savageseadog
Well-Known Member
I need to do some survey work for depths, obstructions (shallow water less than 10m) etc has anyone used depth sounders/fish finders for this sort of work and found a sensible way of recording the depth and position?
DIY Marine Surveying (Small Scale)
- Thread starter savageseadog
- Start date
electrosys
Well-Known Member
Is putting a diver down out of the question ?
john_morris_uk
Well-Known Member
I have watched the work done on survey vessels - but I am not a surveyor.
Officially you set a tide gauge and using a differential GPS you run lines using a multibeam sonar and a snazzy computer system and it maps the bottom in 3D.
If you haven't go that kit (only joking) then you revert to the old fashioned way of surveying. You run lines of soundings - either with an echo sounder or with a lead line. Inshore, they used to check their position with horizontal sextant angles, but you might manage with a compass and running a series of bearings. You need to make a note of the time so that you can reduce your soundings to LAT from the best tidal data you can get. Run the lines of soundings as parallel to each other as you can and then cross them with a few sample lines perpendicular as a check against your first set of lines.
Lots of calculations and you will have a chart.
If you can convince the Hydrographic Office of your accuracy and working, they might even accept the data, but don't hold your breath - they are very fussy.
If you have EGNOS (or whatever its called nowadays) on your GPS, then you can try using that - but without differential the positions wonder about over a few metres on the average GPS, so you might have to repeat the exercise several times to get good results.
May we ask where you want to survey?
Officially you set a tide gauge and using a differential GPS you run lines using a multibeam sonar and a snazzy computer system and it maps the bottom in 3D.
If you haven't go that kit (only joking) then you revert to the old fashioned way of surveying. You run lines of soundings - either with an echo sounder or with a lead line. Inshore, they used to check their position with horizontal sextant angles, but you might manage with a compass and running a series of bearings. You need to make a note of the time so that you can reduce your soundings to LAT from the best tidal data you can get. Run the lines of soundings as parallel to each other as you can and then cross them with a few sample lines perpendicular as a check against your first set of lines.
Lots of calculations and you will have a chart.
If you can convince the Hydrographic Office of your accuracy and working, they might even accept the data, but don't hold your breath - they are very fussy.
If you have EGNOS (or whatever its called nowadays) on your GPS, then you can try using that - but without differential the positions wonder about over a few metres on the average GPS, so you might have to repeat the exercise several times to get good results.
May we ask where you want to survey?
JayBee
Well-Known Member
You might try contacting the Clyde Cruising Club: http://www.clyde.org/
For many years they have compiled their excellent sailing directions from Hydrographic Office surveys, supplemented by amateur surveys in the more remote and less accessible anchorages and their approaches.
I remember reading about an amateur hydrographer on the west coast of Scotland and his surveying equipment a couple of years ago, but I haven't managed to find any trace of the article on my bookshelves or on the web.
For many years they have compiled their excellent sailing directions from Hydrographic Office surveys, supplemented by amateur surveys in the more remote and less accessible anchorages and their approaches.
I remember reading about an amateur hydrographer on the west coast of Scotland and his surveying equipment a couple of years ago, but I haven't managed to find any trace of the article on my bookshelves or on the web.
pcatterall
Well-Known Member
If you need further help pm me. The big challenge is that you dont have a recording sounder ( either chart paper type or digital recorder) Principle will be to run 'straight lines' preferably across the contour. Control the lines with GPS, transits etc. You could write down representative soundings as you go along each line.
Getting the tidal correction will be critical; if you can erect a temporary tide pole near the site ( possibly with an assistant reading it every 15 mins) and do a tidal transfer calculation from the nearest 'official tide gauge' and record times for start an end of your survey lines this will suffice.
Getting the tidal correction will be critical; if you can erect a temporary tide pole near the site ( possibly with an assistant reading it every 15 mins) and do a tidal transfer calculation from the nearest 'official tide gauge' and record times for start an end of your survey lines this will suffice.
prv
Well-Known Member
If you can get NMEA into a computer it ought to be a very simple program to fish out the depth figures and write them to a file.
Pete
Signed Out
Well-Known Member
If you have a sounder or fish finder which can output NMEA, try using Hyperterminal (Start, programs, accessories, communications) to log your data on your laptop, if you have one that is. With windows, that is too.
savageseadog
Well-Known Member
Thanks for the input so far. Will a fish finder produce reasonably useful and accurate recordable data ?
I'm looking at areas of perhaps up to 100 to 200m square (ie 100 x 100 and so on)
I'm looking at areas of perhaps up to 100 to 200m square (ie 100 x 100 and so on)
tillergirl
Well-Known Member
Not too difficult - see what I do on the website. You need a data logger to log GPS and depth simultaneously and then reduce the sounding to LAT. I use a Russian data logger that inputs the data straight to Excel for easy conversion. 100 to 200 sq metres is pretty easy. You need to check your readings to confirm accuracy of the soundings and then know the height of tide. Take that from the nearest tide gauge, interpolate for distance from that tide gauge. Then you need to draw it. Get the ratio of Lat to Long right. You can buy a hugely expensive programme like Surfer to plot the data. Actually downloading the Surfer free download is worthwhile to get an image of the contours but you cannot save it without buying the programme which you won't want to do for that sort of area. I use a simple CAD programme to draw the chartlets.
savageseadog
Well-Known Member
Can't find that
pcatterall
Well-Known Member
You may consider hiring a sounder with a paper chart such as the Ratheon suitcase model. I'm not sure about digital data from a yacht type sounder or fishfinder, the system would really need to mean out sampling groups of data and present them to the recorder. Is the survey just to represent the sea bed rather than pick up objects?
savageseadog
Well-Known Member
It's to pick up rocks etc but if I can make a chartlet so much the better
planteater
Well-Known Member
I'm not how accurate your survey needs to be this but this might help - http://www.lowrance.com/Products/Marine/Mark-Elite-Series/Mark-5x-DSI/
Looks like a fun toy for £250.
Looks like a fun toy for £250.
tillergirl
Well-Known Member
Not sure what you could not find. Look here
http://www.crossingthethamesestuary.com/page6.html
and scroll down for the downloads - Bradwell for example.
You will find yacht equipment tricky to pick up smallish rocks accurately because of the delay issues between reading and displaying but it should be possible. You will need to know that the GPS and depth are really coinciding. You could for example have an instant GPS reading but 4 seconds delay on the echo sounder. Or you might not. I get a reading a second so the Bradwell chartlet is made up from over 10,000 individual soundings criss-crossed over and along the channels. I was picking up quite small lumps (sinkers?) between the moorings so if there was any point I could have produced a quite detailed chart of parts. But for detailed accuracy probably worth looking at the care that Team Survey goes into for the accuracy of data.
http://www.crossingthethamesestuary.com/page6.html
and scroll down for the downloads - Bradwell for example.
You will find yacht equipment tricky to pick up smallish rocks accurately because of the delay issues between reading and displaying but it should be possible. You will need to know that the GPS and depth are really coinciding. You could for example have an instant GPS reading but 4 seconds delay on the echo sounder. Or you might not. I get a reading a second so the Bradwell chartlet is made up from over 10,000 individual soundings criss-crossed over and along the channels. I was picking up quite small lumps (sinkers?) between the moorings so if there was any point I could have produced a quite detailed chart of parts. But for detailed accuracy probably worth looking at the care that Team Survey goes into for the accuracy of data.
pcatterall
Well-Known Member
Survey for obstructions may need some special consideration!
Your line spacing needs to be close enough to ensure that any obstruction is captured.
Consider the sounders beam width aginst the depth of water to calculate this and make sure there will be beam overlap suficient to allow for off course error.
With limited equipment ( and especially without side scan) you could consider using a fish finder type sounder as you can get a decent visual impression as you go. Sound along your chosen survey line watching the sea bed on your sounder and fix the position of any obstructions you see.
You can return to these later to confirm and even use a wire sweep to get the exact position and depth. (A metal pole slung under the boat and dragged very slowly over the obstruction). Do a confirmatory check on your tide guage readings/calcs for each obstruction.
Good luck!
Your line spacing needs to be close enough to ensure that any obstruction is captured.
Consider the sounders beam width aginst the depth of water to calculate this and make sure there will be beam overlap suficient to allow for off course error.
With limited equipment ( and especially without side scan) you could consider using a fish finder type sounder as you can get a decent visual impression as you go. Sound along your chosen survey line watching the sea bed on your sounder and fix the position of any obstructions you see.
You can return to these later to confirm and even use a wire sweep to get the exact position and depth. (A metal pole slung under the boat and dragged very slowly over the obstruction). Do a confirmatory check on your tide guage readings/calcs for each obstruction.
Good luck!
Signed Out
Well-Known Member
Hasn't been mentioned yet, but is important to be sure your transducer is measured in, and you are certain to which point you are measuring- i.e. the transducer, or offset to surface (for which you need to check draft of transducer). If not measuring speed of sound in water- probably not for your purposes, you may want to calibrate the device, if not perhaps just confirm the offset. Traditional method being "bar-check"- bung a big beam on measured length strops and dangle under your transducer to compare true to output.
Probably been more answers since started this- been tied up, so sorry if repeated something another has said in last couple of hours...
By the way, as pcatteral said, a fishfinder will be better than a standard "singlebeam", but if you must use a normal singlebeam, then identifying point hazards and such will be very difficult. Your resolution is only as good as your beamwidth, and it will always measure to the nearest point. And remember your vessel motion too- roll and pitch will make an effect, so without motion sensors, try to minimise these as much as possible.
And take lots of notes!
Probably been more answers since started this- been tied up, so sorry if repeated something another has said in last couple of hours...
By the way, as pcatteral said, a fishfinder will be better than a standard "singlebeam", but if you must use a normal singlebeam, then identifying point hazards and such will be very difficult. Your resolution is only as good as your beamwidth, and it will always measure to the nearest point. And remember your vessel motion too- roll and pitch will make an effect, so without motion sensors, try to minimise these as much as possible.
And take lots of notes!
pcatterall
Well-Known Member
Sorry, very basic requirement as pointed out above ( the bar check!!). At the very least you could check with a lead line if you knew you were on a flat hard bottom.
That does not gaurentee that the readings will be correct for the whole range range but would be better than nothing.
Just re-read the OP and note that the depths may ony be 10 m. Depending on the beam width of the sounder ( check the spec) this may indicate maximum cover of 5m per line and that ,even with perfect conning of the boat, lines would have to be run at a max of 5 m apart. ( 2.5m would be safer)
You really should have all the tracked lines plotted so that you can see and re-run any gaps.
That does not gaurentee that the readings will be correct for the whole range range but would be better than nothing.
Just re-read the OP and note that the depths may ony be 10 m. Depending on the beam width of the sounder ( check the spec) this may indicate maximum cover of 5m per line and that ,even with perfect conning of the boat, lines would have to be run at a max of 5 m apart. ( 2.5m would be safer)
You really should have all the tracked lines plotted so that you can see and re-run any gaps.
Signed Out
Well-Known Member
Just remembered that recently in PBO; perhaps last but one issue, there was an article about a new scheme for public data acquisition. Some guy would come along and fit a little data-logger to your boat and measure in the transducers, etc., and then you just sent in the files. Admit I didn't read the whole article, being a little busman's for my liking...
smartcom
Well-Known Member
Hi,
Have a look at the TeamSurv project (www.teamsurv.eu).
Here we are using crowd sourced GPS and depth data for surveying.
If you sign up, you get the free loan of a data logger that will hook in to the NMEA0183 or Seatalk output from your instruments. Upload the data to the server, and we correct for tides using tide height predictions and tide gauges, and we're just bringing online speed of sound corrections for the depth sounder.
We also have a free software tool, NMEA to CSV, that takes the logged data files and outputs them as a CSV file, which you can read into Excel, Surfer or whatever.
Have a look at the TeamSurv project (www.teamsurv.eu).
Here we are using crowd sourced GPS and depth data for surveying.
If you sign up, you get the free loan of a data logger that will hook in to the NMEA0183 or Seatalk output from your instruments. Upload the data to the server, and we correct for tides using tide height predictions and tide gauges, and we're just bringing online speed of sound corrections for the depth sounder.
We also have a free software tool, NMEA to CSV, that takes the logged data files and outputs them as a CSV file, which you can read into Excel, Surfer or whatever.