SENSING A PHAEOCYSTIS BLOOM IN THE WESTERN TAIWAN STRAIT FROM RADIOMETRIC MEASUREMENTS WITH AN UAV
We present results of a phaeocystis bloom event (up to 100 - 200 gel matrix/L) in the Weitou Bay located in the Western Taiwan Strait captured by a low-altitude (300 m) unmanned aerial vehicle (UAV), where measurements of water color were made at high spectral and spatial resolutions. A novel approach was developed to obtain remote sensing reflectance (Rrs) from the radiometric measurements from the UAV platform. It is found that the Rrs acquired from the UAV (Rrs_u) were quite consistent with the concurrent Rrs data obtained in situ. The root mean square difference at log scale (RMSD) between the two sets of Rrs ranging 0.035 - 0.289 (equivalent relative difference ~7 – 54%) for wavelengths of 400 - 750 nm, with an averaged RMSD of 0.136. The extent of the phaeocystis bloom was further evaluated from the obtained Rrs_u. For the bloom waters, the estimated surface chlorophyll a concentration (Chl) ranged 6 – 98 mg/m3, which is 3 – 50 times of the Chl under normal conditions in this bay. This effort demonstrates for the first time a successful retrieval of both water color and Chl information from UAV measurements, which advocates further the employment of UAVs for monitoring the quality of nearshore or difficult-to-reach waters due to its flexibility, low cost, and high spatial resolution.
Shang, S., Xiamen University, China, email@example.com
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