Airborne Electromagnetics as a Method for Arctic Wide Sea Ice Thickness Retrieval

The purpose of this thesis was to mount Airborne Electromagnetic (AEM) sensors for sea-ice thickness retrieval under the wings of long range airplanes and to quantify existing noise sources. Another aim was to determine and to characterise thickness distribution functions of several regions in the central Arctic. The accuracy of a prototype aeroplane EM system was found to be /- 0.5 m. The accuracy was reduced due to wing flexure, which produces noise of equal amplitude as the wanted ocean signal. Other noise sources are inductive ocean-aeroplane coupling and pitch which may disturb the measurements by another 10 percent of the signal. It is suggested to take the 90° out of phase response signal, since wing flexure noise mainly is 180° out of phase. On transects in the central Arctic mean thickness standard errors as low as 0.2 m could be obtained for 10 km long profiles in less deformed ice independently of the age of the ice regime. In a deformed multi year ice (MYI) regime standard errors of 0.2 m were obtained on transects as long as 100 km. These results show that a reduction of central Arctic mean sea-ice thickness by 1.8 between 1991 and 2007 was higher than typical spatial variability

Performance limitations of subband adaptive filters

In this paper, we evaluate the performance limitations of subband adaptive filters in terms of achievable final error terms. The limiting factors are the aliasing level in the subbands, which poses a distortion and thus presents a lower bound for the minimum mean squared error in each subband, and the distortion function of the overall filter bank, which in a system identification setup restricts the accuracy of the equivalent fullband model. Using a generalized DFT modulated filter bank for the subband decomposition, both errors can be stated in terms of the underlying prototype filter. If a source model for coloured input signals is available, it is also possible to calculate the power spectral densities in both subbands and reconstructed fullband. The predicted limits of error quantities compare favourably with simulations presented

Rare dental anomalies in two sympatric European bat species (Pipistrellus spp.)

Over the past twenty years, we documented striking non-lethal anomalies in the dentition of the common pipistrelle (Pipistrellus pipistrellus) during field work in various parts of Germany. In 2019 we got knowledge of two bat nurslings (P. pipistrellus, P. pygmaeus) from the Rhine-Main area (Hesse, Germany) with ultimately fatal dental anomalies. The aberrations were documented with high-resolution X-ray techniques. Here we discuss our results in the context of published, but mostly minor and obvious non-lethal teeth anomalies in bats