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- ItemGeophysical investigation of a freshwater lens on the island of Langeoog, Germany – Insights from combined HEM, TEM and MRS data(Amsterdam [u.a.] : Elsevier Science, 2017) Costabel, Stephan; Siemon, Bernhard; Houben, Georg; Günther, ThomasA multi-method geophysical survey, including helicopter-borne electromagnetics (HEM), transient electromagnetics (TEM), and magnetic resonance sounding (MRS), was conducted to investigate a freshwater lens on the North Sea island of Langeoog, Germany. The HEM survey covers the entire island and gives an overview of the extent of three freshwater lenses that reach depths of up to 45 m. Ground-based TEM and MRS were conducted particularly on the managed western lens to verify the HEM results and to complement the lithological information from existing boreholes. The results of HEM and TEM are in good agreement. Salt- and freshwater-bearing sediments can, as expected, clearly be distinguished due to their individual resistivity ranges. In the resistivity data, a large transition zone between fresh- and saltwater with a thickness of up to 20 m is identified, the existence of which is verified by borehole logging and sampling. Regarding lithological characterisation of the subsurface, the MRS method provides more accurate and reliable results than HEM and TEM. Using a lithological index derived from MRS water content and relaxation time, thin aquitard structures as well as fine and coarse sand aquifers can be distinguished. Complementing the existing borehole data with the lithology information estimated from MRS, we generate a map showing the occurrence of aquitard structures, which significantly improves the hydrogeological model of the island. Moreover, we demonstrate that the estimates of groundwater conductivity in the sand aquifers from geophysical data are in agreement with the fluid conductivity measured in the boreholes.
- ItemMeteor radar observations of mesopause region long-period temperature oscillations(Göttingen : Copernicus, 2016) Jacobi, Ch.; Samtleben, N.; Stober, G.Meteor radar observations of mesosphere/lower thermosphere (MLT) daily temperatures have been performed at Collm, Germany since August 2004. The data have been analyzed with respect to long-period oscillations at time scales of 2–30 days. The results reveal that oscillations with periods of up to 6 days are more frequently observed during summer, while those with longer periods have larger amplitudes during winter. The oscillations may be considered as the signature of planetary waves. The results are compared with analyses from radar wind measurements. Moreover, the temperature oscillations show considerable year-to-year variability. In particular, amplitudes of the quasi 5-day oscillation have increased during the last decade, and the quasi 10-day oscillations are larger if the equatorial stratospheric winds are eastward.
- ItemValidation of the radiation pattern of the VHF MST radar MAARSY by scattering off a sounding rocket's payload(Göttingen : Copernicus Publications, 2015) Renkwitz, T.; Schult, C.; Latteck, R.; Stober, G.The Middle Atmosphere Alomar Radar System (MAARSY) is a monostatic radar with an active phased array antenna designed for studies of phenomena in the mesosphere and lower thermosphere. Its design, in particular the flexible beam forming and steering capability, makes it a powerful instrument to perform observations with high angular and temporal resolution. For the configuration and analysis of experiments carried out with the radar it is essential to have knowledge of the actual radiation pattern. Therefore, during the time since the radar was put into operation various active and passive experiments have been performed to gain knowledge of the radiation pattern. With these experiments the beam pointing accuracy, the beam width and phase distribution of the antenna array were investigated. Here, the use of a sounding rocket and its payload as a radar target is described which was launched in the proximity of the radar. The analysis of these observations allows the detailed investigation of the two-way radiation pattern for different antenna array sizes and beam pointing positions.
- ItemD region observations by VHF and HF radars during a rocket campaign at Andøya dedicated to investigations of PMWE(Göttingen : Copernicus Publications, 2019) Latteck, Ralph; Renkwitz, Toralf; Strelnikov, BorisIn April 2018 the PMWE1 sounding rocket campaign was conducted at the Andøya Space Center involving coordinated measurements with rockets and ground instruments to measure parameters relevant for testing of the existing theories of polar mesospheric winter echo (PMWE) formation. The Middle Atmosphere Alomar Radar System (MAARSY) was operated to detect PMWE with multiple beam directions to detect favorable launch conditions. A dedicated experiment configuration with five different beam positions was used to point the radar beam along the planned trajectory of the payload. This special radar experiment allowed to obtain basic information about the spatial structure of the PMWE and its dynamical behavior around the flight of the two rockets. PMWE with signal strengths between 10-17 and 1015 m1 have been observed by MAARSY during the whole campaign period, starting with a moderate occurrence at the beginning which decreased towards the end of the campaign. Furthermore real common-volume observations by rocket instruments and radar soundings have been carried out at PMWE altitudes on up-leg and down-leg of the rocket flights. The Saura MF radar was operated during both flights probing the mesosphere with a multiple beam scan experiment to derive horizontal winds and electron density profiles. The obtained PMWE characteristics as signal strength and spectral width of the received radar signals as well as estimated horizontal winds and electron densities are presented with particular emphasis to the launch times of the sounding rockets. © Author(s) 2019.
- ItemInterpolation algorithm for asynchronous ADC-data(Göttingen : Copernicus Publications, 2017) Bramburger, Stefan; Zinke, Benny; Killat, DirkThis paper presents a modified interpolation algorithm for signals with variable data rate from asynchronous ADCs. The Adaptive weights Conjugate gradient Toeplitz matrix (ACT) algorithm is extended to operate with a continuous data stream. An additional preprocessing of data with constant and linear sections and a weighted overlap of step-by-step into spectral domain transformed signals improve the reconstruction of the asycnhronous ADC signal. The interpolation method can be used if asynchronous ADC data is fed into synchronous digital signal processing.