3. Different contributors to night-time illuminance

3.1 Introduction

On the surface of the Earth, at night and in the open air, there is no such thing as total darkness. Several contributors are superimposed, giving the different lighting conditions encountered at night. Knowledge of these, and of their variability, is essential to assess the ultimate signal-to-noise ratio that can be achieved. This analysis need not be limited to the Visible spectral range, as technological capabilities and spectral illumination conditions may give an advantage to the exploitation of infrared spectral bands between 1 and 2.5 µm (IR1 band or SWIR: Short Wave Infra-Red).

The various contributors to the E ₁ illumination of the night scenes reviewed are as follows:

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