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| 2. |
- Dorigo, Wouter, et al.
(författare)
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The International Soil Moisture Network : Serving Earth system science for over a decade
- 2021
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 25:11, s. 5749-5804
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Forskningsöversikt (refereegranskat)abstract
- In 2009, the International Soil Moisture Network (ISMN) was initiated as a community effort, funded by the European Space Agency, to serve as a centralised data hosting facility for globally available in situ soil moisture measurements . The ISMN brings together in situ soil moisture measurements collected and freely shared by a multitude of organisations, harmonises them in terms of units and sampling rates, applies advanced quality control, and stores them in a database. Users can freely retrieve the data from this database through an online web portal (https://ismn.earth/en/, last access: 28 October 2021). Meanwhile, the ISMN has evolved into the primary in situ soil moisture reference database worldwide, as evidenced by more than 3000 active users and over 1000 scientific publications referencing the data sets provided by the network. As of July 2021, the ISMN now contains the data of 71 networks and 2842 stations located all over the globe, with a time period spanning from 1952 to the present. The number of networks and stations covered by the ISMN is still growing, and approximately 70 % of the data sets contained in the database continue to be updated on a regular or irregular basis. The main scope of this paper is to inform readers about the evolution of the ISMN over the past decade, including a description of network and data set updates and quality control procedures. A comprehensive review of the existing literature making use of ISMN data is also provided in order to identify current limitations in functionality and data usage and to shape priorities for the next decade of operations of this unique community-based data repository.
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| 3. |
- Larson, Kristine, et al.
(författare)
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Coastal Sea Level Measurements Using a Single Geodetic GPS Receiver
- 2013
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Ingår i: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 51:8, s. 1301-1310
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method to derive local sea level variations using data from a single geodetic-quality Global Navigation Satellite System (GNSS) receiver using GPS (Global Positioning System) signals. This method is based on multipath theory for specular reflections and the use of Signal-to-Noise Ratio (SNR) data. The technique could be valuable for altimeter calibration and validation. Data from two test sites, a dedicated GPS tide gauge at the Onsala Space Observatory (OSO) in Sweden and the Friday Harbor GPS site of the EarthScope Plate Boundary Observatory (PBO) in USA, are analyzed. The sea level results are compared to independently observed sea level data from nearby and in situ tide gauges. For OSO, the Root-Mean-Square (RMS) agreement is better than 5 cm, while it is on the order of 10 cm for Friday Harbor. The correlation coefficients are better than 0.97 for both sites. For OSO, the SNR-based results are also compared with results from a geodetic analysis of GPS data of a two receivers/antennae tide gauge installation. The SNR-based analysis results in a slightly worse RMS agreement with respect to the independent tide gauge data than the geodetic analysis (4.8 cm and 4.0 cm, respectively). However, it provides results even for rough sea surface conditions when the two receivers/antennae installation no longer records the necessary data for a geodetic analysis.
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| 4. |
- Larson, Kristine, et al.
(författare)
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The GPS Tide Gauge Problem Revisited
- 2011
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Ingår i: American Geophysical Union Fall Meeting 2011, 5-9 December, San Francisco, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It is well-known that GPS instruments can be used to measure local sea level. In most experiments, two antennas are deployed at a coastal site. A geodetic antenna - optimized for RHCP signals - is used in the traditional orientation and tracks the direct signal. The second antenna is optimized for reflected signals - which are primarily LHCP - and is pointed towards the ocean. The sea surface can then be estimated by analyzing the carrier phase data. While the data from the "up" antenna are dominated by the direct signal, the effects of signals reflected from the ocean are also present in its data. Thus in principle, one might be able to estimate sea level using only data from the "up" antenna. This is similar in concept to recent multipath studies where geodetic GPS installations are being used to measure soil moisture variations and snow depth.We have analyzed GPS data for a three-month period from a GPS tide gauge installation at the Onsala Space Observatory. It is located on the western coast of Sweden. We used the SNR data from the "up" antenna only. The data were windowed by azimuth for ocean-reflections and elevation angles from 18-40 degrees. This provides hourly sea level measurements. Comparisons were made to an average for tide gauge records 18 km south and 33 km north of Onsala. The standard deviation of the residual between our solutions and the tide gauges is 4.9 cm. This is less precise than the combined up-down antenna system of 2.6 cm. These precision values include errors associated with real tidal motion at the GPS site. While the "down" antenna performs poorly in high-wind conditions (> 8 m/s), we found that the "up" antenna performs significantly better at these times.
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| 5. |
- Löfgren, Johan, 1983, et al.
(författare)
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Remote Sensing of the Coastal Ocean with Standard Geodetic GNSS-Equipment
- 2012
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Ingår i: European Geosciences Union General Assembly 2012, 22-27 April, Vienna, Austria.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We use standard geodetic Global Navigation Satellite System (GNSS) equipment to perform remote sensing measurements of the coastal ocean. This is done by a so-called GNSS-based tide gauge that uses both direct GNSS-signals and GNSS-signals that are reflected off the sea surface. Our installation is located at the Onsala Space Observatory (OSO) at the west coast of Sweden and consists of a zenith-looking Right Hand Circularly Polarized (RHCP) and a nadir-looking Left Hand Circularly Polarized (LHCP) antenna. Each antenna is connected to a standard geodetic-type GNSS-receiver.We applied two different analysis strategies to our GNSS data set. The first strategy is based on a traditional geodetic differential analysis [Löfgren et al., 2011] and makes use of the data from both receivers; connected to the zenith and the nadir looking antennae. This approach results in local sea level that is automatically corrected for land motion, meaning that the GNSS-based tide gauge can provide reliable sea-level estimates even in tectonic active regions. The second strategy focuses on the Signal-to-Noise Ratio (SNR) recorded with the receiver connected to the zenith-looking antenna [Larson et al., 2011]. The SNR is affected by multipath originating from the sea surface reflections. Analysis of the SNR data allows to determine the distance between the antenna and the reflecting surface, and thus to measure sea surface height. Results from both analysis strategies are compared to independently observed sea-level data from two stilling-well gauges operated by the Swedish Meteorological and Hydrological Institute (SMHI), which lie in a distance of several km from OSO. The root-mean-square agreement between the different time series of several month's length is on the order of 5 cm and better. These results indicate the large potential for using coastal GNSS-sites for the monitoring of the coastal ocean.References:Löfgren J.S., Haas R., Scherneck H-G., Bos M.S., (2011), Three months of local sea level derived from reflected GNSS signals, Radio Science, 46 (RS0C05).Larson K., Löfgren J.S., Haas R., (2011), The GPS tide gauge problem revisited, AGU Fall Meeting, 5-9 December, San Francisco, USA, Poster.
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| 6. |
- Löfgren, Johan, 1983, et al.
(författare)
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Sea Level Records from Geodetic GPS Receivers: a New Coastal Sea Level Dataset
- 2012
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Ingår i: American Geophysical Union (AGU) Fall Meeting, 3-7 December 2012, San Francisco.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Global sea level rise and local sea level variations due to climate change has the potential for a significant impact on coastal societies. Thus, it is of great importance to monitor and understand how the sea level is changing. Existing techniques to measure sea level have provided important insights in this field during the last decades. However, further observations are necessary in order to fully understand the underlying processes.We present the possibility of a new coastal sea level dataset based on analysis of Signal-to-Noise Ratio (SNR) data from existing permanent GPS stations at the coast. For a GPS antenna close enough to the ocean, the multipath signals, reflected off the sea surface, interfere with the direct satellite signals. This becomes especially visible as oscillations in the recorded SNR data. The analysis of the SNR oscillations provides the distance between the sea surface and the GPS antenna phase center. Thus, such an installation can be called a GPS tide gauge and can be used to monitor sea level.The advantage of a GPS tide gauge is that it allows both determination of the sea level and determination of the position with respect to the International Terrestrial Reference Frame, using a single geodetic instrument. This is particularly valuable in areas with land surface motion where the usefulness of traditional tide gauges is restricted.The technique has been verified through comparison to traditional tide gauges at two sites. The comparison of more than three months long time series resulted in correlationcoefficients of better than 0.97 for both sites. For the station with low and high tidal range, the root-mean-square agreement between the GPS results and the tide gauge records were better than 5 and 10 cm, respectively.In this presentation we show preliminary results for sea level records world wide by applying this technique to several existing permanent GPS stations.
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| 7. |
- Marouli, Eirini, et al.
(författare)
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Rare and low-frequency coding variants alter human adult height
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 542:7640, s. 186-190
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Tidskriftsartikel (refereegranskat)abstract
- Height is a highly heritable, classic polygenic trait with approximately 700 common associated variants identified through genome-wide association studies so far. Here, we report 83 height-associated coding variants with lower minor-allele frequencies (in the range of 0.1-4.8%) and effects of up to 2 centimetres per allele (such as those in IHH, STC2, AR and CRISPLD2), greater than ten times the average effect of common variants. In functional follow-up studies, rare height increasing alleles of STC2 (giving an increase of 1-2 centimetres per allele) compromised proteolytic inhibition of PAPP-A and increased cleavage of IGFBP-4 in vitro, resulting in higher bioavailability of insulin-like growth factors. These 83 height-associated variants overlap genes that are mutated in monogenic growth disorders and highlight new biological candidates (such as ADAMTS3, IL11RA and NOX4) and pathways (such as proteoglycan and glycosaminoglycan synthesis) involved in growth. Our results demonstrate that sufficiently large sample sizes can uncover rare and low-frequency variants of moderate-to-large effect associated with polygenic human phenotypes, and that these variants implicate relevant genes and pathways.
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