of mathematical symbols used Symbol Description Units λ 0,X Emission/observation wavelength m r Range from instrument m z Vertical height above the instrument m c Speed of light in vacuum m s −1 H[x] Heaviside step function, which equals unity for x > 0 and zero otherwise — P (λ, r) Number of photons observed at wavelength λ from range r counts η(λ) Instrument detection efficiency at λ — σ(λ) S...

1. As in [l], 51 will denote a space of points P with a countably additive, non-negative measure y(E); all sets and functions considered will be 7-measurable; e will always denote a set of finite measure; E will be called purely infinite if y(E) = <» and eC-E implies y(e) =0. X is a length function if \(m) is defined, with O^X(m) fk °° , for every non-negative function u=u(P), and satisfies: (L...