Hemispheric Directional Reflectance

The hemispherical directional reflectance (HDR) of a surface is defined as the ratio of the total energy reflected into the subtending hemisphere to the energy incident on the surface from the direction Theta, Phi. The measured directional reflectance of a surface may be used to compute two important properties required for radiative heat transfer analysis, viz. the directional emittance and the solar absorptance.

A transmissive material may transmit electromagnetic radiation in one of the following two ways. First, as a collimated beam of light propagates through the material it may be scattered into a hemisphere of 2 p steradians upon exiting the material. Materials that exhibit this type of property ( Scattered Transmittance, Ts) are called translucent.

Secondly, if the transmitted beam is parallel to the incident beam across the width of the entire beam, the transmittance is referred to as Collimated Transmittance (Tc). Materials of this type are called transparent.Utilizing either the Cary 5000 UV/VIS/NIR reflectometer, the SOC-100 or SOC-400T IR reflectometer HDR or T measurements can be made from the UV out to the very long IR. Data is recorded directly to ascii text files on the PC and is importable into ExCel or other spreadsheet software.

Features & Benefits

  • HDR measurements can be made as a function of incident angle (8 to 80° from normal) vs. most competitors who are restricted to near-normal incidence.
  • HDR measurements in the IR utilize the SOC100 gold plated hemi-ellipse vs. competitors who utilize diffuse integrating spheres. This allows HDR measurements to be made far into the IR (out to 100um) as opposed to 12-15 microns for companies using just integrating spheres.
  • HDR measurements can also be partitioned into Diffuse (DDR) and Specular (SDR) components without altering the test set-up. Competitors must set up for measuring each component separately, if they can measure them at all.
  • Transmittance measurements (either Ts or Tc) can be made from normal incidence out to 60° from normal. Most competitors can only make normal incidence T measurements.

Applications

Aerospace

  • Verification of paint and coating
  • Determination of solar absorptance & thermal emittance

Energy and Solar Power

  • Determining the specularity (mirror-like qualities) of reflective components.
  • Mirror Qualification
  • Determination of solar absorptance & thermal emittance

Military

  • Military defense
  • Aircraft and ground target signature modeling

Remote Sensing

  • Simulator scene generation
  • Ground truth
  • Material mapping

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