Field spectroradiometers are widely used to measure reflectance factors in visible and near infra-red wavelengths. Recent developments in spaceborne and airborne instruments with multiple view angle (MVA) capabilities have resulted in a demand for ground measurements to support these missions.
Field spectroradiometers are widely used to measure reflectance factors in visible and near infra-red wavelengths. Recent developments in spaceborne and airborne instruments with multiple view angle (MVA) capabilities have resulted in a demand for ground measurements to support these missions. Lightweight portable spectroradiometers offer an appropriate means of collecting MVA spectral reflectance factor data because they are more easily manoeuvrable than conventional spectroradiometers, but their suitability and performance for this task are unknown.
This project used a miniature Ocean Optics USB2000 instrument for the measurement of MVA reflectance factors. The instrument was mounted on a lightweight A-frame, which was positioned on an azimuthal mount made from a bicycle wheel. Pegs fixed in the spoke mountings provided accurate azimuthal increments, and an electronic inclinometer provided accurate view zenith angles. The whole apparatus was accurately aligned in the solar principal plane by aligning the projected image of the Sun to a fixed mark on the frame.
The spectro-goniometer has been used in several student projects, and has also proved useful for research on soil surface modelling (Anderson et al., 2011). In this case, MVA hemispherical-conical reflectance factors (HCRF) were collected in situ from soil surfaces whose roughness was determined using a laser profiling survey. The results showed a significant negative relationship (R2 = 0.74; p<0.01) between directional reflectance factors measured at 870 nm in the forward-scattering region, and a soil structural measure derived from laser profiling data.
Reference
Anderson, K., Croft, H., Milton, E.J., & Kuhn, N.J. (published on-line 18 May 2011). A simple spectro-goniometer for collection of multiple view angle reflectance factors. Remote Sensing Letters, 3(2), 131-140. doi 10.1080/01431161.2010.543181