A strip field telescopic spectroradiometer for gathering data along an entire narrow line of a two-dimensional field of view simultaneously. The optical axis of a concentric telescope is folded into the collimator axis of a concentric spectrograph by a spherical field mirror. The spectrograph includes an array of charge coupled devices as a detector at its final image surface.

Optical radiation generated by an auroral event is gathered by a fish-eye optical objective (12, 21, 22) and focussed by a telecentric lens (23) to a focal region where a two-passband filter (24) is located. The filter (24) passes two narrow bands of optical radiation, each band of which is centered on a specified wavelength. Rays in the two specified wavelengths are passed by a condenser lens (25) and a collimator lens (26) through an aperture stop in which a blocking filter (27) is located. The blocking filter (27) comprises two side-by-side half-size filters, each of which transmits a corresponding one and suppresses the other of the two specified wavelengths. A prism (28) diffracts rays each of the specified wavelengths by a different amount so that separated images in the two specified wavelengths are formed. A reimaging lens (29) relays the separate images to correspondingly different portions of a detector (30).

A spectral photometer emits light towards an object of interest, receives e light reflected back from the object of interest, and includes a timer or synchronizer operative for causing the spectral photometer to produce an output signal whose successive values correspond to the intensity of the spectrum derived from the object of interest at successive wavelengths. The spectral photometer output signal is applied to an oscilloscope for display of the thusly generated spectrum. The oscilloscope screen is provided with interpretation marks at characteristic points of the displayed spectrum, either by providing such marks on a transparent plate mounted in front of the screen, or by applying to the oscilloscope signals causing the scope itself to generate these marks. These marks may be curves shaped and located to be intersected by both maxima of an oxygenated-hemoglobin spectrum irrespective of the degree of oxygenation. The distance between the interpretation marks automatically provided can be automatically measured to generate an indication of their wavelength difference. The interpretation marks can also be in the form of a complete reference or comparison spectrum, selected out from a storage storing a plurality of such reference spectra, and applied as a signal to the scope to effect superimposed display of both the spectrum derived from the spectral photometer and the selected reference spectrum.

Apparatus and method are disclosed for obtaining from a two dimensional field of view containing numerous unresolved sources of irradiation of various unknown wavelengths, the wavelengths incident on objects in the field using significantly fewer pixels than required if a conventional imaging spectrometer were employed. A reflective telescope (10, 12) includes a concave reflective grating (14) after the secondary mirror (12). Undiffracted radiation from the grating forms an image on a first detector array (16). Diffracted radiation forms an image on a second detector array (18). The zero order images provide spatial identification of the objects and a set of wavelength independent reference locations from which the relative displacement of the diffracted radiation provides spectral information.

There is provided a photodetector wherein charging current to a photodiode is integrated to determine an amount of discharge due to conduction of photoelectric current through the photodiode and thereby to measure intensity of photon flux incident to the photodiode, so that linearity of light input intensity versus output voltage characteristics can be improved and dynamic range of the measurement can be extended.