The O-STATES Sounding Rocket Project - First Results

Abstract:

In October 2015, the sounding rocket project O-STATES was conducted from Esrange Space Center (67.9°N, 21.1°E) in northern Sweden. The acronym O-STATES stands for “Oxygen Species and Thermospheric Airglow in The Earth´s Sky” and the basic idea is that comprehensive information on the composition, specifically atomic oxygen in the ground state O and first excited state O(¹D), and temperature of the lower thermosphere can be obtained from a limited set of optical measurements. Starting point for the analysis are daytime measurements of the O₂(b¹∑_g⁺ − X³∑_g⁻) Atmospheric Band system in the spectral region 755-780 nm and the O(¹D-³P) Red Line at 630 nm. In the daytime lower thermosphere O(¹D) is produced by O₂ photolysis and the excited O₂(b) state is mainly produced by energy transfer from O(¹D) to the O₂(X) ground state. In addition to O₂ photolysis, both electron impact on O and dissociative recombination of O₂⁺ are major sources of O(¹D) in the thermosphere.

Recent laboratory studies at SRI demonstrate that the O₂(b) production populates the vibrational levels v=1 and v=0 in a ratio of ~4. While O₂(b, v=0) is essentially unquenched, O₂(b, v=1) is subject to collisional quenching that is dominated by O at altitudes above 160 km. Hence, the ratio of the Atmospheric Band emission from O₂(b, v=1) and O₂(b, v=0) is a measure of the O density. Finally, the spectral shape of the O₂ Atmospheric Band is temperature dependent and spectrally resolved measurements of the Atmospheric Bands thus provide a measure of atmospheric temperature.

This O₂ Atmospheric Band analysis has been advocated as a technique for thermospheric remote sensing under the name Global Oxygen and Temperature (GOAT) Mapping. With O-STATES we want to characterize the GOAT technique by in-situ analysis of the O₂ Atmospheric Band airglow and the underlying excitation mechanisms. By performing this dayglow analysis from a rocket payload, detailed local altitude profiles of the relevant emissions and interacting species can be obtained. In particular, the optical measurements are combined with independent detection of O and O₂ (resonance fluorescence and electrochemical detection) as well as measurements of electron and ion densities. Here we describe the O-STATES project and present first results.