# Presentation: 666121

## Accurate Marine Magnetic Survey of Shallow Water Littoral Area 

**Accurate Marine Magnetic Survey of Shallow Water Littoral Area**

**B. Ginzburg ****1****, E. Weiss ****1****,* T. Ram Cohen ****1****, H. Zafrir ****1****, R. Alimi ****1****,N. Salomonski ****1****, J. Sharvit ****2**
- 1 * R&D Integrated System Section, Propulsion Division, Soreq NRC, Yavne 81800, Israel
- 2 ** Israel Antiquities Authority, Marine Archaeology Unit, P.O. box 272, Or-Akiva 30600, Israel

## Introduction

- Shallow water – depths 1 – 10 meters.

- In the case of complex bottom topography there is a danger the tow fish can be caught by prominent rocks or debris. Solution – floating platform.

- Numerous examples of such sites are found in the field of underwater archeology.
- Reason - rise in sea level over the shallow continental shelf flooding prehistoric settlements and eventually burying them under sand.

- One of the primary purposes of the current survey was to search for the wreck of a T-6 Harvard airplane that crashed in 1960.

**Introduction**

**Integrated system for precise magnetic measurements, data acquisition, and    navigation.**
**Target .**
**Survey area characterization.**
**Survey results**.

## Slide 3

## Non-magnetic katamaran

## Electronics box

**Electronics box**

- Careful non-magnetic design
- Choice of proper materials and components
- Compensation of stray fields

- Magnetic interference of the platform has been reduced down to about 50 pT level.

## Tow boat

- Towed catamaran

## Target - wreck of a T-6 Harvard airplane that crashed in 1960.

- Measurement of engine magnetic moments.

**Target - wreck of a T-6 Harvard airplane that crashed in 1960.**

- Engine of radial internal-combustion type - model Pratt and Whitney R-1340 "Wasp".

- _Engine magnetism_: (8.5; 9.0; 11.0) Am2 - induced components for 0.3 Oe external field
- 		(5.5; 2.0; 4.5) Am2 – remanent components

- Estimated anomaly is about 0.2 nT @ 25 m (max depth of survey area) in dipole approximation.

- Trapeze shaped - roughly 1.8 km wide and 2 km long.
- It is located about 1 km northwest of the Atlit Crusader fortress promontory off the Israeli Mediterranean coast at a water depth ranging from 7 to 25 meters.

**Survey area**

**Château Pèlerin**,
- also known as **Atlit Castle** and **Castle Pilgrim**

## Magnetic features of the survey area

- Because of the proximity to the shore line, the seabed sediments comprise materials swept away from the shore in addition to sand overburden. These sediments, especially iron-rich "humra“ (cmass=71×10-6 cgs) and sandstone bedrock "Calcareous" ((mass=4×10-6 cgs) that are exposed along the shoreline, cause an extra complication of magnetic relief.
- Survey area is located in a zone where thousands of years of intense seafaring have left numerous ancient relics on the sea floor. Therefore, considerable contamination with ferro-metallic debris and archeological remains was expected.
- It is likely that shore-based iron structures also contributed to magnetic picture of the area.

**Magnetic features of the survey area**

## Survey area with the actual survey lines.

**Survey area with the actual survey lines****.**

- The survey was carried out along North–South parallel lines with ~10 m spacing between them as well as a few East–West tie lines

## Slide 11

## Slide 12

## Band pass filtered magnetic map of survey area

## Slide 14

## Detailed analysis of the survey map revealed 59 target-like anomalies in an area of approximately 3.5 km2. The anomalies were ranked according to their probability of being anomalies created by the airplane wreckage.

- Detailed analysis of the survey map revealed 59 target-like anomalies in an area of approximately 3.5 km2. The anomalies were ranked according to their probability of being anomalies created by the airplane wreckage.

## Slide 16