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Modern monitoring network in the Indian Ocean

Three public authorities in Sri Lanka are responsible for various tasks in water management and they all depend on hydro-meteorological data. However, the existing monitoring network was in poor condition and reliable, up-to-date measurement values were often missing. Now the hydro-meteorological monitoring network has been extended and updated with the latest technology.

Read a detailed project description here

water level radar sensor for surface water applications

OTT RLS - Radar Level Sensor

Non-contact water level sensor for long term surface water measurements

The OTT RLS is a non-contact radar level sensor with pulse radar technology that is ideal for monitoring in remote or hard to reach locations.

  • Surface water
  • Water level / distance to water
  • Non-contact pulse radar
  • Measures water level or depth to water from a bridge, pier or mounting arm
  • 0.4 … 35 m
  • 0.8 … 2 m: ± 10 mm; 2 … 30 m: ± 3 mm; 30 … 35 m: ± 10 mm
  • No
  • SDI-12, RS-485 (using SDI-12), or 4 ...20 mA
OTT PLS - vented pressure transducer

OTT PLS - Pressure Level Sensor

Robust ceramic pressure transducer for water level measurement

The OTT PLS, SDI-12 or 4 ... 20 mA pressure probe, measures water level, depth to water, or pressure using an integrated controller and ceramic pressure-measuring cell.

  • Surface water Groundwater
  • Vented pressure cell
  • Water level, Pressure, Temperature
  • Water level and temperature measurement - for use with external data logger
  • 0 … 4, 10, 20, 40, and 100 m
  • ± 0.05% FS
  • No
  • SDI-12, RS-485 (using SDI-12), or 4 … 20 mA
Fixed installation of water flow sensor

OTT SLD - Side Looking Doppler Sensor

Water flow meter for longterm data collection of velocity and discharge measurements

The OTT SLD uses acoustic Doppler technology for continuous measurement of water velocity and level in streams, rivers, and canals.

  • Fixed installation
  • Acoustic
  • Flow velocity
  • Side-Looking-Doppler for continuous discharge measurement in rivers and open channels. Discharge calculation based on velocity - index - method. Integrated vessel filter algorithm, Modbus interface and output of total volume of flow (max. interval 1 day).
  • ± 10 m/s
  • ± 1 % of measured value ± 0.5 cm/s
Weather sensor-temperature-humidity-with-protective housing-OTT-TRH-horizontal


Weather sensor for humidity and temperature

The digital weather sensor reliably measures the relative humidity and temperature. Equipped with a protective housing it can be used in a large variety of applications.

  • Air temperature and relative air humidity (measured), absolute air humidity, dewpoint and mixing ratio (calculated)
  • PT1000, capacitive
  • Low power draw, long-term stable, suitable for extreme temperatures, protective housing included
  • SDI-12 V1.3
High accuracy precipitation gauge in harsh weather conditions

OTT Pluvio² - Weighing Rain Gauge

All-weather, high accuracy rain gauge for continuous data collection

The OTT Pluvio² is an all-weather precipitation gauge that uses superior weight-based technology to measure the amount and intensity of rain, snow, and hail.

  • Cumulative precipitation, precipitation intensity, bucket content in real time and non real time
  • Weighing principle
  • All-weather precipitation gauge without moving parts according to WMO guide line No. 8
  • SDI-12 / RS-485, pulse
Multichannel IP datalogger

OTT netDL Data Logger

Data loggers for remote data collection & long term monitoring

The versatile OTT netDL 500 and 1000 data loggers were developed specifically for use in hydrology and meteorology stations. In addition to recording data, the loggers are extremely low power and offer flexible data transfer options via the internet and mobile networks, providing a logging and telemetry solution for every project.

  • Ethernet USB-Host USB-Device RS-232 Satellite Cellular Industrial Communication
  • High data availability due to large memory and redundant communication, Multitasking capability for short polling cycles, Communication via TCP/IP, Integrated Web Server, Ultra low power consumption, Design for harsh environments, Industrial communication
  • Yes
  • SDI-12, RS-485 (SDI-12), Modbus RTU, analogue-in (voltage and current), Impulse Input, Status Input

There is a long tradition of building dams and monitoring water resources in Sri Lanka. However, the existing monitoring network was too loosely-knit and many devices were no longer in working order. A renewal of the network was indispensable. The new system solution was meant to work fully automated and operate reliably under harsh tropical conditions. Real-time data were to be provided to the main data centre at the Hydrologic Division headquarter in Colombo.

In October 2012, OTT Hydromet took over the assignment as general contractor and the responsibility for all stages of the project:

  • Establishment and upgrading of 122 hydro-meteorological stations.
  • Establishment of a central database system for hydro-meteorological data and information
  • Provision of flood forecasting and reservoir management tools, including support and training
  • Provision of procedures, tools and training for real time analysis of flood situations
  • Capacity building of local staff

To provide an effective long-term solution OTT Hydromet worked closely with the following partners:

  • Analytical Instruments Pvt. Ltd. as a local partner for Civil engineering, installation, commissioning and maintenance.
  • Danish Hydraulic Institute (DHI) as expert for hydrological forecasting
  • Aquatic Informatics Inc. for water data management.

 Read a detailed project description here

The new monitoring network was completed in 2016. More than a hundred OTT Pluvio² weighing rain gauges are stationed across the country. The measuring equipment is completed by water level gauges, Doppler flow measurement systems and weather stations. All stations are equipped with the IP-enabled datalogger OTT netDL 1000, a satellite transmitter, solar power, overvoltage and vandalism protection.

Automatically saved data is sent to the data centre both via GPRS through the datalogger’s internal modem and by satellite. This redundancy concept guarantees a high degree of data availability.

Prior to commissioning, the data centre in Colombo had to be set up. Services included the provision of:

  • Hardware such as servers, routers, switches, uninterruptable power supply (UPS), desktops, printers, and a self-triggering diesel generator
  • Software for data reception and plausibility checks
  • SQL data base for storing and providing data
  • Aquarius Time-Series and WebPortal software for data management and publishing.
  • Mike 11 software for hydraulic modelling

Quality assurance played a major role in each phase of the project. Moreover, intensive training and a well-thought out maintenance scheme have been designed to ensure a lasting benefit.

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