The solar FUV-UV spectrometer flight experiment onboard high-altitude balloon

Abstract An experiment measuring the solar far-ultravoilet-ultraviolet (FUV-UV) irradiance with spectral-resolution bettern than 0.1 nm in the wavelength range between 170 to 400 nm, was carried out by the “HongHu-6” high-altitude balloon that flight to the bottom region of the near-space in September 2022. This experiment was based on the fact that solar FUV-UV penetrates through a complex cross-section window of the upper atmosphere, from outer space to the near space. The solar FUV-UV deposits energy in the upper atmosphere, which provides a key to answer scientific questions on the most important energy contributor to overall heating sources of the near space and how the near-space environment responds to solar activities. In the wavelength band between 150 to 210 nm, irradiance maps from active regions of the solar corona, the comparative small cross-section of molecular oxygen allows certain wavelengths of the band to arrive at altitudes between 20 and 30 km above the ground, indicating solar flares could directly impact the bottom region of the near space. The solar UV irradiance in wavelength 170–400 nm is absorbed by the upper atmosphere as a function of wavelength, and deposits energy vertically in the lower regions of the near space. This experiment provides precise experimental data to assess the top-down energy input to the lower regions of the near-space. The solar FUV-UV spectrometer (SUVS) is a compact instrument based on improved Roland circle optics to adapt to the “HongHu-6” balloon payload platform. In this paper, we introduce the scientific goals of the solar FUV-UV spectrum measurement experiment, information on the SUVS instrument, preflight calibration, and the first results from the flight data.