Which term defines the fraction of solar radiation reflected by a surface?

• A. Albedo
• B. Emissivity
• C. Absorptivity
• D. Transmissivity

Answer: (A)

Albedo is the fraction of incoming solar radiation that is reflected by a surface. It’s a value that ranges from 0 to 1 (0% to 100%), with bright surfaces like fresh snow or light-colored ice reflecting most light, and dark surfaces like asphalt absorbing most of it and having a low albedo. In energy terms, the incident radiation is partitioned into reflected, absorbed, and possibly transmitted parts; for most land surfaces, transmission is negligible, so albedo essentially represents the portion not absorbed. Emissivity describes how well a surface emits infrared energy, not how much sunlight it reflects. Absorptivity is the portion absorbed (and, for opaque surfaces, is closely related to 1 minus reflectivity), while transmissivity is the portion that passes through the material, which is minimal for solid surfaces on the Earth. Therefore, the term defined as the fraction of solar radiation reflected is albedo.