Remote control boat sonar mapping
The idea of this project is to produce a cheap and simple system to map the bottom
Of a lake, river ect.
The boat above has a echo sounder 10o beam width from 0.5m to 100m depth,
and a build In GPS which can give +-1-3m on a good day.
By using some GPS software called Trimble you can pick the best time of day
to do the survey for the best sat light positions in the sky.
The boat has a SD card logging system where the GPS and depth is updated
To the SD card as lat/log/depth from this a 3D map or 2D with overlay
Can be constructed.
The data is in NMEA format for GPS , Depth , Temperature
Sample data below.
NMEA format
$GPGGA,162321.000,5134.8271,N,00000.5965,E,1,10,0.9,27.5,M,47.0,M,,0000*62 GPS
$SDDBT,2.5,f,0.7,M,0.4,F*02 Depth
$YXMTW,13.3,C*13 Water temperature
The data can be displayed in many ways but I like with goggle earth as can
see easy where data was missed.
The system is simple to setup no trailer needed for car for boat, as remote control
Boat fits in a bag, you drive the boat up/down the lake to build up as many points
As needed keeping a slow speed.
Mapping surveys below...
Mapping of small lake in laindon essex.
Above boat mapping the lake
The lake is not very deep mainly 0.25metes, but you can see the bottom left
Corner has a deep bit of 0.63 which could be a danger for small children.
Lake Hollow ponds Leytonstone( Overlay with depths)
Overlay temperature
Another Lake in laindon
You can see here the deepest part is to the north bank around 1m deep.
Survey details
After the data is collected it is re-encoded to goggle earth format so a track can be
Displayed to see how many points where collected, then a 2D map with colour coded
Depth is produced see above.
By driving slowly you get more GPS points so you can get a better fix by selecting the best fix’s using the PDOP signal.
The GPS receives a signal called PDOP and this gives you the error see below.
|
DOP Value |
Rating |
Description |
|
1 |
Ideal |
This is the highest possible confidence level to be used for applications demanding the highest possible precision at all times. |
|
2-3 |
Excellent |
At this confidence level, positional measurements are considered accurate enough to meet all but the most sensitive applications. |
|
4-6 |
Good |
Represents a level that marks the minimum appropriate for making business decisions. Positional measurements could be used to make reliable in-route navigation suggestions to the user. |
|
7-8 |
Moderate |
Positional measurements could be used for calculations, but the fix quality could still be improved. A more open view of the sky is recommended. |
|
9-20 |
Fair |
Represents a low confidence level. Positional measurements should be discarded or used only to indicate a very rough estimate of the current location. |
|
21-50 |
Poor |
At this level, measurements are inaccurate by as much as 300 metres with a 6 meter accurate device (50 dop * 6 meters) and should be discarded. |
The day above I was getting PDOP 1.5 which gives +-2m from my test.
Errors in system.
There are bits of the system that will give errors listed below.
1) Echo sounder beam width calculations.
At 5m it will see a area of 2 meters on the bottom
At 10m it will see a area of 4 metres on the bottom
So the reflection from the highest point will give the depth.
2) GPS the error here depends on the PDOP value
Some days are better than others but can be selected.
From testing if you select a good pdop I have got a error +-2-3 metres.
3) Speed of boat this will effect how many samples you get so best to take
Your time!!.
Below some more pictures of the electronics.
The boat can be hired for surveys just contact for a price spencer1565@hotmail.com