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AGRG Lidar Mission Update

 Dr. Tim Webster, Kevin McGuigan, Candace MacDonald, Kate Collins, and Nathan Crowell)

Researchers from the Applied Geomatics Research Group (Left to right: Dr. Tim Webster, Kevin McGuigan, Candace MacDonald, Kate Collins, and Nathan Crowell) have teamed up with staff from Leading Edge Geomatics to conduct these inaugural surveys using the new sensor recently acquired by AGRG-NSCC from a Canada Foundation for Innovation research grant. Now that the flying and data acquisition is complete, the team has begun the task of processing the large volume of data that were collected by the sensor. Initial processing is being conducted to ensure the planned study areas were all flown and collected with no major gaps. The initial processing of the Little Harbour area including Melberby Beach Provincial Park (northeast of New Glasgow) looks very encouraging where the lidar penetrated the water and was able to survey the seabed and provide detailed elevations. These data can be used to aid in navigating the channels, used as inputs to hydrodynamic models to understand the tidal currents and flushing rates of the harbour, and map what is on the seabed, for example sand or sea grass, which can provide information on the ecosystem health of the harbour.

The sensor collects information from two lasers, a near-infrared that reflects off of objects on the land the the sea surface and a green laser that penetrates the water column, depending on water clarity, and reflects off of the seabed. By measuring the precise timing of these laser pulses, the elevation of the land, sea surface and seabed can be measured.  As can be seen from the figure below the sensor was able to measure the seabed topography across the harbour and map the two channels. The top map shows just some of the lidar points the and the white line in the centre represents the cross-section location. The graph below shows the lidar points along the cross-section and the depth of the two channels.Harbour Penetration Sample

In addition the sensor is equipped with two cameras; a low resolution 5 MPix camera to assist in quality control and interpreting the laser returns, and a Leica RCD30 50 MPix aerial mapping camera that is capable of capturing photos in the visible and near-infrared part of the spectrum. The result of the lidar survey is represented by a series of laser pulse waveforms that show when the laser reflected off the water surface and when it reflected off the seabed, and perhaps objects in the water such as vegetation.

These waveforms are then converted to discrete points based on where the peaks area located as seen in the figure below. The waveform is on the left - the red line is the waveform and the blue and yellow vertical lines depict the peak locations of the water surface (blue) and seabed (yellow). The top middle map shows the location of the cross-section (white line) which cross the bay and includes the dune at Melmerby Beach on the right. The top right inset shows an example of the low resolution 5 MPix camera that is associated with the laser returns in the left graph along a part of the cross-section. The cross-section of the derived lidar points is at the bottom and shows the seabed was mapped for the entire extent of the bay and the dune at Melmerby beach is seen on the right with additional seabed features out into the ocean along the Strait. The colour of the points in the cross-section represent elevation.

Harbour Waveform

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