Abstract: Techniques to improve the measurement of electromagnetic fields based on noise cancellation are disclosed. Sensors placed at the earth's surface measure electromagnetic fields emanating from within the earth, and/or perform electromagnetic telemetry. In one embodiment, signal processing techniques are applied to the acquired signals, either in real time or near real time to reduce or cancel the noise to enable the signal of interest to be measured. In another embodiment, the location of the plurality of sensors is judiciously chosen to improve the measurement of the signal of interest.