Our soundings using UnderSee Explorer
A Garmin 441s fishfinder was used to gather GPS and depth data. This, together with a terminal strip and a lighter socket, were mounted on an epoxied oak board for portability. The lighter socket is used for an iverter, to power a laptop computer.
The 441s is connected to the laptop with a USB cable. Communication is done using NMEA 0183 protocols.
A program named UnderSee Explorer was used for data capture, analysis, and display. This screenshot shows the path driven in the boat to collect the data. The red line is comprised of a series of points, with each point representing a lat/lon/depth reading. The program allows layering of an aerial photograph for orientation.
The program automatically draws contour lines as the data are collected.
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An "area of interest" is drawn to outline the area to be dredged.
The program then overlays the area of interest with a virtual grid--typically 200 x 200. Using triangulation, an average depth is calculated for each square in the grid. This information allows calculation of the amount that would need to be removed for each square, and the sum of these is the total amount to be dredged. The following are the data for these measurements:
ft m sq m cu m cu yards -18 -5.5 25285.4 40363.9 52794.0 -17 -5.2 24799.5 32833.8 42945.0 -16 -4.9 22104.4 25690.1 33601.4 foot meter -15 -4.6 18511.4 17623.4 23050.5 1 0.3048 -14 -4.3 16254.2 12431.6 16259.9 2 0.6096 -13 -4 14193.4 7843 10258.3 3 0.9144 -12 -3.7 9641 4251.2 5560.4 4 1.2192 -11 -3.4 5176 1984.9 2596.2 5 1.524 -10 -3 2555.6 972.8 1272.4 6 1.8288 -9 -2.7 1455.7 366.3 479.1 7 2.1336 -8 -2.4 270.7 139 181.8 8 2.4384 -7 -2.1 173.6 73.7 9 2.7432 -6 -1.8 100.9 33 -5 -1.5 48.5 11.1 -4 -1.2 14.2 2.1 -3 -0.9 1.4 0.1 1 foot = 0.3048 meters