1.
2.
Löfgren, Johan, 1983, et al.
(författare)
Sea Level Monitoring Using a GNSS-Based Tide Gauge
2009
Ingår i: 2nd International Colloquium - Scientific and Fundamental Aspects of the Galileo Programme, 14 - 16 October 2009, Padua, Italy.
Konferensbidrag (övrigt vetenskapligt/konstnärligt) abstract
Global climate change is believed to result in the melting of large masses of ice in Polar Regions, bringing freshwater into the ocean, and changing the sea level. The traditional way to measure the sea level, by tide gauges, results in measurements relative to the Earth’s crust. However, in order to fully understand the sea level changes, absolute measurements (change in sea level in relation to the Earth’s center of gravity) are necessary, in particular in regions affected by post-glacial uplift, e.g., Fennoscandia. Satellite techniques, e.g., GNSS can be used to determine the motion of the Earth’s crust in relation to the center of gravity. By measuring reflected GNSS-signals from the sea surface, information of the sea level change can be obtained. Therefore a GNSS-based tide gauge is proposed.The proposed GNSS-based tide gauge installation consists of two antennas, one zenith looking right hand circular polarized (RHCP) and one nadir looking left hand circular polarized (LHCP), mounted back-to-back on a beam over the ocean. The RHCP antenna receives the GNSS-signals directly, whereas the LHCP antenna receives the signals reflected from the sea surface. Because of the additional path delay of the reflected signal, the LHCP antenna will appear to be a virtual GNSS-antenna located below the sea surface. When the sea level changes, the path delay of the reflected signal changes, thus the LHCP antenna will appear to be in a new position. The vertical position change corresponds to twice the sea level change, and therefore monitors sea level changes.Multiple satellites with different elevation and azimuth angles are observed each epoch and will give rise to reflected signals with different incidence angles from different directions. This means that the estimated sea level change can not be considered to originate from one specific point on the surface, but rather represents the change of an average surface formed by the reflection points.An experimental setup was installed in December 2008 over the ocean at Onsala Space Observatory (OSO) at the west coast of Sweden. Data was collected during three days using two Leica GRX1200+ receivers (one for the direct and one for the reflected signal). The receivers recorded 40 hours of continuous 20Hz data. The signal-to-noise ratio (SNR) as determined by the two receivers was used as a first data quality check. On average the SNR difference between the directly received and the reflected signals was less than 3dB.The data was analyzed using an in-house developed software in MATLAB. Solutions were made using L1 phase delays for relative positioning. Two approaches to estimate the vertical difference between the RHCP and the LHCP antenna were tested: hourly estimates of the vertical difference, and high-rate estimates of the vertical difference. For the hourly estimates 40 hours of continuous 1Hz data (reduced for faster processing using the TEQC software) were used. Each solution was made using 20 minutes of data every full hour, solving for differences in the local vertical components together with receiver clock and phase ambiguities differences for each epoch.The solution for the high-rate vertical component was made in two steps. First, the phase ambiguity differences were determined. This was done using equally distributed short intervals of ~1 second (21 epochs) from ~20 minutes of 20Hz data, solving for difference in phase ambiguities and receiver clocks every epoch together with differences in vertical coordinate for each short interval. The processing was done based on the assumptions that the sea surface does not change significantly during ~1 second and that the satellite geometry changes considerably in ~20 minutes. Second, the differences in phase ambiguities were rounded to the nearest integer and inserted as known values for a reprocessing of the 20Hz data. In this reprocessing the receiver clock parameters were estimated every epoch and the vertical coordinate difference with different time resolutions (e.g. 0.05s, 1s, 30s).The resulting time-series for the sea level change from the hourly solutions were compared to data from two traditional tide gauges operated by the Swedish Meteorological and Hydrological Institute at Ringhals and Göteborg, about 18 km south of and 33 km north of OSO, respectively. The GNSS-derived sea level change resembles reasonably well the independently observed sea level change. This indicates that the GNSS-tide gauge gives valuable results for sea level monitoring. Furthermore, the use of the high-rate GNSS-receivers additionally allows a flexible time resolution for sea level monitoring.
3.
Carn, Simon, et al.
(författare)
Daily monitoring of Ecuadorian volcanic degassing from space
2008
Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273. ; 176:1, s. 141-150
Tidskriftsartikel (refereegranskat) abstract
We present daily measurements of sulfur dioxide (SO2) emissions from active volcanoes in Ecuador and southern Colombia between September 2004 and September 2006, derived from the Ozone Monitoring Instrument (OMI) on NASA's EOS/Aura satellite. OMI is an ultraviolet/visible spectrometer with an unprecedented combination of spatial and spectral resolution, and global coverage, that permits daily measurements of passive volcanic degassing from space. We use non-interactive processing methods to automatically extract daily SO2 burdens and information on SO2 sources from the OMI datastream. Maps of monthly average SO2 vertical columns retrieved by OMI over Ecuador and S. Colombia are also used to illustrate variations in regional SO2 loading and to pinpoint sources. The dense concentration of active volcanoes in Ecuador provides a stringent test of OMI's ability to distinguish SO2 from multiple emitting sources. Our analysis reveals that Tungurahua, Reventador and Galeras were responsible for the bulk of the SO2 emissions in the region in the timeframe of our study, with no significant SO2 discharge detected from Sangay. At Galeras and Reventador, we conclude that OMI can detect variations in SO2 release related to cycles of conduit sealing and degassing, which are a critical factor in hazard assessment. The OMI SO2 data for Reventador are the most extensive sequence of degassing measurements available for this remote volcano, which dominated regional SO2 production in June–August 2005. At Tungurahua, the OMI measurements span the waning stage of one eruptive cycle and the beginning of another, and we observe increasing SO2 burdens in the months prior to explosive eruptions of the volcano in July and August 2006. Cumulative SO2 loadings measured by OMI yield a total of ~ 1.16 Tg SO2 emitted by volcanoes on mainland Ecuador/S. Colombia between September 2004 and September 2006; as much as 95% of this SO2 may originate from non-eruptive degassing. Approximate apportionment of the total SO2 loading indicates that ~ 40% originated from Tungurahua, with ~ 30% supplied by both Reventador and Galeras. These measurements of volcanic SO2 degassing in Ecuador confirm OMI's potential as an effective, economical and risk-free tool for daily monitoring of SO2 emissions from hazardous volcanoes.
4.
Xu, Shulan, et al.
(författare)
Effects of compartmental model structure and long-term inflow on model predictions
2005
Ingår i: Radioprotection - Revue de la Societé Francaise de Radioprotection. - : EDP Sciences. - 0033-8451 .- 1769-700X. ; 40:1, s. 477-483
Tidskriftsartikel (refereegranskat) abstract
Model predictions of solute transport in a wetland were compared with tracer experimental data to illustrate that the number of compartments in a compartmental model should be selected according to certain rules to accurately describe the transport process. If the input pulse is short, the model structure affects the output significantly. The temporal moments of the residence time distribution was obtained from a general solution of the compartmental model in the Laplace domain derived with an arbitrary inflow pollutograph. The variance of the residence time can be used as a useful tool to analyse the effect of model structure and long-term inflow pollutograph on the response of the model predictions.
5.
Mouyen, Maxime, 1982, et al.
(författare)
Expected temporal absolute gravity change across the Taiwanese Orogen, a modeling approach
2009
Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 48:3-5
Tidskriftsartikel (refereegranskat) abstract
The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several μGal yr-1. By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 μGal yr-1 with the thin-skinned tectonic and 0.3 μGal yr-1 with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements.
6.
Jones, Ashley, 1977
(författare)
Validation and time series analysis of global stratospheric data sets
2009
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The depletion of ozone from the stratosphere and the impact of global warming have been identified as phenomena caused as a result of anthropogenic activity. Scientists are thus trying to find quicker and more reliable ways to analyse these environmental problems. Remote sensing of the atmosphere using satellites is perhaps the most cost effective method. One beneficial application is the acquisition of vertical profiles of atmospheric species on a global scale with good spatial and temporal resolutions. An example of an instrument that can achieve this is the Sub-Millimetre Radiometer (SMR) aboard the Odin satellite that launched in 2001, which retrieves vertical limb profiles of numerous trace gases, including stratospheric ozone. This thesis presents a validation summary for primarily the Odin/SMR ozone data products, v1.2, v2.0 and v2.1 (for the 501.8 GHz band in the microwave region). Comparisons are made to v4.61 data obtained from the Interferometer for Passive Atmospheric Soundings (MIPAS) instrument, on board the ENVISAT satellite. Further analysis compares Odin/SMR mixing ratios to balloon sonde data. It is suggested from the results found here that Odin/SMR v2.1 ozone data should be used for scientific purposes. Odin/ SMR is also compared to its sister instrument, the Optical Spectrograph Infra-Red Imaging System (Odin/OSIRIS). Results show an excellent agreement between coincident profiles (typically
7.
Mattsson, Eskil, 1981, et al.
(författare)
Tropisk avskogning måste lösas globalt
2007
Ingår i: Göteborgsposten. ; :12 dec 2007
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt) abstract
Det pågående klimatmötet ska ta ställning till hur den tropiska avskogningen ska minska. Ett förslag är att låta markägare få större ekonomisk kompensation än den intäkt en avverkning skulle ge. Norge går före genom att satsa 17,5 miljarder kronor och Världsbanken har gått in med stora summor, skriver Eskil Mattsson, Madelene Ostwald och Matilda Palm, som är på plats på Bali.
8.
Jakobson, E., et al.
(författare)
Diurnal variability of precipitable water in the Baltic region
2007
Ingår i: Proceedings of the Fifth Study Conference on BALTEX, Ed. H.J. Isemer, International BALTEX Secretariat, GKSS Research Center, Geesthacht, Germany. - 1681-6471. ; :38, s. 119-120
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
9.
Pramualsakdikul, Surat, 1961, et al.
(författare)
Sensing of diurnal and semi-diurnal variability in the water vapour content in the tropics using GPS measurements
2007
Ingår i: Meteorological Applications. - : Wiley. - 1350-4827 .- 1469-8080. ; 14:4, s. 403-412
Tidskriftsartikel (refereegranskat) abstract
The diurnal and semi-diurnal variability of the integrated precipitable water vapour (IPWV) was studied by using Global Positioning System (GPS) data (1998-2004) from 14 International GNSS Service (IGS) stations located between latitudes 20°S and 20°N, and longitudes 70°-170°E. The phases and amplitudes of the EPWV are compared to the corresponding estimates from two numerical weather models (NWMs). Results reveal that there are diurnal amplitudes of more than 0.4 mm for most sites, except sites on small islands in the ocean. The maximum diurnal amplitude is 3 mm at Bakosurtanal, Indonesia. The estimated semi-diurnal signals are in general small. The maximum of the IPWV typically occurs between 1200 and 2400 local solar time. The results suggest that GPS data are useful for high-temporal-resolution studies of IPWV. The accuracy of the estimated diurnal amplitudes is limited by the use of a simple model for the mean temperature of the wet refractivity, and the accuracy of the estimated semi-diurnal amplitudes is likely to be improved by a higher temporal resolution of the ground pressure data at the GPS sites. Copyright © 2007 Royal Meteorological Society.
10.
Mossmark, Fredrik, 1975, et al.
(författare)
Recovery from groundwater extraction in a small catchment area with crystalline bedrock and thin soil cover in Sweden
2008
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 404:2-3, s. 253-261
Tidskriftsartikel (refereegranskat) abstract
An experiment has been in progress since 1997 in a small catchment area (28,000 m2) with crystalline bedrock and thin soil cover to study the conceivable impact on groundwater conditions of tunneling and the use of groundwater. The impact on hydrology and hydrochemistry from intensive extraction of groundwater at a depth of 50 m in the bedrock has been studied at Lake Gårdsjön in Sweden. The catchment area was first monitored under pristine conditions, followed by four and a half years of extraction and then a recovery phase. The geological conditions result in a low buffer capacity and high sensitivity to acidification. During the period of extraction, the surface runoff decreased by approximately 50% compared to a nearby reference area. The groundwater extraction caused increased fluctuation in groundwater levels in a wetland, which in turn caused oxidation of reduced sulfur to sulfate. The sulfate concentrations increased almost 100-fold in some instances, causing a lowering of the pH by one unit in shallow groundwater. Since extraction of the groundwater was discontinued, the pH has gradually risen and the sulfate concentrations have decreased. However, the concentration of sulfate in groundwater in the wetland has remained stable at approximately double the pre-experiment levels. Magnesium concentrations were lower after the experiment, caused by exhaustion of the magnesium pool in the wetland through acidification. The extraction of water from the bedrock shortened the retention times and increased the recharge of groundwater in the bedrock. After extraction was terminated, the groundwater levels in the boreholes recovered within a month to levels similar to those before extraction. The hydrochemistry of the bedrock groundwater, which was strongly affected by the hydrochemistry of shallow groundwater during the experiment, has also gradually begun to regain its pre-extraction signature. However, the surface runoff has remained low during the first 2 years of recovery, at about 60% of the volume compared to the unaffected catchment area. This could be explained by delayed recovery in resaturation of the shallow rock that was unsaturated during the experiment.
