Thanks for the link to Senix, Tom. Their water level sensor has a dead band of 1 foot, and a repeatability of 0.2% of full scale, which works out to 0.14 inch at 30 feet full scale. Specs may be stretched thin in reality; given wind, temperature, ripples or turbulence on the surface etc. It does have the great advantage of being non-contact when a good support like a bridge is available. It might be hard to set up on a rover though.
I've set up a raft to float on the surface and bounce ultrasound off the bottom.
There are strong standing waves set up in the container, but I need to try it in something with wide horizontal extent. I'd want the strongest standing wave to be the one directly below the raft. Really, this is just a curiosity, not practical I think.
It's not clear at this point if the project will be funded. They may have been looking for an off-the-shelf-high-tech-zero-R&D method. It may go back to a guy walking around with a gauge pole, perhaps with a data logger and sensor instead of a notepad.
Have you guys any idea what the bottom of these rice paddies looks like to ultrasound? I've heard they are kinda squishy, even spongy-feeling, which is why people can stick the tiny rice plants into the bottom. I would think an ultrasound might not be able to tell quite where the bottom is because, well, it might be hard to tell where the water ends and the earth begins.
Another thought .... could you measure the resistance of the water? From a layout guy, resistance is measured in Ohms per square with the unit being arbitrary. One square inch would have the same resistance as One square mile as One square centimeter, etc. Typically we have a fixed value for Ohms/square but this is determined based on the height thickness of the Metal used in the process. In your situation this would be the depth. If you took your measurement's differentially / ratio-metrically you might be able to get an accurate volume reading that would be impervious to Ph variances since that would cancel out in any differential measurements. Essentially your Ohms per square would vary proportionally based on depth... if your "square" was a standard or fixed size then various readings could be made without using any kind of a float/drag mechanism.
There's definitely a squishyness factor. So many of the methods depend on sinking into the muck, more or less, one way or another, and the muck in reality and its water content are important. "Squishy" in a wider sense also applies to measurements that are indirect and therefore require calibration, or to those that have a large number of extraneous factors and tolerances that have to be accounted for. The question then shifts to how to calibrate the squishy method, back to those that are direct and have few or no extraneous factors. The amount of irrigation water flowed onto the field would still seem to be the most direct. I'm still asking people in the business what's what about that.
Yet another thought.... how about shining underwater a laser (perhaps 2) or some other source of strong and focused light at say 30 deg angle to "bounce" it back from the bottom and "capture" the reflected result with an array of light sensors (camera?). Kind of repeat of the simple Dam Buster contraption for Lancaster's distance to water measurement scenario where 2 strong projectors shining at the same angle but from different wings were collimated at the same point to keep each bomber flying at a certain very low and precise altitude just before dropping their cargo of bouncing bombs.
However. the depth measurement scenario needs to be an inverse to what they used during WW2 as the raft travels on water surface while the light sources should be able to adjust their shining angle accordingly to the received and reflected from the bottom of rice paddies signal(s).
I envision 2 underwater light sources to shine from 1 foot apart at say 30 deg towards the movement of the raft. whereas the receiver light sensor(s) array to be located at raft's bow. Thus signal's feedback will adjust the shining angle(s) and allow to calculate water depth using some formula(s) ... but that's obviously to be left as an exercise for the students
Also, shooting ultrasound under water at certain angles can be seen in this example from Sontek...
There's definitely a squishyness factor. So many of the methods depend on sinking into the muck, more or less, one way or another, and the muck in reality and its water content are important. "Squishy" in a wider sense also applies to measurements that are indirect and therefore require calibration, or to those that have a large number of extraneous factors and tolerances that have to be accounted for. The question then shifts to how to calibrate the squishy method, back to those that are direct and have few or no extraneous factors. The amount of irrigation water flowed onto the field would still seem to be the most direct. I'm still asking people in the business what's what about that.
Premixing the additives to the required concentrations is by far the most practical way of doing this, and probably less costly as well.
I was wondering about that, too. You could then add the pre-mix to the infill at a fixed rate to get the required final concentration. As a bonus, you'd be sure that the additive was uniformly distributed over the entire paddy, which might not be the case if it's added after the paddy is full of water.
I was wondering about that, too. You could then add the pre-mix to the infill at a fixed rate to get the required final concentration. As a bonus, you'd be sure that the additive was uniformly distributed over the entire paddy, which might not be the case if it's added after the paddy is full of water.
-Phil
I wasn't thinking of adding the pre-mix to the infill, just putting enough additive to a known volume of water to get the required final concentration. If the tank or reservoir was not large enough to flood the entire paddy to the desired depth then mix in batches until the paddy is full. Adding pre-mix to the infill is a good idea if the flow rates are well controlled.
Thanks John, that's interesting, "Sonar Mapping of Storage Ponds". To summarize, they customarily do the survey from a 10' aluminum boat with outboard, and a "single beam echo sounder system, incorporating a three-transducer array" and "typically working at 33kHz and/or 200kHz", to measure the echo return time of pulses. For more hazardous locations they (PW Makar Coatings Inspection Ltd.) came up with a 27kg, 2 meter long remote control craft. It has GPS, 1500 meter wireless link, and it feeds data to software to produce 3D plotting sludge and sediment maps. Pretty nifty. I'll pass that along, but it won't be directly applicable to the rice paddies.
The project is waiting for a meeting next week.
I do have inklings of what is not possible. The situation is nowhere near as high tech as you might imagine.
-- The paddies are strung out and separated by mud barriers that are opened or closed by a Cat. There is no way to measure the water in and out, and there are sometimes unplanned blockages or releases. The flow rate is low, ~2 liter per second per hectare. Maybe a weir could be installed and instrumented. But there is no way in place to empty the paddy and then fill it with a known amount of water.
-- The concentration of the pesticide is very low ppm and cannot be monitored in real time. That requires an expensive and time consuming liquid chromatography column (reverse HPLC).
-- Only standing water is to be counted, not the water content of the mud. Compare with touching the bottom with the wide end of a T-shape probe stick. The mud is consolidated, but if you step on it, you sink in 20 to 30 cm.
-- The paddies are strung out and separated by mud barriers that are opened or closed by a Cat.
I once had a cat. I'm glad somebody has figured out how to get one some use out of one. Every time I told mine to do something it would just look at me like I was some kind of idiot and go back to sleep.
Here's something a little different. It's build from two white (or blaze orange) floating rectangles, one black sinking square, and some thin, rigid material to connect them:
When positioned on the bottom, the separation of the two rectangles will vary, depending upon the depth of the water. With an array of these spread over the entire paddy, an aerial photo could be scanned to determine the depth at each location. Because the rectangles are of a known size, each station would be self-calibrating, regardless of aerial altitude or angle.
Phil,
What do you have in mind for the thin, rigid material? As I see it, the arms of the rigid V would come up through holes in the centers of the floating blocks (circular?), constraining their distance apart vs depth. Your diagram depicts an solid connection though from the bottom plate to the floating block, but how could the length of that connection change with depth?
I was thinking of something that was loosely hinged to the top and bottom plates. Metal rods with loops in the end, connected to the flat pieces via screw eyes would work. You'd have to brace them X-fashion with fishing line, say, to keep the top plates from paralellogramming.
I'd be afraid that anything that slides might get jammed.
Now that is ingenious. Simple to build using inexpensive materials, self calibrating, and easy to read. Also a great excuse to buy a quad/hex copter with a camera. Best idea to date IMHO.
But there is no way in place to empty the paddy and then fill it with a known amount of water.
Can a paddy be emptied and then filled with an unknown amount of water? If so, you could then implement my original suggestion where aerial photos are taken as the paddy fills, and a contour map is built up from the photos. Based on the contour map, a chart of volume versus level could be generated for each paddy.
John, It would be nice if nothing at all needs to sit on or be dragged over the mud, because that is bound to stir it up and mess up the light beam. That is true of the line-scan camera idea too, but the question really hinges on how clear the water is, dragging or not. I don't know, and my intuition cries out, "don't count on it!". I do appreciate the advantage of avoiding mechanical linkages, complicated ones anyway. Some of the ideas here have consisted of nothing more than a pivot. But the light beam ideas are very intriguing and we will talk them over I'm sure.
Phil, I see what you mean. It could even be thin silicone rubber bands at top and bottom. The top pads could be round disks to avoid the parallelogram issue. Operationally though, It's hard to imagine them sprinkling 200 or 300 of these around, take the aerial photo, and then pick them up and move them to the next paddy. Now, if the bottom pad could drive around, while quad-copter with the camera hovers above...
Dave, I'll have to ask about that. They might consider it a PITA. The contour would change with each planting. Also, from a measurement standpoint, there are bound to be local dips and hills that don't necessarily fill evenly when water is fed in from the side. As Phil pointed out earlier, they might be able to do that sort of thing during a rainstorm, or with sprinklers. If the paddy is empty there may be some easier way to map the contour with a flyover and a laser.
Other quad-copter, dragonfly dipper ideas:
1) A quad-copter carries around a hollow sphere containing an accelerometer, and the sphere is suspended on a thin supple data cable. The copter dips vertically at a controlled rate, the sphere hits the water, the cable goes slack, the sphere sinks, the logger records the time between the water impact and the impact on the bottom. The sphere has known buoyancy and sink rate.
2) A quad-copter carries around a 10cm long cylindrical capacitance probe on a supple cable as above. It dips the probe in the water and has some means (accelerometer) to detect when it hits the bottom. The probe is direct reading, fast. There must be means to hold the probe vertical or to compensate for deviations (accelerometer).
Operationally though, It's hard to imagine them sprinkling 200 or 300 of these around, take the aerial photo, and then pick them up and move them to the next paddy.
I was thinking they'd just be left in place permanently, unless they'd interfere with harvesting equipment.
Here's something a little different. It's build from two white (or blaze orange) floating rectangles, one black sinking square, and some thin, rigid material to connect them:
THAT is awesome. To take it a step further- position them throughout the pond, all over it, like you explained. Take the aerial photo and do as you've described. But afterwards, you can evaluate and group sets of plates showing the same depth, then eliminate the redundancies and use the known value of the volume of water they represented. This should eliminate a ton of the plates from the paddy. The plates that are left are all unique values which represent all the missing plates... and hence the volume of water for each group. If enough plates can be removed maybe there will be few enough of them to use something like an Xbee, distance sensor (to measure the distance between the plates) and solar power to report the distances to a base unit and allow for real time calculations of the volume of water in the paddy. That's assuming the contour of the bottom stays fairly constant, of course.
Once the paddy is full enough to cover all the islands the extra volume is just the extra depth times the surface area. At that point it doesn't make sense to scatter lots of fill sensors (or are they Phil(tm) sensors?) around the paddy. You just need a single depth measuring stick to determine the volume of the paddy. The problem then becomes being able to measure the volume at level0, where all the islands are just covered. This can be done with aerial photography correlated with simultaneous depth measurement at the deepest point in the paddy. This technique would require digging trenches to connect isolated depressions in the paddy so they fill uniformly with the rest of the paddy. An alternative to this is to build a device to monitor the volume of water that is added to an empty paddy as it is filled to volume0.
This measurement will happen prior to transplanting the seedlings, and the paddy tractors and equipment will subsequently roll over everything in their path and change the bottom contour. But by that time the treatment will have been made. The agricultural environment can be brutal. The vorpal blade went snicker-snack!
Dave, the volume Vo at the point where all the islands are just covered is key to a possible solution, I do see your point. I've been told that the paddy will never be empty near the time when have to apply the pesticide. But suppose it were possible to empty it. I'm still in the dark about how many islands and depressions there might be, and therefore how much work it would be to dig trenches between them. If one can assume that the percolation rate into the ground is constant across the area, then one might take the aerial photos and watch as the water disappears, with depth = k * time. I'm in the dark too about the typical variability (5 +/- ? cm) to expect in the bottom contour, or the accuracy expected of the measurement. With ~1cm uncertainty in ~5cm depth, the uncertainty in volume is ~20%.
I've heard that beer is good for control of snails. It is also a good fertilizer and root stimulant. Maybe they could use known volume of beer as the marker for a concentration assay?
And so, ever since the construction of the Egyptian pyramids, beer solves everything.
Having seen governmental support for agriculture at work in Taiwan, Thailand, and the USA, I expect that any place with a decent rice crop would have their own experts that would be quick to come up with a solution to optimize treatment and minimize costs to the farmer.
I am convinced that a mixture of the treatment and some tracer could be combined and a kit to test the concentration in the water would eliminate all the folly of trying to get the actual volume of water in the rice paddy. After all, it is the true target. So why not go directly after it?
Just consider if the tracer modified the pH of the water and did not affect the treatment, a simple pH test of the water before and after the treatment would pretty much do the trick. I suspect that you are always going to standby with extra stock of chemical to add if needed anyway.
BTW, the treatment is actually an alkali, so just measuring the pH may be all that is required without any added tracer.
I grew up on a wheat farm in Kansas, so I don't know much about rice farming. However, from what I can tell the paddies are dry during harvest and during the time that the ground is worked. Pesticides and fertilizer are applied after the paddy has been flooded, and the rice has already sprouted. The paddies are flooded prior to planting, and Vo can be determined at that time. The paddies are filled from a reservoir of water, so another way to measure Vo is to measure the reduction in volume of the reservoir to reach Lo. The surface area of the reservoir can be determined by aerial photography, or if it is rectangular it is just length times width. Vo is then just the reservoir surface area times the reduction in the depth to fill the paddy to Lo.
I think you're correct. If a known chemical is used, and we know our initial water supply used to fill the paddy has none of that chemical in it, then we only need to know the exact volume of chemical we put into the water. Suppose we add this chemical (say 10 gallons of it as an example) right when we first start filling the paddy, at a location such that the water flowing into the paddy causes extremely thorough agitation (titration) ... ie. we get it mixed up thoroughly.
When we stop filling the paddy (presumably because it's full) we sample and analyze the water in the paddy from a few different locations. We know we can determine the volume of water in the paddy because we have a certain ppm of the chemical in the water. I'd imagine it could be 98% accurate or better. The tricky part (for me, at least) is determining which chemical to use. It should have a few certain properties- stability at various temperatures, minimal evaporation rate, stable in the presents of whatever happens to be in the paddy beforehand, doesn't harm the rice crop, etc... just a plain ole stable trace compound we can measure.
I think a poly-phosphate would work for this, but I have no idea how it would affect the rice crop. I know that a few phone conversations with a local water testing lab would probably yield a great solution. Environmental Testing Solutions, Inc. is a semi-local one to me. They're all over the place.
Have not read all posts so if already been discussed then...
With the quad maybe have a landing gear that will keep the rest of it out of the water. That way just land it on the bottom then power down the motors to save power and take the readings ( depth,gps,battery life,etc) transmit them back and power up and go to the next spot.
If there is a mechanical or electrical issue then the quad itself stays out of the water and does not get damaged.
Along the lines of markers have a biodegradable pole with a base that gets wet and keeps the pole upright. The pole (of consistent length) would have markings along its length for gauging. Maybe also some markings for identification. Some high res photos to do the recording.
Comments
I've set up a raft to float on the surface and bounce ultrasound off the bottom.
There are strong standing waves set up in the container, but I need to try it in something with wide horizontal extent. I'd want the strongest standing wave to be the one directly below the raft. Really, this is just a curiosity, not practical I think.
It's not clear at this point if the project will be funded. They may have been looking for an off-the-shelf-high-tech-zero-R&D method. It may go back to a guy walking around with a gauge pole, perhaps with a data logger and sensor instead of a notepad.
However. the depth measurement scenario needs to be an inverse to what they used during WW2 as the raft travels on water surface while the light sources should be able to adjust their shining angle accordingly to the received and reflected from the bottom of rice paddies signal(s).
I envision 2 underwater light sources to shine from 1 foot apart at say 30 deg towards the movement of the raft. whereas the receiver light sensor(s) array to be located at raft's bow. Thus signal's feedback will adjust the shining angle(s) and allow to calculate water depth using some formula(s) ... but that's obviously to be left as an exercise for the students
Also, shooting ultrasound under water at certain angles can be seen in this example from Sontek...
-Phil
I wasn't thinking of adding the pre-mix to the infill, just putting enough additive to a known volume of water to get the required final concentration. If the tank or reservoir was not large enough to flood the entire paddy to the desired depth then mix in batches until the paddy is full. Adding pre-mix to the infill is a good idea if the flow rates are well controlled.
In case you're still contemplating it here's what I found in http://esemag.com/magazine.html see page 52
Cheers,
John
The project is waiting for a meeting next week.
I do have inklings of what is not possible. The situation is nowhere near as high tech as you might imagine.
-- The paddies are strung out and separated by mud barriers that are opened or closed by a Cat. There is no way to measure the water in and out, and there are sometimes unplanned blockages or releases. The flow rate is low, ~2 liter per second per hectare. Maybe a weir could be installed and instrumented. But there is no way in place to empty the paddy and then fill it with a known amount of water.
-- The concentration of the pesticide is very low ppm and cannot be monitored in real time. That requires an expensive and time consuming liquid chromatography column (reverse HPLC).
-- Only standing water is to be counted, not the water content of the mud. Compare with touching the bottom with the wide end of a T-shape probe stick. The mud is consolidated, but if you step on it, you sink in 20 to 30 cm.
I once had a cat. I'm glad somebody has figured out how to get one some use out of one. Every time I told mine to do something it would just look at me like I was some kind of idiot and go back to sleep.
Here's something a little different. It's build from two white (or blaze orange) floating rectangles, one black sinking square, and some thin, rigid material to connect them:
When positioned on the bottom, the separation of the two rectangles will vary, depending upon the depth of the water. With an array of these spread over the entire paddy, an aerial photo could be scanned to determine the depth at each location. Because the rectangles are of a known size, each station would be self-calibrating, regardless of aerial altitude or angle.
-Phil
What do you have in mind for the thin, rigid material? As I see it, the arms of the rigid V would come up through holes in the centers of the floating blocks (circular?), constraining their distance apart vs depth. Your diagram depicts an solid connection though from the bottom plate to the floating block, but how could the length of that connection change with depth?
I'd say 2 light beams (see my msg #96 - ex-Dam Busters idea) and no need to have any mechanical joints/floats - not ?
I was thinking of something that was loosely hinged to the top and bottom plates. Metal rods with loops in the end, connected to the flat pieces via screw eyes would work. You'd have to brace them X-fashion with fishing line, say, to keep the top plates from paralellogramming.
I'd be afraid that anything that slides might get jammed.
-Phil
Now that is ingenious. Simple to build using inexpensive materials, self calibrating, and easy to read. Also a great excuse to buy a quad/hex copter with a camera. Best idea to date IMHO.
Phil, I see what you mean. It could even be thin silicone rubber bands at top and bottom. The top pads could be round disks to avoid the parallelogram issue. Operationally though, It's hard to imagine them sprinkling 200 or 300 of these around, take the aerial photo, and then pick them up and move them to the next paddy. Now, if the bottom pad could drive around, while quad-copter with the camera hovers above...
1) A quad-copter carries around a hollow sphere containing an accelerometer, and the sphere is suspended on a thin supple data cable. The copter dips vertically at a controlled rate, the sphere hits the water, the cable goes slack, the sphere sinks, the logger records the time between the water impact and the impact on the bottom. The sphere has known buoyancy and sink rate.
2) A quad-copter carries around a 10cm long cylindrical capacitance probe on a supple cable as above. It dips the probe in the water and has some means (accelerometer) to detect when it hits the bottom. The probe is direct reading, fast. There must be means to hold the probe vertical or to compensate for deviations (accelerometer).
-Phil
THAT is awesome. To take it a step further- position them throughout the pond, all over it, like you explained. Take the aerial photo and do as you've described. But afterwards, you can evaluate and group sets of plates showing the same depth, then eliminate the redundancies and use the known value of the volume of water they represented. This should eliminate a ton of the plates from the paddy. The plates that are left are all unique values which represent all the missing plates... and hence the volume of water for each group. If enough plates can be removed maybe there will be few enough of them to use something like an Xbee, distance sensor (to measure the distance between the plates) and solar power to report the distances to a base unit and allow for real time calculations of the volume of water in the paddy. That's assuming the contour of the bottom stays fairly constant, of course.
Dave, the volume Vo at the point where all the islands are just covered is key to a possible solution, I do see your point. I've been told that the paddy will never be empty near the time when have to apply the pesticide. But suppose it were possible to empty it. I'm still in the dark about how many islands and depressions there might be, and therefore how much work it would be to dig trenches between them. If one can assume that the percolation rate into the ground is constant across the area, then one might take the aerial photos and watch as the water disappears, with depth = k * time. I'm in the dark too about the typical variability (5 +/- ? cm) to expect in the bottom contour, or the accuracy expected of the measurement. With ~1cm uncertainty in ~5cm depth, the uncertainty in volume is ~20%.
I've heard that beer is good for control of snails. It is also a good fertilizer and root stimulant. Maybe they could use known volume of beer as the marker for a concentration assay?
Having seen governmental support for agriculture at work in Taiwan, Thailand, and the USA, I expect that any place with a decent rice crop would have their own experts that would be quick to come up with a solution to optimize treatment and minimize costs to the farmer.
I am convinced that a mixture of the treatment and some tracer could be combined and a kit to test the concentration in the water would eliminate all the folly of trying to get the actual volume of water in the rice paddy. After all, it is the true target. So why not go directly after it?
Just consider if the tracer modified the pH of the water and did not affect the treatment, a simple pH test of the water before and after the treatment would pretty much do the trick. I suspect that you are always going to standby with extra stock of chemical to add if needed anyway.
BTW, the treatment is actually an alkali, so just measuring the pH may be all that is required without any added tracer.
I think you're correct. If a known chemical is used, and we know our initial water supply used to fill the paddy has none of that chemical in it, then we only need to know the exact volume of chemical we put into the water. Suppose we add this chemical (say 10 gallons of it as an example) right when we first start filling the paddy, at a location such that the water flowing into the paddy causes extremely thorough agitation (titration) ... ie. we get it mixed up thoroughly.
When we stop filling the paddy (presumably because it's full) we sample and analyze the water in the paddy from a few different locations. We know we can determine the volume of water in the paddy because we have a certain ppm of the chemical in the water. I'd imagine it could be 98% accurate or better. The tricky part (for me, at least) is determining which chemical to use. It should have a few certain properties- stability at various temperatures, minimal evaporation rate, stable in the presents of whatever happens to be in the paddy beforehand, doesn't harm the rice crop, etc... just a plain ole stable trace compound we can measure.
I think a poly-phosphate would work for this, but I have no idea how it would affect the rice crop. I know that a few phone conversations with a local water testing lab would probably yield a great solution. Environmental Testing Solutions, Inc. is a semi-local one to me. They're all over the place.
I still like Phils widget idea the best though!
With the quad maybe have a landing gear that will keep the rest of it out of the water. That way just land it on the bottom then power down the motors to save power and take the readings ( depth,gps,battery life,etc) transmit them back and power up and go to the next spot.
If there is a mechanical or electrical issue then the quad itself stays out of the water and does not get damaged.
Along the lines of markers have a biodegradable pole with a base that gets wet and keeps the pole upright. The pole (of consistent length) would have markings along its length for gauging. Maybe also some markings for identification. Some high res photos to do the recording.