twenty-thousand leagues under the seafrom seabed to satellites

The Journal of Ocean Technology, Vol. 8, No. 3, 2013 47

Who should read this paper?Any scientist who works with remotely sensed data, ocean meteorology, or climate change would profit from reading this paper. Also, any individual with an interest in communications technology, environmentalism, and in particular, satellite technology, would benefit from this review. Why is it important?The capacities and constraints of satellite remote sensing technology and data transmission are intimately connected with what ocean knowledge we can establish. The necessity for this research is felt by legislators, business people, and civilians alike who are affected by concerns regarding climate change, by extreme weather, by ecological change, and our less-than-adequate predictive models. This review features the technology with which we attempt to acquire data about the ocean, specifically in the context of moored buoy networks and the satellites with which they communicate. As the authors indicate, data acquired in-situ is increasingly integrated with remotely sensed data, and the new ‘norms’ in ocean research depend increasingly on consistently transmitted data, continuously, from a network of locations. Buoy networks such as the Early Tsunami Warning system are vital for the well-being of coastal populations, where the accuracy of data and its timely receipt and interpretation can have literal life-or-death consequences. Insofar as meteorology depends on numerical simulation, the capacities of our buoy networks determine the stability of the information upon which we make predictions. This review invites scientists to consider seriously the relationship between information and communications technology, and data. It provides an account of moored surface buoys, the networks of which they are a part, the radio frequencies with which they transmit data, the types of satellites to which that data is sent, and how that data is then formatted. The authors indicate what sort of significance for governments their research holds, with great emphasis on the Tsunami Early Warning system.

About the authorsThe authors work at the National Institute for Ocean Technology in India. R. Venkatesan has a PhD, MTech, and PGD, specializing in Mechanical Engineering, Materials Engineering, and Ocean Policy and Management. M. Arul Muthiah has a Master of Engineering degree. K. Ramesh holds a Bachelor of Engineering (Electrical Communication Engineering). S. Ramasundaram has an M.Sc. in Information Technology. He was awarded a "Certificate of Merit" for the outstanding contributions in the field of Ocean observations Systems. R. Sundar has a Bachelor of Engineering in Computer Science. M. A. Atmanand is the Director at the National Institute of Ocean Technology. He has a PhD in Instrumentation, and an MTech in Electrical Engineering.

Venkatesan et al get real about real-time data from the ocean.

Twenty-thousand leagues under the sea…from seabed to satellites

R. Venkatesan

K. Ramesh

S. Ramasundaram

R. Sundar

M. A. Atmanand

M. Arul Muthiah

Copyright Journal of Ocean Technology 2013

48 The Journal of Ocean Technology, Vol. 8, No. 3, 2013 Copyright Journal of Ocean Technology 2013

SATELLITE COMMUNICATION SYSTEMS FOR OCEAN OBSERVATIONAL PLATFORMS: SOCIETAL IMPORTANCE AND CHALLENGES

R. Venkatesan, M. Arul Muthiah, K. Ramesh, S. Ramasundaram, R. Sundar, and M. A. AtmanandNational Institute of Ocean Technology, Ministry of Earth Sciences, Chennai, India

ABSTRACT

Moored buoy systems have been deployed for many years to record and report a wide range of sub-surface, surface and atmospheric parameters in the oceans. Realtime data from these platforms are used for scientific research, as well as in support of weather and marine forecasts and as an aid to climate modelling and prediction. Natural disasters such as storms, cyclones, hurricanes and tsunamis have pushed the scientific community, weather forecasting organizations, disaster warning agencies, and governments to work towards effective and timely communication methodologies at national, regional, and global levels. This paper describes possible communication options, limitations and also explains individual groupings such as Geostationary Earth Orbit (GEO), Mid-altitude Earth Orbit (MEO) and Low Earth Orbit (LEO) satellite types. We have described the major satellite systems used by data buoy operators within each of these categories. This paper discusses future trends in Earth system science and in satellite communication technology for realtime data transmission. In addition to global issues, this paper also describes an Indian Ocean Observation network that envisages a gamut of sensors deployed in shallow and deep waters in the Indian Ocean to collect a variety of meteorological and oceanographic data.

KEYWORDS

Moored buoy, Satellite telemetry, realtime data, INMARSAT, ARGOS, IRIDIUM, INSAT

The Journal of Ocean Technology, Vol. 8, No. 3, 2013 49Copyright Journal of Ocean Technology 2013

INTRODUCTION

Oceanographers have explored and sampled the ocean for more than two centuries through conventional ship-based observations. However, the ocean is a dynamic and complex environment where physical, chemical, biological and geological processes are continuously interacting over time-scales ranging from seconds to millions of years and on spatial scales ranging from centimetres to global. The study of the oceans is entering a new phase in which scientists will establish interactive ocean observatories that use Information and Communications Technology (ICT) to link the scientist with observatory, be it on the seabed, in the water column, or floating on the surface of the sea. Our future understanding of ocean, atmosphere and climate systems will need increasing and more diverse amounts of data that must be reliable and economical to collect. This will necessitate new technology for observational platform development, improvements in sensor technology and near-realtime data transmission, largely through satellite channels. Such sustained observations naturally place a greater emphasis on affordability and reliability than on pure technical innovation. Ocean observational platforms are now being built specifically with sustained observations as a design goal and with cost per profile or per kilometre as a key specification. In addition, in-situ observations in themselves are but one facet of an observing system; their systematic integration with remotely sensed data and numerical simulation is becoming the norm [Griffiths et al., 2009].

Satellite-based remote sensing has revolutionized oceanography through the routine daily

collection of terabytes of data, but the kinds of data sets/parameters that can be collected are limited. On the other hand, most in-situ platforms return at most a few thousand bytes of data per day. The harvest of data from in-situ platforms must increase by orders of magnitude if scientists are ever to understand the complexities of the Earth's climate[Shaumeyer and Borden, n.d]. Advances in technology have recently seen the deployment of a new generation of mobile platforms (Autonomous Underwater Vehicles and gliders) that can provide simultaneous spatial and temporal sampling capabilities throughout the water column, and complement the existing networks of moored and free-drifting surface buoys. Mobile platforms such as gliders, AUVs, Argo floats and drifters provide oceanographers the means to deploy sensors and move them through space, both horizontally and vertically. Drifting buoys move away from their deployment point shortly after being put into the water. However, they have a limited operational lifetime for reasons such as battery life, sensor failure, transmitter failure, running ashore, etcetera. Both moored and drifting buoys normally provide observations of a subset of the following parameters: surface pressure, air temperature, air humidity, wind velocity, radiation, ocean current velocity, sea surface temperature (SST), 3D wave spectrum, wave direction, wave period and wave height, and precipitation. As they are fully automatic systems, this observed subset is reduced compared to what can be observed by ships or synoptic sea stations (e.g., clouds and present/past weather are not observed by buoys). The advantage of the fully automatic systems is that the observation frequency can be quite high.


SIGNIFICANCE OF MOORED SURFACE BUOYS

Surface moorings are distinguished by having their principal buoyancy element at the surface (a buoy), while subsurface moorings have one or more flotation elements below the surface. Moored platforms provide the means to deploy sensors at fixed depths between the sea floor and the sea surface, and to deploy packages that profile vertically at one location by moving up and down along the mooring line or by winching themselves up and down from a point of attachment on the mooring or the seafloor. The basic objectives of moored met-ocean buoys are to continuously measure surface met-ocean parameters and to understand the upper ocean thermohaline structure.

Moored buoy observatories have certain advantages. They can be located in very remote areas, far from land, where the cost of laying fibre optic cable would be prohibitive. They can be portable and potentially used for short-term studies and provide greater flexibility to reconfigure experiments. The ability of moored buoys to make long-term measurements of on-going processes anywhere in the world’s oceans also gives them the potential to play an important role in other oceanographic and climate studies [McPhaden et al., 1998]. As well as making conventional met-ocean observations, moored buoys have been used to deploy biogeochemical, acoustic, optical and ocean current sensors in support of studies as diverse as climate modelling, ecosystem monitoring and marine mammal tracking. However, moored buoys do suffer from some limitations in terms of their energy-carrying capacity and telemetry bandwidth. In these areas cabled observatories may

prove more attractive despite the considerable additional expense.

Buoy ParametersMarine meteorological variables include those needed to characterize fluxes of momentum, heat and fresh water across the air-sea interface, namely surface winds, SST, air temperature, relative humidity, short and long wave radiation, barometric pressure and precipitation. Physical oceanographic variables include upper-ocean temperature, salinity and horizontal currents. From these basic variables, derived quantities such as latent and sensible heat, net surface radiation, penetrative shortwave radiation, mixed-layer depth, ocean density, and dynamic height (the baroclinic component of sea level) can be computed. Given the importance of good surface pressure data coverage and of the technological capacities for measuring pressure, a pressure sensor is required to be fitted in all buoys. The surface wind is important as well, but with a less dense network than pressure. Wind data, when available, are used in synergy with surface pressure measurements and with space-based surface wind measurements such as scatterometers and microwave instruments. SST global coverage is important both for Numerical Weather Prediction (NWP) and for ocean modelling. Ocean current velocity information is valuable for oceanographic analysis and modelling, and wave parameters are very important for marine services and applications. The observation of precipitation is particularly important for the calibration of satellite data over the oceans. This data is useful for both weather and ocean forecasts and for research. Importantly, in-situ data of many kinds can be used to validate remotely-sensed data algorithms and operational models.


Figure 1: Global moored and drifter buoy network (Data Buoy Cooperation Panel, n.d).

GLOBAL OCEAN OBSERVATION

The Global Tropical Moored Buoy Array (GTMBA), a multinational effort to provide data in real time for climate research and forecasting has a number of components, including the Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON) in the Pacific, the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA), and the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) in the Indian Ocean. Additionally, the Data Buoy Cooperation Panel (DBCP) of the Joint World Meteorological Organization – Intergovernmental Oceanographic Commission (WMO-IOC) Technical Commission for Oceanography and Marine Meteorology (JCOMM) strives to coordinate a global network of 1,250 drifting buoys

deployed to meet a grid spacing of 5 degrees by 5 degrees. For global and regional NWP, the most important parameter observed by buoys is surface pressure, and efforts are focused on trying to improve the global near-realtime coverage of this dataset. Figure 1 depicts the existing global moored and drifter buoy network.

Realtime Data Systematic realtime meteorological and oceanographic observations are necessary to improve oceanographic services and predictive capability of short-term and long-term climatic changes. Time-series observations are vital to improve the understanding of ocean dynamics and its variability. Realtime data is crucial in the tsunami buoy network that monitors sea level to allow the forecasting centres to generate life-saving early warnings of tsunamis. In the above ways, realtime


observational data from buoys are closely linked to societal benefits.

MODE OF COMMUNICATION FOR DATA TRANSFER

Realtime data from moored buoys can be transmitted ashore via cable or by a variety of radio systems, including Very High Frequency (VHF), Ultra High Frequency (UHF), Global System for Mobile Communication (GSM) and satellite modems. Selection of the communication method largely depends on how far the buoy is from shore and the data bandwidth required, though other factors such as timeliness, cost and energy requirements also play a role. In the case of a moored buoy close to shore any of the above systems may be selected. For platforms far away offshore, satellite communication is the only realistic

option. Figure 2 shows different modes of realtime communication.

Radio Frequencies for Data CollectionThe World Meteorological Organization / International Telecommunications Union (WMO/ITU) Handbook on the “Use of Radio Spectrum for Meteorology: Weather, Water and Climate Monitoring and Prediction” [World Meteorological Organization, 2008] describes satellite Data Collection Systems (DCSs) that, as far as radio frequency management issues are concerned, come under the Earth-to-space communications component of meteorological satellite services (MetSat). MetSat in turn falls under the Earth Exploration Satellite Service (EESS), where the frequency 401-403 MHz (Metsat “Earth-to-space”) is allocated to this service [World Meteorological Organization, 2012]. Other frequencies are

Figure 2: Different modes of communication.


used for commercial satellite systems. In general, satellite systems are classified according to orbit altitude as:

• GEO-GeostationaryEarthOrbit, approximate altitude: 35,000 km • MEO-Mid-altitudeEarthOrbit, approximate altitude: 10,000 km

• LEO-LowEarthOrbit,approximate altitude: < 1,000 km

Globally, buoy user communities widely use three satellite communication systems:INMARSAT, ARGOS and IRIDIUM. Table 1 shows global observational buoy programme groups and the corresponding communication satellites being used for data telemetry [Data Buoy Cooperation Panel, n.d.].

Table 1: Communication satellites used by global observational buoy programme groups.

DESCRIPTION OF SATELLITE SYSTEMS FOR OCEAN OBSERVATION

Two GEO satellite systems that are widely used for buoy data telemetry are INMARSAT and INSAT. LEO systems are ARGOS and IRIDIUM. The salient features of satellite systems used for data buoy application are described below.

GEO Satellite Communication SystemsINMARSAT system overviewThe International Mobile Satellite Organization (IMSO) that operates INMARSAT is not involved in commercial activities. INMARSAT operates ten GEO satellites offering near-global broadband communications at speeds from 600 bps to 492 kbps without bundling. Inmarsat-C service is supported by Inmarsat-3 constellation in which there are four satellites


used for global beam converge. Inmarsat-C service is widely used for moored buoy applications and is capable of two-way telex, email and data. Inmarsat-C is a store and forward service. Data from an Inmarsat mobile terminal is sent directly to the satellite overhead, which routes it back down to a gateway on the ground called a Land Earth Station (LES). From the LES, the data is passed to a shore side address. Inmarsat-C has two primary services, Data reporting and polling. For buoy operations Data reporting allows for the transmission of information in packets on request or at prearranged intervals. Polling allows the user base to interrogate a Mobile Earth Station (Inmarsat-C Terminal) at any time, triggering automatic transmission of the required information. Inmarsat-C is an existing and

developed services based on the pioneer technology. The new generation of IsatData Pro which was newly launched in 2011 offers a significant increase in payload capacity compare to IsatM2M, delivering up to 10,000 bytes to the device and up to 6,400 bytes from the device (Figures 3 and 4).

INSAT system overviewThe Indian satellite INSAT-3E is a GEO communication satellite built by an Indian government agency, the Indian Space Research Organization. INSAT is designed to provide high-speed communication, television, Very Small Aperture Terminal (VSAT) and tele-education services. The satellite is positioned at 55 degree east longitude and carries 24 normal C-band transponders, delivering an

Figure 3: INMARSAT - Data flow diagram and frequency of operation.


Figure 4: The Space Segment – INMARSAT Coverage (National Oceanic and Atmospheric Administration, 2006).

edge of coverage Effective Isotropic Radiated Power (EIRP) of 37 dBW, and 12 Extended C-band transponders with an edge of coverage EIRP of 38 dBW over India. Additionally, INSAT has deployed two transponders on GEO satellites explicitly for data communication: the INSAT-3C Mobile Satellite System (MSS) Reporting Service has 24 C-band transponders, 6 Extended C-band transponders and 2 S-band transponders, while the INSAT-3A - Data Relay Transponder (DRT) Service operates in the UHF band, primarily serves realtime hydro-meteorological data collection from unattended terrestrial locations. The data are then relayed in extended C-band to a central location (Figures 5 and 6).

LEO Satellite Communication SystemsARGOS satellite system overviewARGOS is a system designed and dedicated to science. ARGOS has been used by the oceanographic community for more than three decades, and is a dependable, true polar,

operational data collection and platform location system. Traditionally, communication is one-way only, at 400 baud, with practicable data rates of the order of 1 Kbyte per day. Transmissions by the mobile in this mode are unacknowledged by the system and therefore have to incorporate redundancy if data transfer is to be assured. The system enjoys a particularly clean part of the spectrum (401.65 MHz), with minimal interference from other users. Polar orbiting satellites flying at an orbit of 850 km above the Earth pick up the signals and store them on-board and relay them back to earth to over 50 antennas around the globe. Data are either received in realtime by a regional antenna in the satellites' path or stored on board and relayed to the nearest global antennas. The next generation ARGOS equipment (ARGOS 3) features two-way communication with Platform Messaging Transceivers (PMTs), and offers uplink data rates of up to 4.8 kbps. Platform remote control and programming is also possible as users have the opportunity to send short


Figure 5: INSAT data flow diagram and frequency of operation - Data Relay Transponder (DRT).

Figure 6: The Space Segment - INSAT Coverage (source: dishtracking website).


messages (up to 128 bits) to their platforms via the Downlink Message Management Centre (DMMC). The system is one of the few that offers true global coverage (Figures 7 and 8).

IRIDIUM satellite system overviewThe IRIDIUM constellation operates as a fully meshed network and is the largest commercial satellite constellation in the world via 66 in-orbit satellites. The low-earth-orbit (LEO)

Figure 8: ARGOS Data Latency [University of Washington, 2004].

Figure 7: ARGOS - data flow diagram and frequency of operation.


IRIDIUM satellites positioned in 6 planes at a height of approximately 780 km can deliver low-latency communications and true global coverage. Data communication modes include a short burst data (SBD) service of up to1960 bytes max per message [Stalin. n.d.], as well as a dropout-tolerant direct Internet connection at up to 2.4kbps. The maximum length of a Mobile originated-SBD message is 1960 bytes. The maximum length of a Mobile Terminated-SBD message is 1,890 bytes. Global network transmit latency for message delivery ranges from 5 seconds for messages of 70 bytes to approximately 20 seconds for maximum length messages, additional latency may occur across the Internet. The system is bi-directional and SBD messages may also be queued for the mobile. Energy costs are also low for both modes of access (~20J/kbyte), largely because of continuous satellite availability and the implementation of spot beams to reduce the mobile transmitter power requirement. Satellites communicate with neighbouring satellites via inter-satellite links to relay communications to and from ground stations. Typical global latency of modern modems is less than 30 seconds with excellent coverage in the 1616.0 to 1626.5 MHz range. Most of the tsunami buoys systems for Tsunami Early Warning application use IRIDIUM satellite telemetry (Figures 9 and 10).

Comparison of GEO, MEO and LEOSatellite communication is a special technology in the field of electronic communication systems. Since the satellite footprint decreases in size as the orbit gets lower, LEO and MEO systems require larger constellations than GEO satellites in order to achieve global coverage and avoid data delays. Less energy is, however, generally required for LEO and MEO satellite

communication because of the shorter average distance between transmitter and satellite. IRIDIUM provides a greater data throughput capacity than ARGOS without the associated latency. In the ARGOS system, data are often stored on tape for later downlink with associated latency issues. In addition, as IRIDIUM satellites orbit at 780km above Earth, considerably less energy is required to relay data as compared to the GEO INMARSAT system, positioned 35,876 km above the Earth. ARGOS has many disadvantages including one-way communications, non-continuous temporal coverage, low data transmission rate, long message latency and high cost due to low volume market. During a satellite overpass, each Platform Transmitter Terminal (PTT) can normally transmit at an ARGOS assigned repetition period ranging from 40 to 240 seconds. The average duration of PTT visibility by the satellite or the “window” during which the satellite can receive messages from the PTT is about 10 minutes for each satellite pass [Meldrum, 2007a; 2009]. While ARGOS cannot effectively be used for realtime data collection, the system is ideal for equipment tracking, since the transmitters for ARGOS are very small and lightweight.

Figure 11 illustrates a comparison of latency of GEO and LEO satellite telemetry used for a moored buoy application. Highest latency is seen in ARGOS and least is observed in IRIDIUM, due to its much denser constellation. Figure 12 depicts power consumption for satellite terminals: the power requirement is very high for GEO satellite telemetry compared to LEOs owing to the much greater distance of GEOs from the Earth. INMARSAT requires an average of 24 W for transmission compared to IRIDIUM of about 170 mW.


Figure 9: IRIDIUM - data flow diagram and frequency of operation.

Figure 10: The Space Segment – IRIDIUM Coverage (David Meldrum, 2007b).


Figure 11: Latency of different satellite communication systems.

Figure 12: Satellite terminal transmitter power requirement.

Figures 13: Data transmission rate of short burst data.


Figure 13 shows the data transmission rate of IRIDIUM SBD is 2,400 bps, whereas the transmission rate of ARGOS is 400 bps, and for INMARSAT it is 600 bps.

Data FormattingThe data from buoys are generally reported in binary, along with platform identification numbers. These data have to be converted to physical units, quality controlled andformatted prior to insertion on the Global Telecommunication System (GTS) for use by the global forecasting centres and archival agencies. JCOMM, the Joint Technical Commission for Oceanography and Marine Meteorology, is an intergovernmental body of technical experts that provides a mechanism for international coordination of oceanographic and marine meteorological observing, data management and services, combining the expertise, technologies and capacity development capabilities of the meteorological and oceanographic communities. These systems are operated as part of the IOC-WMO-UNEP-ICSU Global Ocean Observing System (GOOS), which is led by the Intergovernmental Oceanographic Commission (IOC) of UNESCO. The Data Buoy Cooperation Panel (DBCP) at its twenty-seventh session in Geneva in October 2011 (DBCP-27) reported that, for many users, the costs of operating IRIDIUM platforms were apparently much less than for ARGOS counterparts. However, IRIDIUM did not offer an equivalent of the full ARGOS service, which included a number of value-added functions, including conversion of raw data to physical units, both realtime and delayed mode QC, GTS formatting and insertion, archiving, and open access to all parts of this chain by the JCOMMOPS. As a result, many operators had created their own

‘back-office’ services and took care of their own GTS insertion using their existing infrastructure. Table 2 shows details of candidate satellite systems for ocean observation used for data telemetry.

INDIAN MOORED BUOY PROGRAMME

The Indian Ocean is unique among the three tropical ocean basins in that it is blocked at 25°N by the Asian landmass. Seasonal heating and cooling of the land sets the stage for dramatic monsoon wind reversals, strong ocean–atmosphere interactions, and intense seasonal rains over the Indian subcontinent, Southeast Asia, East Africa, and Australia. Recurrence of these monsoon rains is critical to agricultural production that supports a third of the world's population. The Indian Ocean also remotely influences the evolution of El Niño–Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), North American weather, and hurricane activity. Despite its importance in the regional and global climate system, the Indian Ocean is the most poorly observed and least well understood of the three tropical oceans [McPhaden et al., 2009a; 2009b].

The Ocean Observation Systems (OOS) erstwhile National Data Buoy Programme was established in 1996 with the prime objective to operate, maintain and develop moored buoy observational networks and related telecommunication facilities in Indian seas. OOS also monitors the overall efficiency of the observing systems and, as necessary, recommends and coordinates changes designed to improve it. OOS has inherited the lead responsibility for a number of important and well-established observational programs. The shore station at the National Institute of Ocean


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Technology (NIOT) receives data from the moored buoys located in the Indian seas. The shore station is manned all hours of day and night, all days of the year.

Met-Ocean BuoysThe moored met-ocean buoys measure wave, meteorological and subsurface parameters every hour, waves are measured using a MRU (Motion Reference Unit) accelerometer sensor, the meteorological parameters are measured using wind, humidity, and air pressure sensors, and the subsurface parameters are measured using an Acoustic Doppler Current Profiler (ADCP) and Conductivity and Temperature (CT) sensors (Figure 14). The buoy is powered with a lithium battery pack and is equipped with position indicating system Global

Positioning System (GPS). Data sets are stored on an in-house hard disk within the data logger (data acquisition and processing unit) and also transmitted to the shore station using INMARSAT satellite. The sensors are programmed to acquire data samples for a specified duration of time and frequency. The data buoy starts the sampling process approximately 30 minutes before the transmission of data in synoptic mode. The data acquisition and processing of various sensors are carried out in parallel. The averaging of the data is done at the end of the sampling process and the data is transmitted to the data reception facility at NIOT at every three hours. The details of the data sampling sequence of the sensors are given in Figure 15. The data logger in the buoys have a built-in intelligence

Figure 14: Floating moored buoy with background of Indian Research Vessel Sagar Nidhi of the west coast of India.


such that whenever the signal strength is poor the acquired and processed data along with its time stamp and signal strength information will be stored in the temporary memory of the data logger and in the next consecutive transmission stored data is also transmitted to the shore station.

Tsunami BuoysAs a part of the Tsunami Early Warning system established by the Indian government at the Indian National Centre for Ocean Information Services (Hyderabad), moored buoy observational networks to detect tsunamis were established. The main objective is to collect and disseminate water level data using a Bottom Pressure Recorder (BPR) deployed at selected locations in the Bay of Bengal and the Arabian Sea. This tsunami buoy system consists of two units, the surface buoy and the BPR, which are deployed at ~4000 m depth

and are linked acoustically to transmit data underwater. These data sets are transmitted from the surface buoy to the data reception centre at the NIOT. This data centre is manned all hours of day and night, all days of the year. As vital information on natural hazards is to be provided, it is important that there is no loss of data during transmission from the buoys to the shore station.

Fifteen Years of Experience using INMARSAT Satellite TelemetryNIOT has been using INMARSAT communication since 1997, when the first met-ocean buoy was deployed off Chennai (on eastcoast of India). Since then nearly 550 moored buoy systems have been deployed for collecting meteorology, ocean, and tsunami water level data, ranging from coastal waters to deep ocean. The range of coverage of deployment of these buoys range from 63 degrees east to 93 degrees

Figure 15: Data sampling sequence of sensors.


east and 6 degrees north to 20 degrees north (Figure 16). NIOT has had a share of data return from the moored buoys using INMARSAT Satellite Telemetry which has varied from 92% to 98%. These systems were used to record extreme weather conditions, such as 17 cyclones from 1997 to 2012, and maximum wind speed of 33.3 m/sec. The terminal fitted for data reception has been used to receive nearly 4.4 million data sets over the past 15 years out of which 52% is marine meteorology data, 40% is ocean data, 6% is wave data and 2 % is water level data from these Met-Ocean and tsunami moored buoys. The transmitted data packets varied from 45 to 53 bytes in met-ocean buoys, 90 to 110 bytes in the ocean moored buoy network for the Northern Indian Ocean (OMNI) buoys, and 128 to 190 bytes in tsunami buoys

through INMARSAT telemetry. The longest surviving met-ocean buoy transmitter deployed in the Arabian Sea worked for 800 days and transmitted 320 Kbytes of data. The signal strengths of INMARSAT collected from the buoys showed variations under different environmental conditions. Four different variants of Thrane & Thrane terminals were used. Thanks to the technology and quality control of the product, one of the INMARSAT transceivers at the NIOT data reception centre has been working continuously since 1997 until now and has received more than 2.5 gigabytes of data. This shows the robustness of the system for such continuous data receipt.

Indian tsunami buoys are also deployed with INMARSAT communication systems. NIOT

Figure 16: Locations of Indian moored buoy data collection for 15 years.


uses Government of India approved INMARSAT satellite telemetry systems for data reception and two way communication in all the moored buoy systems. Important factors that determine the most appropriate satellite communication link to be used for buoy systems are power consumption of the transceiver electronics, high data rate, and low latency.

Tsunami buoys presently working globally use either IRIDIUM or INMARSAT satellite communications. IRIDIUM satellite terminals support 2400bps with very low power consumption of 250 mW in standby mode and around 2.5 W in transmit mode. Compared to this, INMARSAT terminals operate at a low data rate of 600 bps with high power consumption of 2W in standby mode and 23W in transmit mode. Hence IRIDIUM communication is used in more than 90% of the tsunami buoys operating globally. Due to the inherent disadvantages of high power consumption and low data rate of INMARSAT communication, it was observed on a number of occasions that (i) the batteries on the buoys require frequent replacements, (which is tedious due to non-availability of ship time) and (ii) high data latency and data gaps exist while buoys are operating in tsunami event mode. In comparison, the buoys with built-in IRIDIUM communication are working with extreme reliability giving continuous and timely data. Due to the low power consumption, these buoys can also be equipped with redundant communication electronics thus improving the reliability and availability of the system. The major challenge in using INMARSAT in buoy systems is its high power requirement, which is nearly 130 times greater than IRIDIUM. However, both IRIDIUM and INMARSAT enable two way communications.

Power Requirement for Moored BuoysOne of the major challenges faced in moored buoy systems is the primary or secondary battery with solar panel. Initially, buoys were powered by alkaline batteries. However, alkaline batteries have drawbacks such as low energy density (causing alkaline packs to be large and heavy), high self-discharge (making these cells unsuitable for long term scientific experiments), and unreliable performance in extreme temperatures. Lithium batteries are often preferred for high current pulse marine applications due to their inherent long life and high energy density. These applications typically require a battery power system that can withstand extreme temperatures and harsh marine environments. Long life and reliability are also important concerns, as battery failure will result in total system failure for stand-alone systems in remote locations with no back-up power source. Safety is always a major concern. Reduced size and weight are important requirements for transportation. Of all the different types of lithium chemistries, bobbin-type lithium-thionyl chloride (Li/SOCL2) cells are best suited for remote applications due to their high energy density, high cell voltage, good low temperature performance, low self-discharge rate and good safety characteristics. It is estimated that the power consumption of a moored buoy using INMARSAT is approximately 5 times greater than that of a similar buoy system using IRIDIUM satellite telemetry. This leads to higher energy density battery, bigger buoy, larger pay load and related higher cost. Considering the overall cost involved in maintenance of buoys located in remote sites far away from shore, presently 3000 Ah batteries are being used as the buoy system would require power consumption of 8 to 10


amps per day that allows one year buoy service intervals. Handling the safety aspects of such high energy batteries is a huge challenge and well managed by the Indian moored buoy programme.

ENABLING TECHNOLOGY FOR OCEAN OBSERVATION

Over the past decade development of several types of autonomous platforms and enabling technologies has opened up the promise of more precise and cost effective measurements within the ocean [e.g., Rudnick and Perry, 2003]. Yet there are still substantial gaps in terms of capabilities and reliability, especially for science in the deep oceans. With the knowledge and technologies available now and expected over the next few years we are well placed to fill some of the highest priority gaps, in terms of operating depth, more intelligent measurement strategies and long range, long duration reliable operations [Natural Environment Research Council, 2010]. Marine science and technology have the opportunity to embrace rapidly developing infrastructures for communications and information sharing. In general, scientists have not been keeping up with these paradigm shifts in communications and information technology [Nature, 2005].

Remote ocean observation systems is a peculiar field of knowledge, bringing together specific complementary knowledge in mechanical and electrical engineering, and also in computer science. In the last decade, with the impressive improvements in computational power and battery technology, and the miniaturization of electronic systems, observational tools became less cumbersome and more amenable to be used. As smaller, lighter and less expensive

equipment became available, the access to operational vehicles was further facilitated and more and more prototypes became accessible for testing new algorithms and solutions. The design of ocean observatories must fulfil the needs of the scientific community who will use the facilities. From a technical point of view, some new systems do offer significantly enhanced capabilities compared to traditional carriers. Potential advantages include two-way communication, more timely observations, and greater data rates and volumes. Some systems are also proving to be considerably less expensive and more energy efficient than traditional channels.

Ocean observatories may be designed either as a surface buoy containing an autonomous power source and wireless communications or as a submarine fibre optic/power cable connecting one or more seafloor science nodes to the terrestrial power grid and communications. These options provide significantly different capabilities and associated costs. The moored buoys can provide a limited amount of power and bandwidth. Realtime satellite connectivity at 1 Mb/s is available, but higher data rates are difficult to achieve at present. Cable-based installations can provide much greater amounts of power and bandwidth. Tens to hundreds of kW can be delivered to cabled observatories. State-of-the-art submarine telecommunications technologies can transport 1 Tb/s across transoceanic distances on a single cable. The major challenge in cabled observatory design lies in reliability engineering [Chave et al., 2003]. However, the electronic infrastructure required in implementing an ocean observatory will always be more complex than that used in submarine telecommunication systems.


Designing an installation which delivers the required performance and is maintainable at a reasonable cost is critical in realtime. Hence, it seems moored observatories will remain for-ever to fulfil the scientific demand and cannot be replaced by highly expensive and complex tethered observatory systems [Woods Hole Oceanographic Institution, n.d.].

Presently the global ocean observation community uses several models and makes of sensors from various manufacturers. These sensors need to be interfaced with a centralized Data Acquisition System (DAS) of any observing system. The diversity of sensors and DAS leads a manufacturer to closed, less-flexible, and generally more expensive solutions. This, in turn, will require the development of software to define the handshake protocol of the particular sensor, and details of the data acquisition and processing techniques for that particular parameter. This will consume time and resources, and this delay needs to be accounted for when planning a project. The major constraint is that the software is not generic, and each and every user must either develop it themselves or do additional work in order to use a particular sensor with their system. In the above case the user has to verify the correctness of the interface, the calibration validity and for every instance that requires trouble shooting the user has to open the system. The cost and time involved in developing software for interfacing various sensors is high. This configuration also will not easily allow the addition of other sensors without modifying the interface software. The proposed “plug-and-play” system for ocean observation will have accentral processor/DAS which will have the necessary firmware/software to accommodate sensors/transducers that are developed

satisfying certain predefined standards. This will enable the system to detect and configure with little or no user involvement and also without the user needing special knowledge about hardware configurations. The system will have a piece of hardware and software that acts as a bridge between transducers and the DAS. The bonding layer works by running algorithms that process the data received by both sides (the sensor and DAS) which then determine the next state of the system.

The required interface protocol needs to be standardized for open, common, independent communication interfaces for connecting transducers (sensors or actuators) to microprocessors, instrumentation systems, and control/field networks. One of the key elements of these standards is the definition of the Electronic Data Sheet (EDS) for each transducer. The EDS is a memory device attached to the transducer which stores transducer identification, calibration, correction data, and manufacturer-related information. The goal is to allow the access of transducer data through a common set of interfaces whether the transducers are connected to systems or networks via a wired or wireless means. Major challenges include integrating data streams of individual sensors and instrumentation in realtime and the correlation of data streams. The instruments interface for “plug-and-play” operation, full sensor suite integration and development, calibration and maintenance of new and robust instrumentation. In future, new ideas could be emerging to develop technology on web connected sensors from buoys. Embedding metadata within sensors and instruments will allow a foundation to be established with the aim of automatic cascading corrections down to the relevant calibration


data and metadata leading to automatic recalibration of sensors.

Societal NeedThe Bay of Bengal and the Arabian Ocean Basins are the locations in which a large portion of the Southern Asian coast generated cyclones and coastal impacts are felt. They are comparatively more frequent and devastating, especially when they strike coasts bordering the North Bay of Bengal. Tsunamis are an ever-present threat to lives and property along the coasts of most of the world’s oceans. In the Indian Ocean, there are two tsunamigenic zones, the Andaman-Sumatra trench and the Makran coast. The 2004 Indian Ocean tsunami was one of the most devastating disasters in modern history and the second largest earthquake ever recorded on a seismograph. Because of the heavy socio-economic impact suffered along the coast of Bay of Bengal annually due to cyclones, it is important to track any change in frequencies. The highest number of severe cyclones occurs in November with an average of one per year [Singh et al., 2000]. The Intergovernmental Panel on Climate Change 2007 report [United Nations International Strategy for Disaster Reduction, 2007] gives alarming scenarios on the potential sea level rise; it is expected to rise by at least 40 cm by 2100, inundating vast areas on the Asian coastline. Bangladesh, India, Maldives and Sri Lanka, with extensive low-lying areas just above sea level, are likely to be hard hit. Coastal erosion is a universal problem and it has been estimated that 70% of all the beaches in the world are eroding. Most of the existing and potential coastal erosion hazard problems arise due to coastal development having been undertaken too close to the sea. Coastal erosion is primarily associated with dynamic

natural shoreline fluctuations and changes. These societal needs force newer technological developments, outward thinking, and a change in data collection mode, such as observational tools like moored buoys. It is proposed in this paper that monitoring systems at sea should be designed to change sampling patterns to collect and transmit data in shorter intervals rather than the regular 3 - hour mode. The user should be able to have effective two-way communication that enables remote mode of change in data collection or in auto-trigger mode. This is similar to the tsunami buoy system, wherein during tsunami mode, water level data is transmitted at 5 minute intervals. The above conditions call for robust, highly reliable satellite telemetry with advanced instrumentation and smart sensors within met-ocean buoy systems.

CONCLUSION

It is well established that global climate change environmental factors that are expected to have the greatest direct effects on estuarine and marine systems are temperature change, sea-level rise, availability of water from precipitation and runoff, wind patterns, tsunamis and storminess. Natural disasters and shoreline erosion are two of the main threats that coastal communities face, which threaten lives, property, and economies. Such communities are particularly vulnerable to hurricanes and tsunamis, and as more people move to the coast, the potential of such events causing catastrophic loss of life and property damage also rises. New scientific advances are helping government agencies and local communities deal with coastal hazards more effectively and develop long-term hazard management plans. There is an urgent need to understand the earth


system as a whole through observational tools, satellite data and effective model predictions. Rapidly evolving technology is creating dynamic opportunities for remote oceanographic sensing equipment capable of delivering realtime information that expands the boundaries of scientific knowledge. In this paper we speculate that moored buoy observations make long-term measurements of ongoing processes anywhere in the world’s oceans possible. As computer and electronics technology inevitably becomes more complex and miniaturized, increasingly sophisticated power management solutions are required, which will enable design engineers to pack more product features into less space, with less weight, and longer service life. As technology is advancing quickly, future users should be able to access the buoy system to get data with the requisite high resolution, faster sampling rate, and polling of data at desired intervals with much less latency from Ocean-to-Desktop. ACKNOWLEDGEMENTS

We thank the Ministry of Earth Sciences MoES, Government of India, for funding the ocean observation network programme, and the members of the National Expert Committee for evolving this programme. We express our sincere thanks to Dr. David Meldrum, Scottish Marine Institute, UK for reviewing this manuscript. Directors of NCAOR, Goa and INCOIS, Hyderabad are thanked for providing all the facilities and logistic support. We also thank the staff of Ocean Observation Systems (OOS) group, Vessel Management Cell of the NIOT and ship staff for their excellent help and support on board.

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