The Must Have Box (MHBox) project focuses on understanding the causes of residual, non-tidal sea levels and currents (anomalies) in the Singapore region and from the understanding to develop a potential maritime decision support system for various potential stakeholders.
Scope of Study
The scope of the study to achieve the goals is summarized in the figure below.
Region of Interest
The main region of interest are the Singapore coastal waters which is part of the Sunda shelf surrounded by large ocean bodies (Andaman sea, South China sea, Indian Ocean and Java seas).
Principal Investigators: Herman Gerritsen (Deltares), Vladan Babovic (NUS)
Interesting Observations / Key Findings
Residual (non-tidal) currents are important phenomena in the Strait of Malacca and Strait of Singapore. At times, they can dominate the regular (e.g. tidal) flow conditions. The hypothesis is that a major contribution to residual currents results from regional water level variations, called Sea Level Anomalies (SLA’s). SLA’s may occur on different time scales (months, weeks or days) and preliminary analyses show that there may be considerable spatial variability within such periods. Persistent basin-scale monsoon winds over the South China Sea and Andaman Sea have been shown to be major contributing factors, creating differences in water levels that drive residual currents through the Straits. Non-tidal water level and current features occur on smaller time-scales as well, e.g. monsoon transition periods. Tropical storm fields in the region contribute on a timescale of up to a week with large spatial scales, just as the so-called “Sumatera’s”, generate strong anomalies on the time scales of hours with relatively small spatial scales.
- Satellite altimetry for better spatial resolution of Sea Level data:
Altimetry data from Jason-1 and Envisat satellites are combined and the interpolated time series data is extracted at the cross over points of both the tracks. The SLAs extracted from these altimetry data are validated with measured SLA (SLA obtained from in-situ measurements, available at select few locations in the region) and with SLA maps obtained from RADS/DUACS database.
- Judicious tidal analysis to derive SLA:
Careful tidal analysis of in-situ coastal water level data around Singapore reveals the presence of strong annual (seasonal) variation in residues. This annual variation can be represented as a tidal signal by additionally prescribing tidal constituent ‘SA’ (with almost one year period). After this correction, the water level residue gives a better SLA (non-tidal) signal for further analysis.
- SLA profiles show spatial and temporal variation:
SLA profiles derived for various locations around Singapore show different profiles. We observe non-tidal SLA as high as 60 cm near the Singapore coast. The inter-annual SLA variations are non-stationary. Intra-annual profiles exhibit season dependent extreme SLA events. Strong positive SLA events are observed during the monsoon seasons.
Water level anomalies also exhibit strong spatial variation in the region, highlighting the importance of covering a larger domain for SLA analysis.
- Residual currents v/s SLA gradients:
An initial study has shown correlation between SLA gradients and residual currents. The significance levels of these correlations depends on the location and the path being considered. The figures below show correlations (in blue) between SLA gradients and residual currents
- SLA correlation with Weather:
In order to investigate the association between the SLA and local meteorological conditions weather parameters are compared with SLA time profiles. The regional wind velocity profiles (direction and speed) appear to show significant correlations with SLA events in the region. The SLA propagation appears to be following the seasonal wind directions.
- Genetic Programming based models can be effective local SLA forecast models:
Different data driven SLA modelling techniques have been tried. Regression based local linear time series models like ARMAX, ARX, impulse response models were also tested. Initial results for the SLA forecasts (for 2 to 12 hr ahead prediction) obtained using GP derived models show promising results with prediction accuracy errors in the range of 5 to 10 cm. Further utility of other data based models like ANN/SVM are under investigation.
Tools and Experties
A variety of tools have been developed along with the necessary expertise to setup these tools and to properly interpret results from these tools.
- OpenDA-Delft3D for Model Sensitivity Analysis
The development of OpenDA-Delft3D as a sensitivity analysis tool has been carried out as part of this project. This tool allows for multiple parameter variation to be carried out semi-automatically thus reducing the workload of researchers while still allowing for model parameters such as depth, roughness and tidal constituent amplitude and phase to be varied simultaneously and with scientific oversight. Kurniawan et al. (2011) has further details of this tool and the methodology to carry out such sensitivity analysis.
As an example this tool has allowed us to carry out a detailed reanalysis of the sensitivity of the Singapore Regional Model. This reanalysis has shown the large sensitivity of the model response as shown in the figure below:
- Data Assimilation
Experience and expertise has been developed within the following areas with regards to data assimilation of observations with the numerical models.
In addition the project team has worked on the integration of the Kalman Filter to the OpenDA-Delft3D framework and has developed expertise in these and other integrative frameworks for Data Assimilation.
- Operational Management System (OMS) Development
A pre-operational OMS has been developed and is presently running. The OMS schedules and coordinates the many different steps required to obtain forecasts; these include obtaining data, scheduling model runs and for users to visualize results.
- Thin-Client for Forecast Delivery
A pre-operational thin-client has been developed for delivering forecasts to low-bandwidth devices or locations. This tool has been designed to be modular and interactive. More details of this thin-client architecture are in Zemskyy et al. (2011).
- Kurniawan, A., Ooi, S.K., Hummel, S., and Gerritsen, H. Sensitivity analysis of the tidal representation in Singapore regional waters in a data assimilation environment. Ocean Dynamics, DOI:10.1007/s10236-011-0415-6.
- Sun, Y., Babovic, V. and Chan E. S. Multi-step-ahead model error prediction using time-delay neural networks combined with chaos theory. Journal of Hydrology, December 2010.
- Sun, Y., Sisomphon, P., Babovic, V., and Chan, E.S. Efficient data assimilation method based on chaos theory and Kalman filter with an application in Singapore regional model. Journal of Hydro Environmental Research, March 2009.
- Sun, Y., Sisomphon, P., Babovic, V., and Chan, E.S. Applying local model approach for tidal prediction in a deterministic model. International Journal for Numerical Methods in Fluids, September 2008.
- Rao, K.R., Wang, X., Ooi, S.K., Babovic., V., and Gerritsen, H. Improving predictions of water levels and currents for Singapore regional waters through Data Assimilation using OpenDA. Proceedings of the 34th IAHR Biennial Congress, Brisbane, Australia, 26 June – 1 July 2011.
- Ooi, S.K., Kurniawan, A., Sisomphon, P., and Gerritsen, H. Modelling of Sea Level and Current Anomalies in the Singapore Region. Proceedings of the 34th IAHR Biennial Congress, Brisbane, Australia, 26 June – 1 July 2011.
- Zemskyy, P., Umashankar, S., Ooi, S.K., and Babovic, V. A thin-client delivery system for forecasts of currents and water levels in Singapore regional waters for efficient navigation. 3rd International Maritime-Port Technology and Development Conference, Singapore, 13-15 April 2011.
- Kurniawan, A., Twigt, D., Babovic, V. and Gerritsen, H. Modelling and forecasting water levels and currents in Singapore regional waters. 3rd International Maritime-Port Technology and Development Conference, Singapore, 13-15 April 2011.
- Sun, Y., Zemskyy, P., Ooi, S.K., Sisomphon, P., and Gerritsen, H. Study on the correlations between current anomaly and sea level anomaly gradients in Singapore and Malacca Straits. 4th IPWE, Singapore, 4-6 January 2011.
- Rao, K.R., Wang, X., Babovic, V., and Gerritsen, H. Data assimilation scheme triggered by Kalman Filter for forecasting the Sea Level Anomaly and Tidal Prediction. 4th IPWE, Singapore, 4-6 January 2011.
- Kurniawan, A., Ooi, S.K., Gerritsen, H., and Twigt, D. Calibrating the Regional Tidal Prediction of the Singapore Regional Model using OpenDA. HIC-2010, Tianjin, China, 7-11 September 2010.
- Wang, X., Rao, R., Babovic, V., and Gerritsen, H. Artificial Neural Network as a Data Assimilation Tool for Error Distribution and Correction. HIC-2010, Tianjin, China, 7-11 September 2010.
- Rao, R., Gerritsen, H., van den Boogaard, and Babovic, V. Influence of Regional Wind on the Mechanism Governing the Sea Level Anomalies around Singapore Coast. HIC-2010, Tianjin, China, 7-11 September 2010.
- Sun, Y., Babovic, V., Chan, E.S., and Sisomphon, P. Model Error Prediction using Neural Networks Combined with Chaos Theory. HIC-2010, Tianjin, China, 7-11 September 2010.
- Zemskyy, P., Tkalich, P., Gerritsen, H., and Babovic, V. Storm Surges Modelling in South China Sea. IAHR-APD, Auckland, New Zealand, 21-24 February 2010.
- Ooi, S.K., Gerritsen, H., Kurniawan, A., and Twigt, D. Parameter Optimization and Data Assimilation to improve the Tidal Prediction of the Singapore Regional Model. IAHR-APD, Auckland, New Zealand, 21-24 February 2010.
- Rao, R., and Babovic, V., Genetic Programming based Sea Level Anomaly forecasting models as Data Assimilation tools. IAHR-APD, Auckland, New Zealand, 21-24 February 2010.
- Rao, R., van den Boogaard, H., Gerritsen, H., Babovic, V., and Mynett, A. Characterizing Sea Level Anomalies – spatial and temporal analysis in Singapore region. 33rd IAHR Congress, Vancouver, Canada, 10-14 August 2009.
- Rao, R., and Babovic, V. Establishing Sea Level Anomaly Patterns using Mutual Information Theory. 33rd IAHR Congress, Vancouver, Canada, 10-14 August 2009.
- Ooi, S.K., Zemskyy, P., Sisomphon, P., Gerritsen, H., and Twigt, D. The effect of grid resolution and weather forcing on hydrodynamic modelling of South East Asian waters. 33rd IAHR Congress, Vancouver, Canada, 10-14 August 2009.
- Tkalich, P., Vethamony, P., Babu, M.T., and Pokratath, R. Seasonal sea level variability and anomalies in the Singapore Strait. Proceedings of Third International Conference in Ocean Engineering (ICOE2009), Chennai, INDIA, Feb 1-5, 2009, pp 874-880.
- Rao, R., and Babovic, V. Wavelet transformation based data assimilation for improved ocean hydrodynamic modelling – Singapore regional model case study. Proceedings of the 8th International conference on Hydroinformatics, HIC2009, Conception, Chile, 12-16 January 2009.
- Sun, Y., Sisomphon, P., Babovic, V., and Chan, E.S. Comparison of Kalman filter and inter-model correlation method for data assimilation in tidal prediction. Proceedings of the 8th International conference on Hydroinformatics, HIC2009, Conception, Chile, 12-16 January 2009.
- Tay, H. X. S., Sisomphon, P., and Babovic, V. Modelling of Singapore’s coastal waters. Proceedings of the 8th International conference on Hydroinformatics, HIC2009, Conception, Chile, 12-16 January 2009.
- Calkoen, C., Wensink, H., Twigt, D., Sisomphon, P., and Mynett, A. Sea level anomalies from satellite altimetry – retrieval and validation. Proceedings of the 8th International conference on Hydroinformatics, HIC2009, Conception, Chile, 12-16 January 2009.
- Gerritsen, H., Twigt, D., Mynett, A., Calkoen, C., and Babovic, V. MustHaveBox – Analysis and prediction of sea level anomalies and associated currents in Singapore and Malacca Straits. Proceedings of the 8th International conference on Hydroinformatics, HIC2009, Conception, Chile, 12-16 January 2009.
- Babovic, V. Assimilation of Satellite Altimetry Data into Ocean Circulation. Proceeding of XXXII IAHR Congress, Venice (Italy), Venice, Italy, 1 – 6 Jul 2007.
- Zemskyy, P., Ooi, S.K., Kurniawan, A., and Gerritsen, H. Calibrating the tidal prediction of the South China Sea model. JONSMOD2010, Delft (NL), 10-12 May 2010.
- Ooi S.K., Gerritsen H., Zemskyy P., Twigt D., Sisomphon P. The Effect of Grid Resolution, Weather Forcing and Tidal Forcing on Hydrodynamic Modelling of South East Asian Waters. 6th Annual General Meeting AOGS, Singapore, 11-15 August 2009
- Rao, R., Kurniawan, A., Ooi, S. K., Gerritsen, H. and Babovic, V. Numerical model order reduction using ensemble of data driven transfer function models as spatial and temporal interpolators. 6th Annual General Meeting AOGS, Singapore, 11-15 August 2009
- Twigt, J. D., Gerritsen, H., Uittenbogaard, R. E. Modelling of sea level anomaly driven ocean currents – towards a near-real time approach. JONSMOD2008, Bergen (No), 23-25 June 2008.
- Sun, Y., Sisomphon, P., Babovic, V., Chan, E.S. Enhancing tidal prediction accuracy in Singapore regional model using local model approach. 5th Annual General Meeting Asia Oceania Geosciences Society, BEXCO, Busan, South Korea, 16–20 Jun 2008.
- Rao, R., Tay, S.H.X., Babovic, V. Genetic Programming Models for Ocean Hydrodynamic Data Analysis. 5th Annual General Meeting Asia Oceania Geosciences Society, BEXCO, Busan, South Korea, 16–20 Jun 2008.
- Rao, R. and Babovic, V., Genetic Programming Models for Ocean Hydrodynamic Data Analysis, AOGS 2008, 16–20 Jun 2008, Busan, South Korea
- Sun, Y, Sisomphon, P., Babovic, V., Chan, E.S., Enhancing tidal prediction accuracy in Singapore regional model using local model approach, AOGS 2008, 16–20 Jun 2008, Busan, South Korea.