a platform for evaluating the latest hydrological, climatic and water quality sensors and in parallel evaluating the latest dynamic models of these resultant high frequency data
SMART Systems for hydroclimatology, hydrology and water quality: the ideal
Sensor technology should be insensitive to, or removes the effect of exogenous variables (e.g. temperature change, light) in a repeatable and reliable manner. These characteristics should be given as stated tolerances for inclusion within meta-data files.
Analogue variables measured by sensor systems should be capable of accurate calibration against values determined by accredited techniques (e.g. laboratory analysis) or international standards.
Systems should be capable of warning of sensor errors and drifts and have a degree of self-maintenance (e.g. auto-cleaning).
Capacity for very high-frequency monitoring.
Systems should be easy-to-use and have readily available communications by telemetry for gathering data and controlling the datalogger.
Systems should allow for automatic reporting of environmental states (e.g. alarms) via the internet (e.g. river levels in flood, high concentrations of water quality variables).
High frequency monitoring, with capability for accurate calibration
Example 1. S::CAN spectro::lyser.
In-situ spectrophotometer measuring 256 spectral absorbance values between 200 and 732 nm. Capable of measuring at a frequency of 1 minute sampling. We have typically deployed at 15 minute sampling frequencies (e.g. at Llyn Brianne watersheds).
Manufacturer’s global calibration gives values of turbidity, true colour, apparent colour, nitrate-N, dissolved organic carbon (DOC) and total organic carbon (TOC) from spectral absorbance values. Capability to calibrate to true stream values through analysis of local water samples at an accredited laboratory.
Deployed at Llyn Brianne and Plynlimon. At these sites we have typically manually cleaned measurement lenses twice weekly by brushing with a toothbrush for 60 seconds with 10% HCl.
Spectro::lyser taken out of the stream for cleaning at Trawsnant (LI8) watershed, Wales
Example high frequency (15-min) DOC (mg/L) data alongside rainfall (mm/15-min) at four watersheds at Llyn Brianne. Source: Jones, T.D., Chappell, N.A. and Tych, W. 2014. First dynamic model of dissolved organic carbon derived directly from high frequency observations through contiguous storms. Environmental Science & Technology, 48: 13289-13297. view online.
Easy to use, readily available communications by telemetry
Example 2. Hobo RX3000 monitoring station
Easy to use data logging station with telemetry that allows remote access to data through the internet at any time, as well as capacity to adjust settings such as sampling interval online.
Alarm notifications can be set up and managed over the web.
The systems can be used with a wide range of environmental sensors (e.g. rainfall, streamflow). Ideal for deployment in remote locations as long as there is compatible mobile network coverage. Requires solar panel to maintain internal battery.
Multiparameter sonde fits up to 6 sensors and capable of very high frequency measurement (e.g. 1 minute sampling intervals). Compatible with numerous sensors including fluorescent dissolved organic matter (fDOM), blue-green algae, chlorophyll-a, dissolved oxygen, pH, turbidity, and oxidation reduction potential (ORP).
Has a degree of self-maintenance with anti-fouling automatic wiper that can be triggered prior to every measurement to prevent algae/precipitates from building up on sensor lenses. Wireless communication also available for datalogger interrogation.
Memory for >1,000,000 logged readings, and so has space for high-frequency sampling over extended periods.
EXO2 sonde prior to deployment at Trawsnant (LI8) watershed
EXO2 sonde with USB interface attached. Wireless communication also available.
Example 4. i::scan and con::cube
The i::scan is a miniature in-situ spectrophotometer. Provides TOC, DOC, UV254, colour and turbidity according to manufacturer’s global algorithm. Does not provide full spectral signature. Can be accurately calibrated to local stream values measured independently at an accredited laboratory.
Degree of self-maintenance through automatic wiper for 35 mm path length probe and has smart phone enabled communications. Deployed alongside the con::cube control terminal for data acquisition and has large memory for data storage.
i::scan, autowiper and pH probe prior to deployment at the Hosagadde watershed
conc::cube controller box with power supply at Hosagadde watershed
Example of steps in true colour data when self-cleaning of spectro::lyser probe was not available. Arrows indicate where manual weekly cleaning has been performed leaving large steps in the raw data. Data presented at Sensors for Water Interest group meeting, Sept 2014, Glasgow.
Automatic reporting of environmental states (alarms and triggers)
Example 5. Campbell Scientific CR1000 measurement and control datalogger and associated sensors
CR1000 datalogger can be used with a wide range of environmental (and other) sensors, and can be set up to deliver data using a range of telemetry options (radio, satellite, modem etc).
Environmental states can be reported and used as an alarm to trigger other devices. At the Llyn Brianne watersheds we have used water level sensors to trigger automatic water samplers once a certain water level is reached.
Several sensors from Campbell Scientific also have self-maintenance features, such as antifouling mechanisms. For example, at the Llyn Brianneand Baru watersheds we have used OBS-3+ turbidity probes alongside a ‘hydrowiper’ that cleans the sensor every 15 minutes.