9.5.4 Measurement And Computation

Assessment by measurement includes direct readings under actual operating conditions and readings that are subsequently adjusted, averaged, interpolated, or scaled to represent the required condition. Broadband instruments may be suitable for total exposure, whereas frequency-selective instruments are needed when individual sources or frequency-dependent contributions must be distinguished.

Measurement is often preferred for leakage, complex scattering, and reradiation where the field distribution is difficult to predict. The assessor must select instruments, probes, detection modes, frequency ranges, dynamic ranges, and survey procedures that are appropriate to the expected fields and modulation.

Assessment by computation ranges from simplified analytical formulas to full-wave numerical modeling. The choice depends on the field region, the quantity being evaluated, the geometry and propagation environment, the quality of the source data, and the limitations of the method. Computation is particularly useful for planning, for estimating inaccessible or hazardous locations, and for evaluating quantities that cannot be measured directly in a routine site survey.

The two approaches are complementary. Measurements should normally be checked against a simple calculation where practical, and computational results should be validated against measurements, analytical solutions, canonical models, or comparable assessments. A validated model may then extend an assessment to locations or operating conditions for which direct measurement is impractical.