Daytime relapse of the mean radiant temperature based on the six-directional method under unobstructed solar radiation

Noémi Kántor, Tzu Ping Lin, Andreas Matzarakis

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28 Citations (Scopus)


This study contributes to the knowledge about the capabilities of the popular "six-directional method" describing the radiation fields outdoors. In Taiwan, measurements were carried out with three orthogonally placed net radiometers to determine the mean radiant temperature (T(mrt)). The short- and long-wave radiation flux densities from the six perpendicular directions were recorded in the daylight hours of 12 days. During unobstructed direct irradiation, a specific daytime relapse was found in the temporal course of the T(mrt) values referring to the reference shapes of a standing man and also of a sphere. This relapse can be related to the short-wave fluxes reaching the body from the lateral directions. Through deeper analysis, an instrumental shortcoming of the six-directional technique was discovered. The pyranometer pairs of the same net radiometer have a 10-15-min long "blind spot" when the sun beams are nearly perpendicular to them. The blind-spot period is supposed to be shorter with steeper solar azimuth curve on the daylight period. This means that the locations with lower geographical latitude, and the summertime measurements, are affected less by this instrumental problem. A methodological shortcoming of the six-directional technique was also demonstrated. Namely, the sum of the short-wave flux densities from the lateral directions is sensitive to the orientation of the radiometers, and therefore by deviating from the original directions, the T(mrt) decrease on clear sunny days will occur in different times and will be different in extent.

Original languageEnglish
Pages (from-to)1615-1625
Number of pages11
JournalInternational journal of biometeorology
Issue number7
Publication statusPublished - 2014 Sept 1

All Science Journal Classification (ASJC) codes

  • Ecology
  • Atmospheric Science
  • Health, Toxicology and Mutagenesis


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