CRUISE PLAN

RV FRANKLIN

FR08/99

 

 

Title

The Carpentaria Electrical Conductivity Anomaly: A Marine Geophysical Perspective

and

Tropical Rainfall Measurements with Navigational Radar

 

Itinerary

Depart Darwin 1000 hrs, Wednesday 24 November 1999

Arrive Cairns 1000 hrs, Wednesday 15 December 1999

 

Principal Investigators

Dr. Graham Heinson (Chief Scientist)

School of Chemistry, Physics and Earth Sciences

Flinders University of South Australia

GPO Box 2100

Adelaide SA 5001

ph: 08-8201-2607

fax: 08-82011-2676

e-mail: Graham.Heinson@flinders.edu.au

Prof. Matthias Tomczak

School of Chemistry, Physics and Earth Sciences

Flinders University of South Australia

GPO Box 2100

Adelaide SA 5001

ph: (08)-8201-2298

fax: (08)-8201-2676

e-mail: Matthias.Tomczak@es.flinders.edu.au

A/Prof. Antony White

School of Chemistry, Physics and Earth Sciences

Flinders University of South Australia

GPO Box 2100

Adelaide SA 5001

ph: 08-8201-2607

fax: 08-82011-2676

e-mail: Antony.White@flinders.edu.au

Scientific Objectives

Geophysical Experiment (Heinson/White)

The Carpentaria electrical conductivity anomaly is a major geological shear zone extending over a thousand kilometres in an approximately north-south orientation in northern Queensland. It has been mapped on land by various geomagnetic and magnetotelluric arrays, but the relationship between the conductivity anomaly and major tectonic boundaries is not straightforward. The offshore extent of the anomaly is unknown and poorly constrained by land measurements around the Gulf. The scientific objectives are therefore to:

  1. Map the location of the Carpentaria anomaly and examine its spatial relationship with the tectonic structures in the region.
  2. To determine the depth and length of the anomaly into the Gulf, and hence better understand the causes of high electrical conductance within the crust.
  3. To relate the electrical properties to the tectonic evolution of northern Australia.

Oceanographic Experiment (Tomczak)

The purpose of the study is to develop a ship-borne rainfall measuring system based on the navigational radar. The method of measuring rain with the ship’s radar was previously tried during the R/V Franklin voyage FR0796. It was shown that the radar can successfully monitor spatial rain distribution around the ship, which enables quantitative estimates of area-average precipitation using the thresholding technique. In the present proposal we attempt to substantially improve the accuracy of radar rainfall measurements by using advanced radar signal processing and thorough calibration and validation of rainfall measurements.

 

Cruise Objectives

Geophysical Experiment (Heinson/White)

The study will involve the deployment of twelve seafloor magnetotelluric instruments and four seafloor magnetometers in a three-dimensional array across the Gulf of Carpentaria. Figure 1 shows the location of the instruments. Typical distance between sites is of the order of 50 km.

The instruments will be deployed at the beginning of the cruise by free fall from the ship. Typically, instruments sink at a rate of 0.5 m/s, so for a depth of 60 m in the centre of the Gulf, the time taken to sink to the seafloor will be of the order of 2 minutes. Twelve of the seafloor instruments (circles in Figure 1) will be deployed for the whole cruise duration (approximately 18 days). Recovery is by means of an acoustic recall system that has been successfully used in three recent cruises from the Franklin. The other four seafloor magnetotelluric instruments (triangles in Figure 1) record at higher frequencies over 4 days. We intend to cycle these instruments two or three times during the cruise at twelve different locations to maximise the spatial data recovery, hence twelve sites are shown in Figure 1.

Similar equipment has been deployed and recovered by the Franklin by Dr. White in 1986, 1989 and 1994, and with Dr Heinson in 1997 and 1998. In the earliest experiment, four magnetometers were deployed across the continental margin of New South Wales (White et al., Phys. Earth Planet Int., 60, 147-154, 1989; Kellett et al., Tectonophysics, 192, 367-382, 1991), followed by a similar experiment off the coast of South Australia (White and Heinson, J. Geomag. Geoelectr., 46, 1067-1081, 1994). In the most recent deployment, thirty marine deployments and recoveries were made south of Eyre Peninsula, South Australia (Heinson et al., Exploration Geophysics, 1999; Heinson et al., Geophys. Res. Lett., 1999; Popkov et al., Exploration Geophysics, 1999).

Oceanographic Experiment (Tomczak)

The cruise objectives are to:

  1. Calibrate the navigational radar signal in terms of the rainfall intensity. This will allow one to use the radar not only to locate the rainfall patches, but also to measure absolute precipitation rates within them.
  2. Develop a run-time validation procedure in which the radar-derived precipitation rates are assimilated in the mixed layer model and the resulting salinity is compared to the record of the ship’s thermosalinograph.

The cruise objectives will be achieved by deploying 2 raingauges mounted on separate buoys and simultaneously observing rain with the specially designed radar . The radar is a standard FURUNO navigational radar modified to enable continuous logging of radar signal on to the PC. We shall attempt to "chase" the areas of heavy convective rainfall in order to observe rain-induced salinity depressions. Their magnitude will be used to independently quantify the amount of precipitaion.

 

Cruise Track

Figure 2 shows the proposed cruise track. The solid line shows the inward cruise track and the dashed lines show the pick up cruise track. Note that the triangle sites are not all occupied at the same time; rather we wish to occupy the sites in groups of four, for periods of four days.

The experiment will commence after completion of the deployment of geophysical instruments within the framework of the joint project "The Carpentaria Electrical Conductivity Anomaly: A Marine Geophysical Perspective". Two buoys with mounted rain gauges will be anchored at a distance of 8 nm from each other. The ship will then navigate into the areas of heavy rainfall while remaining within the 24 nm range from either buoy.

 

 

 

Time Estimates

Transit from Darwin to site 1:1500 km

72 hours

Geophysical instrument deployments

56 hours

   

Deployment of 2 buoys

4 hours

Radar rain observation and "cloud chasing"

232 hours

Recovery of 2 buoys

4 hours

   

Geophysical instrument recoveries

84 hours

Transit from last site to Cairns: 1500km

72 hours

   

Total oceanography experiment time

10 days

Total Geophysical Experiment time

6 days

Transit time to/from sites

6 days

 

Franklin Equipment

Oceanographic Experiment

  1. Small winch
  2. Meteorology data
  3. Thermosalinograph data
  4. Navigational data
  5. Network connection to Franklin mainframe UNIX computer.

Geophysical Experiment

Bottom mounted 12 kHz transducer as on previous cruises.

 

User Equipment

Oceanographic Experiment

  1. FURUNO navigational radar (emitter-receiver and processing unit)
  2. Desktop PC connected to the radar processing unit
  3. Thoroid buoys (2)
  4. Mooring chains and other hardware
  5. Rain gauges (2)

Geophysical Experiment

  1. Twelve seafloor magnetotelluric instruments
  2. Four seafloor magnetometers
  3. Acoustic deck unit
  4. Towed SP instrument, cables and computers

 

Personnel List

Graham Heinson Flinders University Chief Scientist, Geophysics Instrumentation

Matt Tomczak Flinders University Project Leader, Oceanography

Anthony White Flinders University Project Leader, Geophysics Instrumentation

Ivan Lebedev Flinders University Watch Leader, Oceanography

Ted Lilley ANU Scientist, Geophysics Instrumentation

Wayne Peacock Flinders University Electronics Engineer, Oceanography & Geophysics

Igor Popkov Flinders University Student, Geophysics

Adrian Costar Flinders University Student, Geophysics

TBA ANU Student, Geophysics

Lindsay Pender CMR Cruise Manager & Computing

Daniel Conwell CMR Electronics

Ian Helmond CMR Ocean Engineering

 

 

This cruise plan is in accordance with the directions of the National Facility Steering Committee for the Research Vessel Franklin.

 

 

Signed

 

 

 

Ships Manager

CSIRO Marine Research