Focal Plane

The instrument focal plane is a two dimensional array of light detectors. Each dimension contains 1024 detectors. Along one dimension, the detectors progressively vary in their sensitivity to spectral wavelength or color. Detectors along the other dimension acquire data that are representative of different spatial location. OCO employs all 1024 of the pixels in the spectral dimension but only 220 of the pixels in the spatial dimension. Of the 220 pixels that are used in the spatial dimension, only 160 are exposed to incoming light. The mission uses the remaining 'back-of-slit pixels' to ascertain the effect of other physical phenomena on the focal plane detectors. Of particular interest are thermal emissions generated by the instrument and stray light that may scatter outside the anticipated wavelength and spatial range.

Instrument software sums subsets of spatial pixels that record the same spectral color. Each of these sums is a spectral samples. In glint, nadir and target mode, the instrument downloads complete spectra that contain 1024 summed spectral samples for each of the three instrument channels. Radiometric calibration converts each of these spectral samples into a meaningful radiance. Spectral calibration assigns an accurate wavelength to each sample. Geometric calibration is used to ascertain a representative location on the Earth for each entire spectrum.