Detecting anomalous turbidity patterns in nearshore waters of Québec based on CALIOP waveforms

International audienceCoastal erosion is a major environmental issue affecting diverse infrastructures (e.g., buildings, roads, and ports) in Québec. In situ monitoring of coastal morphological changes and associated modifications on water turbidity is costly and face several challenges related to long-term marine measurements (e.g., biofouling). Here, a new technique based on spaceborne Lidar (Light detection and range) measurements is evaluated for estimating bi-weekly variations on suspended particulate matter off the Québec coast. These preliminary results are part of FLASH (Fluvial bathymetry using spaceborne Laser in SHallow waters), an international project aiming to develop remote sensing tools for tracking unusual patterns of water turbidity linked to coastal desintegration (e.g., sediment plumes) in coastal environments of Canada and France. The experiments were performed in La Boule Bay east of Sept-Iles during April-July 2010 and involved comparisons between CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) measurements (L1_cal-v4 and 0.5 km CPRO products) and in-water turbidity measurements derived from an acoustic doppler current profiler (ADCP). La Boule Bay is an area of the northern shore of the Gulf of St. Lawrence that is undergoing presently a major coastal retreat after stability/advance during 70 years. Contrasting case studies based on high and low turbidity events showed a good correspondance between CALIOP volume backscattering at 532 nm (cross and copolarized channels) and amplitude values of ADCP pings. Turbidity Peaks usually coincided with neap tides, high winds, and larger wave heights