Survey operations were conducted from the 34-m survey vessel Riverside Guardian and comprised analogue high-resolution geophysical survey, UXO search, digital seismic reflection with multichannel analysis of surface waves (MASW), and geo-technical investigations including onshore mobile laboratory testing.
OCEAN TECH TOOLKIT
The geophysical component involved the acquisition and processing of high resolution MBES data (Kongsberg 2040), side scan sonar data (Edgetech 4200), and shallow geology data using both an Innomar sub-bottom profiler (SBP) and an Applied Acoustics 400 TIP Sparker. OmniStar G4+ corrections, tightly coupled POS MV INS, and Sonardyne Ranger 2 USBL tracking ensured the best-in-industry quality positioning on all sensors.
The UXO survey was undertaken using an EIVA Scanfish Katria 3D ROTV to tow a 4x Geometrics G-882 magnetometer array at 5-m line spacing. The MBES data from the geophysical survey was used to plan the UXO survey so that the ROTV could be flown within 4 m of the seabed and the 3D option with USBL tracking allowed steering precise lines to achieve full coverage.
In areas too shallow for the Riverside Guardian, the 8-m aluminum EGS Independence survey launch was used to tow a TVG gradiometer using a GNSS tail buoy to survey over the shallow reef line up to the shoreline. Potential ferrous targets were then investigated using a mini ROV for visual confirmation on magnetic anomalies of interest.
The multichannel seismic work (refraction) was carried out to complement the high-resolution marine seismic survey. Seismic source included mini airguns and acquisition with Geometrics Geode seismograph, deploying streamers using both towed and static modes with a mix of 24 x 1 m/2 m/4 m, and 48 x 1 m arrays.
SEABED SITE INVESTIGATION
Geotechnical investigations were con- ducted utilizing a 6-m vibrocore system and a Datem Neptune Seabed CPT unit. A box corer was also used for some locations and a grab sampler was in the very shallow areas that only the small boat could access. After cutting core samples to 1 m lengths and initial offshore tests the cores were stored onboard in a 20-ft reefer container prior to transferring onshore for further lab testing. EGS mobilized it’s containerized geo-technical processing laboratory to Port Moresby and a 2-month onshore testing campaign followed the offshore sampling. This extensive multidisciplinary survey project demonstrates EGS capabilities in a diverse range of operations using largely EGS-owned technologies. The operations were conducted safely, without any lost time injury, and the data is of excellent quality.
To find out more, visit: www.egssurvey.com.au.
This story was originally featured in ON&T Magazine’s June 2023 issue. Click here to read more.
