Magnetic Methods are used to locate ferrous objects like buried well casings and dishwashers.  Total field magnetometers measure the total magnetic field at a given location.  Since the earth's magnetic field changes slowly over short distances, any changes in the measured total field are associated with local targets. 

The intensity of the earth's field changes depending on your location but typically varies from 25,000 nT to 70,000 nanoTeslas.  The magnetic field intensity associated with a target depends on the size and shape of the target as well as the distance and orientation with respect to the magnetometer, but is usually small compared to the earth's field, and is on the order of tens or hundreds of nanoTeslas.  The accompanying figure gives the calculated magnetic response for four different objects.

Magnetic surveys for environmental concerns often use gradiometers to simplify data collection and reduction.  These instruments measure the horizontal or vertical gradient of the magnetic field and thus highlight areas where the magnetic field changes rapidly.  Since we are often only concerned with the local anomalies associated with buried transformers or Model T graveyards, gradiometers can provide a rapid cost-effective survey.

ECHOTECH uses gradiometers for many environmental applications including:

•  Enhanced Phase I and Phase II Environmental Assessments
•  Locating buried dump sites and delineating landfills
•  Locating buried treasure, like refrigerators and car bodies
•  Finding abandoned well casings
•  Mapping underground metallic pipelines and USTs
•  Mapping geologic faults and lithologic contacts
•  Archaeological investigations, such as finding fire pits or burned ruins