An electromagnetic (em) site survey is a systematic, documented investigation of the amplitudes of radio-frequency (rf) em fields found at one or more locations with respect to frequency, time, and position. Although these ambient em fields may have intrinsic interest, more commonly they will be regarded as radio noise or simply as interference. This noise level establishes the minimum useable signal strength for satisfactory service. Furthermore, it often dictates equipment design decisions intended to reduce any adverse effects of this interference on system performance. Survey sites of interest may be at virtually any indoor or outdoor location. Radio-frequency sampling may involve either airborne or surface platforms.