Richard M. Bingley

Atmospheric models, GPS and InSAR measurements of the tropospheric water vapour field over Mount Etna

[1] Dynamic models of atmospheric movement over the Mount Etna volcano are used to calculate the path delays affecting radar caused by variable water vapour in the troposphere. We compare these model results with the equivalent differential radar interferogram generated by two ERS-2 SAR images taken 35 days apart and the water vapour delay retrievals from a network of fourteen GPS stations distributed over the volcano. The atmospheric model delay field agrees wellwith thelong-wavelength spatial differences measured by InSAR and those measured by GPS. INDEX TERMS: 6924 Radio Science: Interferometry; 1243 Geodesy and Gravity: Space geodetic surveys; 3367 Meteorology and Atmospheric Dynamics: Theoretical modeling; 6964 Radio Science: Radio wave propagation; 8499 Volcanology: General or miscellaneous. Citation: Wadge, G., et al., Atmospheric models, GPS and InSAR measurements of the tropospheric water vapour field over Mount Etna, Geophys. Res. Lett., 29(19), 1905, doi:10.1029/2002GL015159, 2002.

Geodetic estimate of seismic hazard in the Gulf of Korinthos

The recent 15 June 1995, M0 = 6.0 × 1018 N m, Aigion earthquake in the western Gulf of Korinthos has focussed attention on the seismic hazard of the region. Although there have been few large earthquakes in the region during this century, the historical record suggests that there may have been many large earthquakes there in the interval 1750–1900. We present geodetic data that give estimates of the rate of extension of the Gulf of Korinthos during this century and which suggest that less than half of the elastic strain in the central and western Gulf of Korinthos has been released by earthquakes during this century. In contrast, the seismic and geodetic strains in the eastern Gulf of Korinthos are in agreement with each other. If the discrepancy between seismic and geodetic strains in the western Gulf of Korinthos that has accumulated during this century is removed in earthquakes, the moment release will be equivalent to several Ms > 6.5 earthquakes.

Atmospheric water vapour correction to InSAR surface motion measurements on mountains: results from a dense GPS network on Mount Etna

Abstract In order for synthetic aperture radar interferometry (InSAR) to effectively measure the pattern of surface deformations of dynamic phenomena, such as volcanoes, it is necessary to mitigate the effects of water vapour on this signal. One way to achieve this is to use a numerical model of the atmospheric conditions, calibrated using an independent measure of atmospheric water vapour, in order to determine the water vapour-based delay in InSAR. We describe an experiment in which such GPS-derived integrated water vapour (IWV) estimates were made using a dense array of continuous GPS receivers. Fourteen GPS receivers were deployed at stations on Mount Etna and continuous observations were recorded for a 10-day period in August/September 2000 and repeated over a 10-day period in October 2000, coincident with ascending and descending SAR image acquisition by the ERS-2 satellite. The results show maximum variations in IWV of 10 kg / m 2 between the days corresponding to the ERS-2 passes. The variations were not the same at all the stations and equated to variations in the zenith wet delay (ZWD) ranging from a few millimetres to about 6 cm. The differences in ZWD between the two passes would degrade the ability to measure surface deformations significantly if they were not modelled.

Using continuous GPS and absolute gravity to separate vertical land movements and changes in sea-level at tide-gauges in the UK

Researchers investigating climate change have used historical tide-gauge measurements from all over the world to investigate the changes in sea-level that have occurred over the last century or so. However, such estimates are a combination of any true sea-level variations and any vertical movements of the land at the specific tide-gauge. For a tide- gauge record to be used to determine the climate related component of changes in sea-level, it is therefore necessary to correct for the vertical land movement component of the observed change in sea-level. In 1990, the Institute of Engineering Surveying and Space Geodesy and Proudman Oceanographic Laboratory started developing techniques based on the Global Positioning System (GPS) for measuring vertical land movements (VLM) at tide-gauges in the UK. This paper provides brief details of these early developments and shows how they led to the establishment of continuous GPS (CGPS) stations at a number of tide-gauges. The paper then goes on to discuss the use of absolute gravity (AG), as an independent technique for measuring VLM at tide-gauges. The most recent results, from CGPS time-series dating back to 1997 and AG time-series dating back to 1995/1996, are then used to demonstrate the complementarity of these two techniques and their potential for providing site-specific estimates of VLM at tide-gauges in the UK.

Modelling the glacial isostatic adjustment of the UK region

The glacial isostatic adjustment of the UK region has been considered in a number of recent studies. We have revisited this problem in order to: (i) highlight some key issues with regard to limitations in the ice modelling approach adopted in these studies and (ii) consider the constraints provided from observations of crustal motion available via continuous global positioning system monitoring. With regard to the first aim, we have found that: (i) previous studies have significantly overestimated ice thicknesses in regions where trim line field constraints were adopted and (ii) the duration of the glaciation phase of the UK ice sheet is a critical aspect of the model and that discrepancies in this model component have led to inconsistent inferences of Earth model parameters. With regard to the second aim, we have found that predictions of horizontal velocities (relative to a chosen site) based on a UK ice model calibrated to fit the regional sea-level database capture the geometry of the signal well but only account for 10% of the magnitude (for a range of Earth models).

Absolute Calibration of the Jason-1 Altimeter Using UK Tide Gauges

This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1–61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.

Monitoring changes in mean-sea-level to millimeters using GPS

The fiducial GPS technique is now well established in geodesy and geophysics, for determining horizontal and vertical land movements. In particular, the technique is used in crustal dynamics and in monitoring changes in mean-sea-level. The main limiting factor to achieving accuracies of a few millimeters is the reference frame (or datum), as defined by the adopted coordinates of the fiducial stations. This paper summarises a series of tests which have been carried out to assess the quality of alternative global reference frameworks, in order to achieve the highest accuracies for tide gauge heights in the UK.

Using GPS to Separate Crustal Movements and Sea Level Changes at Tide Gauges in the UK

Changes in mean sea level recorded by tide gauges are corrupted by crustal movements, which can be of a similar order of magnitude. A network of permanent, continuous GPS (CGPS) stations has been established in the UK with five stations being sited at tide gauges. Data from these and four other CGPS stations have been analysed. A common mode filtering technique was successfully applied in order to reduce the effect of annually repeating signals on station velocity estimates. The effect of time-dependent correlations in the coordinate time series were accounted for when computing station velocity uncertainties.

Application of the dual-CGPS concept to monitoring vertical land movements at tide gauges ☆

Abstract Recently the concept of using dual-continuous GPS (dual-CGPS) stations for monitoring vertical land movements at tide gauge sites was proposed by a working group of the European Sea Level Observing System (EOSS). In this concept, one CGPS station is established at the tide gauge, in order to monitor the local vertical land movements, and a second CGPS station is established on stable rock, within a few kilometers of the tide gauge further inland. Since 1997, a network of CGPS stations has been established to monitor vertical land movements in the UK. For the dual-CGPS station concept, pairs formed by the CGPS stations at Newlyn tide gauge and Camborne and at Lowestoft tide gauge and Hemsby, have been analyzed over a time span of approximately 2.7 and 2.0 years respectively. It has been shown by numerous authors that temporal and spatial correlations in CGPS coordinate time series can introduce biases in the estimated station velocities and their uncertainties. By analyzing the coordinate time series of two CGPS stations close to each other, spatial correlations can be removed successfully by differencing and a cleaner, difference time series for each coordinate component can be obtained. In this paper, the observed coordinate time series of four CGPS stations have been used to produce synthetic coordinate time series of 6 years in length. Station velocities and their uncertainties have been derived for both observed and synthetic coordinate time series and compared in order to assess the capabilities of the dual-CGPS concept to better describe local and geophysical vertical land movements.

Land motion in the urban area of Nottingham observed by ENVISAT-1

Persistent scatterer interferometry (PSI) analysis of land motion in the City of Nottingham has been undertaken using advanced synthetic aperture radar (ASAR) data from the ENVISAT-1 satellite covering the period between November 2002 and February 2009, and some interesting areas of motion are evident from the results. The aims of this article are twofold: first to relate these areas to other sources of information such as geology, GPS, and precise levelling, and second to discuss a novel method of atmospheric correction for PSI using precise point positioning (PPP) derived GPS zenith wet delay (ZWD) estimates. PSI validation using the various sources of data is discussed with contextual information regarding historical activity. This article shows that land motion in an urban environment can be widespread and anisotropic, with many different causes, with the consequences that sparse networks of ground-based instruments may be incapable of monitoring land motion in such a complex environment. A ZWD correction method is also presented and results are shown, which improve upon those without the correction. The ZWD estimates are produced using an undifferenced global navigation satellite system (GNSS) processing technique known as PPP. This, coupled with the chosen PSI method, provides a low noise solution when compared to similar experiments involving the integration of GNSS and interferometric synthetic aperture radar (InSAR) data. The results show that there is good temporal and spatial correlation between the PPP ZWD estimates and the PSI-derived atmospheric phase contributions. Noticeable improvements in the PSI solution when comparing before and after processing runs to precise levelling observations are shown.