Parameters
Instrumentation Details
The GREON program aims to monitor water quality parameters among specific sites, as well as changes to those parameters over time. The data will be available to a variety of users, and therefore must be generated using standard methods. Unless otherwise noted in this document, GREON follows the procedures outlined in the manufacturer’s user manuals for the calibration, use, maintenance, and storage of monitoring instruments and equipment. The maintenance and calibration procedures for sensors at all GREON sites must be consistent and follow the outlined protocols. Differences in methodology can result in deceptive data showing apparent differences in nutrient concentrations and physical characteristics, rather than actual variation in water quality between sites.
Several water quality parameters (i.e., Chl-a, BGA-PC, and fDOM) are reported in Relative Fluorescence Units (RFU). These units are related directly or indirectly to output measurements using linear or non-linear calculations. GREON℠ technicians from various sampling locations will calibrate sensors in a uniform method to a specific RFU for a given primary standard. Upon retrieval of an EXO2, the sensors can be checked against that same standard to determine the consistency of measurements.
The GREON unit contains the following sensors:
YSI EXO2 Multiparameter Sonde
SeaBird Coastal SUNA V2 UV Nitrate Sensor (5mm path length)
LI-COR Quantum Sensor (LI-190R)
Vaisala Weather Transmitter (WXT520)
Sensor Specifications
EXO Optical Dissolved Oxygen Smart Sensor
The EXO optical dissolved oxygen sensor analyzes a sample by measuring the lifetime and intensity of luminescence that is associated with a chemical dye. A specific wavelength is shone on this dye, which causes it to luminesce. The lifetime of this dye luminescence is measured via a photodiode in the probe.
- 0 to 50 mg/L measurement range
- <5 sec response time
- ±0.1 mg/L or 1% of reading accuracy from 0 to 20 mg/L
EXO Total Algae PC Smart Sensor
The EXO total algae sensor has two outputs. The sensor excites chlorophyll-a using one beam of a specific wavelength, and excites phycocyanin, found in blue-green algae (cyanobacteria), using another wavelength.
- Options for ug/L and RFU outputs
- 0 to 999 FNU measurement range
- <2 sec response time
- 0.3 FNU or ±2% of reading accuracy
EXO fDOM Smart Sensor
The EXO fDOM (Fluorescent Dissolved Organic Matter) sensor measures dissolved organic matter as fluorescence when exposed to near-ultraviolet (UV) light. The units of fDOM are quinine sulfate units (QSUs) where 1 QSU = 1 ppb quinine sulfate.
- 0 to 300 ppb Quinine Sulfate equivalent (QSE) measurement range
- <2 sec response time
- 0.01 ppb QSE resolution
EXO Turbidity Smart Sensor
The EXO Turbidity sensor uses near-infrared light to determine the suspended solid concentration of a sample. Because this sensor used a 90-degree detection method of the near-infrared beam scatter, the default calibration unit for the EXO sensor is in formazin nephelometric units (FNU). Calibration units can be changed to nephelometric turbidity units (NTU), raw sensor signal (RAW), or total suspended solids (TSS) using appropriate standardization data.
- 0 to 4000 FNU measurement range
- <2 sec response time
- 0.3 FNU or ±2% of reading accuracy from 0 to 999 FNU
EXO Conductivity & Temperature Smart Sensor
The EXO Conductivity/Temperature sensor measures conductance using pure-nickel electrodes. Conductance is derived from changes in voltage between the electrodes, and this value (in milliSiemens) is converted to conductivity (in milliSiemens per cm) using the cell constant. The cell constant is set during sensor calibration.
- 0 to 200 mS/cm measurement range
- <2 sec response time
- ±0.5% of reading or 0.001 mS/cm accuracy from 0 to 100
SUNA V2 UV Nitrate Sensor
The SUNA (Submersible Ultraviolet Nitrate Analyzer) is a chemical-free nitrate sensor. The SUNA emits a deuterium light source and measures the amount of light that passes through the sample to determine absorption. Nitrate concentrations are derived from the shape of the UV absorption curve. SUNA also compensates for CDOM using a baseline correction.
- 0.5 to 4000 µM measurement range using a 5mm path length
- ± 2 μM (± 0.028 mg/I-N) or ± 10% of reading accuracy
- Turbidity range: 1250 NTU (absent other absorbing species)
- Calibrated annually by Satlantic
LI-COR Quantum Sensor (LI-190R)
The LI190R has a semiconductor that converts light into current by absorbing photons. It also has a filter to only let in light between 400 nm to 700 nm, which corresponds to wavelengths used by plants for photosynthesis.
- 5 μA to 10 μA per 1,000 μmol s-1 m-2 measurement range
- Maximum deviation of 1% up to 10,000 μmol s-1 m-2
Vaisala Weather Transmitter (WXT520)
The WXT530 uses ultrasound and three transducers to measure wind, a precipitation sensor to detect raindrops, and a PTU module that is housed inside the unit containing separate sensors for pressure, temperature, and humidity measurements.