EXTENDED IMMERSION COEFFICIENT SPECTRUM FOR HYPER SPECTRAL RADIOMETERS

Abstract

Satellite mounted with OCI [Ocean Colour Instrument] must be validated and calibrated periodically while commissioned using hyper spectral radiometers. Absolute calibration of Hyper Spectral Radiometers is done in the air in the optical laboratories, and they are deployed in the ocean [Other than air] while calibrating OCI. Sensors response changes compare to air [Lab] while they are operating in the ocean. Calculated calibration coefficients in air must be corrected as sensors response changes due to changes in refractive index of the medium. Two things affect radiance Measurements. First, Sensor’s solid angle is reduced in-water compare to in-air and therefore lesser light reaches to the sensor. Second, Refractive index of the medium changes when sensor is submerged in water. Value of RI [refractive index] of the sensor’s window is closer to the water value compare to RI of air. Changes in sensors’ response is calculated and measured by experiments so called Immersion Factors and then Immersion factors are applied to the calibrated co efficient calculated in the air. As PACE is designed to operate in UV [350-400nm], Visible [400-700nm] and Near Infrared [700-900nm], it is important for HyperNav, a Hyper Spectral Radiometer to obtain Immersion Factors closer to actual values for the full spectrum range.