MISE: A multiwavelength imaging spectrograph using echelle grating for daytime optical aeronomy investigations

A high-spectral resolution multiwavelength imaging slit spectrograph using echelle grating (MISE) that is capable of measuring daytime optical emissions at multiple wavelengths simultaneously over a large (140°) field-of-view is presented. Optical emissions during daytime (either dayglow or daytime aurora) are buried in the strong daytime solar scattered background continuum and therefore very high spectral resolution measurements are required to obtain their contributions. MISE measures the emission intensities of OI 557.7 nm, OI 630.0 nm, and OI 777.4 nm that originate in the upper atmosphere. The dispersion achieved by the spectrograph at these three spectral regions, respectively, is 0.004, 0.0049, and 0.0059 nm pixel−1. By using an echelle grating as the dispersing element, multiple spectral regions of aeronomic interest are made to fall in the same diffraction angle range so that rotation of grating is avoided. This instrument is immune to ambient temperature fluctuations and vibrations and is suitable for long and continuous field operations. The spectral and intensity calibration of this instrument along with the data analysis methodology are discussed. Sample data of emission intensities from all the three wavelengths mentioned above for a couple of days obtained from Hyderabad (17°N, 80°E; 8.7°N Mag. Lat.) are presented which show a good similarity when compared with those of empirical and photochemical model results. The OI 557.7 nm daytime emissions are measured sparsely from ground-based techniques and ground-based OI 777.4 nm daytime emissions from ground are presented for the first time, to the best of our knowledge. The variability is highlighted and the potential of such measurements to derive information on vertical coupling of atmospheric regions and wave dynamics during daytime are discussed.

► High-spectral resolution multiwavelength imaging spectrograph (MISE) is presented. ► MISE measures daytime optical emissions at multi-wavelengths over a large FOV. ► Emissions measured are 557, 630 and 777 nm that originate in the upper atmosphere. ► Sample data show good similarity with empirical and photochemical model results. ► Potential tool for studies on coupling of atmospheres and wave dynamics during daytime.