maps.

Survey work is not limited to investigations on land. Our waterproof fluxgate system has also been lowered 100 feet into PVC-cased boreholes to locate lost iron-cased wells in preparation for proper abandonment

 

Data is usually acquired with the use of a survey grid constructed onsite and parallel lines "run" across the area of investigation. Factors considered in data collection include the location, orientation and density of the survey lines as well as the digital sampling interval along the lines. The data are then recorded either on analog strip charts or digitally with a datalogger before then being downloaded to a computer in the field. Positions of known ferrous objects onsite are noted and recorded for placement on resulting

procedures; likewise, it has been towed behind a small boat to locate submerged drums in lake sediments.

Detection of non-ferrous or ferrous metallic objects can be accomplished with the Schonstedt MAC-51B pipe/cable locator or with the Aqua-Pulse 2 land/sea metal detector. These are frequently used to quickly sweep an area of concern; data is usually not recorded but simply visually noted and anomalies are marked in the field.

For magnetometry work, Geosphere routinely employs the Foerster Ferex 4.021 magnetometer (also referred to as the MK-26 by the US military). This instrument, with two vertically-mounted fluxgate sensors, can produce a differential field, or gradient, measurement of the vertical component of the Earth's magnetic field. Such readings are expressed in units of nanoTeslas/foot. (The nanoTesla is equivalent to the older unit of gamma).

The magnetometer can be handled by one person for doing survey work on land. Care is taken to avoid erroneous readings which may be caused by improper positioning of the sensors or by the operator carrying ferrous

objects such as tools and steel-toe boots. The greater the sensitivity needed, the greater the effort required to minimize interference.