8.15.6 Why Are Measurements Taken at Several Locations Instead of Just One?
RF fields are often nonuniform, but multiple measurements are not taken simply to produce a vaguely 'typical' value. The assessment objective and applicable method determine whether the assessor must locate a maximum, represent an occupied space, or calculate a prescribed spatial average.
Why Are Measurements Taken at Several Locations Instead of Just One?
A single reading can be valid only if it answers the defined assessment question. Where people move, the field varies, or the standard specifies averaging over a body-sized region, measurements at several locations are required.
RF Fields Are Spatially Variable
Distance, antenna pattern, reflections, diffraction, shielding, and multiple sources can produce local maxima and minima. Near an antenna, the field may also change rapidly with position because of the source geometry and field region.
The Survey Objective Determines the Sampling
A boundary survey may seek the highest accessible value. A workplace assessment may need to represent locations where a person can stand or move. A source-specific procedure may require a fixed grid, a volume scan, or measurements along a defined path.
People Occupy Space and Different Heights
Exposure is not confined to one point at waist or probe height. Depending on the applicable method, measurements may be needed at several heights or across the projected body space so that a local field maximum is not mistaken for a whole-body value—or overlooked entirely.
Near-Field and Far-Field Sampling Differ
Near-field variation may require finer spacing and careful control of probe perturbation. Far-field surveys may allow broader spatial sampling, but reflections, multiple sources, and directional antennas can still make one point unrepresentative.
The Applicable Method Controls the Average or Maximum
The assessor should not choose measurement points after seeing the results merely to obtain a favorable average. Locations, spacing, averaging, treatment of inaccessible points, and the method for selecting a maximum should be defined in advance or justified in the report.
Summary
Several locations are measured because RF fields and human occupancy extend through space. The correct pattern of measurements follows the assessment objective and applicable procedure, whether it seeks a maximum, a representative occupied region, or a prescribed spatial average.
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