Derivation of immersion factors for the hyperspectral TriOS radiance sensor

The new radiance sensor RAMSES ARC of the TriOS system is becoming of increasing importance in the ocean optics community due to its price-performance ratio. The company only provides an absolute radiance calibration for use in air. For absolute calibrated radiance measurements in water, immersion coefficients are important, considering the changes in the wavelength-dependent refractive index in the transition from the air-glass to the water-glass interface. For the first time, immersion factors were directly and indirectly determined for the real material of the optical window over the whole spectral range. With the derived correction factors, the sensor is applicable for the determination of the water-leaving reflectance from underwater measurements of radiance profiles in combination with above-water irradiance measurements, to validate ocean colour satellite sensors.