The SUNA V2 UV nitrate sensor is the ultimate chemical-free solution for autonomous monitoring of nitrogen-based nutrient concentrations in ocean, estuarine and high turbidity freshwater environments.

NOTE: Newer firmware 2.5.1 available here.


  • Universal real-time nitrate processing algorithm*
  • Titanium Housing
  • Adaptive sampling intelligence
  • Accuracy and stability over range of a wide environmental conditions
  • 10 mm pathlength
  • Serial data output and a 500 meter depth rating.
  • SUNACom Windows / Mac software

*Class based freshwater calibration stock. Specific calibration must be added (freshwater, seawater, high range freshwater).

A Versatile UV Nitrate Sensor for Operation in Diverse Environments

The SUNA V2 (Submersible Ultraviolet Nitrate Analyzer) is a chemical-free UV nitrate sensor based on the ISUS (In Situ Ultraviolet Spectroscopy) UV nitrate measurement technology developed at MBARI. Satlantic has adapted the technology to develop the SUNA V2 to measure nitrate in increasingly more challenging environments including extremely turbid and high CDOM conditions. With improved optics and built-in logic intelligence, the SUNA V2 measures nitrate with industry leading accuracy and stability over a wide range of environmental conditions, from blue-ocean nitraclines to storm runoff in rivers and streams.

The SUNA V2 is the ultimate solution for real-time nutrient monitoring. Every SUNA V2 now comes with our proven universal real-time nitrate processing algorithm, which has been upgraded to include adaptive sampling intelligence that automatically adjusts for signal strength. Also included in every SUNA V2 is a 10 mm pathlength, a class based nitrate calibration, serial data output and a 500 meter depth rating.In addition to these standard features, a wide range of optional features provide the ability to customize the instrument to meet your specific research and deployment needs.

Optional Features

  • Reduced 5mm pathlength for high turbidity environments
  • Active fouling control
  • Internal data logging and scheduling with 2 GB memory
  • FullFreshwater & seawater calibrations
  • USB communications and data download
  • SDI-12 interface


See User’s Manual for detailed performance specifications.

Limit of Detection0.5 / 0.20.007 / 0.0028
Range of Detection3000 / 400042 / 56
Accuracy (greater of)2 / N/A0.028 / 0.056
Precision (short term)0.3 / 2.40.004 / 0.034
Drift (per hour lamp time)0.3 / 10.004 / 0.014
Turbidity Range*625 NTU (10 mm pathlength; absent other absorbing species) 1250 NTU (5 mm pathlength; absent other absorbing species)
Drift (per hour lamp time)0.3 µM (SW with T/S corr. processing) 1.0 µM (SW processing)

*Nephelometric Turbidity Units


Path Length10 mm & 5 mm (high turbidity option)
Wavelength Range190-370 nm
Lamp TypeContinuous Wave, Deuterium Lamp
Lamp Lifetime900 h


Input Voltage8-18 VDC
Power Consumption7.5 W (0.625 A at 12 V) nominal


Material Titanium
Depth Rating
500 m
Weight (Acetal/ Titanium)
5.1 kg
1749 cm3


  • Seawater
  • Freshwater
  • Class-based Freshwater

Real-Time temperature-salinity correction available*  (0-35C, 0-40 PSU)

* Requires external T/S data.



Specifications may change without notice.February 2017

Download SUNA V2 Firmware 2.5.1 2.5.1 Firmware

Released February 10, 2015
Package icon for Microsoft Windows


UCI is a graphical software application that makes setup, operation and in field reference checks easy and robust. UCI is the recommended software for HydroCAT, HydroCAT-EP and SUNA.

UCI makes it easy to:

  • Configure instrument settings and control the instrument in various operational modes
  • Complete reference checks with step-by-step reference check wizards, including PDF reports and reference check file comparison
  • Graphically plot engineering units in real time or via file playback
  • Prepare instrument for deployment through the use of a step-by-step deployment wizards including creating a PDF report of all settings and notes
  • Manage data files and offload data

Download UCI 1.2

Released March 30, 2017
Product Data Sheet

SUNA V2 Datasheet

Wednesday, February 22, 2017
PDF icon datasheet_SUNAV2-2017.pdf
Product Manual

UCI Software Manual

Monday, February 13, 2017
PDF icon UCI-1.2-User-Manual.pdf
Product Manual

SUNA V2 Manual

Thursday, March 2, 2017
PDF icon 2017-SUNA-Manual-Ed-C.pdf
White Paper

Nutrient Monitoring in Foreman Branch in Support of the Chester River Watershed Observatory

Monday, January 30, 2017
PDF icon Chester-River-Nutrients.pdf
Scientific Poster


Monday, January 30, 2017
PDF icon Koch-Barnard-Ocean-Sciences-2014-Poster.pdf
Technical Note

Technical Note – CDOM Interference on Nitrate Measurements

Monday, January 30, 2017
PDF icon SUNA-CDOM-Technical-Note.pdf
Technical Note

SUNA Update: SUNA Standard service description and V2 warranty quality upgrade

Monday, January 30, 2017
PDF icon SUNA-Standard-Service.pdf
Technical Note

REMINDER: SUNA V2 Humidity Bulletin: A complete solution for ingress

Friday, April 7, 2017
PDF icon SUNA-V2-Humidity- Bulletin.pdf
Technical Note

Bulkhead Connectors

Monday, January 30, 2017
PDF icon Bulkhead-Connectors.pdf
Technical Note

Nutrient Units Primer

Monday, January 30, 2017
PDF icon Nutrient-Units-Primer.pdf
Technical Note

Real Time Nitrate and Phosphate Monitoring for Ecosystem Modelling

Monday, January 30, 2017
PDF icon Real Time Nitrate and Phosphate Monitoring for Ecosystem Modeling .pdf
Technical Note

In Situ Nutrient Monitoring in the Murderkill Estuary

Monday, January 30, 2017
PDF icon In Situ Nutrient Monitoring in the Murderkill Estuary.pdf

Why is the diameter larger?

The diameter is larger because the pressure case wall thickness was increased to improve the robustness of the instrument for more rugged deployments. As a result, the depth rating also increased to be 500 m from the previous 100 m.

What is "adaptive sampling" and how does it work?

The SUNA V2 contains a 256 channel spectrometer that is programmed to integrate for a specific length of time (usually 300 - 500 ms) while sampling to maximize signal. That is, when the SUNA V2 takes a sample, the spectrograph collects UV light for the length of the integration period. In optically dense waters (e.g. high turbidity or CDOM), very little UV light is transmitted through the water and therefore the spectrometer "sees" a much lower signal. The new SUNA V2 is programmed to automatically increase the integration period to compensate for the low light levels. This enables the instrument to collect a strong signal in extreme environmental conditions.

How does absorption from CDOM affect the SUNA V2 nitrate measurement?

The SUNA V2 determines nitrate concentrations from the shape of the UV absorption curve. The least squares curve fitting algorithm uses calibrated extinction coefficients for nitrate and bromide (strong absorbing species in salt water) to calculate the concentration of nitrate from the UV absorption curve. The algorithm also employs a linear baseline correction that accounts for absorption that is not associated with either nitrate or bromide. The linear baseline correction successfully compensates for CDOM absorption in cases where the CDOM absorption is close to linear in the low UV. The composition of CDOM is dependent on the type of drainage area around a particular watershed and is therefore highly variable. As a result, the shape of CDOM absorption curve can vary from region to region. For this reason, the baseline correction does not always successfully compensate for CDOM absorption. In cases where the CDOM absorption curve mimics the shape of the nitrate absorption curve, a positive bias can occur.

The most common approach for correcting a positive bias caused by CDOM absorption is to correlate the continuous in situ nitrate data provided by the SUNA V2 with nitrate concentrations from discrete water quality samples measured in a laboratory. The bias may then be calculated either as an absolute offset or as a factor. In order to provide the most robust correction possible, the discrete sample size should be sufficiently large to allow for comparisons and the relationship between the in situ and discrete concentrations should be highly correlated. 

How do I tell if my SUNA is a V1 or V2?

You can identify which model of SUNA you have by the firmware revision it is running. The firmware information can be viewed by either starting the SUNA in a terminal emulator (information is in the start-up banner), or connecting the instrument to SUNACom (information is in top left corner, next to serial number). The first digit of the firmware revision identifies the version of the sensor, ie. firmware v1.9.0 indicates a SUNA V1.

When running my SUNA V2 on the bench, the data shows that the lamp is turning on and off. Why is this happening?

This is a safety feature of the instrument, whereby the lamp is turned off when its temperature reaches 35°C (95°F) to prevent damage from overheating. The SUNA continues to output dark frames while monitoring the temperature, and will restart the lamp once it has dropped back below 35°C. If extended in-lab use is required, immersing the SUNA in a cool bath can  prevent this behavior.

My SUNA V2 fails the self-test function when it tries to report the internal voltage measurements?

Although most functions of the SUNA V2 can be accomplished though the USB connection, parts of the self-test require that external power be applied. In this case, connect external power and repeat the test. If the problem persists, please contact Satlantic Customer Support.

How does the free calibration differ from the fresh water calibration?

The included class-based calibration coefficients are average coefficients obtained from our library of historical calibrations. The historical coefficients that are averaged to create the class based coefficients vary by about 10%.

Is an instrument with the class based calibration still within the published specification for accuracy? If not, what is the accuracy?

Instrument specific calibrations are more accurate and correspond to the published accuracy specifications. 

The accuracy of the class based calibration is estimated to be 2.2 uM +/- 20%.

  • Boyle S., Trickett P., Partington A. & Murray C. (2014) Field Testing of an Optical in Situ Nitrate Sensor in Three Irish Estuaries Biology & Environment: Proceedings of the Royal Irish Academy 114 1-7 doi:10.3318/BIOE.2014.02 Read Now
  • Pellerin, B.A., Bergamaschi, B.A., Downing, B.D., Saraceno, J.F., Garrett, J.A., and Olsen, L.D. (2013) Optical Techniques for the Determination of Nitrate in Environmental Waters: Guidelines for Instrument Selection, Operation, Deployment, Maintenance, Quality Assurance, and Data Reporting U.S. Geological Survey Techniques and Methods 1–D5, 37 p Read Now
  • Pellerin, B.A, Saraceno, J, Shanley, J.B., Sebestyen, S.D., Aiken, G.R., Wollheim, W.M., Bergamaschi, B.A. (2011) Taking the pulse of snowmelt: in situ sensors reveal seasonal, event and diurnal patterns of nitrate and dissolved organic matter variability in an upland forest stream. Biogeochemistry doi:10.1007/s10533-011-9589-8 Read Now
  • Sackmann, B.S. (2011) Deschutes River Continuous Nitrate Monitoring. Quality Assurance Project Plan: Deschutes River Continuous Nitrate Monitoring, PUblication Number: 11-03-030 Read Now
  • Heffernan, J.B., Cohen, M.J. (2010) Direct and indirect coupling of primary production and diel nitrate dynamics in a subtropical spring-fed river. Limnol. Oceanogr., 55(2), 677 - 688.
  • MacIntyre, G., Plache. B, M.R. Lewis., Andrea, J, Feener, S, McLean, S.D. (2009) ISUS/SUNA Nitrate Measurements in Networked Ocean Observing Systems. White Paper Read Now
  • Prestigiacomo, A.R. (2009) Nitrate and Bisulfide: Monitoring and Patterns in Onondaga Lake, New York, Following Implementation of Nitrification Treatment, Prestigiacom, A.R, Effler, S.W., Matthew, D.A., Coletti, L.J., Water Environment Research, 81(5)
  • Johnson, K.S., Coletti. L.J. (2002) In situ ultraviolet spectrophotometry for high resolution and long-term monitoring of nitrate, bromide and bisulfide in the ocean. Deep Sea Research 49 1291-1305

SUNA V2 Hydro-Wiper

The Hydro-Wiper is an external anti-fouling system fully integrated with SUNA V2 nitrate sensor. The Hydro-Wiper keeps the SUNA V2 sample windows clean for several months even in the most aggressive fouling environments, helping prevent costly site visits for manual cleaning and loss of data.


SUNA V2 Anti-fouling guard

The SUNA V2 anti-fouling guard is a semi-circular piece of perforated copper attached to a plastic armature that fits into the sample chamber. The anti-fouling guard provides passive fouling prevention through the release of copper ions that inhibit biological growth in the area. The anti-fouling guard provides a reliable and affordable approach to increase deployment time, decrease operating costs, and collect high quality data for mooring applications. 

SUNA V2 Flow cell

The SUNA V2 flow cell is designed to adapt the SUNA V2 for flow through operations on moorings with pumped flow, ship-board underway systems or for laboratory testing and calibration. The flow cell attaches to the SUNA V2 sample chamber and tightly seals against the optical chamber windows. Nylon barbed fittings are provided to connected the flow cell to available pumped flow.

SBE 5P Pump

The pump module is a compact unit consisting of a centrifugal pump head and a long-life, brushless, DC, ball-bearing motor. The pump impeller and electric drive motor are coupled magnetically through the housing, providing high reliability by eliminating moving seals. The 5P has a 600-meter (1960 ft.) plastic housing. 



Alkaline Battery Pack

Satlantic's reliable and user-friendly Alkaline Battery Packs are available in 102 Ah and 51 Ah capacities. The design of the internal battery compartment allows the user to easily change the D-Cell batteries with off-the-shelf replacements. The battery packs consist of an anodized aluminum pressure case, a D-cell battery compartment and a removable end-cap.