The TECPRIME AQUAscat® AOBS is an integrated acoustic and optical Super-Turbidity sensor designed to measure suspended sediment concentration across a broad range of particle sizes.
Formerly known as the Sequoia Scientific LISST-AOBS, the instrument is now manufactured, sold and supported by TECPRIME Technology under the AQUAscat AOBS name. Its measurement technology is licensed from Sequoia Scientific.
The AQUAscat AOBS combines an 8 MHz acoustic backscatter sensor with an 850 nm optical turbidity sensor. These two measurement methods respond differently to changes in sediment grain size. Optical turbidity is particularly responsive to fine particles, while high-frequency acoustic backscatter provides a comparatively stable response to coarse silt and sand.
By applying a predetermined weighting factor to the acoustic and optical measurements, the AQUAscat AOBS produces a combined suspended sediment concentration output with substantially less grain-size sensitivity than either technology used independently. TECPRIME specifies near-constant calibration within a factor of two for grain sizes from approximately 1-500 µm.
The complete system includes an AQUAscat ABS acoustic sensor, a Turner Designs Turbidity Plus optical sensor, an integrated mounting arrangement and a Y-cable providing power and digital communications to both sensors.
Imbros can assist with selecting the appropriate AQUAscat AOBS cabling, datalogger, telemetry, mounting and calibration arrangement for fixed monitoring, profiling and research applications.
Why Choose the AQUAscat AOBS?
- – Combined acoustic and optical measurement: integrates two complementary technologies into one suspended sediment monitoring system.
- – Broad particle-size response: designed to maintain calibration within a factor of two over grain sizes from approximately 1–500 µm.
- – Direct suspended sediment output: the weighted Super-Turbidity result is reported as suspended sediment concentration rather than turbidity alone.
- – Measures fine and coarse sediment: the optical sensor responds strongly to fine material, while the acoustic sensor provides improved sensitivity to coarse silt and sand.
- – Wide measurement range: the acoustic element has a published suspended sediment range of approximately 1–30,000 mg/L, depending on sediment characteristics.
- – Integrated system: supplied as a paired AQUAscat ABS and Turner Designs Turbidity Plus sensor package.
- – Mechanical optical wiper: the Turbidity Plus sensor includes an integrated wiper to help maintain the optical measurement surface.
- – Fouling-tolerant acoustic measurement: the acoustic sample volume is positioned away from the transducer face and does not rely on an optical window.
- – Digital integration: SDI-12 and RS-232 outputs support connection to environmental dataloggers and monitoring systems.
- – Suitable for variable sediment: particularly useful where the particle-size distribution changes during storms, floods, dredging or seasonal flow events.
AQUAscat AOBS at a Glance
| Attribute | Published Specification |
|---|---|
| Instrument type | Integrated acoustic and optical Super-Turbidity sensor |
| Primary measurement | Suspended sediment concentration |
| Additional measurement | Optical turbidity output |
| Acoustic sensor | AQUAscat ABS operating at 8 MHz |
| Optical sensor | Turner Designs Turbidity Plus using an 850 nm optical source |
| Optical measurement method | ISO 7027 turbidity technique |
| Published grain-size response | Near-constant calibration within a factor of two from approximately 1–500 µm |
| Acoustic SSC range | Approximately 1–30,000 mg/L, particle dependent |
| Optical turbidity range | Up to 3,000 NTU following user calibration |
| Acoustic sample volume | Approximately 10 mm diameter × 15 mm long |
| Acoustic sample location | Approximately 55 mm in front of the acoustic transducer |
| Outputs | SDI-12 and RS-232 |
| Depth rating | 100 m |
| Operating temperature | 0–30 °C; not recommended for use in water bodies that freeze |
| Dimensions | 57.2 × 101.6 × 336.5 mm |
| Weight in air | Approximately 0.7 kg |
The optical Turbidity Plus sensor is not supplied factory-calibrated in NTU. A user calibration is required where a traceable turbidity result is needed. Quantitative suspended sediment performance also depends on sediment size, density, shape and composition.
Typical Applications
| Application | How the AQUAscat AOBS Can Be Used |
|---|---|
| River and estuary monitoring | Continuous measurement of suspended sediment during changing flows, tides, floods and catchment-runoff events where both fine and coarse material may be present. |
| Dredge plume monitoring | Monitoring sediment released by dredging, reclamation, excavation and disposal activities across a changing particle-size distribution. |
| Hydropower sediment monitoring | Measuring fine and abrasive coarse sediment entering reservoirs, channels, intakes or turbine systems. |
| Coastal erosion studies | Observing the suspension and transport of sediment generated by waves, currents, erosion and shoreline-management works. |
| Environmental impact assessments | Collecting continuous sediment data before, during and after construction, dredging or other potentially disturbing activities. |
| Flood and storm-event monitoring | Capturing rapid changes in sediment concentration and grain-size composition that may not be represented by periodic grab samples. |
| Reservoir and catchment studies | Quantifying sediment inflows, resuspension and transport through reservoirs and impoundments. |
| Sediment transport research | Investigating the relationship between suspended concentration, grain size, flow conditions and sediment movement. |
| Total suspended solids studies | Developing site-specific relationships between continuous AOBS measurements and laboratory filtration or gravimetric results. |
| Scientific research | Providing simultaneous acoustic, optical and combined measurements for comparison with water samples and other sediment instruments. |
What Is Super-Turbidity?
Conventional turbidity sensors measure light scattered by particles in the water. Their response is normally strongest for fine particles, while the response per unit mass can decrease substantially as particles become larger.
An acoustic backscatter sensor behaves differently. The 8 MHz AQUAscat ABS has a comparatively consistent response to particles from approximately 30–400 µm, but its sensitivity decreases as sediment becomes finer than this range.
The opposing grain-size responses of the two technologies make it possible to combine them:
- – The optical sensor provides strong sensitivity to fine clay and silt;
- – The acoustic sensor responds effectively to coarse silt and sand; and
- – A weighting factor is applied to combine both measurements into one suspended sediment result.
The resulting Super-Turbidity measurement is substantially less sensitive to changes in grain size than either the optical or acoustic measurement alone.
Why this matters: a river monitoring site may contain fine suspended clay during normal flow and substantially coarser material during a flood. A single optical or acoustic sensor may change sensitivity as the sediment changes. The AQUAscat AOBS is designed to reduce this source of measurement uncertainty.
How the Two Sensors Work Together
The AQUAscat AOBS incorporates two physically separate but integrated sensors.
8 MHz Acoustic Backscatter Sensor
The AQUAscat ABS transmits an ultrasonic pulse into the water and measures the sound scattered back by particles in a small sample volume approximately 55 mm in front of the transducer.
The acoustic sensor is particularly useful for measuring coarse silt and sand. It also measures acoustic attenuation so that the backscatter result can be corrected when higher sediment concentrations weaken the transmitted and returned signal.
850 nm Optical Turbidity Sensor
The Turner Designs Turbidity Plus sensor measures scattered near-infrared light using an optical technique based on ISO 7027. It is particularly responsive to fine suspended particles.
The optical sensor incorporates a mechanical wiper to reduce the accumulation of biological growth and sediment on the optical surface.
Weighted Combined Output
The sensors are paired using a weighting factor derived from their relative response to a selected reference particle size. The weighted optical measurement is added to the acoustic measurement to create the combined Super-Turbidity suspended sediment output.
The optical units used during the pairing process do not need to be NTU. The weighting method uses the relative optical response, and the resulting combined measurement is reported as suspended sediment concentration.
AQUAscat AOBS Measurement Outputs
| Output | Purpose | Important Consideration |
|---|---|---|
| Acoustic measurement | Provides the AQUAscat ABS response to suspended particles, with strongest application across coarse silt and sand. | Response becomes more grain-size dependent for particles below approximately 30 µm. |
| Optical turbidity measurement | Provides a sensitive optical response to fine suspended material. | The Turbidity Plus sensor is not factory-calibrated in NTU and requires user calibration where NTU output is required. |
| Combined Super-Turbidity SSC | Combines the acoustic and weighted optical responses into one suspended sediment concentration result. | Designed to maintain calibration within a factor of two across approximately 1–500 µm. |
Measurement, Calibration and Installation
Technical Specifications
| Technical Parameter | Published Specification |
|---|---|
| Sensors | Combined 850 nm optical turbidity sensor and 8 MHz acoustic backscatter sensor |
| Acoustic sensor | TECPRIME AQUAscat ABS |
| Optical sensor | Turner Designs Turbidity Plus |
| Optical wavelength | 850 nm |
| Optical technique | ISO 7027 turbidity technique |
| Optical cleaning | Integrated mechanical wiper |
| Acoustic frequency | 8 MHz |
| Acoustic transducer | 10 mm diameter ceramic transducer |
| Acoustic sample volume | 10 mm diameter × 15 mm long |
| Sample-volume location | Approximately 55 mm in front of the acoustic sensor |
| Published grain-size performance | Near-constant calibration within a factor of two from approximately 1–500 µm |
| Acoustic SSC range | Approximately 1–30,000 mg/L, sediment dependent |
| Optical range | 0–3,000 NTU following calibration |
| Digital outputs | SDI-12 and RS-232 |
Mechanical and Electrical Specifications
| Parameter | Published Specification |
|---|---|
| Dimensions | 57.2 mm high × 101.6 mm wide × 336.5 mm long |
| Weight in air | Approximately 0.7 kg |
| Supply voltage | 9–15 VDC, 12 VDC nominal |
| Current drain | 75 mA at 12 VDC |
| Depth rating | 100 m |
| Operating temperature | 0–30 °C |
| Freezing-water suitability | Not recommended for use in water bodies that freeze |
| Current connector | SubConn MCBH8M |
| Legacy connector | Impulse MCBH-8-MP on AQUAscat ABS serial numbers 6233 and lower |
| Mounting frame | Optional; available separately |
Connector and cable requirements should be checked against the instrument serial number. Legacy LISST-AOBS cables and documentation should not be assumed to match every current AQUAscat AOBS configuration.
AQUAscat ABS or AQUAscat AOBS?
| Consideration | AQUAscat ABS | AQUAscat AOBS |
|---|---|---|
| Measurement technology | 8 MHz acoustic backscatter | Combined 8 MHz acoustic backscatter and 850 nm optical turbidity |
| Best-suited grain sizes | Applications dominated by particles from approximately 30–400 µm | Applications with grain sizes varying broadly from approximately 1–500 µm |
| Fine-particle sensitivity | Reduced below approximately 30 µm | Improved through the integrated optical sensor |
| Coarse-particle sensitivity | Strong response across coarse silt and sand | Retained through the integrated acoustic sensor |
| Turbidity measurement | No optical turbidity measurement | Optical turbidity available following user calibration |
| Optical maintenance | No optical window or wiper | Optical sensor with integrated mechanical wiper |
| System complexity | Compact single-sensor package | Paired two-sensor package with integrated cabling |
| Recommended when | Sediment is predominantly coarse or low-maintenance acoustic monitoring is preferred | Sediment grain size is broad, variable or poorly characterised |
Selection guidance: the AQUAscat AOBS is generally the stronger option where both fine and coarse particles contribute materially to suspended sediment concentration. The simpler AQUAscat ABS may remain preferable where sediment is predominantly coarse and the optical measurement is unnecessary.
