Design and features of the HydroMet Buoy ('My Buoy')

Prepared by Xavier Lazzaro (IRD/BOREA)

It took three years to arrive at the final design of 'Mi Buoy'. First, market availability, features, performance, durability, costs and experiences in other instrumented ecosystems had been surveyed. The large global manufacturer XYLEM Analytics Inc. was selected as the only one capable of combining the latest state-of-the-art equipment from the leading brands in the market to create innovative systems customized to the user's requirements. The intense collaboration between Eng. Pierre Sterling (XYLEM Inc.) and DR. Xavier Lazzaro (IRD) resulted in the following design, combining the best of the leading brands:

- A 3.6 m x 2.0 m pontoon platform, more comfortable for maintenance than a spherical buoy. 

- A complete ultrasonic weather station, with no moving parts. 

- An underwater multiparameter probe equipped with key sensors to assess the level of eutrophication, mounted on a programmable vertical profiler to characterize the entire water column. 

Our technical and cost/performance analysis led us to select the XYLEM HydroMet Profiler Pontoon/Raft buoy from Polimater/BASEFLOW/XYLEM, with a Vaisala 202133 digital sonic weather station and a submersible YSI EXO2 multiparameter sonde. Polimater/BASEFLOW is the official supplier for Latin America of renowned manufacturers such as YSI, Campbell, Vaisala, SonTek, WaterLOG, Aanderaa, among others. XYLEM Analytics is a leading global assembler and manufacturer of market-leading brands, whose success is based on innovation and application within the water and wastewater sectors.

Types of buoys and equipment available on the international market

In order to select the models and brands of the buoy and both meteorological and water quality sensors, we conducted a bidding process of the equipment available in the international market, comparing their technical characteristics and costs. We compared the equipment of the leading brands:

What parameters does 'My Buoy' measure?

The Vaisala 202133 weather station is equipped with a suite of sonic sensors all digital with no moving parts. It measures 5 of the most essential meteorological parameters and solar radiation: 

- Speed (range 0-60 m/s, response time 0.25 s, available variables: average, maximum and minimum, accuracy ± 3% at 10 m/s, resolution 0.1 m/s) and wind direction (azimuth 0-360º, response time 0.25 s, available variables: average, maximum and minimum, accuracy ± 3.0º at 10 m/s); 

- Duration (counting each 10-second increment each time a drop is detected, resolution 10 s; hail: cumulative number of hits against the collection surface, duration: counting each 10 sec increment when hail is detected, resolution 0.1 hits/cm2, 1 hit) and precipitation intensity (cumulative accumulation after last automatic or manual reset, running average of 1 min in 10 sec steps, observation range 0-200 mm/h, resolution 0.1 mm/h, collection area 60 cm2, output resolution 0.01 mm, accuracy better than 5% depending on weather; intensity: running average of 1 min in 10 s steps, hail resolution 0.1 hits/cm2h, 1 hit/h); 

- Barometric pressure (range 600 to 1100 hPa, accuracy ± 0.6 hPa from 0 to +30°C): Barometric pressure is the atmospheric pressure value measured at any point above sea level. 

- Relative humidity (0 to 100% RH, accuracy ± 3% RH at 0-90% RH, +5% RH at 90-100% RH): Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. 

- Air temperature (-52º to +60ºC, accuracy to +20ºC ± 0.3ºC): Temperature is an index indicating the heating or cooling of the air resulting from heat exchange between the atmosphere and the earth. 

- Incident solar radiation using a Li-200 R pyranometer sensor (wavelength range 400-1,100 nm, accuracy 5%, typically < 3%, sensitivity ± 1% linearity). Solar radiation is the set of electromagnetic radiations emitted by the Sun. Solar radiation is distributed from infrared to ultraviolet. Not all radiation reaches the Earth's surface, because the shorter ultraviolet waves are absorbed by gases in the atmosphere.

The YSI EXO2 multiparameter sonde is the most advanced platform for water quality monitoring. It has a depth range of 0-250 m, an autonomy of 90 days with an acquisition rate of 15 min and a frequency of up to 4 Hz. It houses 7 ports, 1 for the antifouling cleaner and 6 for temperature sensors: 

- Temperature (Thermistor, accuracy: from -5 to 35°C: ± 0.01°C, from 35 to 50°C: ± 0.05°C) and Conducivity (accuracy 0.001 mS/cm and resolution 0.0001 to 0.01 mS/cm) within the same sensor. The electrical conductivity of water also depends on the water temperature: the higher the temperature, the higher the electrical conductivity. The electrical conductivity of water increases by 2-3% for a 1 degree Celsius increase in water temperature. 

- pH/ORP (range -999 to 999 mV, accuracy ± 20 mV, resolution 0.1 mV): pH is a measure of acidity or alkalinity that indicates the amount of hydrogen ions present in a solution or substance. ORP is a measure of the reducing and oxidizing capacity of the material. 

- Chlorophyll-a and phycocyanin (cyanobacteria) combined in a single sensor (range 0 to 100 µg/L, resolution 0.01 µg/L): Cyanobacteria, formerly called blue-green algae, are a phylum of the Bacteria domain comprising bacteria capable of oxygenic photosynthesis. They are the only prokaryotes that carry out such photosynthesis, hence they were also called oxyphotobacteria. 

- fDOM (dissolved organic matter fluorescence; more accurate proxy than CDOM, colored dissolved organic matter) (range 0 to 300 ppb QSU - Quinine Sulfate Equivalents, detection limit 0.07 ppb QSU, resolution 0.01 ppb QSU): Dissolved organic matter/dissolved organic molecule comes either from the degradation of dead organisms or from the excretion of living organisms (plankton). 

- Optical DO, dissolved oxygen (range 0 to 50 mg/L, accuracy 0 to 20 mg/L ± 0.1 mg/L i.e. 0.1 % reading, and 20 to 50 mg/L ± 5% reading, resolution 0.01 mg/L): Dissolved oxygen (DO) is the amount of gaseous oxygen that is dissolved in water. Free oxygen is essential for the life of fish, plants, algae, and other organisms; therefore, it has long been considered an indicator of a river's ability to support aquatic life. 

- Turbidity (range 0 to 4000 FNU, accuracy 0-99 FNU with 0.3 FNU or ± 2% reading, 1000 to 4000 NFU with ± 5% reading, resolution 0-999 FNU = 0.01 NFU, 1000-4000 FNU = 0.1 FNU): Turbidity is a measure of the degree to which water loses its transparency due to the presence of suspended particles; Turbidity can impact aquatic ecosystems by affecting photosynthesis (limits the passage of sunlight), respiration and reproduction of aquatic life.

How does 'My Buoy' work?

The XYLEM catamaran pontoon (it has two hulls) is much more stable than a classic buoy in windy conditions, which are quite frequent in Lake Titicaca. Even in these conditions it allows to work on board, program, calibrate and repair equipment. It houses 2 solar panels oriented in different positions capable of generating all the electrical energy necessary for the permanent operation of the equipment, as well as the Vaisala sonic weather station (without moving parts) in the upper part, and in the central compartment the vertical profiler (cable wrapped around a winch) to which the YSI EXO2 submersible multiparameter sounder is suspended. 

The data generated by both sensor systems are stored in two Campbell CR1000 dataloggers (one for the multiparameter sounder and the other for the weather station), and transmitted wirelessly via the Internet through a Sierra Airlink modem. The frequency of data acquisition as well as the frequency of vertical profiling are fully programmable, with minimums of 5 min and 1 hour, respectively. The pontoon is equipped with a Garmin 16X-HVS GPS (high sensitivity, 12 channels, NMEA 0183 output) to detect any drift linked, for example, to the breakage of one of its two moorings, as well as a radar display and a Carmanah M650 beacon with high-power LED lights with a range of 4 miles to avoid night-time collisions. Several software packages allow to synchronize the sensors with each other and to program the output of their data (LoggerNet), to program and analyze the profiled data (YSI Profile Wizard and custom written firmware CR1000 Turn Key System) and to generate automatic alerts in case threshold values are exceeded.

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