Optical Design of the Multi-spectral Limb Photometer for the Waves Explorer (NASA Midex)

摘要

The Mesosphere Lower Thermosphere (MLT) is the most inaccessible and least understood region of the Earth's atmosphere. AtmophericGravity waves play a substantial role in the dominant processes of energy and momentum transport in this region. The WAVES mission (proposed as a NASA Midex) will be the first mission dedicated to studying atmospheric gravity waves, their sources and how they affect the MLT. An instrument, the Multi-spectral Limb Photometer (MLP) will make limb viewing observations to support the WAVES mission. This instrument will observe airglow variations caused by longer wavelength waves passing through the region and will make measurements of temperature and composition in various regions in the MLT. The MLP instrument images the earth atmosphere in limb view in the orbital plane. The resolution in the vertical dimension (altitude) is about 2 km. In the horizontal dimension the MLP collects an averaged intensity over a region of 250 km in width. Vertical imaging vs. horizontal non imaging is realized by cylindrical lenses. The stray light baffling design is specially adapted to allow for day and night observation. The MLP is a single optical channel instrument using a CCD sensor. We propose to use a grille filter spectrometer consisting of a telecentric imager in which a set of narrow vertical strip interference filters are included. The image of the limb is projected onto these strip filters preserving the imaging qualities (vertical dimension). With the interference filter it is possible to realize a spectral function fitting with the multiple spectral bandpass of the emitting species. The full wavelength range is 555-892 nm where about 10 emission lines are to be resolved. The instrument sensitivity is adapted to the intensity and spectral spacing (with respect to neighboring emission lines) of each line: spatial and spectral width of each interference filter strip are independently optimized. This is unique compared to spectrograph using grating technology where spectral resolution and sensitivity are undesirably coupled through the.slit width. Finally, the CCD sensor captures a composite image where columns depict the vertical limb imaging and rows indicate the spectral signature.