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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.

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