Absolutely calibrated, spectrally resolved infrared radiance: A benchmark measurement for climate monitoring.

摘要

A new experiment to observe absolutely calibrated, spectrally resolved infrared terrestrial radiance from a satellite in low earth orbit is described and analyzed. The proposed instrument is designed to meet the particular requirements necessary for monitoring the climate of the earth. Discriminating the small climate changes predicted by model simulations from climate variability requires an instrument with high measurement accuracy, as demonstrated by testing against fundamental measurement standards. The characteristic of high accuracy, reproducible by any experimenter, at any time, defines the category of the benchmark measurement.; Two small Fourier transform spectrometers (FTSs), each with its own calibration standards and electronics, comprise the instrument design. The spectrometers are aligned to view the same footprint on the earth's surface during orbit. Each FTS is capable of making two simultaneous measurements of the same scene. The redundancy of these measurements is part of a calibration strategy designed to provide independent verification of the measurement accuracy during orbit. The thesis surveys the experimental foundations that demonstrate that the instrument design is capable of achieving the required accuracy. The design makes innovative use of existing technology to achieve better instrument performance than previous comparable infrared earth observing experiments.; A numerical model of the instrument is developed to simulate the instrument performance. This model provides a quantitative relationship between the parameters of the instrument subsystems and the radiometric performance as a function of observed radiant intensity and frequency. The measurement accuracy is found to be strongly dependent on observation conditions and details of the instrument design.; A comprehensive plan of experiments is required to properly verify the instrument performance against established metrological standards. This thesis details an appropriate plan, including laboratory experiments, instrument prototyping and deployment on a flight testing platform. The laboratory experiments constrain all significant sources of systematic error within the instrument. The instrument prototype can evaluate a range of infrared standards, providing a necessary link to the wider community of climate researchers. The flight testing will replicate important aspects of a satellite mission, offering a rigorous test of the instrumental and calibration concept.