High performance dual field of view spectroradiometer with novel input optics for, autonomous reflectance measurements over an extended spectral range

In field spectroscopy, estimation of the bi-directional reflectance from a target requires paired, near-simultaneous measurement of downwelling irradiance and upwelling target reflected radiance. The conventional approach to field reflectance measurement adopts a single spectroradiometer with single field of view and reflectance panel to take sequential reference (irradiance) and target (radiance) measurements. However, previous research has shown that significant uncertainties in such measurements are introduced with fluctuations in ambient lighting, poorly defined fields-of-view, and known anisotropies of reference reflectance panels. We present a new field spectroradiometer with novel dual field-of-view input optics for repetitive autonomous reflectance measurement across the V-SWIR spectral range (400 to 1700 nm). Attention to the optical design has minimised uncertainties in field reflectance measurement by ensuring a uniform and well defined field-of-view and high accuracy cosine corrected irradiance fore-optic across the full spectral range of the measurement. The system includes just one set of silicon and InGaAs detector array based spectrometers to provide the dual field-of-view operation, saving on cost, weight and power consumption. An internal microprocessor provides full stand alone control and automation.