G51A-0133
Peat Compaction as a Premier Driver of Mississippi Delta Subsidence
The adverse consequences of coastal subsidence (accelerated relative sea-level rise, shoreline erosion, and wetland loss) and its threats to coastal populations are widely recognized. The Mississippi Delta has become the poster child of coastal hazard following the devastation from Hurricane Katrina, partly attributed to the loss of vast wetlands that could have served as a buffer against storm surge. Several recent studies have focused on the wide variety of components that are believed to contribute to subsidence in the Mississippi Delta and adjacent coastal Louisiana, ranging from lithospheric processes to the compaction of relatively shallow materials. Current estimates of subsidence rates in this area differ by several orders of magnitude. While compaction of Holocene strata is widely believed to be an important contributor to subsidence, surprisingly little is known about compaction rates over centennial to millennial timescales, whether in coastal Louisiana or elsewhere. Measurements of the deformation of a 1500-year-old, originally near-horizontal swamp peat bed in the Mississippi Delta shows that averaged peat compaction rates can be as high as 5 mm/yr, values that exceed recent model predictions. It is conceivable that over decadal to centennial timescales compaction rates can locally be 10 mm/yr or more. Compaction is capable of accounting for a large portion of the exceptionally high rates of land surface subsidence, relative sea-level rise, and coastal wetland loss in the Mississippi Delta, and it is likely a significant cause of subsidence in organic-rich, low-lying coastal plains elsewhere.
G51A-0134
Application of Persistent Scatterer Radar Interferometry to the New Orleans delta region
Subsidence in New Orleans and along the Gulf Coast is currently monitored using a variety of ground- and satellite-based methods, and extensive geophysical modeling of the area seeks to understand the inputs to subsidence rates from sediment compaction, salt evacuation, oxidation and anthropogenic forcings such as the withdrawal or injection of subsurface fluids. Better understanding of the temporal and spatial variability of these subsidence rates can help us improve civic planning and disaster mitigation efforts with the goal of protecting lives and property over the long term. Existing ground-based surveys indicate that subsidence gradients of up to 1 cm/yr or more over length scales of several 10's of km exist in the region, especially in the vicinity of the city of New Orleans. Modeling results based on sediment inputs and post-glacial sea level change tend to predict lower gradients, presumably because there is a large input from unmodeled crustal faults and anthropogenic activity. The broad spatial coverage of InSAR can both add to the existing network of ground-based geodetic surveys, and can help to identify areas that are deforming anomalously with respect to surrounding areas. Here we present the use of a modified point scatterer method applied to radar data from the Radarsat satellite for New Orleans and the Gulf Coast. Point target analysis of InSAR data has already been successfully applied to the New Orleans area by Dixon et al (2006). Our method is similar to the Stanford Method for PS (StaMPS) developed by Andy Hooper, adapted to rely on combinations of small orbital baselines and the inclusion of coherent regions from the time span of each interferogram during phase unwrapping rather than only using points that are stable within all interferograms.
G51A-0135
Examining the evidence for a recent acceleration in the rate of sea-level rise using combined instrumental and proxy data, North Carolina, USA
Whilst accelerated rates of relative sea-level (RSL) rise are potentially one of the most devastating impacts of future climate change, our understanding of decadal scale changes in sea-level is poor. This paper seeks to address this knowledge gap by combining tide gauge and high-precision geological reconstructions of relative sea-level of sufficient resolution and duration to detect any recent acceleration in the rate of sea-level rise. We offer a high resolution relative sea-level history for the last ~2000 years from the Albemarle - Pamlico Estuarine System in North Carolina. Contemporary foraminifera were collected from five back barrier marshes to create a regional scale modern training set. The use of multiple marshes from a region increases the ecological and environmental diversity included within the training set and reduces the probability of a no modern analogue outcome. To merge the five spatially distinct sites and to relate each to local tide levels we used the VDatum transformation tool. This method relates all samples to a common orthometric datum (NAVD88) and reduces error. We developed an accurate and precise transfer function to reconstruct former sea levels based upon the modern observable relationship between foraminifera and elevation with respect to the tidal frame. We applied the transfer function to salt-marsh core(s) from Sand Point (Roanoke Island), North Carolina to produce a late Holocene RSL record. An age-depth model was produced from composite chronologies of 210Pb, 14C and pollen chrono-horizons. We validated our approach by comparing geological based reconstructions and instrumental tide gauge records. Our records show that in the last ~2000 years sea level has risen at a background rate of ~1.1mm/yr. There is evidence for two recent accelerations in the rate of sea-level rise during the late 19th and 20th centuries to a current rate of ~4mm/yr.
G51A-0136
Combining Geological, Geodetic, and Tide-Gauge Data to Estimate Coastal Subsidence and Flooding Hazards in the Mackenzie Delta, Western Arctic Canada
Relative sea-level trends across the Canadian Arctic are highly variable, in part because of the strong imprint of postglacial isostatic adjustment. In many parts of the central Arctic, ongoing uplift exceeds the rate of regional sea-level rise, resulting in continued coastal emergence. In peripheral areas such as the western Arctic coastal plain, models and geological evidence point to ongoing subsidence, adding to relative sea-level (RSL) rise in the Beaufort-Mackenzie region. Additional sources of subsidence in the Mackenzie Delta include long-term sediment loading and sediment compaction, as well as thaw subsidence where thermal changes such as deeper seasonal thaw lead to melting of excess ground ice. Compaction is reduced in ice-bonded sediments and the thickness of ice bonding varies with the depth of permafrost, which ranges from 0 to 100 m in the main body of the Holocene delta and >500 m in areas outside the main valley fill. Ice-bonding is reduced or absent in thaw taliks beneath deep lakes and channels. Differential subsidence rates may play a role in maintaining or expanding lake area on the delta plain and in promoting delta-front erosion. Beginning in 2001, we have established an Arctic network of continuous GPS (CGPS) stations, including CGPS co-located with tide gauges at Tuktoyaktuk and Ulukhaktok. Fixed monuments for episodic GPS observations have been established and occupied repeatedly in the Mackenzie Delta and we are currently developing a network of fixed reflectors for persistent-scatterer InSAR. Velocities from the North American Reference Frame Working Group (consistent with rates from JPL and SOPAC) indicate positive values (uplift) at all CGPS stations, even in the Beaufort-Mackenzie region. However, the long-term tide-gauge record at Tuktoyaktuk shows a 45-year rising RSL trend (1961-2006) of +3.5±1.3 mm/a. If sea-level rise in the Beaufort Sea has been comparable to the global mean trend during this interval, the implied motion at Tuktoyaktuk is about -1.7±1.8 mm/a (subsidence). Preliminary GPS results from the Mackenzie Delta indicate natural subsidence ranging from 0 to 20 mm/a. These results are being used in the environmental review of proposed natural gas production and transportation facilities. Impacts of natural and potential induced subsidence on nesting waterfowl habitat are being assessed by simulating effects on flooding frequency using high-resolution digital elevation models derived from scanning airborne laser altimetry (LiDAR).
G51A-0137
Sea-level Variability in Chesapeake Bay from Autoregressive Decomposition of Tide Gauge Records
Sea-level is a fundamental parameter for the study of regional climate variability, long-term coastal management and the preservation of marine ecosystems. Tide gauge measurements of relative sea-level heights provide a fundamental dataset for examining the variability of coastal sea-level. However, a key issue in the analysis and interpretation of tide gauge records is the separation of seasonal, inter-annual and long term signals. This is a challenging task, requiring the application of specific methodologies, such as autoregressive decomposition; this model-based approach allows to obtain flexible estimates of seasonal, inter-annual and long-term variability within an adequate inferential framework, yielding optimal predictions and error bar estimates for the derived components. In this study, relative sea-level heights from 9 tide gauge stations in Chesapeake Bay, the largest estuary in the US, are analyzed. The time series of relative sea-level measurements are decomposed through autoregressive decomposition into seasonal and long-term signals. The temporal evolution of each of the decomposed signals is further analyzed, specifically by examining the temporal variability of the amplitude and phase of the seasonal signal, and by producing predictions from the long-term signals. The results show a distinct behavior, in terms of both seasonal and low-frequency variability between the 5 sites in the southern, outer part of the estuary and the 4 tide gauge stations in the northern, inner part of Chesapeake Bay.
G51A-0138
Changes in Extremes of Relative Sea-level: the Baltic Sea case study
Long records of relative sea-level heights from coastal tide gauge stations provide valuable information on regional variability. The analysis of such records is usually focused on the estimation of linear slopes by ordinary least squares regression. However, sea-level variability can include not only changes in the mean but also changes in the shape and spread of the sea-level values distribution over time. These variations can be more important than changes in mean sea-level â€" in particular, changes in extreme high waters can impact considerably coastal locations and populations. In this study, this issue is addressed by analyzing the variability of extreme sea-levels in the Baltic Sea through quantile regression. This method allows to derive slopes, along with corresponding uncertainties, for different quantiles of the sea-level distribution. A total of 70 tide gauges along the Baltic sea coastlines are considered. The results show that in the eastern part of the Baltic Sea, including the Gulf of Bothnia and the Gulf of Finland, the rate of change of relative sea-level is significantly higher at the 0.9 quantile (corresponding to the largest 10% of sorted sea-level values) than at the mean. The Baltic Sea is a shallow, semi-enclosed sea. Relative sea-level heights are directly influenced by land uplift, which varies considerably along the Baltic Sea coastlines and by the exchange of water through the Danish Straits, mainly determined by meteorological conditions (particularly winds and atmospheric pressure). The distinct rate of change of high-waters in the upper Baltic Sea seems to be associated with corresponding changes in atmospheric conditions, particularly westerly winds.
G51A-0139
Impacts of Combined Sea Level Rise and Coastal Subsidence, New York City Metropolitan Area
Future sea level rise due to global warming will lead to more frequent flooding of low-lying coastal areas and wetlands, increased land submergence, and enhanced beach erosion. Coastal subsidence exacerbates these overall impacts. In the New York City metropolitan area, rates of relative sea level rise for the last 100 years range between 2-4 mm/yr, to which ongoing glacial isostatic adjustments (GIA) contribute on average ~40 %. While this percentage diminishes as climate-induced sea level trends increase, it remains non-negligible. We apply Ramstorf's (2007, Science, 315, 368-370) semi-empirical methodology that links global temperature change to sea level rise for IPCC SRES A1B, A2, and B1 greenhouse gas emission scenarios, using World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) dataset for 11 global climate models. Sea level projections are corrected for GIA, using Peltier's ICE-5G 1° x 1° gridded dataset. Projected global sea level rise by the end of the 21st century ranges between 48 and 94 cm above the 2001-2005 base period. Projections of regional sea level rise encompassing the New York metropolitan region will be presented. An importance consequence is the increase in flood hazards even with small increments of sea level and constant storm climatology. For example, in New York City, a flood event with a current recurrence interval of 1 in 10 years, is likely to occur once a year or less by the 2080s.
G51A-0140
Subsidence and its Impact on the Quality of Geospatial Data Used in the Planning and Building of Hurricane Protection for New Orleans and Southeast Louisiana
A state-wide digital elevation model (DEM; www.atlas.lsu.edu) based on 1999-2002 LiDAR data is widely used in assessing present and future flooding potential in New Orleans and southeast Louisiana due to storm surge. Although the data were acquired during a time when official vertical controls had been deemed unreliable due to subsidence, the DEM continues to be used for operational modeling and planning. To test its viability, an accuracy assessment of the DEM was performed in 2007 using a statewide real-time kinematic GPS system based on NOAA-sanctioned continuously operating reference stations. Sampling was focused on built structures, i.e., levees, floodwall, and roads, features considered to control surge flow in the low-lying coast. Over 100,000 points were measured and compared to 5X5 m DEM pixels. The vertical accuracy of test points was determined to be +/-10cm (0.3 ft). It is claimed that 90% of the DEM is to accurate to +/-15 cm (0.5 ft).The study had the added benefit of providing a snapshot of the progress being made in augmenting the regional hurricane protection system following the 2005 storms. The study shows that only 40 percent of DEM samples pass the accuracy test, i.e., are +/- 0.8 ft of the true elevation. Where the DEM is too low, it is likely due to: levee augmentation, floodwalls are too narrow to be detected by LiDAR, new levees, and a "levee crown bias", i.e., sampled DEM pixel includes levee slope areas. Where the DEM is too high, the causes can be traced to two factors, inaccurate vertical controls established prior to LiDAR acquisition, and to a lesser degree, post-acquisition subsidence. The DEM south and east of New Orleans overestimates levee elevations by 0-1 m. We conclude, therefore that the state-wide digital elevation model (DEM) is unreliable and inadequate to support present-day surge modeling.
G51A-0141
On the Combined Use of GRACE and Geodetic Observations for Vertical Motion in the Great Lakes Region
As the measurements from geodetic observations become more accurate, they are implemented to not only empirically derive velocity surfaces but also to infer mantle viscosity. Accurate empirical models for vertical crustal motion are of particular interest in the Great Lakes region, where the line of zero motion (hinge line) is an important constraint for postglacial rebound modelling. With the abundance of geodetic observations in this region, the gradient of the velocity surface can be described relatively well. However, the hinge line can deviate from one data set to another due to datum inconsistencies, different time span and accuracy of measurements, different spatial resolution and presence of erroneous data, as well as the underlying mathematical model. Reliably estimated error bounds of the empirical rates of crustal displacement are required to define the uncertainty with which the mantle viscosity profile can be inferred in the inversion of the empirical rates. In this study, we combine the most recent GRACE-observed rates of gravity change converted to vertical crustal motion, water gauge (and altimetry) data, and GPS velocity data. The combined vertical motion model is realized via a least-squares adjustment procedure, which incorporates variance-component estimation and robust outlier detection. The latter is necessary to ensure reliable estimates of relative errors in the combined least-squares adjustment (via re-scaling of covariance matrices) and to ensure that the final vertical motion model is not distorted by erroneous data. The combined vertical motion model shows a subsidence of -2 mm/yr along the southern shores and uplift of 3 – 4 mm/yr along the northern shores.
G51A-0142
GPS and Tide Gauge Constraints on Subsidence and Relative sea Level Rise Along the US East Coast
Relative sea level change has two distinct components, absolute sea level variation and movement of Earth's crust. The movement of the crust can sometimes bias estimation of absolute sea level change as inferred by tide gauge data. We employ high accuracy GPS measurements (Sella et al., 2007) to detect movement of the crust in eastern North America, primarily reflecting areas that are affected by Glacial Isostatic Adjustment (GIA). In particular, these data define the collapse of the "peripheral bulge". We compare the GPS data to relative sea level change as recorded by tide gauges. We use all tide gauge stations along the east coast of North America that have more than 60 years of data, and estimate the rate of relative sea level rise using a model that accounts for annual, semi-annual and decadal signals in the time series. The GPS data show regions with subsidence rate > 2mm/year between Virginia and South Carolina, ~1900--2500km away from the uplift center in Hudson Bay. Tide gauge data in these areas show about 4mm/year relative sea level rise. The inferred global sea level rise rate is about 2mm/year. Thus, land subsidence in these regions effectively doubles the relative sea level rise rate and the corresponding natural hazard.
G51A-0143
Inverse modelling of surface subsidence to better understand the Earth's subsurface
Surface subsidence can have major repercussions. A classic example is the seabed above the Ekofisk oil field, offshore Norway, where excessive subsidence made it necessary to raise the production platform by 6 m in the 1980s. On land, subsidence may significantly increase the risk of damage to buildings and infrastructure. But, observations of subsidence can also give us a better handle on the subsurface processes like compaction behaviour of a reservoir, (un)drained compartments, or the strength of the aquifer. However, to get this information from subsidence data, you have to carefully follow an inversion procedure. This inversion exercise is a big challenge in which all the available knowledge has to be used to the fullest possible extent. Without the use of this prior knowledge the solution will be non-unique or very ill-conditioned. In our method we distinguish and quantify shallow and deep causes of subsidence in a time-resolved procedure. We take full advantage of all the available knowledge in the form of a prior model, the prior model covariance matrix, and the data covariance matrix. The covariances quantify the expected spatial and temporal relationships between the model points and the data points. As an example, the incorporation of the model covariance implicitly guarantees smoothness of the model estimate, while maintaining specific geological features like sharp boundaries. In two examples we demonstrate the strength of the method. The first example shows that prior knowledge in the form of a correct model parameterization (deep and shallow compaction) is crucial for a reliable result. The second example demonstrates the significant added value of fully accounting for the geology and the reservoir engineering information. Probabilistic information is entered using Monte Carlo simulations with a standard reservoir simulator, with several driving parameters being uncertain. The Monte Carlo runs deliver the prior model estimate and its covariance matrix. The inversion results in a good approximation of the driving parameters, even while their effects in terms of subsidence are highly correlated.
G51A-0144
Observational evidence for volcanic impact on sea level and the global water cycle
It has previously been noted that there are drops in global sea level (GSL) following some major volcanic eruptions. However, observational evidence has not been convincing as there is substantial variability in the global sea level record on periods similar to those at which we expect volcanoes to have an impact. To quantify the impact of volcanic eruptions we average monthly GSL data from 830 tide gauge records around 5 major volcanic eruptions. Surprisingly, we find that the initial response to a volcanic eruption is a significant rise in sea level of 9 ± 3 mm in the first year after the eruption. This is followed by a drop of 7 ± 3 mm in the period 2-3 years after the eruption relative to pre-eruption sea level. These results are statistically robust and no particular volcanic eruption or ocean region dominates the signature we find. Neither the drop nor especially the rise in GSL can be explained by models of lower oceanic heat content. We suggest that the mechanism is a transient disturbance of the water cycle with a delayed response of land river runoff relative to ocean evaporation and global precipitation that affects global sea level. The volcanic impact on the water cycle and sea levels is comparable in magnitude to that of a large El Niño-La Niña cycle, amounting to about 5% of global land precipitation.
G51A-0145
Inter-comparison of multi-sensor results for high-speed rail risk analysis
The Taiwan high speed rail (THSR) is one of the most important national infrastructures. Because of its high speed, a stringent code of construction is demanded. To ensure a safe operation, the differential settlement rate of rail track should be less than 1/1000. Surface or underground subsidence will lead to failures of the foundations of rail structures and deformations of rail tracks. The effect of subsidence on the THSR structure varies with the depth of soil formation where consolidation (or groundwater withdrawal) occurs. If soil consolidation occurs above the bearing layer of the pile foundation, it will interact with the pile foundation and produce a negative skin friction, which reduces the pile bearing capacity and degrades the vertical capacity of the viaduct foundation. In the Yunlin County of Taiwan, a section of the THSR rail passes through an area undergoing significant subsidence (the current maximum rate is 10 cm/year). In an area close to the THSR, the cumulative subsidence between 1992 and 2006 is 100 cm. In order to monitor the subsidence along this section, an integrated sensor system, including INSAR, GPS, leveling and monitoring well, are deployed. INSAR will be used to map the 2-d surface deformation. Wells with observing rings at different depths are used to measure the compaction rates at various layers of strata. GPS receivers are mounted on pillars attached to the rail track to observe its vertical motion. A precision leveling network is established to measure the surface deformation. These sensors provide data revealing the surface and underground deformations around this area. This paper presents an inter- comparison of the deformations from these sensors and presents vital information for drafting a safety code for the THSR
G51A-0146
Monitoring Sea Level At L'Estartit, Spain
Sea level is an environmental variable which is widely recognised as being important in many scientific disciplines as a control parameter for coastal dynamical processes or climate processes in the coupled atmosphere-ocean systems, as well as engineering applications. A major source of sea-level data are the national networks of coastal tide gauges, in Spain belonging to different institutions as the Instituto Geográfico Nacional (IGN), Puertos del Estado (PE), Instituto Hidrográfico de la Marina (IHM), Ports de la Generalitat, etc. Three Begur Cape experiences on radar altimeter calibration and marine geoid mapping made on 1999, 2000 and 2002 are overviewed. The marine geoid has been used to relate the coastal tide gauge data from l'Estartit harbour to off-shore altimetric data. The necessity to validate and calibrate the satellite's altimeter due to increasing needs in accuracy and long term integrity implies establishing calibration sites with enhanced ground based methods for sea level monitoring. A technical Spanish contribution to the calibration experience has been the design of GPS buoys and GPS catamaran taking in account the University of Colorado at Boulder and Senetosa/Capraia designs. Altimeter calibration is essential to obtain an absolute measure of sea level, as are knowing the instrument's drifts and bias. Specially designed tidegauges are necessary to improve the quality of altimetric data, preferably near the satellite track. Further, due to systematic differences a month instruments onboard different satellites, several in-situ calibrations are essentials to tie their systematic differences. L'Estartit tide gauge is a classical floating tide gauge set up in l'Estartit harbour (NE Spain) in 1990. It provides good quality information about the changes in the sea heights at centimetre level, that is the magnitude of the common tides in theMediterranean. In the framework of a Spanish Space Project, ref:ESP2001- 4534-PE, the instrumentation of sea level measurements as been improved by providing this site with a radar tide gauge and with a continuous GPS station nearby. This will have a significant incidence in the satellite altimeter calibration activities. The radar tide gauge with data recorder and transmitter is a Datamar 3000C with 26 GHz frequency, 1mm resolution, 8º beam width incorporating a GPS receiver for automatic clock synchronization and a Thales Navigation Internet-Enabled GPS Continuous Geodetic Reference Station (iCGRS) with a choke ring antenna. It is intended that the overall system will constitute a CGPS Station of the ESEAS (European Sea Level) and TIGA (GPS Tide Gauge Benchmark Monitoring) networks. A Partenavia P-68 airborne LIDAR campaign carrying an Optech Lidar ALT-3025 has been made in June 2007 to test the potential of Lidar to connect sea level measurements from tide gauges at the coast with satellite (as Jason-1 or Envisat) altimetry measurements offshore. The calibrated airborne Lidar can then be used over ocean to detect the sea surface height. In consequence, the objective is to check that the coastal sea level can be observed with GPS buoys and may be Lidar campaigns for get detailed regional geoid and sea surface topography models for referencing satellite altimeter measurements.
G51A-0147
Seafloor Crustal Deformation Close to the Nankai Trough, Japan
\ \ \ The Nankai Trough is one of the active plate boundaries in the world. Major subduction earthquakes, Nankai and Tonankai earthquakes, repeatedly occur with intervals of 100-150 years at the Nankai Trough. The last large earthquakes occurred in 1944 and 1946. Therefore, the 50-years probabilities of next major earthquakes are 80- 90 %. It is necessary to monitor crustal deformation above the source regions for the sake of earthquake prediction and disaster prevention. The source regions of the earthquakes are located beneath the sea bottom, to the south of the Japan Islands. \par \ \ \ One of the useful tools to monitor seafloor crustal deformation is the observation system composed of the acoustic ranging and kinematic GPS positioning techniques. We have installed seafloor benchmarks for acoustic ranging at the Nankai Trough region. We repeatedly observed at the two sites from 2004. The result of the repeated observation shows that the repeatability of the measurement is +/- 2-3 cm for the horizontal components. Also we detect crustal deformation related to plate convergence using our system. The velocity vectors derived from our repeated observation are (7.0 cm/yr, N78W) and (5.2 cm/yr, N87W), which is consistent to the on-land continuous observations.\par \ \ \ This study is promoted by Ministry of Education, Culture, Sports, Science and Technology, Japan. We are grateful to the captains and crews of Research Vessels, "Asama"and "Hokuto."
G51A-0148
An analysis of kinematic GPS from a buoy during the event of September 5th, 2004 the Kii peninsula earthquake
A tsunami due to the 2004 M7.4 September 5th earthquake off of the Kii peninsula, was recorded at the GPS buoy established about 13 km off of the Muroto Promontory, southwestern Japan. The buoy GPS data, differenced with that of a base station in Muroto, were used successfully to sense, in real-time, the tsunami waves as they went by at the point. The main challenge, now, is to detect tsunami with buoys placed much farther from shore, so as to give much earlier warning to the coastal populations likely to be affected. Long-baseline GPS solutions are intrinsically less precise than short-baseline ones. This is primarily because there are fewer satellites in the common view of the both the receiver and base station. To understand better how to get reliable and sensitive early tsunami detection, the GPS buoy data have been reprocessed with a precise, long-baseline differential GPS positioning technique, using dual-frequency carrier phase with floated ambiguities, implemented in the Bernese GPS software (BSW) version 5.0. In this paper, we also investigated the possible use of the kinematic GPS point positioning method in BSW. The GPS results shows excellent agreement with both the tidal record from a gauge near Muroto, where they arrived some 12 minutes later, and the predicted tsunami record based on preliminary source model. As indicated, GPS buoy relative to long-baseline land base may served as a powerful tool for monitoring tsunami as a part of the countermeasure for tsunami disaster mitigation.
G51A-0149
Mapping the Coastline Limits of the Mexican State Sinaloa Using GPS
This research work presents the delimitation of the coastline limits of Sinaloa (one of the richest states of northwestern Mexico). In order to achieve this big task, it was required to use GPS (Global Positioning System) together with leveling spirit measurements. Based on the appropriate selection of the cited measurement techniques, the objective was to map the Sinaloa's state coastline to have the cartography of approximate 1600 km of littoral. The GPS measurements were performed and referred with respect to a GPS network located across the state. This GPS network consists of at least one first-order-site at each of the sixteen counties that constitute the state, and three to four second-order-sites of the ten counties of the state surrounded by sea. The leveling spirit measurements were referred to local benchmarks pre-established by the Mexican agency SEMARNAT (SEcretaría Del Medio Ambiente y Recursos NATurales). Within the main specifications of the GPS measurements and equipment, we used geodetic-dual-frequency GPS receivers in kinematic mode for both base stations (first and second order sites of the GPS state network) and rover stations (points forming the state littoral) with 5-sec log-rate interval and 10 deg cut-off angle. The GPS data processing was performed using the commercial software Trimble Geomatics Office (TGO) with Double Differences (DD) in post-processing mode. To this point, the field measurements had been totally covered including the cartography (scale 1:1000) and this includes the specifications and appropriate labeling according to the Mexican norm NOM-146-SEMARNAT-2005.