solar reference reflected only measured (＋SIF) OCO-2 SIF window
move the SIF slider ↓
continuum radiance — solar line depth — observed line depth — retrieved SIF —

Show the retrieval, in one equation

In a narrow window the at-sensor radiance is reflected sunlight (which carries the sharp Fraunhofer structure) plus a spectrally smooth fluorescence term that does not:

L(λ) = (ρ/π)·E₀(λ)·T + F

Sample the measured radiance at a Fraunhofer line core (L₀) and in the nearby continuum (L_c). Let d = E₀(core) / E₀(continuum) be the line's true depth ratio, known from a high-resolution solar reference. The reflected term scales by d at the core but the additive F does not, so:

L_c = R_c + F L₀ = d·R_c + F

⇒ F = ( L₀ − d·L_c ) / ( 1 − d )

That is the "retrieved SIF" readout above — and it recovers the slider value exactly, whatever the reflectance or sun angle. The real OCO retrieval is the least-squares version of this over ~hundreds of wavelengths, with a low-order polynomial standing in for ρ/π·T.