radiometrische

Radiometry, in German often rendered as Radiometrie, is the branch of metrology that deals with the measurement of electromagnetic radiation. It covers absolute and relative quantifications of radiant energy across wavelengths, with emphasis on the optical and infrared ranges used in science and industry. Radiometry is distinct from photometry, which concerns perceived brightness, and from radiative transfer theory, which models how radiation propagates through media.

Core quantities include radiant flux (phi, measured in watts), irradiance (E, W/m^2), radiance (L, W/(sr·m^2)), spectral radiance (L_lambda), radiant intensity (I, W/sr), and radiometric temperature. Measurements can be broadband or spectrally resolved, yielding radiometric data that characterize light sources, surfaces, and detectors.

Instruments used in radiometry include radiometers and spectroradiometers, pyranometers and pyrometers, and calibrated detectors such as photodiodes and bolometers. Calibration relies on traceability to international standards, often using blackbody radiators, integrating spheres, or calibrated lamps to ensure accuracy and comparability across instruments and laboratories.

Standards and practice are governed by international metrology organizations, with SI units applying to radiometric quantities (for example, irradiance in W/m^2, radiance in W/(sr·m^2), radiant flux in W). Uncertainty assessment and documentation of calibration history are central to credible measurements.

Applications of radiometry span remote sensing, astronomy, climate research, solar-energy assessment, material testing, and industrial process monitoring. Accurate conversion from sensor output to physical radiance or irradiance values enables meaningful interpretation and cross-instrument comparability.

Note on terminology: in geology, radiometric dating refers to dating techniques based on radioactive decay and is distinct from radiometric measurements of light energy.