Nico Sneeuw

Nico Sneeuw
Universität Stuttgart · Institute of Geodesy

Prof. Dr.-Ing.

About

233
Publications
47,887
Reads
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3,219
Citations
Additional affiliations
July 2005 - present
Universität Stuttgart
Position
  • Professor (Full)
Description
  • Head of Institute
July 2001 - July 2005
The University of Calgary
Position
  • Professor (Assistant)
July 1993 - May 2000
Technische Universität München
Position
  • Research Assistant

Publications

Publications (233)
Article
High mountain glaciers (HMGs), called the water towers of the world, are vulnerable to the effects of climate change and thus are rapidly shrinking. Monitoring and evaluating large-scale glacier and snow (GS) mass changes are critical for humans and ecosystems. Although modern gravity satellites monitor GS on a global scale, the contemporary Gravit...
Article
Study area Iran. Study focus Iran, once a pioneer of sustainable water management, is currently facing water bankruptcy. Aggressive exhaustion of non-renewable water has led to a suite of environmental and socio-economic problems across the country. Nevertheless, the understanding of Iran’s water loss is still incomplete due to a lack of conclusiv...
Article
Prevalent north–south striping (NSS) noise in the spherical harmonic coefficient products of the satellite missions gravity recovery and climate experiment greatly impedes the interpretation of signals. The overwhelming NSS noise always leads to excessive smoothing of the data, allowing a large room for improvement in the spatial resolution if this...
Preprint
Full-text available
The Congo Basin is of global significance for biodiversity and the water and carbon cycles. However, its freshwater availability remains highly unknown. Here, we leverage a new method to characterize the relationship between drainable water storage and river discharge across the entire basin. We estimate that the Congo Basin currently holds 481 ± 2...
Article
Ocean tide aliasing is one of the largest error sources in satellite gravimetry. Despite its importance, the aliasing mechanism of ocean tides in satellite gravimetry is only partially understood. This paper explains tidal aliasing as a two-step mechanism. The primary aliasing is caused by orbit undersampling of original tidal signals. The secondar...
Article
Full-text available
The number of active gauges with open‐data policy for discharge monitoring along rivers has decreased over the last decades. Therefore, spaceborne measurements are investigated as alternatives. Among different techniques for estimating river discharge from space, developing a rating curve between the ground‐based discharge and spaceborne river wate...
Article
Global gridded precipitation datasets have been developed using rain gauges, satellite observations, and data assimilation techniques to fulfill the need in regions with a limited contribution of ground observations like Iran. This study presents a comprehensive evaluation of currently available precipitation datasets over Iran at monthly (44 datas...
Article
Hydrological changes, which are affected by climate variability and human activities, pose challenges to the sustainable management and conservation of water resources. As such, it is important to improve our understanding of how climate and anthropogenic activities impact land water storage. Previous studies using Gravity Recovery and Climate Expe...
Article
Full-text available
Northeast Brazil is one of the most populated semiarid regions in the world. The region is highly dependent on reservoirs for human water supply, irrigation, industry, and livestock. The objective of this study was to validate water level time series from the satellites Envisat, SARAL, Sentinel-3A/-3B, Jason-2/-3 in small reservoirs in Northeast Br...
Preprint
Full-text available
Against the backdrop of global change, both in terms of climate and demography, there is a pressing need for monitoring the global water cycle. The publicly available global database is very limited in its spatial and temporal coverage worldwide. Moreover, the acquisition of in situ data and their delivery to the database are in decline since the l...
Article
Full-text available
A harmonic scalar field has a Laplacian (i.e., both source-free and curl-free) gradient vector field and vice versa. Despite the good performance of spherical harmonic series on modeling the gravitational field generated by spheroidal bodies (e.g., the Earth), the series may diverge inside the Brillouin sphere enclosing all field-generating mass. D...
Article
Full-text available
the Gravity Recovery and Climate Experiment (GRaCE) satellite mission recorded temporal variations in the Earth's gravity field, which are then converted to Total Water Storage Change (TWSC) fields representing an anomaly in the water mass stored in all three physical states, on and below the surface of the Earth. GRACE provided a first global obse...
Article
Full-text available
Monitoring changes in freshwater availability is critical for human society and sustainable economic development. To identify regions experiencing secular change in their water resources, many studies compute linear trends in the Total Water Storage (TWS) anomaly derived from the Gravity Recovery And Climate Experiment (GRACE) mission data. Such an...
Article
Satellite altimetry is increasingly considered as a valuable source of information in many hydrological and hydraulic applications. However, the accuracy of different sensors adopted for monitoring the water level from satellite and the limited temporal resolution that characterizes each sensor (i.e. revisit time most of time varying from 10 to 35...
Preprint
Full-text available
This paper presents an innovative approach, STREAM – SaTellite based Runoff Evaluation And Mapping – to derive daily river discharge and runoff estimates from satellite soil moisture, precipitation and terrestrial water storage anomalies observations. Within a very simple model structure, the first two variables (precipitation and soil moisture) ar...
Article
Full-text available
The spatiotemporal changes of lake water resources objectively reflect not only the process of the water resources balance, but also the ecological environment changes in the lake area. In recent decades, climate changes and human activities have caused great impacts on the spatial distribution of the earth’s water resources and the spatiotemporal...
Article
Full-text available
Earthquakes have been studied by means of seismometers recording the elastic waves travelling through the interior of our planet. Global Navigation Satellite System and Synthetic Aperture Radar surveys, measuring surface displacements, have provided additional information on earthquakes, as well as on those solid Earth processes responsible for the...
Article
Full-text available
The 2004 Sumatra, 2010 Maule, and 2011 Tohoku great earthquakes triggered tsunamis as large as a few decimeters over a few 100 km in the open ocean. The transient ocean mass redistribution propagating as tsunamis changed the Earth’s gravity field enough to perturb the GRACE satellites’ orbits at ~ 500 km above the surface. The on-board microwave ra...
Article
Lake Urmia, located in the North West of Iran, was once the most extensive permanent hypersaline lake in the world. Unsustainable water management in response to increasing demand together with climatic extremes have given rise to the lake's depletion during the last two decades. The Urmia Lake Restoration Program (ULRP) was established in 2013 and...
Chapter
In this paper, the three kind of solutions of TLS problem, the common solution by singular value decomposition (SVD), the iteration solution and Partial-EIV model are firstly reviewed with respect to their advantages and disadvantages. Then a newly developed Converted Total Least Squares (CTLS) dealing with the errors-in-variables (EIV) model is in...
Article
An increasing number of studies suggest that climate change causes variation in the terrestrial water cycle. It is known that the precipitation as the source of water storage change on land and ocean is directly influenced by sea surface temperature (SST). At scales larger than, say, 350 km such water storage variation can be monitored by the satel...
Chapter
Many studies in the past have discussed potential orbit configurations of future satellite gravity missions. Most of those works have targeted orbit optimization of the satellite missions of the next generation in the so-called Bender formation. The studies have investigated the impact of the Keplerian orbital parameters, especially the influence o...
Presentation
Full-text available
The complex spherical harmonic coefficients can be represented in terms of their amplitude and phase as opposed to their real and imaginary parts. This representation is called the polar-form of spherical harmonics. This alternative representation has been demonstrated to show novel insight into the filtering mechanism of GRACE spherical harmonic d...
Article
Full-text available
As the first satellite altimetry mission operating in sar (delay-Doppler) mode, CryoSat-2 is an interesting mission to analyze its performance for water level monitoring over inland water bodies. It offers the opportunity to make comparison of sar and conventional altimeters by a multi-mode altimeter mounted on the same platform with a long repeat...
Article
Full-text available
GRACE satellites have detected regional‐scale pre-seismic, co-seismic, and post-seismic gravity changes associated with great earthquakes during the GRACE era (2002‐2017). Earthquakes also excite global‐scale transient gravity changes associated with free oscillations that may be discerned for a few days. In this study, we examine such global gravi...
Chapter
Full-text available
The Laplace equation represents harmonic (i.e., both source-free and curl-free) fields. Despite the good performance of spherical harmonic series on modeling the gravitational field generated by spheroidal bodies (e.g., the Earth), the series may diverge inside the Brillouin sphere enclosing all field-generating mass. Divergence may realistically o...
Article
Full-text available
As changes in gravity are directly related to mass variability, satellite missions observing the Earth’s time varying gravity field are a unique tool for observing mass transport processes in the Earth system, such as the water cycle, rapid changes in the cryosphere, oceans, and solid Earth processes, on a global scale. The observation of Earth’s g...
Article
Full-text available
Analysis of Global Positioning System (GPS) position time series and its common mode components (CMC) is very important for the investigation of GPS technique error, the evaluation of environmental loading effects, and the estimation of a realistic and unbiased GPS velocity field for geodynamic applications. In this paper, we homogeneously processe...
Article
Full-text available
For future gravity satellite missions, aliasing of high frequency geophysical signals into the lower frequencies is one of the most challenging obstacles to recovering true gravity signals, i.e., to recover the truth. Several studies have investigated the impact of satellite groundtrack pattern on the quality of gravity recovery. Among those works,...
Article
Full-text available
Natural wetland ecosystems provide not only important habitats for many wildlife species, but also food for migratory and resident animals. In Shanghai, the Chongming Dongtan International Wetland, located at the mouth of the Yangtze River, plays an important role in maintaining both ecosystem health and ecological security of the island. Meanwhile...
Article
Full-text available
Mass redistribution of the atmosphere, oceans, and terrestrial water storage generates crustal displacements which can be predicted by environmental loading models and observed by the Global Positioning System (GPS). In this paper, daily height time series of 235 GPS stations derived from a homogeneously reprocessed Crustal Movement Observation Net...
Article
Full-text available
The mass change information from the Gravity Recovery And Climate Experiment (GRACE) satellite mission is available in terms of noisy spherical harmonic coefficients truncated at a maximum degree (band-limited). Therefore, filtering is an inevitable step in post-processing of GRACE fields to extract meaningful information about mass redistribution...
Code
This collection of Matlab scripts implements the data-driven approach introduced by Vishwakarma et al. 2016 and Vishwakarma et al. 2017. It uses a few matlab functions from Filter bundle, GSHS bundle, and uberall bundle. Therefore we suggest that please dowload all the bundles from: http://gracebundle.tuxfamily.org Please use the following citatio...
Article
In the Amazon River basin, water stored for months to years in the soils and subsurface provide a persistent resource that regulates local and global climate via teleconnections and provides water to plants in times of little rain. While Gravity Recovery and Climate Experiment (GRACE) satellites have provided the hydrological community with large a...
Poster
Full-text available
In this contribution we investigate the relationship between the total water storage change over China with the Niño indices: Niño 1+2, Niño 3, Niño 4, and Niño 3.4. We found several hot-spots which exhibit strong positive or negative correlation.
Article
Full-text available
The Global Positioning System (GPS) records monsoonal precipitable water vapor (PWV) and vertical crustal displacement (VCD) due to hydrological loading, and can thus be applied jointly to diagnose meteorological and hydrological droughts. We have analyzed the PWV and VCD observations during 2007.0–2015.0 at 26 continuous GPS stations located in Yu...
Article
Full-text available
One of the major sources of uncertainty in mass change estimates from level 02 GRACE products comes from the signal degradation due to filtering of noisy gravity field products. Filtering suppresses noise but also changes the signal via attenuation and leakage. Therefore, many methods have been devised to tackle the unavoidable signal loss due to f...
Article
Full-text available
The proposed Surface Water and Ocean Topography (SWOT) mission aims to improve spaceborne estimates of river discharge through its measurements of water surface elevation, river width and slope. SWOT, however, will not observe baseflow depth, which limits its value in estimating river discharge especially for those rivers with heterogeneous channel...
Presentation
Full-text available
Before the launch of the spaceborne gravimetry mission GRACE in 2002 filter theory on the sphere was still in its infancy in the geodetic literature. At the most the spherical versions of some familiar isotropic filters like the box-car filter or the Gaussian filter were used as a common tool. The satellite pair GRACE changed the field drastically....
Poster
The fresh water availability over land masses is changing rapidly under the influence of climate change and human intervention. In order to manage our water resources and plan for a better future, we need to demarcate the role of climate change. The total water storage change in a region is observed by the GRACE satellite mission, while many climat...
Article
In this study, we apply Tikhonov’s regularization algorithm for a 3-D density inversion from the gravity-gradiometry data. To reduce the non-uniqueness of the inverse solution (carried out without additional information from geological evidence), we implement the depth-weighting empirical function. However, the application of an empirical function...
Article
Full-text available
Representing the spherical harmonic spectrum of a field on the sphere in terms of its amplitude and phase is termed as its polar form. In this study, we look at how the amplitude and phase are affected by linear low-pass filtering. The impact of filtering on amplitude is well understood, but that on phase has not been studied previously. Here, we d...
Poster
The monthly GRACE products are contaminated with short wavelength noise. Therefore, filtering is essential for minimizing noise and extracting meaningful signal. However, filtering also affects the signal by introducing leakage that changes its phase and amplitude, which is a source of uncertainty in GRACE products. In order to minimize this uncert...
Poster
Full-text available
The noisy level 02 GRACE products from various groups need to be filtered in order to obtain meaningful information about water mass transport within the Earth system. Filtering affects signal, which increases the uncertainty in the filtered GRACE observed total water storage time series. The signal loss is restored using a correction strategy that...
Article
Full-text available
Our knowledge of the spatio-temporal variation of river hydrological parameters is surprisingly poor. In situ gauge stations are limited in spatial and temporal coverage, and their number has been decreasing during the past decades. On the other hand, remote sensing techniques have proven their ability to measure different parameters within the Ear...
Article
Many geoscience disciplines push for ever higher requirements on accuracy, homogeneity and time- and space-resolution of the Earth’s gravity field. Apart from better instruments or new observables, alternative satellite formations could improve the signal and error structure compared to Grace. One possibility to increase the sensitivity and isotrop...
Article
Seismic data are primarily used in studies of the Earth's lithospheric structure including the Moho geometry. In regions where seismic data are sparse or completely absent, gravimetric or combined gravimetric-seismic methods could be applied to determine the Moho depth. In this study we derive and present generalized expressions for solving the Ven...
Article
Full-text available
The Gravity Recovery and Climate Experiment (GRACE) satellite mission has provided time variable gravity information since its launch in 2002. Due to short-wavelength noise, the total water storage variations over a catchment observed from GRACE are usable only after filtering. Filtering smooths both the signal and the noise, inevitably changing th...
Chapter
Geodetic time series obtained via space-geodetic techniques, e.g. site displacements from continuous gps observations and aggregated basin water storages from grace, display a seasonal behavior. Much focus has been given to separate such periodic signal from other signals buried in the geodetic time series, e.g. linear or non-linear trends. Convent...
Article
2D Fourier series representation of a scalar field like gravitational potential is conventionally derived by making use of the Fourier series of the Legendre functions in the spherical harmonic representation. This representation has been employed so far only in the case of a scalar field or the functionals that are related to it through a radial d...
Poster
Full-text available
The gravity field products from Gravity Recovery And Climate Experiment (grace) satellites are usable only after filtering. Filtering suppresses noise, but also changes the signal. There are methods to minimize the signal change, and most of them depend on a hydrological model to compute leakage, scale factor or bias for improving the time-series s...
Article
Limitations of satellite radar altimetry for operational hydrology include its spatial and temporal sampling as well as measurement problems caused by local topography and heterogeneity of the reflecting surface. In this study, we develop an approach that eliminates most of these limitations to produce an approximately 3-day-temporal resolution wat...
Chapter
The launch of the GRACE mission brought a broad interest within the geophysical community in monitoring temporal gravity field variations. Due to the limited lifetime of GRACE, several studies have been conducted for the search of optimal GRACE follow-on and future satellite gravity missions. These studies mainly discuss the use of alternative form...
Chapter
Full-text available
Interest in filtering on the sphere was rejuvenated by the necessity to filter GRACE data, which has led to the development of a variety of filters with a multitude of design methods. Nevertheless, a lacuna exists in the understanding of filters and filtered fields, especially signal leakage due to filtering and resolution of the filtered field. In...
Chapter
Ocean tides cause notable aliasing errors in the gravity field from single pair space-borne gravimetry missions like GRACE. Several studies into future gravity missions have shown that constellations with two or more GRACE-like tandems lead to a significant reduction of aliasing error from all kinds of high-frequency signal sources. Despite such re...
Article
A key feature of geodetic adjustment theory is the description of stochastic properties of the estimated quantities. A variety of tools and measures have been developed to describe the quality of ordinary least-squares estimates, for example, variance-covariance information, redundancy numbers, etc. Many of these features can easily be extended to...
Article
Full-text available
In order to cope with the steady decline of the number of in situ gauges worldwide, there is a growing need for alternative methods to estimate runoff. We present an Ensemble Kalman Filter based approach that allows us to conclude on runoff for poorly or irregularly gauged basins. The approach focuses on the application of publicly available global...
Article
Full-text available
The Rosborough approach was developed in the 1980s for the modeling of orbit perturbations of altimeter satellites. It is a formalism that is rooted in the so-called time-wise approach, in which gravitational functionals are described as an along-orbit time series. Nevertheless, through a transformation of the orbital variables, the along-orbit fun...