The Dugout Canoes of Lake Phelps
The intention of the 1992 Lake Phelps Survey Project was multifaceted: to locate undiscovered log canoes and lithological features buried beneath the bottom sediments of Lake Phelps, North Carolina through the use of sub-surface exploration radar; to test, record, and map said sites; to develop and refine a ground penetrating radar survey methodology suitable for archaeological survey in a fresh-water marine environment; and to develop a signature library suitable for research and comparison of resources in like environments.
The Lake Phelps survey was divided into two phases to be carried out consecutively during the period of September 19 to September 25, 1992.
Phase I was to be conducted with the objective of testing three discrete transects with marine-deployed sub-surface radar. Each transect was to be divided into twenty lanes of ten feet width each, and 500 feet in length. Each lane would be marked by a pole driven into the bottom at either end of the lane. A twine line would then be run from pole to pole to serve as a lane guide for the survey craft. In shallow waters of three feet or less, the survey craft bearing the radar units and the operator would be manually guided and towed by several assistants. In waters of over three feet in depth, the unit was to be towed by an aluminum pram powered by an electric trolling motor.
Transect selection was based upon environmental variables, the known (or problematic) distribution of in situ sites, accessibility, and depth. Each transect was to total an area of 100,000 square feet. The total projected area of all three transects scheduled for survey was 6.887 acres of bottomland. Transect A was to include the reach between Bee Tree Canal and Bonarva Canal where bottom sediments were composed of organic rich muds; Transect B would cover an area to the immediate west of the Pettigrew State Park boat ramp at Thirty Foot Canal, investigating an sector where no sites had thus far been discovered, and which was reportedly composed of a bottom dominated by white sands; Transect C was to incorporate a largely untested area to the immediate west of Little Point and off Big Point. Based upon the distribution patterns of sites discovered during the earlier surveys, transect areas were to be established at ranges of 150 to 350 feet from the shore and running parallel to the shoreline. Transect A, however, would extend from 500 to 700 feet from shore to test the possibility of sites resting in deeper waters. Time permitting, a fourth alternative transect between Bonarva Canal and Somerset Canal, encompassing conjectured historic as well as prehistoric resources, was also to be tested in a similar fashion. Target areas of significant anomalies (Page 46) were to be marked by tags attached to the lane lines adjacent to target hits or other sgnificant features. Their locations were to be documented by the GPS positioning system, and standard survey techniques. Their parameters would be determined, extremities marked, and precise locations recorded.
In concert with the North Carolina State Underwater Archaeologist and his staff, and with the assistance and logistical support of the Superintendant of Pettigrew State Park and his staff, ground truthing of each significant anonily or feature, when possible, would be conducted to assemble information regarding site typology, characteristics, dimensions, stratigraphy, and to conduct limited sampling oforganic materials for C-14 dating. Each site was to be drawn and/or photographed when possible. No removal of any site component or artifact would be undertaken without the expressed approval of the State Underwater Archaeologist or the State Archaeologist. Upon completion of the survey, all sites were to be backfilled, markers removed, and site exposures covered.
Copies of all field notes, record sheets, drawings, photographs, and the final report were to be made available to the State Archaeologist, the State Underwater Archaeologist, and the Superintendent of Pettigrew State Park. All field notes would be made available upon termination of the project and submission of the final report.
The principal survey instrumentation for location and positional survey management to be employed in the Lake Phelps survey was to be the Subsurface Interface Radar System (SIR), commonly referred to as ground penetrating radar, or GPR, and the Sony Pyxis Global Positioning System, or GPS.
The Subsurface Interface Radar System
The Subsurface Interface Radar (SIR) System is a broad-band video-pulse radar system capable of detecting and graphically displaying subsurface soil interfaces and artificially emplaced objects to depths as much as 100 feet (30M). The SIR System consists of eight units:
1. Control Unit (Mainframe & Control Module)
2. Graphic Recorder
3. Model 07 Power Distribution Unit
4. Model 20 Remote Control Unit
5. Transducer/Control Cable
6. Model P731 Calibrator
7. Transducer (Antenna & Transmit/Receive Electronics)
In normal operation, all units except the transducer are operated in a suitable vehicle, while the transducer is towed by the vehicle or manually by an operator. (During the 1992 survey, the transducer unit was to be mounted in an inflatable raft, while the control unit and recorder would be mounted in a John boat). Power for the system is from a 12-volt DC source, normally the vehicle battery or a 12-volt storage battery, or from an AC power source through a Model 06 Power Supply. The Model 07 Power Distribution Unit is used to supply DC power to the control unit and recorders.
Description of SIR System Components
The Geophysical Survey Systems, Inc. Control Unit Model 4800 controls system operations functions as follows. The control unit transmits power (+12 volts DC, -12 volts DC and +150 volts DC) to the electronics and a synchronizing signal to the pulse generator in the transducer. Whenever the transducer detects a reflected radar pulse, travelling at near the speed of light, the signal is transmitted to the receiver. Tle receiver converts this electromagnetic signal, only a few nanosec- onds in duration, to an analog signal tens of milliseconds in duration and transmits this signal to the control unit. The signal is electronically processed and then sent to the graphic recorder and/or tape recorder.
The graphic recorder used in the SIR System-8 is an ADTEK Model SR-8004H line scan recorder. The graphic recorder accepts the analog signal from the receiver and produces a continuous, permanent chart display on electro-sensitive paper. By recording a vertical intensity modulated scan for every few inches of transducer travel, a continuous profile is developed showing reflections from subsurface strata and anomalies within the strata. The graphic recorder also reproduces data stored on tape with exact synchronization.
All system components operate on 12VDC, and the Model 07/03 provides three outlets for one input. If it is necessary to operate the system on AC power, a Model 06 Power Supply can be employed from GSSI. The Model 06 can be adjusted internally to operate on 100, 120, or 240 volts, 50-60 Hz.
The SIR system transducer is a light-weight unit for which there are ten different model transducers are available for various applications. Three units would ultimtely be employed during the survey of Lake Phelps. In operation, the transducer is normally towed on land by a vehicle or manually by an operator and is connected to the control unit by a control cable having a maximum (Page 50) length of 200 feet (61M), unless a pulse-booster is used. Mounted within the top center of the antenna is the transceiver electronics, which transmits a radar impulse into the ground at a rate of 50 KRz. The antenna receiver section receives reflected energy and sends a replica of the reflected pulse though the control cable to the control unit and recording instruments in the vehicle.
The Model 2OPremote marker provides a means for the operator to control the recorders from a short distance away from the control unit. It also provides the ability to insert markers on the record data. The Model P761 calibrator can be connected to the control unit in place of the transducer and provides a pulse train at approximately ten nanosecond intervals, to be used as a time (Depth) calibration standard.
The SR-8100 is a single channel mechanical line scanning graphic recorder that can print shades of grey lines that are proportional to input analog voltage levels. Data is printed on a 200 ft. (61M) continuous roll of dry electro-sensitive paper (ADTEK type 85200), which is installed in a removable cassette. The operator can allow printed data to be fed out of the recorder or automatically spooled within the cassette. A plastic belt with four sets of styli attached is driven across the paper by a pulley connected to a stepping motor. The electrical signal to be recorded is applied to the print bar and transferred to the paper through the signal and paper styli. The speed of the stepping motor is controlled electronically by various frequencies referenced to a quartz crystal oscillator. The rotational speed of the stylus belt can be adjusted by front panel controls. Scan speeds can be selected which control the time it takes for each stylus to travel from one edge of the paper to the other. The scan times are calibrated in both milliseconds/scan and scans/sec. The SR-8 100 has five scan speeds from two to 32 scans/sec.
Stylus belts are disposable and a new one is normally installed with each new roll of paper. Because the shape of the stylus is critical to print quality, each stylus is shipped from the factory prebent. Other functional controls include paper speed, paper take-up mode, scale lines, marker, print polarity, phasing, run/standby, AC/DC input, intemal/external clock and signal level controls. Input and output signals and controls are connected to the recorder through a front panel mounted 25 pin male connector. The SR-8100 is furnished with both horizontal or vertical paper orientation and is mounted in standard 19" racks in either orientation.
The recorder frame is a precision casting made of high strength aluminum-zinc alloy and provides a light-weight durable housing for all electrical and mechanical components. All electronic circuits are solid state on printed circuit cards interconnected by a plug terminated wiring harness. The unit can be configured for either DC (SR-8104) or AC (SR-8105) power operation. An input (Page 51) power cord and connector is fumished with proper wiring for either DC or AC. The AC power option can be configured for two voltage ranges, 100-130V or 200-24OV. The AC power module supplied with the SR-8105 will also accept 24-30VDC if a DC power cord is used.
Sony Pyxis GPS Global Positioning System
Designed for and maintained by the U.S. Government, GPS provides information from a system of satellites orbiting at an altitude of 12,625 miles --covering the entire surface of Earth 24 hours per day. Each satellite has its own unique "footprint," coded identification signal, and highly accurate atomic clock. Earth stations continuously monitor all satellites, sending back information on their relative position and correcting for any atmospheric conditions that might affect signal accuracy.
The Pyxis OPS receiver tracks four satellites simultaneously, creating a three-dimensional positioning framework that forms the basis of latitude, longitude, altitude, course, and velocity information. Pyxis automatically receives updated constellation, clock and correction information (ephemeris data), determines the satellites with the strongest signals and best geometry, and calculates a position fix with updates every two seconds. With selfcontained power supply and illuminated display, Pyxis combines navigating functions of multiple instruments, including compass bearing, real time, and so forth. One key advantage of Sony Pyxis GPS navigation is its three-dimensional position fix, providing not just latitude and longitude, but also accurate altitude information.
With simultaneous four-channel satellite tracking, the accuracy of Pyxis GPS reciever unit information system is capable of providing accurate positioning to within 30 to 100 meters. Tle unit weighs 1 lb. 5 oz., including four AA batteries, and is water resistant. The antenna and compact keyboard with 2-line, 40 character LCD display are detachable. Brackets and connecting cord permit each component to be mounted separately. Tle Pyxis NAV display shows distance to destination or to an intermediate specified waypoint. The Pyxis receiver can store up to 100 waypoints and markpoints in memory, with identifying names of up to six characters each. In EDIT mode, these points can be edited before departure. The MARK model permits current position to be automatically entered while en route. Pyxis NAV display shows the distance and direction to a destination or next waypoint, as well as current speed and heading. In addition to numerical readout, Pyxis graphic display mode permits comparison of current heading with the true course. The Pyxis TRACK mode displays both relative altitude from starting point and absolute altitude based on local coordinates. In TRACK mode, it is possible to display a graphic representation of course from starting to current (Page 52) position. Pyxis POS display shows the present time in hours/minutes/seconds based on local time. The Pyxis screen displays the estimated time to any waypoint based on current speed and can be set to signal automatically as the approach to each waypoint is in progress.
GPR radar equipment, GPS gear, aluminum pram, trolling motor, rubber inflatable, site markers, buoys, line, fuel, video and 35mm cameras, film, and miscellaneous photographic supplies, archaeological supplies, and miscellaneous tools were supplied by National Geographic and by Claude E. Petrone. Mapping, drafting and duplicating, as well as diving gear, were supplied by Donald G. Shomette. Two Boston Whalers, an aluminum Coleman canoe, underwater excavating equipment, and miscellaneous diving and land survey gear were provided by the North Carolina Division of Archives and History's Underwater Archaeology Unit. Additional boats, survey pilings, miscellaneous tools, manpower, and work space for secured storage and repairs, as well as camping facilities, were provided by Pettigrew State Park.
Project personnel consisted of the following: Principal Investigator, Claude E. Petrone, National Geographic Society, Washington, D.C.; Project Director, Donald G. Shomette, Nautical Archaeological Associates, Upper Marlboro, Maryland; Photographer, Craig Buck, National Geographic Society; State Underwater Archaeologist, Richard Lawrence, Kure Beach, North Carolina, Archaeologist, Mark Wilde-Ramsing, Kure Beach, North Carolina; Archaeological Conservator, Leslie Bright, Kure Beach, North Carolina; Marine Equipment Specialist, Julep Gillman-Bryan; Draftsperson, Carol A. Shomette, Nautical Archaeological Associates, Upper Marlboro, Maryland; Line Assistant, Mary Petrone; Volunteers, Mark Bryan, Paris Trail. (Page 53)
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