On monitoring a vertical datum with satellite altimetry and water-level gauge data on large lakes

Using TOPEX satellite altimetry, water-level-gauge data, and a geoid model, the geopotential, W ₀, of the International Great Lakes Datum of 1985 (IGLD85) is determined. This is compared to an analogous determination using GPS and leveling data in the region. The two sets of data yield generally consistent results at the few-decimeter level and both indicate a tilt of about 33 cm in the computed datum across the region. On the basis of this and other studies, it is conjectured that the source of the tilt is a regional error in G99SSS. Further analysis of the altimetry and water-level data indicate that the geoid model, G99SSS, is in error by up to 20 cm at scales of about 100–150 km. In addition, the analysis of 8 years of altimeter and water-level data shows varying trends (up to 2 mm/yr) in crustal uplift throughout the region, generally consistent with an independent post-glacial rebound (PGR) model, ICE-4G. AcknowledgmentThis research was supported in part by the Ohio Sea Grant Program, grant no. NA86RG0053 (R/CE-5). A. Mainville kindly provided data and information for Canadian stations. The authors are grateful to M. Bursa, M. Poutanen, D. Zilkoski, and an anonymous reviewer for contributing significantly to the improvement of the paper.     

Computation of spherical harmonic coefficients from gravity gradiometry data to be acquired by the GOCE satellite: regularization issues

The issue of optimal regularization is investigated in the context of the processing of satellite gravity gradiometry (SGG) data that will be acquired by the GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) satellite. These data are considered as the input for determination of the Earths gravity field in the form of a series of spherical harmonics. Exploitation of a recently developed fast processing algorithm allowed a very realistic setup of the numerical experiments to be specified, in particular: a non-repeat orbit; 1-s sampling rate; half-year duration of data series; and maximum degree and order set to 300. The first goal of the study is to compare different regularization techniques (regularization matrices). The conclusion is that the first-order Tikhonov regularization matrix (the elements are practically proportional to the degree squared) and the Kaula regularization matrix (the elements are proportional to the fourth power of the degree) are somewhat superior to other regularization techniques. The second goal is to assess the generalized cross-validation method for the selection of the regularization parameter. The inference is that the regularization parameter found this way is very reasonable. The time expenditure required by the generalized cross-validation method remains modest even when a half-year set of SGG data is considered. The numerical study also allows conclusions to be drawn regarding the quality of the Earths gravity field model that can be obtained from the GOCE SGG data. In particular, it is shown that the cumulative geoid height error between degrees 31 and 200 will not exceed 1 cm. AcknowledgmentsThe authors thank Dr. E. Schrama for valuable discussions and for computing the orbit used to generate the long data set. They are also grateful to Prof. Tscherning and two anonymous reviewers for numerous valuable remarks and suggestions. The orbit to generate the short data set was kindly provided by J. van den IJssel. Computing resources were provided by Stichting Nationale Computerfaciliteiten (NCF), grant SG-027.     

Satellite-Derived ERS scatterometer sea-surface wind-stress curl in the southwestern Indian Ocean

Surface marine wind data base from ERS-1 scatterometer has been processed to define the characteristic seasonal distribution of wind-stress curl throughout the southwestern Indian Ocean between January and December 1994. A compact model to obtain satellite-derived wind-stress curl fields on smaller scales than previously available is proposed and evaluated. The results indicate the strong capability of the ERS-1 scatterometer to monitor wind-driven variations in the mesoscale ocean patterns. To cite this article: M. Petit et al., C. R. Geoscience 338 (2006).     

Defining a DORIS core network for Jason-1 precise orbit determination based on ITRF2000: methods and realization

In view of the future adoption of the new precise orbit determination (POD) standards for the TOPEX/Poseidon and Jason-1 satellites, we propose a method to evaluate terrestrial reference frames for POD. We applied this method to the ITRF2000 realization of the DORIS network using local geodetic ties, plate motion models, the recent DORIS IGN04D02 cumulative solution and DORIS weekly time-series of coordinates. We propose to adopt a selection of the ITRF2000 realization based on specific criteria that we define here, and to extend it with ground stations for which we propose new coordinates and velocities. Only 13 out of 131 stations were considered to be inappropriate for POD activities. The result is a robust and well-distributed DORIS core network of 118 stations (DPOD2000) suitable for POD during the 1993–2008 period considered here.     

三江平原土地利用分类研究

本文描述了利用卫星遥感技术，结合GPS、GIS，以2002年2景陆地卫星TM图像为主要信息源，前进镇为中心，对三江平原部分地区进行土地利用现状和耕地资源调查分类研究．制定了分类指标，生成三江平原2002年土地利用分类图。经地面调查检验，分类结果与实际下垫面情况基本吻合，分类精度较高。     

Discharge and transport processes along the German Baltic Sea Coast

The western Baltic Sea infront of the German coast is a highly variable dynamical system, dominated by a complex and small-scale morphometry, the water exchange between the Baltic and North Seas, and driven by local wind. Neither data collection, nor satellite images or model simulations alone were able to explain the observed spatial patterns and transport processes. Therefore, all these methods were combined to explain the dynamical features and to systematise them according to the typical local wind pattern and time series. The aim was to develop an instrument for regional authorities which supports the interpretation of coastal water monitoring data and forms a basis for an improved monitoring strategy. Satellite data of sea surface temperature and ocean colour from the sensors NOAA-AVHRR and SeaWiFS were applied for synoptic investigations in the entire region and Landsat-7-ETM+ for regional studies. Model simulations were performed for the western Baltic using a 3D model MOM-3 and for the Szczecin Lagoon using 2D model FEMFLOW. For the first time, regional particularities in the coastal dynamical features and processes are derived for the main wind directions and for transitions between dominant wind situations west and east as derived from wind statistics. The simulated transport of particles released from different coastal and open sea sources indicate the affected areas during changing forcing conditions. The results support the interpretation of acquired coastal monitoring data as well as the assessment and optimisation of the monitoring programme.     

Geologic controls of submarine groundwater discharge: application of remote sensing to north Lebanon

Typical of Mediterranean countries, the Lebanese shoreline is well known for its littoral and offshore groundwater discharges, the so-called submarine springs. The tectonic framework of the terrain explains its interruption by dense geologic structures, i.e., fracturing, faulting, karstic routes, as well as acute dips of rock strata seaward. All of these structures serve as hydrologic agents transporting groundwater to the sea. The study aims to locate these groundwater discharges, and to interpret their geologic controls on land. For this purpose, two major lines of approach were followed. The first is an airborne thermal infrared (TIR) survey using radiometers to identify thermal anomalies, thereby determining the exact location of submarine groundwater discharges (SGDs). The second line of approach is the analysis of satellite images (Landsat 7ETM⁺) to delineate the geologic features that govern the mechanism of water flow, thereby determining their sources on land. Twenty-seven major SGDs were identified, 10 of these being offshore springs, the others littoral springs. The springs show a large variety of discharge configurations and extents, mainly parallel or perpendicular to the shoreline or rounded. Three major structural controls were identified to contribute to the transport of groundwater to the sea. These are karstic galleries, faults, and tilted rock strata, their contributions being 48, 37, and 15%, respectively. The SGDs associated with linear passageways, i.e., karstic galleries and faults, are connected with land aquifer formations several kilometers away from the shoreline. Moreover, the presence of impervious rock formations at many localities along the coastline results in a confined hydrologic system, promoting the flow of SGDs into the sea.     

Targeted GOES Satellite Observations to Improve Hurricane Track Forecast: A Case Study of Hurricane Floyd

This study performs a set of Observing System Simulation Experiments (OSSEs) using Geostationary Operational Environmental Satellite (GOES) soundings. The primary objective of the OSSEs is to demonstrate that targeted observations can improve forecast accuracy by enhancing the initial conditions and mitigating their uncertainties. Hurricane Floyd (1999) is chosen as a study case. The main reason for choosing hurricane Floyd as a test case is that the movement of the storm was dictated by a mid-level complex polar jet steering flow region. This well-defined feature allowed us to examine the inaccuracy of analysis over the steering flow area using GOES soundings as targeted observations and its impact on the forecast track error. The set of experiments starts from a baseline forecast of hurricane Floyd using the Operational Multiscale Environment model with Grid Adaptivity (OMEGA). From GOES satellite soundings, atmospheric vertical profiles were extracted to simulate targeted observations. These data extracts were assimilated in the initial conditions to simulate new forecasts of hurricane Floyd which were then compared against both the baseline track and observed track. It was found that targeted observations in a forecast sensitive area can help to reduce hurricane forecast track error. Assimilation of only the subset of data (about 50 soundings) from the subjectively chosen fully sampled target region produced a considerable reduction of the track forecast errors (about 30%) within the first critical three days of the forecast.     

高分辨率卫星影像GPS像控点数据库建设研究

本通过对SPOT2.5m高分辨率卫星影像数据校正采用的各类控制资料的分析,阐述了GPS像控点数据库建设的必要性,通过对像控点的选取、外业施测、精度评价及GPS像控点数据库建设等论述,提出了选用GPS控制点作为SPOT2.5m高分辨率卫星影像数据校正控制资料,可保证影像校正精度、节省时间和减少投资。