Zigbee based buoy network platform for environmental monitoring and preservation Temperature profiling for better understanding of Mucilage massive blooming Sieber, A. 1)2), Cocco, M. 3), Markert, J. 4), Bedini2), R., Dario, P. 5) and Woegerer, C.1)
[email protected] 1) 2) 3) 4) 5)
Profactor GmbH, Seibersdorf, Austria CNR, Istituto di Fisiologia Clinica, Pisa, Italy Park of the Tuscany Archipelago, Italy University of Applied Science Frankfurt, Germany Scuola Superiore Sant’Anna, Pisa, Italy
1 Introduction: The global climate changes are expected to influence the behaviour of marine organisms. In the past several events of Mucilage massive blooming were observed, which led in many cases to the death of the Red Gorgonia. A novel Zigbee based buoy platform was developed, enabling a monitoring of environmental parameters especially temperature profiling with high spatial resolution. This novel tool will be of importance for marine environmental preservation, as it allows obtaining a reliable picture of the present scenario along with a prediction of future changes. Moreover it will lead to the better understanding of inter-dependendencies of Mucilage blooming, water temperature, currents (sensu Hutchinson 1957, i.e. the field of tolerance of a species to the principal factors of its environment) and of mucilage impact on gorgonians in the Tyrrhenian sea (Italy). Mucilage’s massive blooming is a periodical phenomenon in Tyrrhenian Sea (Italy) that is occurring with a seasonal frequency. Also the type and the extent of the impact of mucilages depend on the season (Giuliani, 2005): three species of algae (Nematochrysopsis marina, Chrysonephos lewisii and Acinetospora crinita) constitute the principal components of the mucilaginous aggregates. In general, the first two species occur during the spring season, down to 20 m, while A. crinita occurs at greater depths. In July, when the mucilages reach their maximum development, C. lewisii is the predominant species. This species mainly affects E. cavolinii and E. singularis while A. crinita mainly affects P. clavata, which colonizes greater depths. Empirical considerations often connect the abnormal appearance of mucilage to a warmer water temperature during spring months as well as to the lack of early summer gales, as a consequence of an anticipated settling of the Azzorre’s anticyclone over the Western Mediterranean basin. In June 2003 a anomalous mucilage growth was recorded along the submarine rocky cliffs of the Tuscany Archipelago resulting in negative effects on many benthic taxa.This event differed from any others previously occurred in the northern Tyrrhenian Sea in that the mucilage aggregates were formed by the free-living form of the Phaeophyceae Acinetospora crinita (Harvey) Kornmann, a not usually dominant species in mucilage aggregates from the north Tyrrhenian Sea (Schiapparelli, 2007). The damage suffered by the benthic organisms living in this area was curtailed by a severe storm, occurred in July, which moved the mucilage to deeper depths, preventing irreversible damages. This
anomalous mucilage event occurred in coincidence with the 2003 European heatwave and the anomalous temperature increase of seawater. The dependence of abnormal mucilage blooming from water temperature gradient is not scientifically proofed mainly due to lack of detailed data about temperature gradients and temperature zones in the concerned regions. An instrument, that allows temperature profiling with high spatial resolution would be of enormous benefit for the understanding and the scientific documentation of anomalous mucilage growth events, which is of high importance for the conservation of the marine environment. Gorgonian, also known as sea whip or sea fan, is an order of sessile colonial cnidarian populating the Mediterranean and Tyrrhenian Sea. Each gorgonian polyp has eight tentacles which catch plankton and particulate matter that is consumed. This process, called “filter feeding”, is facilitated when the "fan" is oriented across the prevailing current to maximise water throughput and hence food supply. Thus the surviving chances of the colony depends upon the catching capacity of polyps, and can be seriously reduced if the colony branches are covered by massive mucilage blooming for a long time. The most frequently species of Gorgonians that can be found in Tyrrhenian Sea are Paramuricea clavata, Eunicella Cavolinii, and Eunicella Singularis.
Figure 1a: P. clavata wood (Formiche della Zanca, Isle of Elba, Tuscany Archipelago), Figure 1b: Mucilage affection of P. clavata colonies (Pianosa Island, Tuscany Archipelago, 2007)
P. clavata, also as known as Red Gorgonia (figure 1), is the most famous and characteristic mediterranean gorgonia. It belongs to the Paramuricedae Family. It is tree/fan shaped, with dense, dark red coloured branching, which can reach up to 1 mt height. Colonies have the appearance of underwater woods, whose branches hosting a noteworthy biodiversity made of several different kinds of fishes and invertebrates. It is a typical species of the Mediterranean Sea living from 25-30 mt depth up to more than 100 mt. During past years, Red Gorgonia colonies were quite a lot diffused, today being sadly declined as a consequence, amongs others, of fishery net impact. The impact of water warming and mucilage coverage after overblooming is considered as negatively affecting the colony survival, even though not yet proofed. In summer ’99, a massive mortality of anthozoa as well as other animals (molluscs, sponges, tunicates, briozoa) occurred in Ligurian Sea in concomitance with a high water temperature that reached –40 mt depth (Pastor, 2007; Perez, 2000). Mostly injuried species were red, white and yellow gorgonias (Paramuricea clavata, Eunicella Singularis, Funicella cavolini), red corals (Corallium rubrum), Leptogorgia sarmentosa, Cladocora caespitosa and Parazoanthus axinellae.
In some cases the mortality rate was reported between 60% and 100% of the existing colonies (Cerrano, 2000). Due to still unknown reasons, mortality mainly hit female polyp colonies (Cerrano, 2004). Further studies demonstrated that gorgonias were subjected to a severe stress because of the high water temperature, thus ending up to be damaged by a high variety of microrganisms, including fungi and protozoa. Following this, the pathology was claimed as “Fungus-Protozoa Syndrome (FPS) Those episodes were not being remained isolated: in Parazoanthus axinellae colonies death has been occurred for a few years, significantly reducing the population of the gorgonians with particular reference to the area of Portofino Promontory as well as in other zones of Ligurian Sea. In these cases too, the death is commonly attributed to the high temperature inducing the proliferation of pathogenic agents like Porphyrosiphon cyanobacteria (Cerrano, 2006). During 2003, further death episodes of antozoa in Mediterranean Sea were reported. This time striking not only France and Italy coasts, but also Spain waters: in the marine reserve of Columbretes Islands a wide death episode of P. Clavata and Cladocora Cespicosa was recorded (the last subjected to necrosys) (Kersting and Templado, 2006). These facts were related to the excessive increase of mucilage (Kersting and Linares, 2006) and involved more than 60% of the colonies. Same episodes were reported simultaneously in different zones of the Spanish Mediterranean Sea, from Cabo de Creus to Cabo de Palos (Coma, 2006) In all these cases, the mortality episodes were coincident with anomalous, high temperature water warming. The same cause was attributed to the death of P. clavata colonies in the Messina Strait, where temperature increase induced an overblooming of filamentous algae (Tribonema marinum e Acinetospora crinita) (Sartoni, 1992; Mistri, 1995), as well as “bleaching” episodes of coral species like Cladocora caespitose, Balanophyllia Europea, Oculina patagonica, in other distinct areas of Western and Eastern Mediterranean Sea (Kushmaro, 1997; Kushmaro, 1998; Metalpa, 2000) For the better understanding of the relation between abnormal mucilage blooming and the water temperature gradient, a system is required to enable temperature profiling with high spatial resolution. Buoys, equipped with temperature sensors along the mooring can therefore be used. The high spatial resolution requires then a large amount of such buoys. Such a buoy should offer: -
temperature profiling additional analog inputs for the connection of other sensors (for example current meters) autonomous and maintenance free operation over a long period small, leightweight and rugged design low cost networking capabilities easy deployment/recovery lowest power consumption
Profiling the temperature on different locations then also allows to check for a relation between current and mucilage outbreak. Moreover currents often influence the mucilage attachment on the colonies, so a cross-comparison of temperature vs current presence vs mucilage covering can be made with possible interesting results.
Since the thermal changes are not so frequent due to the high thermal capacity of water, a sampling rate of few hours should be sufficient to detail the scenario. The only exception might arise in presence of strong current episodes as well as during gales, when abrupt changes of temperature even in the deeper water layers may occur. Also the overall electrical current has to be considered when defining a sampling rate (the higher the sampling rate the higher the power consumption). A good compromise is a sampling rate 1 profile / 6 hours. Nevertheless when greater and/or faster changes are expected, the sampling rate can be remotely changed to a higher value.
2 Methods Buoys for monitoring of environmental parameters are normally custom designed according to the requirements. Therefore different buoys especially designed for a specific task are available on the market. One drawback of these custom designed buoys is their high price starting from around 10.000€ per buoy. Additional to this, actually available buoys use satellite transmission technologies like Geos, Inmarsat, ARGOS. ORBCOM or alternatives like VHF or GSM. All these systems have in common relatively high power consumption, presenting the need of a large power supply, diesel generators or solar panels. These needs then define the overall dimension of the buoy and with that, also the overall weight. The costs for a proper mooring plus deployment and recovery are rising with size and weight of a buoy, thus a miniaturisation enabled by a low power design is one of the main goals pursued in this paper. Our buoy platform is designed as an open architecture with a variety of analogue and digital interfaces, thus allowing an easy attachment of additional, partially already existing, sensor modules or hardware, that were not specifically developed for this buoy. The low price of the overall buoy allows a deployment of a large amount of buoys thus enabling a monitoring of the coastal areas with high spatial resolution. The buoys form a mesh network. Traditional large ower consuming telemetry, like satellite supported or VHF is not needed anymore and is substituted with a completely new approach - a ZigBeebased long range design allows a communication and data transmission between the buoys and to a server without the need of powerful transmitters. Each buoy can forward data received from its neighbour, thus a buoy does not need to be able to reach the receiver of the central computer. Moreover the mesh network design is self healing. A possible failure of one buoy will not lead to a breakdown of the whole network. Data connection to the server will also be established by ZigBee, but in cases where the network of buoys is situated far from the server, the network coordinator buoy can optionally be equipped with a GSM or satellite modem.
The presented buoy therefore stands for: - an easy adaptable modular design - easily configurable - thus: buoy can easily be adapted to specific requirements. - ultra low power design allowing power supply via batteries - thus: long autonomous operation without maintenance - small size - lightweight - easy and cheap mooring (due to the small size and the low weight) - easy deployment and recovery - robustness
2.1 ZigBee ZigBee is an open standard for short range wireless networks based on the Physical Layer and the Media Access Control from IEEE 802.15.4, focusing on minimizing the overall power consumption and at the same time maximizing network reliability. [IEEE 2003], [ZigBee Alliance, 2003] The first version 1.0 was published by the ZigBee alliance in 2004. This alliance was founded in 2002 and has nowadays more than 200 international members working on the continuous improvement and further development of this standard. This has led to the actual two versions ZigBee and ZigBee Pro, which were published in 2007. Typical ZigBee modules use the 2.4 GHz Band (16 channels) with transmission powers between 0.5mW to 10mW. Additionally in the United states 10 channels in the 915 MHz Band, and in Europe one Channel at 868 MHz can be used for ZigBee applications. The typical transmission range is 100m in free line of sight with a maximum data transmission rate of 250kBit/s. The half duplex ZigBee transmission requires a special protocol to avoid communication problems when many nodes share the same channel. Thus the Carrier Sense Multiple Access/Collision Avoidance CSMA/CA protocol is implemented, which is working at the underlying 802.15.4 level. Additionally random waiting times are used between the transmissions. IEEE 802.15.4 and ZigBee are offering the developer three kind of devices to form a so called personal area network (PAN). [ZigBee Alliance, 2008] 1. End-devices, which in general periodically collect data and transmit them. Furthermore for minimizing power consumption in such end-devices advanced sleep modes are implemented 2. Routers play an important role in a network, they collect data from end-devices and forward them to the destination (like another router or to the final coordinator). For the correct function of a network a router always has to be active. Thus sleeping modes are not possible and therefore are also not implemented. 3. Coordinator: One routers in a PAN is usually configured as coordinator. It’s main function are parameterization and management of the PAN and the collection of the networks data.
2.2 Meshnetics Meshnetics is a company providing a complete and user friendly solution for wireless communication based on ZigBee. Actually they deliver two Module types: ZigBit, and the enhanced version ZigBit Amp, software development kits and demo kits to minimize the overall development time. Both modules are available with a variety of antennas or antenna-connectors.
Figure 2, Meshtronics ZigBit modules are based on Atmels ZigBee bundle
2.3 ZigBit Amp Module Hardware Platform ZigBit Amp is based on the Atmel ZigBee bundle consisting of the 8 Bit Risc ATmega 1281v micro controller and the the AVR Z-Link AT86RF230 transceiver. Additional onboard amplifiers increase the transmission power by +20dBm and improve the receiving sensitivity to -104dBm enabling low power medium transmission range wireless communication up to 4 km. This large transmission range is unique for ZigBee modules and makes them suitable for our application in a small to medium mesh size buoy network for environmental monitoring with high spatial resolution. The following list highlights the key features of the ZigBit Amp module: -
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Ultra compact size (38.0 x 13.5 x 2.0 mm) Highest RX sensitivity (-104 dBm) Up to +20 dBm output power Outperforming link budget (124 dB) Very low power consumption: o 10 μA in sleep mode, o 23 mA in RX mode, o 50 mA in TX mode Ample memory resources (128K bytes of flash memory, 8K bytes RAM, 4K bytes EEPROM) Wide range of interfaces (both analog and digital): o Up to 30 Digital I/O’s including 2 free IRQ lines o 4 ADC channels (up to 9 lines with JTAG disabled) o 1 ADC channel for monitoring the battery voltage o UART with CTS/RTS control o USART o I2C o SPI o 1-Wire 4 MHz clock additional onboard 32kHz crystal IEEE 802.15.4 compliance 2.4 GHz ISM band extensive development software available: o eZeeNet embedded software o UART bootloader o AT command set Low prize, ~ 30€ per piece
2.4 Meshtronics eZeeNet Software Stack Meshnetics development kit includes eZeeNet, a IEEE 802.15.4 and ZigBee compliant software stack based on the Operating System TinyOS. With it’s API and several included demo applications it allows an easy and fast development of wireless sensor networks. It offers the following key features: -
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ZigBee 2006 compliant Mesh and tree topologies o coordinator, routers or end-devices available o max 32 children on one level o max 32 routers o 15 hops maximum network depth up to 12 user defined timers available Easy to use Application Programming Interface (API) Automatic PAN selection capability Powerful framework with cooperative multitasking Support for a large number of nodes Reference drivers for all ZigBit peripherals and hardware interfaces AT commands over UART Channel/networks scan selection Software development under AVRStudio4 [Atmel] and Winavr GNU C compiler
Figure 3: eZeeNet Block Diagram
The eZeeNet consists of three main parts: 1. eZeeNet Stack is running on end-devices, routers and coordinator to enable networking. 2. eZeeNet Framework gives access to system resources, using multitasking for user code besides networking. 3. Hardware Abstraction Layer (HAL) is the interface between the User and the Hardware. It provides access to the hardware always under the aspect to keep the system in a stable state. Thus direct access to the hardware is not allowed, the use of the API is recommended. eZeeNet supports autorouting. As soon as a router/end device is within the transmission range of the network, it automatically connects and, in the case of a failure, will retry to establish the connection.
2.5 Buoy hardware: Detailed temperature profiling with high spatial resolution is one of the main requirements as described in the introduction. Components for the buoy have to be selected in order to minimize power consumption and maximizing the overall maintenance free autonomous operation time.
Figure 4, principle hardware layout
The core element of the buoy hardware is a Meshtronics ZigBit Amp module. A DCF77 module allows time synchronization of the buoys within the network (DCF77 is a atomic clock based time signal transmitting station in Germany. The signal can be received in a maximum distance of 2000km around Frankfurt, Germany. Transmission power is 50kW at a frequency 77.5 kHz [Piester 2004]). Along the mooring line several MAX6575 [Maxim] temperature sensors are mounted (maximum 8x8 sensors). Their time coded signal is processed via a separate 8 Bit Risc Microcontroller (Atmega32L, Atmel). Alternatively we envisage to use 1-wire temperature sensors [Maxim] directly connected to the ZigBit Amp module. Optionally a GSM module can be connected to interface networks in inaccessible areas. A GPS receiver can be connected via serial port (NMEA0813). This is an interesting feature, as buoys always face the risk of broken mooring lines. In such a case, the buoy can determine it’s position with the inbuilt GPS receiver and send the data to the network if the buoy is still in the network range. This facilitates then necessary recovery actions.
2.6 Buoy software The buoy software is based on the Meshtronics eZeeNet. As development environment we used the Atmel AVRStudio4 and the WinAVR GNU C compiler.
Figure 5, Network structure
One Zigbit Amp module is configured as coordinator and directly connected to a personal computer via serial port. If the buoy network is installed in a inaccessible are, this serial link can be substituted by a optional GSM modem. Each buoy has to be able collect data, transmit them but also to forward data from other buoys in the network. Thus we decided just to use “router” configured ZigBit Amp modules in the network and no end-devices. During normal operation of a buoy, the central ZigBit Amp module will collect temperature data from the Maxim temperature sensors via the ATmega32L microprocessor. Then the data are transmitted in a data package consisting of at maximum 127 bytes (framesize is defined in IEEE 802.15.4). From these 127 bytes at maximum 102 bytes are available when using ZigBee. Each data package consists of 14 fields:
Field Number
Field Length, bytes
Field Description
1
1
MSG_DATA
2
1
Node type
3
8
IEEE address
4
2
5
4
6
4
7 8
2 1
9
2
10 11 12 13 14
1 1 1 1 Sensor data size
Node short address eZeeNet Software version WSN channel mask PANID WSN working channel Parent short address LQI RSSI Board type Sensor data size Sensor data
Table 1: eZeeNet data package
30 bytes are used for communication and networking purposes, thus 72 bytes are available for data transfer. Typical data transfer of one buoy includes the coordinates (initially stored during the deployment of the buoy), the buoy onboard time (to check for synchronization), the buoys battery voltage and of course the temperature profile data. As the buoy is designed as open platform, additional sensors can be connected via digital I/O lines or to one of the four analog inputs. As described above, router software does not support sleeping modes. For temperature profiling a recording interval of 6 hours is usually sufficient. In the meanwhile, a network operation is not needed. Thus we decided to implement additional “sleep” modes functions based on time synchronized buoys (DCF77 clock). As the buoy prototypes are situated in the northern Mediterranean sea within the range of the DCF77 signal, we preferred the precise time information form a DCF module to protocol based time synchronization like described in [Sundararaman, 2005]. After receiving temperature data packages the central personal computer sends a “sleep” command to the routers in the buoy network. This sleep command includes time at which the buoys shall enter the sleep mode (usually ~ 30s after transmission of the command) and the requested sleep duration. When processing the sleep command, the ATmega1281v on the central Zigbit amp module will switch off the ZigBee transceiver (Shutdown pin of the AT86RF230) and the attached components. Afterwards it will enter sleep mode “extended standby”. Timer 2 is clocked via the onboard 32 kHz crystal offering a precise time base. Every 6 seconds the module wakes up to update the internal clock and then will enter sleep mode again. After the predefined sleep duration the buoys “wake up” again, start the ZigBee transceiver and the net work is formed again. This implemented “sleep” feature allows a reduction of the power consumption during the sleep mode to about 20µA resulting in an overall maintenance free autonomous operation time of more than a year (including periodically measurements every 6h).
2.7 Data visualization: A user front end panel was developed under National Instrumetns Labview 8.5. Collected data are stored in ASCII text files (for each buoy one file). The recored data of each buoy can be visualized in graphs. Furthermore a small chart shows the position of the buoys. Also a function is implemented to define the “sleep” periods.
Figure 6, First prototype of the LabView front end panel
2.8 Deployment of the buoys Once a proper mooring place for a the buoys if found, a anchoring point is deployed. After mooring the buoy to the anchor, the buoy electronics is configured by attaching the deployment vessels GPS via NMEA0813 and powering up the buoy. In this initialisation phase the actual coordinates are written into the EEPROM of the Atmega1281v. Alternatively a GPS module can be optionally installed on a buoy, enabling the buoy to determine it’s position itself. Considering that moorings can break leading to the loss of buoys this makes sense, as with such an installed GPS the buoy is able to detect it’s position and an eventual position change. If the mooring broke, the buoy may send it’s coordinates to the server enabling an easier recovery.
3 Results Several Buoy prototypes were build up. Their specifications are: - heigh: 1.5m (over water) - weight: 3,5 kg - positive buoyancy: 5 kg - power supply: 3 x 1,5V alkaline D cell, (17Ah) - power consumption during transmission: 60 mA - power consumption in sleep mode: ~20µA - autonomous maintenance free operation: >1y For testing the transmission and the networking capabilities first prototypes were deployed on the italien coast south from Livorno (figure 7a,b). Next steps are then the deployment on the coast of Elba/Italy. First results from long term deployment and from temperature profiling will be presented in the final version of this paper.
Figure 7a, b: First deployment for test purposes of a buoy prototype at the coast south from Livorno/Italy.
4 Conclusion Global climate changes and global warming have influence on the marine environment. An increased water temperature even in greater depths seems to be one of the main factors for Mucilage massive blooming. Mucilage attached on Red Gorgonias disturbs the gorgonias “filter feeding” mechanism, a fact that can lead to their death. Better understanding of and scientific research on Mucilage massive blooming related to temperature changes requires a tool for monitoring water temperature with high spatial resolution. The presented buoy allows temperature profiling. Due to its cheap components, low power consumption and small size and weight, an overall low system price (including the mooring, deployment and operational costs) that allows deployment of a larger amount of buoys that can then work in a ZigBee mesh network configuration. A large amount of buoys is the key for a detailed three dimensional temperature profiling. Furthermore the buoy is designed as an open platform. Thus other additional environmental sensors like for example current meters or sun radiation sensors can be easily integrated in the monitoring system.
5 References Cerrano C., Arillo A., Azzini F., Calcinai B., Castellano L., Muti C., Valisano L., Zega G. & G. Bavestrello (2004). Gorgonian population recovery af ter a mass mortality event. Aquatic Conservation: Marine and Freshwater Ecosystems. Volume 15, Issue 2 , Pages 147-157. Cerrano D., Bavestrello G., Bianchi C. N, Cattaneo-vietti R., Bava S., Morganti C., Morri C., Picco P., Sara G., Schiaparelli S., Siccardi A. & F. Sponga (2000). A catastrophic mass-mortality episode of gorgonians and other organisms in the Ligurian Sea (Northwestern Mediterranean), summer 1999. Ecology Letters 3 (4), 284-293. Cerrano C., Totti C., Sponga F. & G. Bavestrello (2006). Summer disease in Parazoanthus axinellae (Schmidt, 1862) (Cnidaria, Zoanthidea). Italian Journal of Zoology. Volume 73, Number 4: 35-361. December 2006. Coma R., Linares C., Ribes M. & M. Zabala (2006). A large scale disturbance espisode af fecting Paramuricea clavata populations along the Mediterranean peninsular coast of Spain in 2003. XIV Simposio Ibérico de Estudios de Biología Marina. CosmoCaixa Barcelona, Museo de la Ciencia de la Obra Social “la Caixa” 12-15 septiembre 2006. Giuliani S., Virno Lamberti C., Sonni C. and Pellegrini D., Mucilage impact on gorgonians in the Tyrrhenian sea, Science of The Total Environment , Volume 353, 340-349, 15 December 2005 Hutchinson, G. E. (1957). "Concluding remarks, Cold Spring Harbor Symposium." Quant. Biol, 22, 415-427
Kersting D. K. & C. Linares (2006). Mortandad de Paramuricea clavata asociada a un evento de macroagregados mucilaginosos (“llepó”) tras el verano de 2004 en Islas Columbretes. XIV Simposio Ibérico de Estudios de Biología Marina. CosmoCaixa Barcelona, Museo de la Ciencia de la Obra Social “la Caixa” 12-15 septiembre 2006. Kersting D. K. & J. Templado (2006). Evento de Mortandad masiva del Coral Cladocora caespitosa (Scleractinia) en las Islas Columbretes tras el calentamiento anormal del agua en el verano de 2003. XIV Simposio Ibérico de Estudios de Biología Marina. CosmoCaixa Barcelona, Museo de la Ciencia de la Obra Social “la Caixa” 12-15 septiembre 2006. Kushmaro A., Rosenberg E., Fine M., Haim Y. B. & Y. Loya (1998). Effect of temperature on bleaching of the coral Oculina patagonica by Vibrio AK-1, Mar. Ecol. Prog. Ser. 171(1998) 131-137. Kushmaro A., Rosenberg E., Fine M. & Y. Loya (1997). Bleaching of the coral Oculina patagonica by Vibrio AK-1, Mar. Ecol. Prog. Ser. 147 (1997) 159–165; Metalpa R. R., Bianchi C. N. & A. Peirano A. (2000). Coral mortality in NW Mediterranean, Coral Reefs 19 (2000) 24.–24; Mistri M., Ceccherelli V. U. (1995). Damage and partial mortality in the gorgonian Paramuricea clavata in the strait of Messina (Tyrrenian Sea), Mar. Life 5 (1) (1995) 4349. Pastor X., Aguilar R., I Coralli del Mediterraneo, OCEANA, Fondazione E.Zegna Eds, April 2007 Perez T., Garrabou J., Sartoretto S., Harmelin J.- G., Francour P. & J. Vacelet (2000). Mortalité massive d’invertébrés marins: un événement sans précédent en Méditerranée nord-occidentale. C. R. Acad. Sci. Paris, Sciences de la vie / Life Sciences 323 (2000) 853-865 Sartoni G. & C. Sonni (1992)., Tribonema marinum J. Feldmann e Acinetospora crinita (Carmichael) Sauvageau nelle formazioni mucillaginose bentoniche osservate sulle coste toscane nell’estate. La crisi del Mediterraneo in seguito alla fioritura di masse algali, Accad. Intern. Sci. Tecn. Sub. Ustica 9 (1992) (1991) 37-46; Schiaparelli S., Castellano M., Povero P., Sartoni G., Cattaneo-Vietti R. A benthic mucilage event in North-Western Mediterranean Sea and its possible relationships with the summer 2003 European heatwave: short term effects on littoral rocky assemblages, Marine Ecology 28 (3) , 341–353 (2007) Institute of Electrical and Electronics Engineers, Inc., IEEE Std. 802.15.4-2003, IEEE Standard for Information Technology . Telecommunications and Information Exchange between Systems . Local and Metropolitan Area Networks . Specific Requirements . Part 15.4: Wireless Medium Access, Control (MAC) and Physical Layer (PHY) Specifications for Low Rate Wireless Personal Area Networks (WPANs). New York: IEEE Press. 2003 ZigBee Alliance, ZigBee, Document 053474r17, www.zigbee.org, 2003
ZigBee Alliance, ZigBee Specification, Document 053474r17, www.zigbee.org, 2008 Meshnetics, ZigBit Amp OEM Modules ZDM-A1281-PN/PN0 REVISION 2.1, Doc. M251~03 V.2.1, 2007 Meshnetics, ZigBitAMP RangeMeasurement, Doc. AN-481~05 v.1.1, 2007 Meshnetics, Doc. M-251-02 V.1.14 EZEENET™ IEEE802.15.4/ZIGBEE™ SOFTWARE Adding Wireless Connectivity & Interoperability to Your Products, Doc. M-251~02 V.1.14, 2007 Piester, D., Hetzel, P., Bauch, A., Zeit- und Normalfrequenzverbreitung mit DCF77, in: PTB-Mitteilungen, Vol. 114, S. 345–368, 2004 Sundararaman, B., Buy, U., Kshemkalyani, AD, Clock synchronization for wireless sensor networks: a survey, in: Ad Hoc Networks, Vol 3, Pages 281-323, 2005
