Monitoring coastal sea level using reflected GNSS signals

A continuous monitoring of coastal sea level changes is important for human society since it is predicted that up to 332 million people in coastal and low-lying areas will be directly affected by flooding from sea level rise by the end of the 21st century. The traditional way to observe sea level is using tide gauges that give measurements relative to the Earth’s crust. However, in order to improve the understanding of the sea level change processes it is necessary to separate the measurements into land surface height changes and sea surface height changes. These measurements should then be relative to a global reference frame. This can be done with satellite techniques, and thus a GNSS-based tide gauge is proposed. The GNSS-based tide gauge makes use of both GNSS signals that are directly received and GNSS signals that are reflected from the sea surface. An experimental installation at the Onsala Space Observatory (OSO) shows that the reflected GNSS signals have only about 3 dB less signal-to-noise-ratio than the directly received GNSS signals. Furthermore, a comparison of local sea level observations from the GNSS-based tide gauge with two stilling well gauges, located approximately 18 km and 33 km away from OSO, gives a pairwise root-mean-square agreement on the order of 4 cm. This indicates that the GNSS-based tide gauge gives valuable results for sea level monitoring

Sea Level Monitoring Using a GNSS-Based Tide Gauge

A continuous monitoring of sea level changes is important for human society since more than 50% of the world's population live within 60 km of the coast. Sea level is traditionally observed with tide gauges that give measurements relative to the Earth's crust. To improve the understanding of sea level changes it is necessary to perform measurements with respect to the Earth's center of gravity. This can be done with satellite techniques, and thus a GNSS-based tide gauge is proposed that makes use of both GNSS-signals that are directly received and that are reflected on the sea surface. A test installation at the Onsala Space Observatory shows that the reflected GNSS-signals have only about 3 dB less signal-to-noise-ratio than the directly received GNSS-signals. A comparison of relative sea level observations from the GNSS-based tide gauge to traditional tide gauges gives an RMS-agreement on the order of 4 cm

High-rate local sea level monitoring with a GNSS-based tide gauge

We present first results from the analysis of high-rate observations with a GNSS-based tide gauge at the Onsala Space Observatory. The goal is to determine local sea level with high temporal resolution. The GNSS-based tide gauge makes use of right-hand circular polarized GNSS signals that are directly received and left-hand circular polarized GNSS signals that are reflected from the sea surface. An experimental setup of the GNSS-based tide gauge was operated in the spring of 2010 and data were recorded with a sampling rate of 20 Hz. We analyzed data decimated to 1 Hz using different temporal resolution between 5 and 240 seconds, and the resulting time series of local sea level were compared to each other and to results from two stilling well gauges. The comparison with the data from the stilling well gauges shows a common trend. The comparison of the results from analyses with different temporal resolution show consistent results. There is also an indication that the GNSS-based tide gauge might be able to give information on the sea surface state

Laboratory diagnosis of Lyme neuroborreliosis: a comparison of three CSF anti-Borrelia antibody assays

The diagnosis of Lyme neuroborreliosis (LNB) requires the detection of intrathecal synthesis of Borrelia-specific antibodies, but in very early disease, the sensitivity may be low. We compared the performance of the second-generation IDEIA Lyme Neuroborreliosis test (Oxoid), based on purified native flagellum antigen, with two newly developed tests based on several recombinant antigens for the diagnosis of LNB. Patients investigated for LNB during 2003 through 2007 were included (n = 175); 52 with definite LNB, four with possible LNB and 119 non-LNB patients. Serum and cerebrospinal fluid (CSF) were analysed with the IDEIA Lyme Neuroborreliosis (Oxoid), VIDAS Lyme IgG (bioMérieux) and recomBead Borrelia IgM and IgG (Mikrogen) assays. Intrathecal antibody indices (AIs) were calculated according to the manufacturers’ protocols. The IDEIA test performed with an overall sensitivity (IgM and IgG AIs taken together) of 88 % and a specificity of 99 %. The VIDAS test showed a sensitivity of 86 % and a specificity of 97 %. An overall sensitivity of 100 % and a specificity of 97 % were achieved by the recomBead test. We conclude that the three assays performed equally well regarding specificity, but our data suggest an improved diagnostic sensitivity with the recomBead Borrelia test

Long-term changes in acidification and recovery at nine calibrated catchments in Norway, Sweden and Finland

International agreements to reduce the emissions of acidifying pollutants have resulted in major changes in deposition of sulphur and nitrogen in southern Scandinavia over the past 25 years. Long-term monitoring of deposition and run-off chemistry over the past 12-25 years at nine small calibrated catchments in Finland, Norway and Sweden provide the basis for analysis of trends with special attention to recovery in response to decreased sulphur and nitrogen deposition in the 1980s and 1990s. During the 1980s and 1990s sulphate deposition in the region decreased by 30 to 60%, whereas inorganic nitrogen deposition showed very little change until the mid-1990s. Deposition of non-marine base cations (especially calcium) declined in the 1990s most markedly in southern Finland. Run-off response to these changes in deposition has been rapid and clear at the nine catchments. Sulphate and base cations (mostly calcium) concentrations declined and acid neutralising capacity increased. Occasional years with unusually high inputs of sea-salt confound the general trends. Trends at all the catchments show the same general picture as that from small lakes in Scandinavia and in acid-sensitive waters elsewhere in Europe.</p> <p style='line-height: 20px;'><b>Keywords: </b>acidification, recovery, Scandinavia, catchment, trend analysi

Analog Computer Research

Contains reports on three research projects

Symmetry of two terminal, non-linear electric conduction

The well-established symmetry relations for linear transport phenomena can not, in general, be applied in the non-linear regime. Here we propose a set of symmetry relations with respect to bias voltage and magnetic field for the non-linear conductance of two-terminal electric conductors. We experimentally confirm these relations using phase-coherent, semiconductor quantum dots.Comment: 4 pages, 4 figure

Long-term changes in acidification and recovery at nine calibrated catchments in Norway, Sweden and Finland

International audienceInternational agreements to reduce the emissions of acidifying pollutants have resulted in major changes in deposition of sulphur and nitrogen in southern Scandinavia over the past 25 years. Long-term monitoring of deposition and run-off chemistry over the past 12-25 years at nine small calibrated catchments in Finland, Norway and Sweden provide the basis for analysis of trends with special attention to recovery in response to decreased sulphur and nitrogen deposition in the 1980s and 1990s. During the 1980s and 1990s sulphate deposition in the region decreased by 30 to 60%, whereas inorganic nitrogen deposition showed very little change until the mid-1990s. Deposition of non-marine base cations (especially calcium) declined in the 1990s most markedly in southern Finland. Run-off response to these changes in deposition has been rapid and clear at the nine catchments. Sulphate and base cations (mostly calcium) concentrations declined and acid neutralising capacity increased. Occasional years with unusually high inputs of sea-salt confound the general trends. Trends at all the catchments show the same general picture as that from small lakes in Scandinavia and in acid-sensitive waters elsewhere in Europe. Keywords: acidification, recovery, Scandinavia, catchment, trend analysi