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The Environmental Characterization Optics (ECO) series of sensors incorporates a common set of options with a single basic design to make them ideal for a wide variety of deployments.

The Environmental Characterization Optics (ECO) combination fluorometer and backscattering sensor allows the user to measure chlorophyll fluorescence at 470 nm and backscattering at 700 nm within the same volume.

The fluorometer allows the user to monitor chlorophyll concentration by directly measuring the amount of chlorophyll-a fluorescence emission from a given sample volume of water. Chlorophyll, when excited by the presence of an external light source, absorbs light in certain regions of the visible spectrum and re-emits a small portion of this light as fluorescence at longer wavelengths.

A blue LED (centered at 470 nm and modulated at 1 kHz) provides the excitation source. The blue light from the sources enters the water volume at an angle of approximately 55–60 degrees with respect to the end face of the unit. Fluoresced light is received by a detector positioned where the acceptance angle forms a 140-degree intersection with the source beam. A red interference filter is used to discriminate against the scattered blue excitation light. The red fluorescence emitted is synchronously detected by a silicon photodiode. Scattering is measured simultaneously by detecting the scattered light from a 700 nm LED at 140 degrees to the same detector used for fluorescence. The scattering measurement is performed at the same 140 degree angle as the chlorophyll fluorescence.


  • Combines two biogeochemical measurements into one instrument
  • Combines unparalleled fluorescence sensitivity with market leading optical backscattering
  • Multiple ranges available to tailor the instrument response to the environment
  • User controlled data averaging for assessment of chlorophyll and particle concentration variability
  • Digital and analog output for integration into analog CTD packages or serial data streams
  • Provides excellent precision and reliability at a fraction of the size and cost of similar instruments

Model Options:


Diameter 6.3 cm

12.7 cm (standard) / 17.78 cm (deep)

Weight in air

0.4 kg (standard) / 1.3 kg (deep)

Weight in water

0.02 kg (standard) / 0.75 kg (deep)

Pressure housing   Acetal copolymer (standard) / Titanium (deep)



Chlorophyll EX/EM 470/695 nm
Chlorophyll sensitivity 0.015 μg/l
Fluorescence range 0 - 30 μg/l
Linearity 99%  R2
Backscattering wavelength 700 nm
Backscattering sensitivity* 0.0015 m-1
Backscattering range* 0 - 3 m-1
Linearity 99%  R2



Digital output resolution 12 bit
RS-232 output 19200 baud
Connector MCBH-6-MP
Input 7-15 VDC
Data output rate 8 Hz
Operating current typical 60 mA
Operating current max. 140 mA



Calibrated Temperature Range -2 to 30°C
Working Temperature Range

-10 to 50°C

Storage Temperature Range -20 to 70°C
Depth rating standard 600 m
Depth rating with wiper* 300 m
Depth rating deep

6000 m



*Backscattering specifications are given in beam cp (m-1) based on the regression of the response of the instrument relative to the beam cp measured at the coincident wavelength using an ac-s spectrophotometer. Scale factors for backscattering incorporate the target weighting function and the solid angle subtended.

**The water temperature range through which the instruments are tested. The –2 deg C minimum covers all natural waters on Earth. Please contact WET Labs for testing to higher temperatures.

***The limit depth for ECO with Anti-fouling Bio-wiper™ and Internal Batteries (models B, S and SB) rated to 300 m.

Model Options:

  • FLbb(RT)— Analog and RS-232 serial output with 4,000-count range. Unit operates continuously when power is supplied
  • FLbb(RT)D—Provides the capabilities of the FLbb(RT) with 6,000-meter depth rating
  • FLbbB—The capabilities of the FLbb with internal batteries and memory for autonomous operation
  • FLbbS—The capabilities of the FLbb with an integrated anti-fouling Bio-wiper™
  • FLbbSB—The capabilities of the FLbb with internal batteries for autonomous operation
  • FLbb2k—Designed for float applications but can be use for applications down to 2000m
The list below includes (as applicable) the current product brochure, manual, and quick guide; software manual(s); and application notes.

ECOView host software provides a graphical user interface that allows you to configure, collect, view, and upload data from a variety of ECO fluorometers.

Version 1.23 released April 9, 2013
File ECOView123.exe for Windows 7/8/10

How do I change the ASV resolution?

How do I change the ASV resolution?

See the following Technical Note: Getting the Highest Resolution on your ECO_v1 [PDF]

What is the back scattering angle of my ECO instrument?

WET Labs ECO Centroid Angles for Back Scatter Measurements

The WET Labs’ ECO sensors have multiple back scattering angles depending upon type of sensor. This document will describe these angles based upon the type of ECO sensor selected by the customer.

Single Channel Sensors:
Single channel ECO back scatter sensors have an in-water centroid angle of 124°.  These include the following ECO models: bb, NTU.

Dual Channel Sensors:
Dual channel ECO back scatter sensors (back scatter at 700nm paired with chlorophyll fluorescence) have an in-water centroid angle of 142°. These include the following ECO models: FLNTU and FLBB versions along with OEM variants of these sensors (AP2, 2K, SLC, RTD, SB variants).

Three Channel Sensors:
Three channel ECO back scatter sensors (individually paired LED source with detector) have an in-water centroid angle of 124°. These include the following ECO models: bb3, BBFL2, BB2FL and Triplet-w family.

Combined Three Channel Sensors:
WET Labs’ combined three channel ECO back scatter sensors (back scatter at 700nm paired with chlorophyll fluorescence along with either another back scatter or FDOM channel) have an in-water centroid angle of 124°.

These include the following ECO models:
FLBB-CD, FLBB-BB along with OEM variants of these sensors (2K, AP2, SLC, REM, BOSS, 6K). MCOMS and SeaOWL UV-A: WET Labs’ MCOMS and SeaOWL UV-A back scatter sensors (back scatter at 700nm paired with chlorophyll fluorescence along with either another back scatter or FDOM channel) have an in-water centroid angle of 150°.

What is the input voltage range for my instrument?

Deriving the vertical diffuse attenuation coefficient (Kd) from the absorption coefficient (a).

Derivation of Kd from a
In what follows we have left off the dependence on wavelength. In addition we have left off effects due to inelastic scattering.
Modeling Kd(z) requires the inclusion of the depth dependence of the shape of the radiance
distribution. This can be accomplished by using Gershun's equation:
K(z) = a(z) / μ − (z)
where a(z) is the absorption coefficient and μ(z) is the average cosine of the light field.
Kd(z) differs from K(z) by only a few percent, so that we may set:
Kd(z) ≈ a(z) / μ − (z) .
Berwald et al. (1995) have derived a parametric model for the dependence of ⎯μ(z) on ωo for a vertical sun in a black sky. We will assume the same depth dependence for an ordinary sky. This is not precise, but the average cosine varies slowly and has a typical range of only about 10%. The model is:
ωo= b / c, where b and c are the total scattering and attenuation coefficients, including water.
τ = cz, is the optical depth.
μ∞(τ) = μ∞ + (μ(0) - μ∞ ) exp(-Ptt ).
μ∞ = - 1.59 ωo4 + 1.71 ωo3 - 0.467 ωo2 - 0.347 ωo + 1
μ(0)= cosine of refracted solar zenith angle
Pτ(ωo) = - 0.166 ωo2 + 0.341 ωo + 0.0305
Berwald et. al. Limnology and Oceanography 1995, vol. 40, no8, pp. 1347-1357 .


How do I protect my ECO from bio-fouling?

ECO instruments are designed for long term deployment capabilities with low power requirements, a large memory and an available Bio-wiper™. The Bio-wiper™ on the ECO was designed to protect the optical surface and has been very effective under most conditions.

If extra protection is required to prevent marine organisms from attaching to the instrument body near the optical head and interfering with the operation of the Bio-wiper™ we suggest using copper foil tape. The GoMOOS project developed a technique for their ECO sensors and WET Labs recommends this technique:

Apply electrical tape under the area where copper tape will be applied. This protects the meter from the significant adhesive residue of the copper foil tape.

Apply the copper tape to the prepped surfaces. There are different width copper foil tape options, with non-conductive adhesive, available from McMaster-Carr. NOTE: when applying the coper tape, the adhesive should not be touched. This will cause the tape to not stick to the electrical tape on the meter. When submerged in salt water, the copper will adhere more closely to the meter.

As long as the electrical tape is used, this technique does not violate the ECO warranty and WET Labs will service instruments that have had copper tape applied to them.

Important! Do NOT apply copper tape directly to the meter. Its adhesive is extremely difficult to remove. Meters returned to WET Labs wrapped in copper tape without the electrical tape preparation will have additional service charges applied.


What is the fluorescent stick that came with my meter used for?

Checking Meter Output with the Fluorescent Stick
ECO meters ship with a stick of fluorescent material with which you can check your meter's output response.
    •    With the meter on and outputting data, hold the stick approximately 1/2-in (1 cm) from the lit detectors. Be careful to NOT touch the sensor face, as it scratches easily.
    •    Pivot the stick to parallel with the meter's optics; the output in the  meter's "signal" column should increase to near maximum output as given on the meter's characterization or calibration sheet.
    •    As you move the stick away, the output will decrease.


What is the memory capability?

    •    Not included on the "RT" units!!
    •    The memory is stored in "Flash" memory, an integrated circuit chip on the electronic board set.
    •    There is no removable card, no upgrade in memory capacity.
    •    The total sample records available for a single channel ECO = 108,000.
    •    Typically, the ECO output is set to 1 sample/sec.

What should I use to lubricate bulkhead connectors?

We recommend keeping the connectors on your meter lubricated using a good quality silicone spray lubricant, such as 3M Silicone Spray or Loctite 8021 spray. These can be purchased at your local hardware store. Avoid silicone grease. It is messy and attracts contaminants.

Do not use WD-40. It will destroy connectors.

What type of batteries are in ECO's?

    •    We recommend the use of Lithium batteries in all of our ECO battery units.
    •    There is a very significant battery life increase in comparison with Alkaline cells.
    •    We use Ultralife Lithium +9V batteries.
    •    Ultralife has 3 different part numbers (used with different sales packaging) for the long-life batteries we use in our ECO's:
    ◦    U9VL
    ◦    U9VLX
    ◦    U9VLBP
    •    Ultralife batteries have Aluminum/Mylar housing providing:
    ◦    Protection against humidity and heat from entering the battery. Humidity and heat reduce efficiency and shelf-life.
    ◦    Batteries that are much more leak-resistant.
    •    Ultralife batteries have a 7-10 year shelf-life.
    •    The batteries are customer replaceable with easy access to the battery pack.
    •    The battery pack has 6 batteries: 2 layers of 3 +9V Lithium cells.


How do I get started using my new ECO?