Sequoia Scientific

LISST-AOBS Super-Turbidity Sensor

Super-Turbidity Sensor

The LISST-AOBS Super-Turbidity sensor is a patent pending, simple, low-cost sensor to measure suspended sediment concentration (SSC).

Super-Turbidity is a patent pending technology developed by Sequoia Scientific, Inc. It involves pairing a LISST-ABS with a turbidity sensor using a weight factor, which results in a single, combined output from the two sensors. Once paired, the LISST-AOBS retains near-constant calibration for SSC over a wide grain-size range. The LISST-AOBS Super-Turbidity sensor is supplied by Sequoia as an integrated and paired turbidity and acoustic sensor with a variety of cabling and data logger options.


  • Paired acoustic and optical technologies
  • Near-constant calibration within a factor of two for grain-sizes from 1–500 µm
  • Complete, integrated package pairing a LISST-ABS and a Turner Designs Turbidity Plus™
  • Includes Y-cable providing power and integrated SDI-12 communication to and from both sensors
  • Tolerant to biofouling (LISST-ABS); integrated wiper (Turbidity Plus™)


Parameters measured

  • Suspended Sediment Concentration (SSC; mg/l)
  • Turbidity (V)

Concentration range

  • 1 mg∙L-1 to 30,000 mg∙L-1 (LISST-ABS) or
  • 0 NTU to 3,000 NTU (Turbidity PlusTM)
    (NOTE: Turbidity Plus Sensors are not factory-calibrated)


  • Combined 850 nm optical turbidity sensor and 8 MHz acoustic backscatter sensor
  • Optics per ISO 7027 turbidity technique
  • Mechanical wiper for turbidity sensor
  • SDI-12 and RS-232 output
  • Sample volume (acoustic; Ø × L): 10 mm × 15 mm @ 55
    mm from transducer

Mechanical and electrical

  • Dimensions [H × W × L]: 5.72 cm × 10.16 cm × 33.65 cm
    (2.25” × 4” × 13.25”)
  • Weight, air: 0.7 kg (1.54 lbs)
  • Transducer Ø: 8 mm ceramic
  • Power supply: 9 VDC to 15 VDC (12 VDC nominal)
  • Current drain: 75 mA @ 12V
  • Depth rating: 100 m
  • Temperature range: 0 to 30 C (not recommend for use in bodies of water that freeze)


LISST-AOBS Item # and Description

Item #DescriptionThumbnail
SEQ-FP-AOBSLISST-AOBS Super-Turbidity Sensor
Acoustic-optic, sensor package pairing a LISST-ABS and a Turner Designs Turbidity PlusTM turbidity sensor using Sequoia’s patent pending methodology. Includes Y-cable for power and SDI-12 communication to and from both sensors. Resistant to biofouling (LISST-ABS); integrated
wiper (Turbidity PlusTM).
NOTE: SENSORS ONLY with Y- cable included (item #SEQ-AC-AOBS-Y-CABLE).
NO OTHER CABLING INCLUDED AT ALL. It is highly recommended that a LISST-ABS cable also be purchased; see LISST-ABS/AOBS accessory list.


One-time service of instrument within 36 months after delivery.
Includes one-way return shipping from Sequoia, all evaluation, diagnosis, testing and calibration.
Parts and labor for repairs not included.
Must be purchased together with new instrument.
NOTE: End-user responsible for return shipment DDP to Sequoia.
No picture

LISST-AOBS Accessories

Item #DescriptionThumbnail
SEQ-AC-AOBS-CBL022 m Integrated Communication and external power cable for LISST-AOBS
Used to connect LISST-AOBS to computer USB port for testing. Power for LISST-AOBS comes via included power brick.
NOTE: Not for use with the LISST-ABS.
Single piece with stainless steel screw, for securing the LISST-ABS and the Turner Designs Turbidity PlusTM turbidity sensor.
NOTE: Included with LISST-AOBS instrument.
Connects the LISST-ABS and Turner Designs Turbidity PlusTM turbidity sensor.
NOTE: Cable included when purchasing the LISST-AOBS instrument. Only for use with the LISST-ABS and Turbidity PlusTM. SDI-12 output only.
SEQ-AC-AOBS-CALSuper-Turbidity Pairing Package
Includes instructions and particles for pairing the LISST-ABS with any turbidity sensor.
No picture

LISST-ABS / -AOBS Common Accessories

Item #DescriptionThumbnail
SEQ-AC-DL-X2-FLOATLISST-ABS or LISST-AOBS X2-SDL Submersible Float Kit (for use with the X2-SDL data logger)
28 inch Stainless Steel Instrument Cage
Mount for X2-SDL Logger w/ bolts and straps
Mount for LISST-ABS
Two 11-inch floats (18.5 lbs buoyancy)
3/4-10 rod threaded stainless, 3/4 nut eye stainless, 3/4-10 Nut Slotted 18-8 stainless, 1/8 x 1-1/4 Cotter Pin.
LISST-ABS including battery powered X2-SDL data logger, stainless steel frame and floats

Mooring Package, allows mounting of LISST-ABS and X2-SDL data logger

LISST-ABS / -AOBS / LISST-Tau Datalogger Options

VERY IMPORTANT: Dataloggers DO NOT include cabling to connect datalogger to LISST-ABS/-AOBS.
To order, e.g., a 25 m cable to connect datalogger to ABS/-AOBS, order:
Item #DescriptionThumbnail
SEQ-AC-DL-X2-KITNexSens X2 Env Data Logger [X2]
NexSens X2 Data Logger Pole Mounting Kit 1.5 to 2 Pipe [PM2]
NexSens X2 Power Adapter 3m [UW6-PW]
Cable Assembly NexSens X2 Direct Connect USB PC Cable [UW6-USB-485P]
SEQ-AC-DL-X2-SDL-KITNexSens X2-SDL Submersible Data Logger [X2-SDL]
Cable Assembly NexSens X2 Direct Connect USB PC Cbl [UW6-USB-485P]
Cable Assembly NexSens 1m [UW-ABS-1]
SEQ-AC-DL-UWCBLBNexsens Datalogger-to-LISST-ABS/-AOBS cable base.
*MUST* order with qty xx SEQ-AC-DL-UWCBL, where xx is cable length in m.
No Picture
SEQ-AC-DL-UWCBLUnderwater orange data logger cable for Nexsens X2 / X2-SDL loggers *ONLY*.
*MUST* order with qty 01 x SEQ-AC-DL-UWCBLB

LISST-AOBS custom length cables

NOTE: These cables are ONLY for the LISST-AOBS, not the LISST-ABS.
To order any cable, order qty 1 base item #, and qty xx cable item #, where xx is cable length in integer m.
E.g., to order a 45 m cable with USB + Power only (no adapters), order:
Base Item #Topside ConnectionCable Design
SEQ-AC-LISST-CBL8FUPLISST-AOBS cable base with USB connection for data only. Power brick for 12 V external power included.
No pigtail adapters for data; USB ONLY.
*MUST* order w/ xx m SEQ-AC-LISST-CBLG where xx is cable length in m.
SEQ-AC-AOBS-CBLBLISST-AOBS cable base with USB and pigtail adapters for data:
Power is supplied externally via included 12 V power supply.
*MUST* order w/ xx m SEQ-AC-LISST-CBLG where xx is cable length in m.
Cable Item #DescriptionThumbnail
SEQ-AC-LISST-CBLGGreen submersible cable. Lightweight. Not reinforced. For LISST-ABS / -AOBS only.
Must order with



Why is there a problem with turbidity?

The sensitivity (Volts/[mg/L] ) of optical turbidity sensors varies inversely with grain size. Turbidity sensors are highly sensitive to fine particles, and insensitive to large particles.

For a constant concentration, a turbidity sensor will show a large response to fine particles (e.g. 5 µm), and – for the same concentration – a much smaller response to larger particles, e.g. 75 µm. To calibrate a turbidity sensor to suspended sediment concentration one must therefore know the grain-size, or assume that it doesn’t vary.

Want more detail? Read this paper: Bundgaard K, Lumborg U, Nyborg L, Jakobsen BH (2019): Challenges of optical backscatter monitoring in mixed sediment environments. Terra et Aqua 154: 22-28, which you can download here (external link) – pay particular attention to Figure 2 in the paper.

How does the LISST-AOBS solve the problem with turbidity?

The sensitivity (Volts/[mg/L] ) of optical turbidity sensors varies inversely with grain size. Turbidity sensors are highly sensitive to fine particles, and insensitive to large particles.

The LISST-ABS has a nearly constant sensitivity (Volts/Concentration) for particles larger than about 30 µm, out to about 500 µm. Below about 30 µm, LISST-ABS response is also size dependent: relatively insensitive to fine particles, and sensitive to large particles – the opposite of optical turbidity.

The combination of acoustics and optics, when done properly, compensates these opposite tendencies of change with grain size, and produces a system that is substantially (but not totally) independent of grain size variations in this range.

What are the benefits of the LISST-AOBS?

Because of the near-constant calibration for the LISST-AOBS Super-Turbidity sensor, the measurements of suspended sediment concentration are far more accurate, over a wide grain size range, than either turbidity (optical backscatter) or LISST-ABS (acoustic backscatter) individually.

Due to size dependence, individual calibration of the turbidity and LISST-ABS sensors is normally required when operating alone. Because of the fixed calibration achieved by the combination of ‘paired’ LISST-ABS and turbidity sensors, the need for calibration of either sensor is greatly reduced. This is a major convenience to experimentalists!

Can I combine past data that I already have?


If you have concurrent, historical LISST-ABS and turbidity data you can combine them into one. A single patent pending calibration method finds a critical weight factor that then is used to combine past data. The step involves obtaining one measurement of sensitivity of the optical turbidity sensor at a given grain size (30 µm). A weight factor is found as the ratio of LISST-ABS output and turbidity sensor output. This weight factor then allows the weighted sum of the two instrument outputs, thus correcting past data also.

How does it work?

From the calibration of the turbidity, the response (Volts/[g/L]) is measured for 30 µm particles. A weight factor is computed using this value. The two outputs – LISST-ABS and turbidity – are combined with this weight factor applied to the turbidity data, resulting in the Super-Turbidity data. The figure below shows the sensitivity of the optical turbidity and LISST-ABS, working alone, and after weighted addition.

AOBS response

The COMBINED response (black) from the LISST-AOBS as a function of grain-size, compared with the response from OBS (red) and LISST-ABS (Blue).

How well does it work?

The figure below shows the sensitivity of a LISST-ABS and a turbidity sensor for a wide range of narrow grain sizes (in legend) and powders from PTI. Combining the two produces the LISST-AOBS Super-Turbidity Meter output. It is evidently that the combined results are substantially improved over either technology. If not combined, the individual technologies produce errors of a factor of ~100. When combined, the errors are within a factor of ~2.

ABS and OBS responses to changing concentrations and grain-sizes

AOBS vs concentration

LISST-AOBS vs actual sediment concentration for a range of sediment grain-sizes.

Is the LISST-AOBS a method or an instrument?


Sequoia has applied for a patent on the methodology and method whereby one can ‘pair’ concurrent data from a LISST-ABS and any turbidity sensor. This will give the user the combined output, the AOBS data.

Sequoia also offers an instrumentation package, called the LISST-AOBS. This package is made up of a standard LISST-ABS and a Turner Designs Turbidity Plus(TM) turbidity sensor. The instrumentation package is delivered as a turnkey system with the two sensors fully paired by Sequoia, and includes a bracket and Y-cable for powering and combining the signal from the two sensors into a unified SDI-12 output. Nexsens data loggers are available as accessories from Sequoia.

Does Sequoia offer to pair other turbidity sensors with the LISST-ABS?


Sequoia will not pair the LISST-ABS with any other turbidity sensor than the TurbidityPlus sensor from Turner Designs.

Users can purchase the complete, paired LISST-AOBS instrumentation package, consisting of a LISST-ABS integrated with a Turner Designs TurbidityPlus(TM) sensor from Sequoia. This is the only combined package Sequoia offers for sale.

Users who wish to use another turbidity sensor must provide their own cabling, wiring, data logger(s), and do the pairing between their LISST-ABS and turbidity sensor themselves.

How do I do the pairing?

You don’t need to do the pairing if you buy the complete instrumentation package from Sequoia.

If you have your own turbidity sensor and you want to pair it with a LISST-ABS, Sequoia offers for sale a license that includes a vial of particles designed for pairing, including written instructions.

Is the TurbidityPlus sensor calibrated to NTU?


  • The TurbidityPlus sensor is NOT calibrated to NTU. The output from the TurbidityPlus sensor is in V only.
  • Please note that
    • It is completely irrelevant for the pairing of the two sensors if the TurbidityPlus is calibrated to NTU or not.
    • Sequoia will not offer NTU calibration of the TurbidityPlus sensor. The customer is responsible for any NTU calibration.
    • The Turner Designs TurbidityPlus manual provides instructions on how to calibrate the sensor to NTU if desired.

What data loggers work with the LISST-AOBS?

  • Any SDI-12 enabled data logger will work with the LISST-AOBS.
  • Sequoia recommends that an X2 or X2-SDL data logger is purchased with the LISST-AOBS:
    • If the LISST-AOBS is purchased with an X2 or X2-SDl datalogger and cable, all delivered by Sequoia, the datalogger will record three data strings: ABS output (in mg/l), TurbidityPlus output (in V), AND the paired output – Total Concentration – (in mg/l).
    • If the LISST-AOBS is purchased without datalogger, the output is ABS output (in mg/l) and TurbidityPlus output (in V) ONLY.

      • In this case, customer is fully responsible for pairing the two outputs to get the paired SuperTurbidity output using the pairing factor and instructions provided with the instrument.

Can I rent the LISST-AOBS?