Coastal Bio-Optical Properties Derived from Empirical Line Calibration of Aircraft and UAV Remote Sensing Imagery

A field experiment was conducted during Spring, 2018 in the Mississippi Sound to study coastal ocean front features resulting from opposing wind and tidal forces. One such front was observed on April 5, 2018. Hyperspectral remote sensing imagery was collected with a microSHINE sensor mounted on an aircraft and a Headwall Nano-Hyperspec sensor mounted on an Unmanned Aerial Vehicle (UAV). Prior to deployment, the microSHINE sensor was calibrated to radiance units with an integrating sphere. However, the aircraft measurements contain both water-leaving radiance and atmospheric path radiance components, so atmospheric correction is required to isolate the water spectra. Coincident with the overflights, we collected water reflectance spectra at specific locations near the front using an Analytical Spectral Devices (ASD) hand-held spectroradiometer on board a small vessel. An Empirical Line Calibration (ELC) was performed by pairing radiance values from the microSHINE imagery and collocated ASD reflectance values. This generated a linear equation to convert all the microSHINE radiance values to reflectance values, effectively removing the atmospheric signal. The atmospherically corrected reflectance images were then convolved to the relative response function of the VIIRS sensor and input into the Naval Research Laboratory Automated Processing System which generates standard bio-optical products (chlorophyll, absorption and backscattering coefficients). The UAV scenes did not cover the locations of the ASD spectra collection. So, the microSHINE reflectance scenes were then used as source data to pair with corresponding hyperspectral drone scenes and the ELC process was used again to convert the drone data to remote sensing reflectance values. The bio-optical products generated from the microSHINE and UAV hyperspectral were used to investigate in-water characteristics on both sides of the front.