Pierre Leon

Monte-Carlo-based channel characterization for underwater optical communication systems

We consider channel characterization for underwater wireless optical communication (UWOC) systems. We focus on the channel impulse response and, in particular, quantify the channel time dispersion for different water types, link distances, and transmitter/receiver characteristics, taking into account realistic parameters. We use the Monte Carlo approach to simulate the trajectories of emitted photons propagating in water from the transmitter towards the receiver. During their propagation, photons are absorbed or scattered as a result of their interaction with different particles present in water. To model angle scattering, we use the two-term Henyey-Greenstein model in our channel simulator. We show that this model is more accurate than the commonly used Henyey-Greenstein model, especially in pure sea waters. Through the numerical results that we present, we show that, except for highly turbid waters, the channel time dispersion can be neglected when working over moderate distances. In other words, under such conditions, we do not suffer from any inter-symbol interference in the received signal. Lastly, we study the performance of a typical UWOC system in terms of bit-error-rate using the simple on-off-keying modulation. The presented results give insight into the design of UWOC systems.

Channel modeling for underwater optical communication

We consider in this paper channel modeling for underwater optical channels. In particular, we focus on the channel impulse response and quantify the channel time dispersion under different conditions of water type, link distance, and transmitter/receiver parameters. We use the Monte Carlo approach to simulate the trajectories of emitted photons propagating in water towards the receiver. We show that in most practical cases, the time dispersion is negligible and does not induce any inter-symbol interference on the received symbols. Our results can be used to appropriately set different system design parameters.

Constraints on Rifting Processes from Refraction and Deep-Tow Magnetic Data: The Example of the Galicia Continental Margin (West Iberia)

The Galicia margin, which is characterised by the presence of a series of tilted fault blocks and underlying seismic reflectors well imaged by multichannel seismic (MCS) reflection profiles, is a classic example of a rifted continental margin. Since the early 1980’s, several models have been proposed for the formation of this margin. All these models were based mainly on seismic imagery obtained from MCS data with age control provided by data collected during DSDP leg 47B and ODP leg 103. To understand fully the evolution of this margin, pertinent geophysical data are needed, especially to constrain seismic reflection interpretations. We discuss a new preliminary seismic refraction model and deep-tow magnetic data collected across the Galicia continental margin and show how they constrain the deep structure in this region and the precise location of the ocean-continent transition.

Underwater wireless optical communication; recent advances and remaining challenges

Because of its ability of providing very high data transmission rates over distances up to several tens of meters, underwater wireless optical communication (UWOC) has attracted considerable interest during the past few years. The underwater channel is a challenging environment, especially because of its high attenuation. The difficulty of precise localization underwater also leads to unavoidable link misalignments that can have an important impact on the link availability and otherwise on the quality of signal transmission. In this paper, after a review of the recent research works on UWOC and the available commercialized systems, we present the performance study of a typical UWOC system under some simplifying assumptions for system modeling. We also address the open issues and the challenges that we are faced with in practice.

TEMPO: a new ecological module for studying deep-sea community dynamics at hydrothermal vents

The major goal of this project, elaborated in the frame of the STREP Exocet/D European project, was to design a first autonomous long-term imaging module equipped with a deep-sea video camera, adequate lightning and sufficient energy storage while taking advantage of most recent progress in imaging and photonics. The new ecological module TEMPO was tested and deployed during the Momareto cruise held from August 6 to September 6, 2006 on the new French oceanographic vessel Pourquoi pas?, with the ROV Victor 6000. The scientific objectives of the Momareto cruise were to study the spatial and temporal dynamics of hydrothermal communities colonizing the MoMAR zone, located on the Azores Triple Junction.

Investigation of suitable modulation techniques for underwater wireless optical communication

For an underwater wireless optical communication system, we consider the use of different intensity modulation techniques, and compare their performance by taking realistic system parameters into account. In particular, we contrast the performances of on-off keying, pulse position modulation, pulse width modulation, and digital pulse interval modulation, when a PIN or an avalanche photodiode is used at the receiver. We discuss the suitability of these modulation techniques to the underwater optical channel by considering the implementation issues.

PASISAR: a new tool for near-bottom very high-resolution profiling in deep water

Detailed sea-bed geology (stratigraphy, faulting, lateral facies variation) of deep water areas (over 300 m water depth) is nowadays being explored, both for scientific purposes such as a better insight into marine sedimentary processes and tectonics, and for future offshore industry developments. This requires us to address new technical challenges.

Investigation of solar noise impact on the performance of underwater wireless optical communication links

We investigate the effect of environmental noise, caused by solar radiations under water, on the performance of underwater wireless optical communication (UWOC) systems. Presenting an analytical and generic model for this noise, we examine its impact on the link performance in terms of the bit error rate (BER). This study is conducted for different photo-detector types in the aim of highlighting practical limitations of establishing UWOC links in the presence of subsea solar noise. We show how the solar noise can impact the performance of UWOC links for relatively low operation depths. The results we present provide valuable insight for the design of UWOC links, which are likely to be established at relatively low depths. They can be exploited not only for the purpose of practical UWOC system deployment but also for in-pool experimental set-ups, since they elucidate the effect of ambient light on the measurements.

Open-Sea Observatories: A New Technology to Bring the Pulse of the Sea to Human Awareness

Historically, observation in Marine Science was mainly based on in situ measurements made mainly over ship surveys and shore measurements. Unfortunately, ship surveys can only be episodic, and are constrained by weather and by the constant rise of ship-time cost. As the data provided by non-communicating moorings are stored in the measurement system, a ship intervention is needed to recover both the mooring and the data after several acquisition months. Further to the rather successful mediumand short-term deployment of these traditional devices, scientists have expected the development of long-term observations and permanent marine system-monitoring tools so as to gain more insight into the observed processes. By providing additional information, satellite technology can partly solve this gap between the reality and expectations. However, even though satellite images provide information over a large time frame (from minutes to years) and a wide range of spatial resolutions (from metres to thousands of kilometres), they only cover the upper layer of the sea. An Open-Sea Observatory is a complementary tool that allows one to make, in the water column and on the seafloor, long-term measurements of many environmental parameters and to acquire them in real-time, or near real-time. In addition to this real-time data transmission, these systems permit remote intervention by humans when needed, and thus can be considered as 2-way communicating devices. Because of these two characteristics, observatories are innovative systems that bring internet to the ocean and make the ocean reality visible to the human eye. According to our definition of an Open-Sea observatory, other very useful observation tools such as gliders, floats, repeated profiler transects, etc. will not be considered in this chapter to only focus on such ocean observatories. Observatory initiatives have been spreading worldwide since the 1990s. In Europe, several initiatives started twenty years ago so as to upgrade free-fall systems from the sea surface (the so-called “landers”) to make them 2-way communicating and to develop bottom

Deep Sea Net: an affordable, and expandable solution for deep sea sensor networks

Deep Sea Net is a new concept of deep sea sensor network built from fiber optic micro cable and battery operated IP access nodes. Deep Sea Net fiber optic transport segments are deployed directly from a standard ROV, avoiding the use of a costly cable layer ship. Deployment skid is abandoned on user site ready to connect local sensors and next transport segment. Deep Sea Net is a low consumption network which can be waked on user (or sensor) demand. Lithium batteries and fine power management will give 10 years of autonomy with 1/4 of hour operation per day. The innovative approach of Deep Sea Net will permit to build, extend and maintain future sensor networks at very competitive prices.