= Uncollected scattering in a radiometric energy balance
\b[Uncollected scattering in a radiometric energy balance] is outgoing scattered radiation that falls outside the measured channels. Assigning every missing joule to <optical absorption> then overestimates the absorbed energy. The <radiometric energy balance> must count disjoint transmitted, reflected, scattered and absorbed terms for the same interval.
For an original collection model, stipulate $100\,\mathrm{\mu J}$ incident, $30\,\mathrm{\mu J}$ transmitted and $20\,\mathrm{\mu J}$ specularly reflected. A separate scattered-light receiver collects $q=10\,\mathrm{\mu J}$. If its calibrated capture fraction is $c=0.25$, the scattered energy is $q/c=40\,\mathrm{\mu J}$, leaving $10\,\mathrm{\mu J}$ absorbed. If all that is known is $0.20\leq c\leq0.50$, scattering can range from $20$ to $50\,\mathrm{\mu J}$ and absorption from $0$ to $30\,\mathrm{\mu J}$. One receiver reading cannot determine both the total scattering and its capture fraction.
The fraction $c$ is an energy fraction, not automatically the receiver's fraction of <solid angle>. Converting geometrical coverage into an energy fraction also needs the scattering distribution.
An <integrating sphere> provides broad angular collection through repeated diffuse reflection. Actual reflectance/transmittance arrangements depend on port geometry, baffles and whether the specular component is included. The primary guide describes excluding that component through a port and using baffles to prevent direct viewing of the illuminated sample.<Integrating Sphere Theory and Applications by Labsphere>[§§3.2–3.2.2, reflectance/transmittance and measurement geometry]{ref} The apparatus therefore needs its own response calibration; calling a receiver integrating does not establish perfect collection.
Back to article page
