Vertical profiles of the measured SoundVelocity, Salinity, and Conductivity.Jason & Khaira performing a sound velocity (SVP) measurement.The 1 km Porpoise array nicely aligned with our survey boat. At the end of the array you can see the chase boat.The terrestrial ends of lava tubes, as observed while surveying along the 30m depth contour line, south of Kailua-Kona.Sometimes the view while surveying isn’t that bad. Note the proximity to the coastline as we tow the array along the 30m depth counter line.A family of Dolphins accompanied us during the transit to Kiholo Bay.
Today we acquired the following datasets: Electrical (CSEM), Magnetic (magnetometer), seafloor Multi-beam (MBES)/Backscatter, and Magnetometer data. The survey got into its own rhythm, where all crew members are working in synergy, making the operation to feel nearly effortless and all done in good spirit! I thank the survey crew members for all of their hard work! as well as Jason & Emily that are doing an excellent job in operating the chase boat, protecting our Porpoise array from transient fishing and leisure boats.
Admiral chart navigational map superimposed by the survey track, representing the multiple data acquisition over the last 2 survey days.Real-time magnetic anomaly detection, as observed in the data stream coming from the G-882 magnetometer, and displayed on the Hypack system.Brenden discusses Jason about the optimization process of the MBES data acquisition.
