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Deep SUNA Nitrate Sensor

The Deep SUNA nitrate sensor is the ultimate solution for monitoring nitrate concentrations with AUVs in deep ocean environments to 2000 m.

Based on the proven MBARI-ISUS nitrate sensor, the Deep SUNA has been redesigned for easy integration with AUVs of all types. Deep SUNA provides real time, chemical-free nitrate calculations in deep ocean environments using Sea-Bird Scientific’s advanced UV absorption technology.

Deep SUNA features include:

  • Full UV spectrum for maximum accuracy 
  • Real-time temperature/salinity compensation
  • Real-time nitrate calculation
  • Corrosion-proof anodized aluminum housing with 2000 meter depth rating
  • Simple software-based, in-field reference checks
  • User-friendly UCI software (Windows and Mac OS X compatible)

For AUV integration details, please ask about our third party integration experience. If you have any questions, please contact

Note: The Deep SUNA is designed to be more aerodynamic than the SUNA V2 and its use on a AUV should not alter the speed significantly. The Deep SUNA sample rate is the same as the SUNA V2 @ - 1Hz.





Limit of Detection 


0.5 µM (SW with T/S corr. Processing)

2.0 µM (SW processing)

Range of Detection

3000 µM

Accuracy (greater of) ± 2 µM (±0.028 mg/l-N) or ± 10% of reading
Precision (short term)
0.3 µM (SW with T/S corr. processing)
2.4 µM (SW processing)
Drift (per hour lamp time)
0.3 µM (SW with T/S corrs. processing)
1.0 µM (SW processing)



Path length 10 mm
Wavelength Range 190-370 nm
Lamp Type Continuous Wave, Deuterium Lamp
Lamp Lifetime 900 h



Input Voltage 8-18 VDC
Power Consumption  7.5 W (0.625 A at 12 V) nominal



Material Anodized Aluminum
Depth Rating 2000 m
Weight 1.8 kg
Displacement 1384 cm3




Real-time temperature-salinity correction available  (0-35oC, 0-40 PSU); Requires T/S data from controller.


The list below includes (as applicable) the current product brochure, manual, and quick guide; software manual(s); and application notes.

Title Type Publication Date PDF File
Deep SUNA Datasheet Product Datasheet Tuesday, September 12, 2017 PDF icon datasheet_DeepSUNA.pdf
Deep SUNA Manual Product Manual Thursday, June 22, 2017 PDF icon Manual-Deep-SUNA-SUNA170517-Rev-D.pdf
Navis BGCi Brochure Product Brochure Monday, January 15, 2018 PDF icon 4 Page Web Seabird_Navis-JAN-2018 7.5x10.pdf
Navis BGCi Data Sheet Product Datasheet Thursday, November 26, 2015 PDF icon SBS-NavisBGCi-112015.pdf
In Situ Nutrient Sensors Brochure Product Brochure Wednesday, November 22, 2017 PDF icon webres-seabird_nutrients-October-2017 x 100.pdf
SUNA Update: SUNA Standard service description and V2 warranty quality upgrade Field Service Bulletins Thursday, June 22, 2017 PDF icon SUNA Standard service description and V2 warranty quality upgrade.pdf
AN118 Nutrient Units Primer Application Notes Friday, June 23, 2017 PDF icon Nutrient-Units-Primer.pdf
AN119 CDOM Interference on Nitrate Measurements Application Notes Friday, June 23, 2017 PDF icon SUNA-CDOM Interference on Nitrate Measurements.pdf
Navis Profiling Float Product Guide - Feature Comparisons Product Brochure Tuesday, January 16, 2018 PDF icon 2018-NavisProductGuide.pdf
In Situ Nutrient Sensors Product Brochure Wednesday, October 11, 2017 PDF icon web-seabird_nutrients-October-2017-4pager.pdf
AUV/ROV/Glider Sensors Brochure Product Brochure Monday, April 16, 2018 PDF icon Brochure-6p-sbs-auv-rov-2018.pdf
Alkaline Battery Packs Operation Manual Product Manual Thursday, June 22, 2017 PDF icon Manual-AlkalineBatteryPack-RevE.pdf
UCI Manual Software Manual Wednesday, September 6, 2017 PDF icon UCI-1.2-User-Manual.pdf


UCI is a graphical software application that makes setup, operation, and in-field reference checks easy and robust. UCI is the recommended software for interacting with HydroCAT, HydroCAT-EP, SUNA, and Deep SUNA.
Version 1.2.5 released January 3, 2018
File UCI-1.2.5-b218-x86.exe for Windows 7/8/10
Binary Data UCI-1.2.5-202-macos-x86_64.pkg for Mac OS X / macOS
Version 2.5.1 released February 10, 2015
Package icon for Windows 7/8/10

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. 

Can I use SUNA V2 that is calibrated for freshwater, in salt water applications and vice versa?

To remove baseline water absorbance spectra, SUNAs are calibrated with nitrate-spiked water, as well as nitrate-free water. The default class-based calibration uses coefficients generated from a library of historical calibrations. For greater accuracy, SUNA sensors are individually calibrated at Sea-Bird Scientific for use in fresh or seawater. Due to difference in absorptivity characteristics of seawater and freshwater, the calibration data for each of these applications is distinct.

Calibrations for instruments to be used in freshwater are determined from aqueous nitrate standards of deionized water with 40 and 4000 µmolar nitrate concentrations and pure deionized water. The second calibration at 4000 µmolar is performed for accuracy in terrestrial applications where nitrate concentrations are large. It is important to note that SUNA units configured for use in freshwater do not give reliable nitrate readings in seawater, as the interference from bromide will not be accounted for without seawater absorption data.

Instruments calibrated for use in seawater use nitrate standards of seawater with 40 µmolar nitrate concentrations and nitrate-free seawater to determine the baseline seawater absorbance spectrum. The use of seawater enables the correction for the UV absorption of bromide and other sea salt components. Instruments calibrated for use in seawater can be used in freshwater applications, but the accuracy will be decreased in regions of high nitrate concentration because the instrument is calibrated for the smaller range of nitrate concentrations typically found in seawater.

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.

Do not attempt removal of the wiper yourself. It requires a return to our service department for this task.


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 connect 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

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.