An apparatus comprising: a probe configured to be pushed into a subsurface soil environment; a transparent window mounted to a side of the probe; a broad-spectrum light source mounted within the probe and positioned such that when the light source is activated broad-spectrum light exits the window; a tunable optical filter mounted within the probe and positioned so as to receive, as an input, light reflected back through the window from the subsurface soil environment, wherein the filter comprises a plurality of settings at each of which the filter is configured to output light within a given wavelength range to the exclusion of other wavelength light ranges; and an imaging system disposed within the probe and configured to capture an image of the output light from the filter at each of the settings at a given depth of the probe in the subsurface soil environment.

A lighting device that emits illumination light from two or more angular directions onto a sample surface to be measured, an imaging optical lens, and a monochrome two-dimensional image sensor are provided. This configuration provides a method and an apparatus that take a two-dimensional image of the sample surface to be measured at each measurement wavelength and accurately measure multi-angle and spectral information on each of all pixels in the two-dimensional image in a short time. In particular, a multi-angle spectral imaging measurement method and apparatus that have improved accuracy and usefulness are provided.

A wideband device for the spectral analysis of a signal of interest includes a source designed to generate the signal of interest; an optical splitter element designed to spatially split the signal of interest into a first signal and a second signal; a first frequency-shifting optical cavity comprising a first frequency shifter designed to shift the optical frequency of the first signal by a first frequency f.sub.1 per round trip in the first cavity, the first cavity having a first trip time .sub.1; a second frequency-shifting optical cavity comprising a second frequency shifter designed to shift the optical frequency of the second signal by a second frequency f.sub.2 per round trip in the second cavity, the second cavity having a second trip time .sub.2; the first and the second optical cavity being designed such that a maximum number of round trips of the signal in the first and the second cavity is equal to predetermined N; a detector designed to coherently detect the first signal transmitted by the first cavity and the second signal transmitted by the second cavity and generate a photocurrent proportional to a luminous intensity detected by the detector, an analog low-pass filter designed to filter frequencies of the photocurrent that are lower than min (f.sub.1/2, f.sub.2/2) a processor configured to compute a square modulus of the photocurrent filtered by the low-pass filter, from which a temporal representation of frequency information of the signal of interest is determined.