Retrieval of Electron Density from Sub-Orbital Rocket Flight Data for Ionospheric E-Layer Detection

Kurzfassung

Sub-orbital flights of research rockets provide unique opportunities for studies in the near-Earth space environment. In the MAPHEUS program of DLR (German Aerospace Center) such flights are conducted for the main purpose of micro-gravity experiments (almost free of residual force). On Nov 11th, 2024 at 7h38 UTC MAPHEUS-15 was launched from Esrange space port (Sweden) to send a scientific payload to about 7 minutes of micro-gravity. During the flight, the payload passed altitudes between 80 km and 310 km at a rather constant attitude with angular rate of change below 1° per second. We use these conditions to study the ionospheric E-layer that can form at altitudes of 90-120 km. E-layer remote sensing is challenging as its contributions are often masked by stronger contributions of F-layer above (250-400 km).

Passing the E-layer during the rocket flight will induce changes of Total Electron Content (TEC) for the specific GNSS satellite links. The payload on the MAPHEUS rocket included different receiver setups that recorded GNSS data: navigation receivers (Septentrio AsteRx-m3 & mosaic-X5) and a remote sensing receiver (based on a Syntony GNSS bit-grabber). A geometry-free linear combination is applied to dual-frequency GNSS phase observations in order to retrieve uncalibrated TEC. The derived TEC gradient along the vertical part of the rocket flight resolves the electron density. Geo-reference of the results is obtained from the GNSS-based trajectory. Phase wind-up in the TEC retrievals has to be considered and corrected using attitude data from the on-board inertial navigation system. Unfortunately, radio interference over Northern Scandinavia strongly affected GPS L1 observations. We concentrate in the retrieval on three Galileo satellite links (results from L1-L5 combination) and on three GLONASS satellite links (results from L1-L2 combination).

In parallel to the rocket flight, the near-by EISCAT UHF incoherent scatter radar in Tromsø (Norway) was used to measure the ionospheric electron density over Northern Scandinavia. These data and the Neustrelitz Electron Density Model (NEDM) provide ancillary data for comparison. Profiles of TEC gradient and electron density are determined for the six GNSS links along the up-leg of the rocket flight. The profiles shows good agreement with the ancillary data for an altitude range of 80-250 km. They resolve the variability at E-layer altitudes (90-120 km). E-layer peaks in the local ionosphere are found towards southern and eastern direction from the rocket. In northern and western direction, the E-layer peaks are missing. The EISCAT measurements validate the E-layer presence. However, they lack the horizontal resolution. In future such findings can help to improve climatological models (like NEDM) that cannot yet resolve the local E-layer presence.