|Pic from epa.gov|
Examples of this method is the electromagnetic Turam. This method is less practical and observation area is limited by the size of the source is made. Another measurement technique is a passive measurement techniques, the use of electromagnetic fields from sources that are not intentionally raised around the area of observation. Electromagnetic waves like this comes from nature and from the low frequency transmitter (15-30 Khz) are used for the benefit of submarine navigation. This technique is more practical and has a wide range of observation areas. methode gpr.