The Near-Space Wind and Temperature Sensing Interferometer: Forward Model and Measurement Simulation

Abstract

Wind and temperature observation in near space has been playing an increasingly important role in atmospheric physics and space science. This paper reports on the near-space wind and temperature sensing interferometer (NWTSI), which employs a wide-angle Michelson interferometer to observe O2(a1Δg) dayglow near 1.27 μm from a limb-viewing satellite, and presents the instrument modeling and observation simulations from the stratosphere to the mesosphere and lower thermosphere. The characteristics of atmospheric limb-radiance spectra and line selection rules are described. The observational strategy of using two sets of three emission lines with a line-strength difference of one order of magnitude is proved to be suitable for extending altitude coverage. The forward modeling and measurement simulation of the expected NWTSI observations are provided, and the measurement uncertainty of the wind and temperature is discussed. The signal-to-noise ratio (SNR) and the limb-view weight work together to affect the precision of the wind and temperature measurements. The simulated results indicate a wind measurement precision of 1 to 3 m/s and a temperature precision of 1 to 3 K over an altitude range from 40 to 80 km, which meets the observing requirement in measurement precision for near-space detection.

Effect of OH emission on the temperature and wind measurements derived from limb-viewing observations of the 1.27 µm O2 dayglow

“…The Doppler shift of the emission line due to the movement of the atmosphere is measured as a phase shift of the Michelson interferometer, and accurate temperature measurement is obtained from the integrated absorbance ratio of two isolated emission lines (He et al, 2019). However, the intensity variation caused by Doppler shift or temperature change is very small.…”

“…The NWTSI, using the combination of a "strong" emission lines group and a "weak" group of the O 2 (a 1 g ) airglow, is a limb-viewing satellite instrument (He et al, 2019). The schematic drawing of the limb-imaging geometry and instrument concept is shown in Fig.…”

“…Large optical path difference (OPD) and field widening involve using 12.240 cm LaKN12 glass and 11.070 cm BK7 glass with corresponding refractive indices 1.733 and 1.516 in the two arms of the interferometer. The OPD between the paths of the two arms of the Michelson interferometer for normal incident can be found from 0 = 2 (n 1 L 1 − n 2 L 2 ) (He et al, 2019), which corresponds to a value of 7.35 cm. In order to avoid errors caused by intensity variations during measurements, the four interferogram samples are taken simultaneously rather than sequentially by dividing one Michelson mirror into four equal segments so the steps are coated permanently onto the mirror.…”

“…The infrared atmospheric band emission (a 1 g → X 3 g ) of O 2 observed near the wavelength of 1.27 µm has remarkable advantages in atmospheric remote sensing due to its bright signal and extended altitude coverage (Mlynczak et al, 2007). The enormous success of the Wind Imaging Inter-ferometer (WINDII) (Shepherd et al, 2012), high-resolution Doppler imager (HRDI) (Ortland et al, 1996) and TIMED Doppler interferometer (TIDI) (Killeen et al, 2006), which measured winds in the upper mesosphere and lower thermosphere using Doppler shifts in visible airglow emission lines, stimulates interest in measuring wind and temperature from limb-viewing satellites using the 1.27 µm dayglow (Wu et al, 2018). Ward et al (2001) designed a high-sensitivity interferometer, WAMI, to provide simultaneous measurements of horizontal wind and rotational temperature by using the combination of a "strong" emission line group and a "weak" group of the O 2 (a 1 g ) airglow.…”

“…In recent years, measuring wind and temperature in the planetary atmosphere of Mars and Venus, for example, was also proposed by using a 1.27 µm band emission of the electronically excited O 2 (a 1 g ) state (Ward et al, 2002;Zhang et al, 2017). Closely following the WAMI concept, we recently proposed a near-space wind and temperature sensing interferometer (NWTSI) for simultaneous measurements of the atmospheric wind and temperature in the near-space from the limb-viewing satellite by observing the O 2 (a 1 g ) dayglow near 1.27 µm (He et al, 2019). The strategy of choosing two sets of three emission lines adopted by WAMI, MIMI and NWTSI is quite ingenious.…”