Mihir Kumar Dash

Wind-wave Climate Projections for the Indian Ocean from Satellite Observations

The oceans play a key role in climate change and their impact has profound implications on the marine ecosystem and multitude activities around the globe. The effects due to climate change can have long-term repercussion. The latest report on the Intergovernmental Panel on Climate Change had identified the importance of wind-wave climate and its key role in global climate models. The present study investigates the impact of climate change on variability of maximum significant wave height and wind speeds over the Indian Ocean basin. The study is based on analysis from the daily observation of satellite altimeter measured wind and waves derived from eight satellite missions covering a period of 21 years from 1992 until 2012. The results signify that the Southern Ocean belt encompassing latitudinal belts between 40°S – 55°S experienced the highest variability due to impact from climate change. Both wind and wave activity has shown an increasing trend in the Southern Ocean, and this rise is more conspicuous in the current decade. The implications from increased wave activity in the Southern Ocean results in swell field that can influence the local wind-generated waves in the North Indian Ocean basin. The wind-wave activity in certain sectors of the tropical North Indian Ocean also increased from impact of climate change.

Assessment of water quality using multivariate statistical techniques in the coastal region of Visakhapatnam, India

The present study was intended to develop a Water Quality Index (WQI) for the coastal water of Visakhapatnam, India from multiple measured water quality parameters using different multivariate statistical techniques. Cluster analysis was used to classify the data set into three major groups based on similar water quality characteristics. Discriminant analysis was used to generate a discriminant function for developing a WQI. Discriminant analysis gave the best result for analyzing the seasonal variation of water quality. It helped in data reduction and found the most discriminant parameters responsible for seasonal variation of water quality. Coastal water was classified into good, average, and poor quality considering WQI and the nutrient load. The predictive capacity of WQI was proved with random samples taken from coastal areas. High concentration of ammonia in surface water during winter was attributed to nitrogen fixation by the phytoplankton bloom which resulted due to East India Coastal Current. This study brings out the fact that water quality in the coastal region not only depends on the discharge from different pollution sources but also on the presence of different current patterns. It also illustrates the usefulness of WQI for analyzing the complex nutrient data for assessing the coastal water and identifying different pollution sources, considering reasons for seasonal variation of water quality.

Oceanic forces and their impact on the performance of mobile underwater acoustic sensor networks

SUMMARY This paper focuses on the performance analysis of Underwater Wireless Acoustic Sensor Networks (UWASNs) with passively mobile sensor nodes moving because of the influence of major oceanic forces. In an UWASN, passive node mobility is inevitable. Therefore, the performance analysis of UWASNs renders meaningful insights with the inclusion of a mobility model, which represents realistic oceanic scenarios. In this regard, the existing works on performance analysis of UWASNs lack the consideration of major dominating forces, which offer impetus for a nodes mobility. Additionally, the existing works are limited to only shallow depths and coastal areas. Therefore, in this paper, we have proposed a physical mobility model, named Oceanic Forces Mobility Model, by incorporating important realistic oceanic forces imparted on nodes. The proposed model considers the effects of node mobility in 3-D space of water. We also present an analysis on the impact of node mobility on the performance of UWASNs in terms of network dispersion and localization. Simulation results indicate performance degradation of UWASNs in the presence of oceanic forces—localization coverage decreases by 36.70%, localization error increases nearly by 21.14%, and average energy consumption increases by 3% approximately. Copyright

Performance analysis of distributed underwater wireless acoustic sensor networks systems in the presence of internal solitons.

SUMMARY In this paper, we have analyzed the performance of distributed Underwater Wireless Acoustic Sensor Networks (UWASNs) in the presence of internal solitons in the ocean. Internal waves commonly occur in a layered oceanic environment having differential medium density. So, in a layered shallow oceanic region, the inclusion of the effect of internal solitons on the performance of the network is important. Based on various observations, it is proved that nonlinear internal waves, that is, solitons are one of the major scatterers of underwater sound. If sensor nodes are deployed in such type of environment, internode communication is affected because of the interaction of wireless acoustic signal with these solitons, as a result of which network performance is greatly affected. We have evaluated the performance of UWASNs in the 3-D deployment scenario of nodes, in which source nodes are deployed in the ocean floor. In this paper, four performance metrics, namely, Signal-to-interference-plus-noise-ratio (SINR), bit error rate (BER), Delay (DELAY), and energy consumption are introduced to assess the performance of UWASNs. Simulation studies show that in the presence of internal solitons, SINR decreases by approximately 10%, BER increases by 17%, delay increases by 0.24%, and energy consumption per node increases by 53.05%, approximately. Copyright

Effects of Wind-Induced Near-Surface Bubble Plumes on the Performance of Underwater Wireless Acoustic Sensor Networks

This paper analyzes the effects of near-surface oceanic bubble plumes on the overall performance of underwater wireless acoustic sensor networks (UWASNs). The existence of bubble plumes in surface and subsurface ocean water columns is inevitable in most windy oceanic environments. There exists studies reporting the anomalous behavior of acoustic signal propagating through oceanic bubble plumes due to absorption and scattering. However, most of the existing network protocols designed for use in UWASNs are ignorant of these effects. In this paper, we first mathematically model the absorption effects of these bubble plumes on the acoustic communication media. Consequently, the overall performance of UWASNs is studied with respect to different parameters. Simulation-based results show that in the presence of bubble plumes, packet delivery ratio decreases by 34% while average energy consumption per node increases by 7%. In addition, signal-to-interference-plus-noise ratio decreases by

Effect of near-surface bubble plumes on the acoustic signal used in UWACNs

\sim 53

Stochastic modeling of internal wave induced acoustic signal fluctuation and performance evaluation of shallow UWANs

% and bit error rate increases by 57% in the presence of bubble plumes in UWASNs.

Extratropical anticyclonic Rossby wave breaking and Indian summer monsoon failure

Shallow water environments exhibit significantly prominent spatio-temporal variability; compared to the ones corresponding to deep oceans. An acoustic signal propagating through a shallow water region faces multiple reflections with the ocean surface as well as with the ocean bottom. So, rendering wireless acoustic communication in such type of unpredictable environment is challenging, as the acoustic signal is subjected to different losses such as multipath fading and absorption. In this paper, we analyze the near ocean surface anomalous behavior of acoustic signals, typically observed in Underwater Wireless Acoustic Communication Networks (UWACNs), due to damping in the presence of sub-surface bubble plumes. Bubbles have profound impact on the acoustical properties in the oceanic environment. The injection of bubble plumes near ocean surface renders the subsurface acoustic signal to behave anomalously.

Variability in the ENSO‐induced southern hemispheric circulation and Antarctic sea ice extent

Oceanic shallow-water environment draws attention of many researchers due to their dynamic nature with respect to time and space. Underwater acoustic channel is involved with multiple inhomogeneities in different respects to the propagation of acoustic signal. Developing “smart” algorithms capable of enabling acoustic communication in such environments is inherently challenging. For long-range communication, multipath fading is well-known to be a major factor for network performance degradation. Additionally, in case of short-range communication, signal degradation through the propagating medium can occur due to signal interaction with different types of turbulent phenomena. In this study, the turbulent phenomenon we have focused on is internal wave. Variation of internal waves shows a non-uniform distribution of refractive index of ocean water, and as a consequence, there is time varying bending of signal, which results in fluctuation of signal strength towards the receiver end. By introducing few metrics, we have analyzed the performance of Underwater Wireless Acoustic Networks (UWANs) in the presence of realistically occurring internal waves.