Antony Joseph

Evaluation of Pressure Transducers under Turbid Natural Waters

Abstract Pressure measurements made in two turbid natural waters have led to the inference that the effective depth-mean in situ density values, ρeff, of these waters are less than (≈2.70%–6.5%) their bulk densities (i.e., densities of water–sediment mixture), and also less than (≈0.4%–4.5%) that of the density of the same water after removal of suspended sediment. The values of ρeff in a given site differed from one tidal cycle to another (≈1.9%). These values varied slightly (<0.8%) from midtide to slack water period of the same tidal cycle, with ρeff being lower at midtide. It was found that the use of bulk density to estimate tidal elevation yielded an underestimation of tidal range (up to 7%). The underestimation has been corrected (to within ±1.5%) with the use of ρeff parameter. For clear waters there was no measurable underestimation in tidal range. The observations indicate an apparent in situ density reduction for turbid natural waters. With the use of two pressure transducers at a known vertica...

Evaluation and Performance Enhancement of a Pressure Transducer under Flows, Waves, and a Combination of Flows and Waves*

Abstract The performance of a pressure transducer, with its inlet attached to differing hydromechanical front ends, has been evaluated in flow flume and wave flume experiments in which laminar and turbulent flows, and regular progressive gravity waves and combinations of flows and waves, were generated. For steady laminar flows, and for waves propagating on quiescent waters, the transducer’s performance improved when the inlet was at the center and flush with a large, thin, and smooth circular horizontal end plate. This enhancement is likely to have been achieved because of the isolation of the pressure inlet from the separated flows and vortices generated by the transducer housing. Flow disturbances, generated by nearby solid structures, deteriorated the performance of the pressure transducer. However, its performance could be significantly improved by protecting the pressure inlet by a sturdy, curved perforated shield. The dynamic pressure error in this case was 2 mb at 100 cm s−1, compared to 8 mb in t...

Integrated Coastal Observation Network (ICON) for real-time monitoring of sea-level, sea-state, and surface-meteorological data

National Institute of Oceanography (NIO) has established an Integrated Coastal Observation Network (ICON) of in-house designed and developed Internet-accessible real/near-real time reporting cellular based sea-level, sea-state, and surface meteorological (Met) stations at several locations on the Indian coasts & Islands (http://inet.nio.org). Subsurface pressure sensors and downward-looking microwave radars are incorporated in the sea-level station network. Sea-level, Met, and surface wave parameters are acquired using dedicated Linux based data loggers and uploaded to an Internet server at 5-, 10- and 30-min intervals, respectively with the use of GPRS cellular modems. The sensors and data loggers are powered from sealed lead acid batteries, which are charged through solar panels. The ICON provides graphical presentation of sea-level information (observed sea-level, predicted tide, residual sea-level); significant wave height and wave direction; and Met information (vector-averaged wind speed & direction, barometric pressure, atmospheric temperature, solar radiation, relative humidity, and rainfall). Installation of sea-level sensors free from the influence of stilling-wells and long narrow tubes renders the measurements ideal for tsunami and storm-surge studies by preventing waveform distortion and non-linearity of largeamplitude short-period signals. The network maintains accurate time-stamp of the dataset through Internet-time synchronization using network time protocol (NTP). Real-time reporting capability of ICON yields several benefits, such as (i) remote monitoring of proper working condition of individual stations; (ii) implementation of repair/maintenance in the shortest possible time, thereby minimizing break in the time-series data stream; (iii) periodic arrival of data stream from all stations at a single central server, thus yielding backup for the data from all the stations; (iv) access to the latest in-situ information; (v) allows possible use of data with automated real-time running numerical models for operational forecast. In contrast to the limited bandwidth provided by INSAT transmitters, coastal observations at high bandwidth at significantly low cost have become realizable using cellular GPRS network. The NIO-network allows, Internet based real/near-real time tracking and monitoring of sea-level, sea-state, and meteorological conditions along the Indian coasts and islands and from almost anywhere - an issue of considerable practical significance during natural disasters such as storm, storm-surge, and tsunami.

Comparison of sea-level measurements between microwave radar and subsurface pressure gauge deployed at select locations along the coast of India

Abstract Sea-level data are obtained from several remote and coastal locations using absolute pressure gauges deployed at known level, known as chart datum. However, to yield correct sea-level measurements from absolute pressure measurements, it is necessary to take into account the atmospheric pressure and water density at the measurement locations. We used data collected from microwave radar and an absolute pressure gauge deployed at Verem, Goa (January 2009 to May 2010), Tuticorin, and Mandapam, Tamil Nadu (June 2010 to March 2011) to carry out comparative studies. The root-mean-square difference between the estimated sea level from radar and pressure gauge (incorporating atmospheric pressure correction) is ∼ 2.69 , 2.73, and 1.46 cm at Verem, Tuticorin, and Mandapam, respectively. Harmonic analysis of the two time-series of sea-level data at Verem produces similar residuals and tidal constituents. Our results indicate the importance of concurrent measurement of atmospheric pressure along with subsurface absolute pressure gauge measurements. Internet-based real-/near-real-time tracking and monitoring of sea level, sea state, and surface-meteorological conditions from a network of several island and coastal stations provides considerable information to disaster managers and local administrators during episodic events such as storms, storm surges, and tsunamis.

An Evaluation of Free- and Fixed-Vane Flowmeters with Curved- and Flat-Bladed Savonius Rotors

Abstract Speed and direction performances of flowmeters, designed by the authors for in-house use, employing an Aanderaa-type curved-bladed Savonius rotor and a free vane and an Aanderaa-type flat-bladed Savonius rotor and a fixed vane, are discussed. It has been observed that accuracy, linearity, and tilt response of a meter using the Aanderaa curved-bladed rotor is superior to those of a meter using the Aanderaa flat-bladed rotor. Analysis showed that the azimuth response of a flowmeter is affected by the presence of support rods surrounding its rotor. The change in azimuth response arises from flow pattern modifications in the vicinity of the rotor, imposed by the changes in the horizontal angle of the support rods of the rotor relative to the flow streamlines. While the use of two support rods may be suitable for a fixed-vane system, it is undesirable for a free-vane system where the meters orientation with respect to the flow direction is not defined. Flow direction calibration results indicated tha...

IOC-UNESCO Tsunami Early Warning Systems

Publisher Summary A tsunami is one of the most dangerous and destructive natural phenomena and one of the most formidable of all natural hazards. The effectiveness of a tsunami warning, in terms of hazard reduction, depends greatly on the availability of accurate tsunami inundation maps. The consequences of the December 2004 global tsunami, which originated in the Indian Ocean, quickly became a tragic lesson for the majority of the countries in the region. The scale of this hazard exceeded all historical cases of catastrophic tsunamis. Therefore, scientists and several national governments are more intensely focused on the problem of how to prevent the consequences of such marine catastrophes, and several individual nations with sea boundaries have begun to install tsunami warning system (TWS) systems. The Indian Tsunami Early Warning System consists of a real-time network of SS, bottom pressure recorders (BPRs), and coastal and island sea-level gauges to detect tsunamigenic earthquakes and monitor tsunamis. The traditional methods of tsunami warnings practiced in most parts of the world are based primarily on seismic information obtained immediately after the earthquake and on calculations of the time of wave propagation and its amplitude at each specific point.

November 2009 tropical cyclone Phyan in the eastern Arabian Sea: Oceanic response along west India coast and Kavaratti lagoon

Spatial and temporal response of the coastal waters of eastern Arabian Sea (AS) and Kavaratti lagoon to the tropical cyclonic storm ‘Phyan’, which developed in the southeastern AS and swept northward along the eastern AS during 9–12 November 2009 and finally made landfall at the northwest coast of India, is examined based on time-series measurements of sea-surface wind (U10), gust, gust factor, barometric pressure, precipitation, atmospheric temperature, SST, and significant wave height from satellite-derived and in-situ measurements. The maximum wind-speed (U10) of ∼16 m/s occurred at Kavaratti Island region followed by ∼8 m/s at Dwarka in Gujarat, where the cyclone landfall occurred, and ∼7 m/s at Diu located just south of Dwarka as well as two southwest Indian coastal locations at Mangalore and Malpe. All other west India coastal locations recorded maximum wind speed of ∼5–6 m/s. Gust factor during peak storm event was highly variable with respect to topography, with steep hilly stations and proximate thick and tall vegetation exhibiting the largest value whereas coastal planes and Island stations exhibiting the least. Rainfall in association with Phyan was temporally scattered, with the highest 24-h accumulated precipitation (∼60 mm) at Karwar and ∼45 mm at several other locations. Impact of Phyan on the west India coastal waters was manifested in terms of intensified significant wave height (∼3 m at Karwar, Panaji, and Ratnagiri), sea surface cooling (∼5°C at Calicut), and surge flooding (∼80 cm at Verem). Several factors such as (i) water piling up at the coast supported by seaward flow of the excess water in the rivers due to heavy rains and westerly cross-shore wind, (ii) water piling down at the coast supported by the northerly alongshore wind (by virtue of Coriolis effect) and upstream penetration of seawater into the rivers, and (iii) possible interaction of upstream flow with river runoff, together resulted in the observed surge flooding at the west India coast. Despite the intense wind forcing, Kavaratti Island lagoon experienced insignificantly weak surge (∼7 cm) because of lack of river influx and absence of a sufficiently large land boundary required for the sustenance of wave/wind-driven water mass which tends to pile up at the land-sea interface.

Telemetry of Sea-Level Data

Tsunami and storm-surge monitoring systems require that the data be reported to the disaster management authorities as soon as possible. There are various communication technologies that could be utilized for real/near-real-time reporting of sea-level data. A variety of real-time communication options are in use today, and newer options are being examined. The telemetry system is driven by a software package running on a personal computer located at the Thames Navigation Service (TNS). A communications interface relieves the host computer of the burden of actually prompting the remote site polling and processing of replies to requests for data. Several methods are available for reporting sea-level data for early tsunami warning purposes, a telephone or an Internet infrastructure is often a part of the overall communication network. A state-of-the-art form of telemetry, a satellite-based system independent of the vulnerable telephone or Internet infrastructure, is the recently introduced Broadband Global Area Network (BGAN) by INMARSAT.

Tsunami Generation and Historical Aspects

This chapter reveals that both tsunamis and tsunami-like waves are generated as a result of various causes, such as an undersea earthquake (also known as a seaquake) rupture process or, more frequently, the secondary triggered phenomena, such as landslides and/or other geodynamic phenomena, such as rockslides, large-scale gas emissions from the seafloor, volcanic eruptions, intense atmospheric disturbances, and asteroid impacts. According to the tsunami database, seaquakes, submarine landslides, volcanic eruptions, and atmospheric disturbances have been responsible for approximately 82%, 6%, 5%, and 3%, respectively, of tsunamis. Most of the historic seaquakes (i.e., earthquakes under the seafloor) have taken place at subduction zones. The presence of a deep-water trench, such as the Aleutian trench in the Alaska-Aleutian subduction zone and the Kuril-Kamchatka trench in the Kuril-Kamchatka zone, is the main characteristic of the subduction zone. The depth at the trench axis is approximately twice as large as an average depth of the Pacific Ocean. Earthquake hypocenters are mainly located under the continental bottom slope. In this case, the opposite slope of this deep-water trench works like an optical lens for tsunami waves.

The Role of IOC-UNESCO in Tsunami Early Warnings

This chapter discusses the role of IOC-UNESCO in tsunami early warnings. A tsunami warning system (TWS) is a network of seismographs, sea-level gauges, and high-speed communication devices intended to predict and warn against the approach of a tsunami wave train. The main objective of a TWS is to detect, locate, and determine the magnitude of earthquakes that have the potential for triggering tsunami waves and validating the warning based on real-time sea-level measurements at multiple locations. Seismic stations that are spread over many spatially distant geographical locations provide earthquake information from each of these locations. If the location and magnitude of an earthquake meet the criteria for triggering a tsunami, the tsunami warning center (TWC) issues a warning of an imminent tsunami hazard. Tsunami warnings, including predicted tsunami arrival times at selected coastal regions and related information bulletins, are disseminated to the appropriate emergency officials and the general public via a variety of communication channels, such as commercial radio, television, weather radio systems, marine radio systems, and so forth.