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AN96: Using Satlantic PAR Light Sensors

Document Number: 
Publication Date: 
Monday, November 14, 2016
appnote96Nov16.pdf809.3 KB


This application note applies to Satlantic PAR sensors used with Sea-Bird CTDs:

  • Underwater Sensor (connected directly to CTD A/D voltage channel and mounted on CTD or CTD cage) ‑ Satlantic PAR Sensor with Logarithmic Analog (voltage) Output. This sensor can be integrated with the following CTDs: SBE 9plus, 16, 16plus, 16plus V2, 16plus-IM, 16plus-IM V2,19, 19plus, 19plus V2, 25, and 25plus CTDs.
  • Surface Sensor (connected to Deck Unit) ‑ Satlantic PAR Sensor with Linear Analog (voltage) Output. If the SBE 11plus, 33, or 36 Deck Unit is configured with the A/D converter, it can acquire the output of a Surface PAR sensor and integrate this into the CTD data stream.
  • A/D converter is standard in all SBE 11plus V2 Deck Units (serial number 489 and greater) and optional in SBE 11plus V1 Deck Units (serial number 488 and lower).
  • A/D converter in SBE 33 and SBE 36 Deck Units is now standard; it was optional prior to 2012.

Seasoft V2 software fully supports the acquisition and display of the data from these PAR sensors (version 7.26.4 and later of Seasave V7 and SBE Data Processing).


Setting Up Deck Unit for Integration with a Surface PAR Sensor

The bulkhead connector on the Deck Unit back panel (labelled Surface PAR  for SBE 11plus and Par Input for SBE 33 and 36) is a 4-pin MS3102A14S-2S. A spare 4-pin MS style connector (MS3106A14S-2P) was supplied if a cable was not provided.

Deck Unit Function Surface PAR Sensor
Pin A Signal (ground) Pin 3
Pin B Power (+12 volts) Pin 4
Pin C Power (ground) - Deck Units with Digital PCB Assembly 40937c or greater use Pin C. All previous versions do not use Pin C. Pin 1
Pin D Signal Pin 2
-- -- Pin 5


SBE 11plus Deck Unit Configuration

Note: This deck unit is used with SBE 9plus CTD.

  1. Set up the Deck Unit to add Surface PAR voltage to the CTD data stream (increasing number of words by 1):
  • SBE 11plus V1: Set DIP switch S3 position 8 to OFF. The surface PAR voltage will be displayed at thumbwheel position B (or position 11 if your Deck Unit thumbwheel is labeled 0 – 15).
  • SBE 11plus V2: Refer to the SBE 11plus manual (V2) to send the appropriate commands. The surface PAR voltage will be displayed on the Deck Unit LED when the thumbwheel is set to position 9.
  1. Plug the cable connected to the Surface PAR sensor into the Surface PAR connector on the back of the Deck Unit.
  2. To convert to actual voltage, divide the number displayed on the Deck Unit LED by 819:
    Voltage = displayed number / 819.

SBE 33 OR 36 Deck Unit Configuration

Note: These deck units are used with SBE 16, 16plus, 16plus V2, 19, 19plus, 19plus V2, 25, 25plus, and 49 CTD.

  1. Set up the Deck Unit to add Surface PAR voltage to the end of the CTD data stream (increasing number of
    Hex data bytes by 3). Setup varies, depending on the Deck Unit firmware version (refer to the Deck Unit manual).
    • Deck Unit firmware < 3.0: Locate the NMEA Interface PCB with optional A/D converter under the bottom cover panel of the Deck Unit. Verify that dip switch S1 position 8 is in the OFF position.
    • Deck Unit firmware > 3.0: In Seaterm, verify that the SBE 33/36 status message on power-up shows Surface PAR enabled. If it does not, type @ to access the setup menu, and then type 6 and press the Enter key to enable Surface PAR acquisition.
  2. Plug the cable connected to the Surface PAR sensor into the PAR Input connector on the back of the Deck Unit.


Configuring Software

Note: In our Seasoft V2 suite of programs, edit the CTD configuration (.con or .xmlcon) file using the Configure Inputs menu in Seasave V7 (real-time data acquisition software) or the Configure menu in SBE Data Processing (data processing software).

Set up the configuration (.con or .xmlcon) file for the appropriate CTD. All example screens shown below are for the SBE 19plus V2.

Underwater Sensor

  1. Select PAR/Logarithmic, Satlantic for the A/D voltage channel corresponding to the CTD bulkhead connector, and click OK. The calibration coefficient dialog appears.
  2. From the calibration sheet, enter a0, a1, and Im, Enter the desired multiplier (multiplier = 1.0 for units of µmol photons/ m2 sec). Click OK.

Surface Sensor (if applicable)

  1. Enable the surface PAR sensor by selecting Surface PAR voltage added.
  2. The Select Surface PAR Voltage Sensor dialog appears. Select Satlantic -> SPAR/Linear, Satlantic, and click OK.

This alters the Channel/Sensor display by adding two additional external voltages. The highest numbered voltage is labeled SPAR/Linear, Satlantic.

  1. Double click on SPAR/Linear, Satlantic in the Channel/Sensor display. The calibration coefficient dialog box appears. Enter a0, a1, Im, and the surface light conversion factor and ratio multiplier in the dialog box and click OK.



Seasoft calculates surface light from a Satlantic logarithmic analog PAR (underwater) sensor as:

PAR = multiplier * Im * 10 (V –a0) / a1


  • V = voltage output
  • a0, a1, and lm are from the PAR calibration sheet that was provided by Satlantic.
  • multiplier = 1.0 for units of µmol photons/ m2 sec.


Seasoft calculates surface light from a Satlantic linear analog PAR sensor as:

surface PAR = Im * a1 * (V − a0) * conversion factor


  • V = voltage output
  • a0, a, and Im are from the Surface PAR calibration sheet that was provided by Satlantic.
  • Conversion factor =1.0 for units of μmol photons/m 2·s
  • Ratio multiplier is used in corrected PAR calculation (see below)


Seasoft calculates corrected PAR as:

corrected PAR = 100 * ratio multiplier * underwater light / surface light
(underwater light is the calculated light output from the underwater PAR sensor)

To compare the shape of data sets taken at disparate light levels, the ratio multiplier can be used to scale the data. For example, a ratio multiplier of 10 would make a 100 μmol photons/m 2·s light level plot as 1000 μmol photons/m 2·s. The ratio multiplier should be set to 1 for normal operations.

Note: To output underwater PAR and Surface PAR in units other than μmol photons/m 2·s, modify the conversion factor. See Application Note 11General to convert units.


Application Note Revision History

Date Description
November 2016 Initial release.
Applies To