depth survey

daveyg · 26 January 2008, 08:44

I'd like to do a depth survey of a lake, the ability to create a paper chart of the depth profile is key.

Specifically, I'm looking to take samples of x, y & z across the the whole lake at say every 5 meters, then go back and do a finer resolution of the shallows.

I've got a Navman 5430 chart plotter linked to a Fishfinder 140, while they can present the perfect data, I've no clue if this kit can record data, then I guess I'll need to get the data off and some get some software to process it.

Does anyone know if it can be done with the equipment I've got ?

MikeCC · 26 January 2008, 11:34

Blimey, that's keen. You must have plenty of time on your hands! Hope it's not Windermere.

You'll probably find that survey outfits have spent thousands on fancy datalogging kit and software to do what you're attempting.

Presumably you want to end up with a corresponding set of GPS positions and depth figures. With your combination, you won't be able to get this information out, as the output NMEA from the 5430 will not include depth data.

For the process to be accurate, you'll also need to go very slowly. There will be timing differences +/-2s between position and depth signals. You'll also be restricted by he 3-10m (in)accuracy of GPS plots.

As for plotting software, I recall a post some time back with some nice 3D bathymetric plots.

daveyg · 26 January 2008, 14:47

Mike, thanks for the advice.

yes, exacly right, GPS + depth

I plan to attach the kit to a boat that cuts the lake weed, it does about 2 knots and covers the entire lake in about 3 weeks.

I'll use differential GPS, subtracting the daily error from a known datum, all this is fairly easy post processing of the data, my challenge is collecting and extracting the data.

J.C. · 26 January 2008, 16:07

Mike is right, we do indeed spend many (tens of) thousands on kit to do exactly this kind of thing. It's not just the GPS, software and electronics, we use much fancier, and more accurate, echo sounders too.

Much as it goes against the grain to advise on how to do something we get paid to do, you probably can get a set of data and compile it into a chart of sorts if you really want to. You'll need NMEA out from the GPS and E/S, some software to log and combine this (laptop in the boat probably) and then some modelling software to create a 3D model.

A word of caution, it's not as easy as it may look. There are a whole host of error sources which will make the data less reliable. Speed of sound in water varies significantly, leisure grade echo sounders with automatic gain control can track spurious bottom definitions, latency in GPS has to be considered, variations in water level (if any) etc etc. Be prepared for a LOT of data editing and examination.

Good luck though... and if you eventually decide you need a better survey, let me know!

JC

MikeCC · 26 January 2008, 16:12

Couple of links:

Brookhouse

Windmill

In fact a quick search for 'NMEA data logger' produced quite a lot!

daveyg · 26 January 2008, 16:57

Wise words, thanks

I saw the NMEA data structure which didnt really phase me, but i was scratching my head on creating a regular grid from the randomly dispersed data, contour lines were another 'issue'

I guess my need is a one shot survey, of a 200+ acre lake in Berkshire, it doesn't really warrant working from first principles.

Any ideas if there is anyone I can hire the kit from ?

It seems a bit of a kerfuffle hiring in a boat to do the job as our weedboat goes everywhere at a mindnummingly slow speed, 30 times a year.

I guess that this would kill 2 birds with one stone, as another job on the to do list is to put GPS on the weed boat to track where its missed, no depth data required for this, however, if I could map the lake bed material this will mean I can target the mud/weed areas from the gravel. I'd imagine quite a market for hiring this type of kit.

Had a mate at uni who did his project on differential sea bed depth sounding, perhaps I should have done that, ahh, but he got a first and I scrapped a desmond ...

Cheers,

Dave.

DJL · 26 January 2008, 18:56

Quote:

Originally Posted by daveyg

Wise words, thanks

I saw the NMEA data structure which didnt really phase me, but i was scratching my head on creating a regular grid from the randomly dispersed data, contour lines were another 'issue'

You don't want to create the grid from your data - that would be a nightmare. Record the data and then just plot the dept at the recorded position.

It wouldn't be very hard to write a program to draw a 3d representation of the data. Drawing contours wouldn't be too difficult either.

Does the weed boat driving in straight lines? or does it manouever around? A standard GPS is going to be really inacurate unless your driving in straightish lines.

9D280 · 28 January 2008, 15:12

Quote:

Originally Posted by daveyg

however, if I could map the lake bed material ......

Grease filled dimple on the end of your lead line? - then you get a confirmation of depth too!

On a more serious note, there are plenty of data loggers out there - some will even draw graphs of your data as you log - just make sure you can export the gathered info to something more useful..... If you were really in "DIY" mode, Velleman do a whole bunch of USB interfacing kits - and as NMEA is vaguely RS232.....

karlT · 01 February 2008, 15:14

Can put your data from excel and plot a 3d map so as djl says no need to use a grid.
Alternatively, use software called Olex, www.olex.no This is what a lot of pro fisherman are now utilising to maximise their catch.

Simon B · 01 February 2008, 17:32

Looked impressive, as did the price! pretty cool stuff though.

karlT · 04 February 2008, 16:36

Had an out of the box sort of idea. You WILL need a decent pair of wellies or waders!

If you are able to drain the lake (assuming it is not a massive lake)!!

Walk the perimiter of the waters edge to give your datum level. Drain say 25cm of water and do the next contour by again walking the waters edge continue this process until you get to basin on lake.

Using a simple GPS or differential if you can back pack it will provide numerous points on the trail as you walk around.

MikeCC · 04 February 2008, 20:05

Quote:

Originally Posted by daveyg

I guess my need is a one shot survey, of a 200+ acre lake in Berkshire

Quote:

Originally Posted by karlT

If you are able to drain the lake

. . .or maybe not!

karlT · 04 February 2008, 20:39

6 month forecast of extreme drought throughout UK may help......

theory could work on much smaller water area

laser · 09 February 2008, 16:58

Have just stumbled across this site, while researching data for my final year project at university:

http://www.windmill.co.uk/seafloormapping.html

Its about mapping sea floors and maybe of some interest to you with what you are trying to do.

Rich

spidermonkey · 11 February 2008, 16:58

have a look at this

http://drdepth.se/

daveyg · 15 February 2008, 09:21

wow, pin outs on one site and decode software on the other, its CHRISTMAS. ok, reality says its no walk in the park, but we're taking small steps.

I'm still looking to target our weedboat more effectively, sharp echo ~= stones, scattered echo ~=mud, where the weed grows

The DIY option looks good as a fall back, but I have to assume that there is a commercial market for this stuff that we can hire / buy

Cheers