On the Edge: History Underfoot

January 1, 2012  - By

Camps-W . Credit: Tracy Cozzens
A U.S. Army camp near Townsville’s suburban areas, circa 1944.

By Tracy Cozzens

Beneath the surface of a tropical paradise in the city of Townsville on Australia’s Sunshine Coast lies a hidden maze of tunnels and underground bunkers, once said to be used by General Douglas MacArthur. Learning the secrets of this labyrinth that was a major World War II staging point for battles in the Southwest Pacific is the passion of Kevin Parkes of Geo Positioning Services, Townsville.

Parkes’ main tool is historic aerial photography, coupled with hours of research in the National Australian Archives and the National Library of Australia. To that he adds geophysical surveys of the infrastructure. Parkes is undertaking the geophysical surveying and mapping using an Ashtech ProMark 100 GNSS receiver and a Willy Bayot PPM Mk 3 magnetometer. He used the magnetometer and GPS receiver in parallel, later processing both data sets.

After the attack on Pearl Harbor and the Japanese advance through Asia, Townsville’s population bloomed from 30,000 to 120,000 by mid-1943. The rapid military influx stretched resources to the breaking point.

The U.S. Army 5th Air Force established the largest aircraft repair and maintenance facility ever built in the southern hemisphere at Townsville, and the site became the technical hub of U.S. military aviation. Air Force Service Command Depot #2 at Townsville was capable of overhauling 300 aircraft engines per month and performed aircraft assemblies, modifications, overhauls, and maintenance. Major resources and facilities serviced the Royal Australian Air Force, Australian and U.S. Armies, Royal Netherlands Air Force, Royal Air Force, Canadian forces, Royal Navy, and other allied forces.

“A visitor to Townsville today would be forgiven in asking where the artifacts of this massive military facility are today,” Parkes said. “There is very little remaining in any built structures that give any idea of what happened in this city 70 years ago.”

Parkes realized that underground cave shelters were most likely used for warehousing and storage, to keep stores out of the weather and protected from enemy action.

He describes one area he investigated, a park in Townsville used as an officer’s accommodation camp. Preliminary magnetic anomaly surveys indicated linear anomalies were beneath the park surface. A high-resolution survey gave samples of about 1.5-meter resolution.

“The difficulty was reducing all noise levels down to a minimum, including the X/Y positioning, so the GPS requirements came down to survey quality,” Parkes said. “It is absolutely critical that the GNSS receiver and magnetometer keep in synchronization during data collecting runs including under the frequently encountered tree canopies.”

To improve accuracy, Parkes avoids using real-time kinematic survey equipment. “That would involve having another electronic device operating and emitting more noise in the signal spectrum,” he said. The need to position the GPS antenna in close proximity to the magnetometer sensor was a major issue with all on-pole RTK systems.

Air-raid-shelter-W . Credit: Tracy Cozzens
A U.S. Army air raid shelter under the officer’s accommodation camp, mapped with GPS and magnetometer data and using Surfer 3D surface mapping software.

With an Ashtech Promark 3, post-processed results were better than 100-millimeter X/Y coordinates. “The unit is lightweight and self-contained,” Parkes said. “The noise from the Ashtech survey-grade external antenna’s effect on the magnetometer data was insignificant.”

Still, this park had a grove of trees that defied every attempt to maintain GPS reception and consequently synchronize the magnetometer. Along came the Ashtech ProMark 100, a lightweight and self-contained receiver with external geodetic antenna with GPS and GLONASS. “My first attempt at surveying under the trees was spectacular to say the least,” Parkes said. “Synchronization with the magnetometer data was near perfect.”

The dual-constellation reception of the ProMark 100 became essential to the success of Parkes’ work. After more than a hundred data-collection passes with the magnetometer and ProMark 100 through the groves of trees, at no time did the Position Dilution of Precision (PDOP) rise to more than three, and at all times more than eight satellites were available. The ProMark 100 data is post-processed to improve accuracy. Parkes noted that ironically many of the most interesting finds have been collected under heavy tree canopy. Without the quality of the geographic positions enabled by the ProMark100 under tree canopy, Parkes said that much of his work would have been impossible to achieve.

Equipment-W .  Credit: Tracy Cozzens
Parkes’ surveying equipment includes a magnetometer and a ProMark 100 GNSS receiver.

In fact, when Parkes first began his mapping project in 2005, he used a single-constellation GPS system and post processed the results against the local International GNSS Service (IGS) reference station. The GPS-only system worked very well until a grove of trees would interfere with the sky. Now with the ProMark 100 GNSS receiver, Parkes surveys using GPS L1 and GLONASS in continuous kinematic mode at a one-second collection rate. He then post processes the data against another ProMark 100 used as a local reference station.

To date, Parkes has mapped an underground railway, artillery observation posts, several shelters, fuel terminals and other yet-to-be-identified pieces of the vast infrastructure.

Rowes-Bay-W .  Credit: Tracy Cozzens

During his Research, Parkes mapped a major magnetic anomaly in Cleveland Bay. In 1770 Captain James Cook in the HMS Endeavour mapped the east Australian coast. Venturing into Cleveland bay, Cook noticed his compass behaving erratically, and named one island Magnetic Island. Today, a 3D surface model reveals a large magnetic anomaly heading across Cleveland Bay and straight towards Magnetic Island, 7 kilometers from Townsville. Experts who have examined the data believe that it is a naturally occurring magnetic anomaly about 800 meters wide. “It would appear that Captain James Cook was indeed a very capable navigator and cartographer,” Parkes said.

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About the Author: Tracy Cozzens

Senior Editor Tracy Cozzens joined GPS World magazine in 2006. She also is editor of GPS World’s newsletters and the sister website Geospatial Solutions. She has worked in government, for non-profits, and in corporate communications, editing a variety of publications for audiences ranging from federal government contractors to teachers.