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Non-contact Discharge Radar Sensors

safe, continuous, machine-learning discharge measurements of open channels with known cross-section profiles

photo RQ-30 mounted on a bridge over a river; non-contact radar sensor takes discharge measurements and keeps public works workers safe. bottom of photo shows a red staff gauge to measure water level

Measuring velocity, water level and discharge

Mount the RQ-30a and RQ-30a-30m from bridges, canal roofs, channel superstructures or cableways for safe, continuous recording of discharge measurements of rivers, channels or canals with known cross-section profile.

Ensure the collection of reliable data without structural work or staff in the water.

Radar technology enables fail-safe operations, especially during high water or flooding. The contactless sensor avoids debris, driftwood and other disruptions to accurate measurements. 

This radar also detects the direction of water flow, affirming its use in tide-influenced rivers.

The measurable velocity range is 0.10 m/s – 15 m/s. The RQ-30a is recommended for water levels 0-15m (49 ft) and the RQ-30a-30m for 0-35 m (115 ft).

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Your benefits


Record fail-safe water level, velocity and discharge measurements

A Doppler frequency shift method monitors velocity, a travel time measurement establishes water level, and cross-section profiles to calculate discharge based on a hydraulic model with multiple k-factors.


Overcome hysteresis effects; operates in backwater & supercritical flows

Radar sensor detects flow direction, recognizes hysteresis effects, and effectively measures in backwater situations.


Ensure staff safety & time-savings when measuring discharge

Mount this sensor over the water to record real-time measurements. Internal algorithms develop a rating curve in 1 month vs. 2 years conventionally.


Maximum uptime & availability of this decision-support tool

This sensor features automatic installation angle correction and low power consumption within vandalism-proof housing; pair with a solar cell.


Very low maintenance needs

The RQ-30 performs a self check with status and error output, in addition to maintaining a long-term 3-point velocity calibration.

How it works

Select your monitoring sites
Mount sensors
Enter known cross-sections
Verify velocity return values
Develop rating curve in a month
Review changes over time

Product Highlights

  • 24 GHz (K-band) radar

    24 GHz (K-band) radar

    A 24 GHz (K-band) radar sensor measures the velocity of the water surface. Radar impulses are transmitted at an angle towards the water surface where ripples and waves induce a Doppler frequency shift detected by the RQ-30.

    The same radar technology measures the water level by registering the travel time of an impulse sent from the sensor to the water surface.

    Then the RQ-30 automatically computes the discharge by vm ∙ A(h), where the mean velocity vm is derived in real time from the surface velocity and additional dynamic factors using a complex hydraulic model with multiple dynamic k-factors. The cross-sectional area A(h) is computed from the water level and the stored profile.

  • Site-specific machine learning

    Site-specific machine learning

    The RQ-30 is programmed to perform machine learning, in order to make compensation of environmental influences and early detection of errors at a given monitoring site.

    In addition, a self-test function reports any abnormal operation and malfunction. Quality indicators ease maintenance and ensure the ongoing, reliable collection of data.

  • Compact, light & weatherproof construction

    Compact, light & weatherproof construction

    The size of the sensor is 338 x 154 x 333 mm (13.31 in x 6.06 in x 13.11 in) and weighs just over 5 kg (<12 lb).

    Operating temperature  -40 °C – 60 °C (-40°F – 140 °F)
    Storage temperature       -40 °C – 60 °C (-40 °F – 140 °F)
    Relative humidity                0 – 100 %
    Protection rating                 IP 67

    Sensor housing is a powder-coated aluminum, vandalism-proof. A stainless steel option is available.
    Integrated protection against indirect lightning features a discharge capacity of 0.6 kW Ppp.

(Using a noncontact radar, we observed) the velocity jumped about an hour prior to the stage [water level], indicating the importance of measuring velocity on rivers (also reveals likely hysteresis in the rating curve). The FLASH forecast model provided >2 hours of lead time prior to the river stage crest at 12 feet. Note that the river rose 9 feet in 1 hour!"

J.J. Gourley, Ph.D., Research Hydrologist with NOAA/National Severe Storms Laboratory

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