Comparison of sequential updating, Kalman filter and variational methods for assimilating Rossby waves in the simulated Geosat altimeter data into a quasi-geostrophic model

1995 ◽  
Vol 6 (1-2) ◽  
pp. 15-30 ◽  
Author(s):  
M. Ikeda ◽  
G. Evensen ◽  
L. Cong
Keyword(s):  
Kalman Filter ◽  
Variational Methods ◽  
Rossby Waves ◽  
Altimeter Data ◽  
Sequential Updating

scholarly journals Nonlinear features of equatorial baroclinic Rossby waves detected in Topex altimeter observations

1996 ◽  
Vol 3 (2) ◽  
pp. 115-126 ◽  
Author(s):  
R. E. Glazman ◽  
A. Fabrikant ◽  
A. M. Greysukh
Keyword(s):  
Rossby Waves ◽  
Propagation Speed ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Wave Regime ◽  
Nonlinear Features ◽  
Wavenumber Spectrum ◽  
Satellite Altimeter Data ◽  
Rule Out

Abstract. Using a recently proposed technique for statistical analysis of non-gridded satellite altimeter data, regime of long equatorially-trapped baroclinic Rossby waves is studied. One-dimensional spatial and spatiotemporal autocorrelation functions of sea surface height (SSH) variations yield a broad spectrum of baroclinic Rossby waves and permit determination of their propagation speed. The 1-d wavenumber spectrum of zonal variations is given by a power-law k-2 on scales from about 103 km to 104 km. We demonstrate that the observed wave regime exhibits features of soliton turbulence developing in the long baroclinic Rossby waves. However, being limited to second statistical moments, the present analysis does not allow us to rule out a possibility of weak wave turbulence.

scholarly journals Non-tidal aliasing in seasonal sea-level variability and annual Rossby waves as observed by satellite altimetry

1997 ◽  
Vol 15 (11) ◽  
pp. 1478-1488 ◽  
Author(s):  
G. Chen ◽  
R. Ezraty
Keyword(s):  
Numerical Simulations ◽  
Systematic Error ◽  
Sea Level ◽  
Satellite Altimetry ◽  
Rossby Waves ◽  
Altimeter Data ◽  
Ocean Tides ◽  
Satellite Altimeter ◽  
Sea Level Variability ◽  
Satellite Altimeter Data

Abstract. It is becoming well known that aliasing associated with ocean tides could be a major source of systematic error in altimeter sea-level measurements, due to asynoptic sampling and imperfect tide modelling. However, it has been shown that signals of non-tidal origin may also contribute significantly to the observed aliasing. In this paper, numerical simulations are performed to demonstrate the full aliasing potential associated with altimeter observations of seasonal sea-level variability and annual Rossby waves. Our results indicate that ignorance of non-tidal aliasing may lead to the possibility of underestimating the total aliasing and misinterpreting or overlooking existing geophysical phenomena. Therefore, it is argued that an entire aliasing picture should be kept in mind when satellite altimeter data are analysed.

scholarly journals A Model Study of the Spectral Structure of Boundary-Driven Rossby Waves and Related Altimetric Implications

2005 ◽  
Vol 35 (2) ◽  
pp. 218-231 ◽  
Author(s):  
Stefano Pierini
Keyword(s):  
Large Scale ◽  
Rossby Waves ◽  
North Pacific Ocean ◽  
Altimeter Data ◽  
Western Boundary ◽  
Spectral Structure ◽  
The North ◽  
Model Study ◽  
General Aspects ◽  
Coastal Kelvin Waves

Abstract A two-layer primitive equation box model of the North Pacific Ocean is used to highlight and analyze some general aspects of the linear large-scale boundary-driven oceanic variability that are detectable through altimeter observations. The model is forced by a white-noise wind, and a spectral analysis of the zonal and meridional, barotropic and baroclinic velocity components is carried out. Several dynamical features are identified in terms of boundary-driven Rossby waves, and their spatial structure and frequency dependence are examined theoretically and discussed in connection with recent studies based on altimeter data. In particular, the following aspects of the variability are analyzed: 1) beta-refracted baroclinic Rossby waves, which are found to be generated along the eastern boundary of the ocean by the passage of coastal Kelvin waves originating from the equatorial waveguide, and 2) westward-intensified barotropic Rossby waves, which originate from the western boundary of the ocean after reflection of longer waves generated in midocean. In the discussion the stress is put on dynamical aspects not yet fully understood and on the possibility that altimetry can provide further insight into their functioning.

scholarly journals Autonomous Orbit Determination for a Hybrid Constellation

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Muzi Li ◽  
Bo Xu ◽  
Jun Sun
Keyword(s):  
Remote Sensing ◽  
Monte Carlo ◽  
Kalman Filter ◽  
Orbit Determination ◽  
Main Idea ◽  
Altimeter Data ◽  
Range Data ◽  
Leo Satellites ◽  
Autonomous Orbit Determination ◽  
Hybrid Constellation

A new orbit determination scheme targeting communication and remote sensing satellites in a hybrid constellation is investigated in this paper. We first design one such hybrid constellation with a two-layer configuration (LEO/MEO) by optimizing coverage and revisit cycle. The main idea of the scheme is to use a combination of imagery, altimeter data, and inter-satellite range data as measurements and determine orbits of the satellites in the hybrid constellation with the help of the extended Kalman filter (EKF). The performance of the new scheme is analyzed with Monte Carlo simulations. We first focus on an individual remote sensing satellite and compared the performance of orbit determination using only imagery with its counterpart using both imagery and altimeter measurements. Results show that the performance improves when imagery is used with altimeter data pointing to geometer calibration sites but declines when used with ocean altimeter data. We then expand the investigation to the whole constellation. When inter-satellite range data is added, orbits of all the satellites in the hybrid constellation can be autonomously determined. We find that the combination of inter-satellite range data with remote sensing observations lead to a further improvement in orbit determination precision for LEO satellites. Our results also show that the performance of the scheme would be affected when remote sensing observations on certain satellites are absent.

Indian Ocean Rossby waves observed in TOPEX/POSEIDON altimeter data and in model simulations

2001 ◽  
Vol 22 (1) ◽  
pp. 141-167 ◽  
Author(s):  
B. Subrahmanyam ◽  
I. S. Robinson ◽  
J. R Blundell ◽  
P. G. Challenor
Keyword(s):  
Indian Ocean ◽  
Rossby Waves ◽  
Altimeter Data ◽  
Model Simulations

The Hybrid Local Ensemble Transform Kalman Filter

2014 ◽  
Vol 142 (6) ◽  
pp. 2139-2149 ◽  
Author(s):  
Stephen G. Penny
Keyword(s):  
Kalman Filter ◽  
Data Assimilation ◽  
Variational Methods ◽  
Hybrid Methods ◽  
Dynamic Error ◽  
Background Error ◽  
Error Covariance ◽  
Small Ensemble ◽  
Ensemble Transform Kalman Filter ◽  
Ensemble Transform

Abstract Hybrid data assimilation methods combine elements of ensemble Kalman filters (EnKF) and variational methods. While most approaches have focused on augmenting an operational variational system with dynamic error covariance information from an ensemble, this study takes the opposite perspective of augmenting an operational EnKF with information from a simple 3D variational data assimilation (3D-Var) method. A class of hybrid methods is introduced that combines the gain matrices of the ensemble and variational methods, rather than linearly combining the respective background error covariances. A hybrid local ensemble transform Kalman filter (Hybrid-LETKF) is presented in two forms: 1) a traditionally motivated Hybrid/Covariance-LETKF that combines the background error covariance matrices of LETKF and 3D-Var, and 2) a simple-to-implement algorithm called the Hybrid/Mean-LETKF that falls into the new class of hybrid gain methods. Both forms improve analysis errors when using small ensemble sizes and low observation coverage versus either LETKF or 3D-Var used alone. The results imply that for small ensemble sizes, allowing a solution to be found outside of the space spanned by ensemble members provides robustness in both hybrid methods compared to LETKF alone. Finally, the simplicity of the Hybrid/Mean-LETKF design implies that this algorithm can be applied operationally while requiring only minor modifications to an existing operational 3D-Var system.

scholarly journals Kalman filter approach for estimating water level time series over inland water using multi-mission satellite altimetry

2015 ◽  
Vol 12 (5) ◽  
pp. 4813-4855 ◽  
Author(s):  
C. Schwatke ◽  
D. Dettmering ◽  
W. Bosch ◽  
F. Seitz
Keyword(s):  
Time Series ◽  
Kalman Filter ◽  
Water Level ◽  
Satellite Altimetry ◽  
Water Levels ◽  
Altimeter Data ◽  
New Approach ◽  
Inland Water ◽  
Filter Approach

Abstract. Satellite altimetry has been designed for sea level monitoring over open ocean areas. However, since some years, this technology is also used for observing inland water levels of lakes and rivers. In this paper, a new approach for the estimation of inland water level time series is described. It is used for the computation of time series available through the web service "Database for Hydrological Time Series over Inland Water" (DAHITI). The method is based on a Kalman filter approach incorporating multi-mission altimeter observations and their uncertainties. As input data, cross-calibrated altimeter data from Envisat, ERS-2, Jason-1, Jason-2, Topex/Poseidon, and SARAL/AltiKa are used. The paper presents water level time series for a variety of lakes and rivers in North and South America featuring different characteristics such as shape, lake extent, river width, and data coverage. A comprehensive validation is performed by comparison with in-situ gauge data and results from external inland altimeter databases. The new approach yields RMS differences with respect to in-situ data between 4 and 38 cm for lakes and 12 and 139 cm for rivers, respectively. For most study cases, more accurate height information than from available other altimeter data bases can be achieved.

scholarly journals The Vertical Structure of Large-Scale Unsteady Currents

2015 ◽  
Vol 45 (3) ◽  
pp. 755-777 ◽  
Author(s):  
Antoine Hochet ◽  
Alain Colin de Verdière ◽  
Robert Scott
Keyword(s):  
Linear Model ◽  
Large Scale ◽  
Vertical Structure ◽  
Rossby Waves ◽  
Ocean Model ◽  
Altimeter Data ◽  
Western Boundary ◽  
Mean Flow ◽  
Low Latitudes ◽  
Barotropic Mode

AbstractA linear model based on the quasigeostrophic equations is constructed in order to predict the vertical structure of Rossby waves and, more broadly, of anomalies resolved by altimeter data, roughly with periods longer than 20 days and with wavelengths larger than 100 km. The subsurface field is reconstructed from sea surface height and climatological stratification. The solution is calculated in periodic rectangular regions with a 3D discrete Fourier transform. The effect of the mean flow on Rossby waves is neglected, which the authors believe is a reasonable approximation for low latitudes. The method used has been tested with an idealized double-gyre simulation [performed with the Miami Isopycnal Coordinate Ocean Model (MICOM)]. The linear model is able to give reasonable predictions of subsurface currents at low latitudes (below approximately 30°) and for relatively weak mean flow. However, the predictions degrade with stronger mean flows and higher latitudes. The subsurface velocities calculated with this model using AVISO altimetric data and velocities from current meters have also been compared. Results show that the model gives reasonably accurate results away from the top and bottom boundaries, side boundaries, and far from western boundary currents. This study found, for the regions where the model is valid, an energy partition of the traditional modes of approximately 68% in the barotropic mode and 25% in the first baroclinic mode. Only 20% of the observed kinetic energy can be attributed to free Rossby waves of long periods that propagate energy to the west.

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