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SAS Solar Tracker

The SAS Solar Tracker works in conjunction with the Surface Acquisition System (SAS) (measures above-water ocean colour) to maintain the correct pointing angle with respect to the sun, and thus permits autonomous operation.

The SAS Solar Tracker works in conjunction with the Surface  Acquisition  System  (SAS) (measures above-water ocean colour) to maintain  the  correct pointing  angle  with respect to the sun, and thus permits autonomous operation.

Bigelow Laboratory for Ocean Sciences® researchers Dr. Barney Balch, Bruce Bowler and David Drapeau developed the Underway Aiming System (UAS™) software to address the challenge in ocean colour measurement of aiming shipboard optical sensors at optimal viewing angles from the sun. The UAS™ solution uses the real-time date, time, ship’s position and course to determine the angle of the sun from the sensors, and to position the sensors at the optimal azimuth angle.  The UAS™ performs this calculation in real-time in response to the constantly changing relative positions of the sun and sensors so that optical measurements may be made autonomously with improved accuracy.

Sea-Bird Scientific collaborated with the Bigelow Laboratory for Ocean Sciences® to bring the UAS™ technology to the ocean research community in the Sea-Bird Scientific Surface Acquisition System (SAS) Solar Tracker.  The SAS Solar Tracker consists of a radiometer instrument frame, rotator, and controller with data logging, GPS, electronic tilt and compass sensor, and ship navigation data feed.  The SAS Solar Tracker hosts Sea-Bird Scientific ocean colour radiometers, and optional pyrometer for measuring sea surface temperature mounted on the instrument frame and connected to the controller.

The SAS Solar Tracker autonomously performs measurements when the elevation of the sun and the orientation of the ship allow, subject to operator settings. For example, the SAS Solar Tracker would not collect data at night, or in daylight when the sun is too low in the sky, or when due to ship’s course, the ship’s structure would block the required view of the water. With data storage for months of operation, the SAS Solar Tracker’s autonomy frees busy science crew for other tasks and makes it suitable for deployment on volunteer observing ships.


  • Drive Unit to adjust the viewing angle of the frame
  • Frame for mounting the sensors
  • Precision Lt, Li and Es measurements
  • Adjustable viewing angles from Nadir and Zenith
  • Orientation (azimuth, pitch, roll) measurements
  • Sea-surface temperature
  • GPS for geo-referencing and time tagging
  • Flexible configuration
  • Internal data logging
  • Low power consumption
  • Compact system design
  • Easy to deploy

Garmin GPS 19x HVS GPS Receiver

  • Embedded receiver and an antenna
  • Precise navigation updates once per second
  • Can access Wide Area Augmentation System (WAAS) and differential GPS services
  • Withstand immersion in 1 m of water for 30 minutes

Miniature Deck Unit (MDU)

  • Serves as both a nominal 48 VDC power source for the Junction Box and as a RS-422 to RS-232 level converter
  • Connects to DC power supply, data logging computer and the Junction Box

Junction Box

  • Converts 48 VDC supplied by the MDU over the power/telemetry cable to 12 and 24 VDC for sensor ports
  • Converts sensor serial data communication from RS-232 to RS-422 for transmission over the power/telemetry cable to the MDU
  • Voltage conversion and serial data communication signal conversion enables duplex communication between the SAS and the data logging computer over a long distance
  • Receives data from sensors and optionally ship navigation
  • Controls the drive unit
  • Streams output via the MDU to a logging computer
  • Logs data internally to USB mass storage device.

SAS Mounting Frame

  • White coated metal, providing a rugged structure for instrument mounting
  • Mounting brackets for the sky radiance, water-leaving radiance, irradiance and pyrometer
  • GPS screwed on the top
  • Junction box is attached to the back
  • Mounted on top of the SAS Solar Tracker Drive Unit
  • Adjustable brackets for the sky radiance and water-leaving radiance sensors for viewing angle between 30 and 50 degrees from zenith or nadir

SAS Solar Tracker Drive Unit

  • Forms the base of the SAS Solar Tracker
  • Rotates the SAS Mounting Frame that is mounted on top for optimal measurement direction
  • Receives power and transmits telemetry via its 6-pin port
  • Receives ship navigation data via its 8-pin port
The list below includes (as applicable) the current product brochure, manual, and quick guide; software manual(s); and application notes.

Version 7.7.19 released April 12, 2016

ProSoft 7.7.19 provides a number of key improvements including support for ancillary SAS sensors, support for  BETA_IRED and BETA_GREEN sensors to calculate backscattering, corrected backscattering coefficient units, robust handling of corrupt timer data, HyperSAS IR camera integration, interruptable processing, and more. For a detailed list of recent fixes and features, please refer to the release notes.

File ProSoft7.7.19-b2_Setup.exe for Windows 7/8/10

What are SIP files?

Files that are delivered with Sea-Bird Scientific and third party equipment to describe the sensors data output and calibration coefficients come in two types. Calibration files or *.cal files and telemetry definition format files or *.tdf files. In some cases, systems are created that network many sensors together and their combined data is provided in one serial output. The simplest example is a HOCR sensor that generates both light and dark frames. A more complex example is a HPROII profiling system that may contain as many as 5 sensors and 7 individual calibration and tdf files. These files must be used to both collect and process the data. This can become quite confusing to keep track of all these files so Sea-Bird Scientific developed SIP files. All CAL and TDF files required for a system are zipped using winzip and the extension changed from *.ZIP to *.SIP. The file name includes the system description (usually the network master serial number) and the creation date. This SIP file can then be used in place of individual files to collect and process data.

What are the main differences between the multispectral and hyperspectral radiometers?

Sea-Bird Scientific multispectral 500 series radiometers measure light at each fixed wavelength with an interference filter/detector assembly.  The analog output of each detector is amplified and digitized.  The amplification stage and noise filtering is fine tuned for each wavelength to produce an optimal saturation limit and frame rate.  This maximizes the signal to noise ratio while ensuring that each channel does not saturate during normal operations.  The frame rate of each radiometer is fixed anywhere between 1 and 24 Hz depending on the customers specific requirements.  4 and 7 channel radiometers can be purchased in several configurations with different field of views.  They have a small diameter to reduce self-shading and generate a digital output for stand-alone operations or they can operate as part of a larger 485 network of sensors (SATNet).  500 series sensors are also very low power devices making them excellent sensors for power limited platforms such as buoys, AUV’s and profiler floats.

Sea-Bird Scientific Hyperspectral HOCR radiometers use a Zeiss spectrograph optimally configured and characterized to measure light between 350 and 800 nm (approximately 136 individual channels).  With the HOCR series, a variable integration time is used for all channels in the array and upper and lower thresholds are set so that no channel saturates within that array.  Thermal dark current changes that occur within the spectrograph are corrected across the full spectrum with the use of a mechanical dark shutter that closes periodically in the radiometer.  A separate frame of data is generated for this dark reading.  Frame rates are dependent on the integration time of the device so are considered variable.  When light levels are high, the integration time and frame rate are also high, so that you are collecting many frames per second.  As the light level decreases, the integration time must increase and therefore the frame rate becomes longer.  Integration times range from 4 ms to 2 seconds.  HOCR sensors also have a small diameter to reduce self-shading and the same telemetry options are offered.  Sea-Bird Scientific also offers a low power, non-SATNet version of the HOCR sensor for remote platforms that are power limited.