It seems like all of the proposed solutions (including mine) are over-kill. The volume of water is just the average depth times the surface area. The paddy should be mostly level, and the complication occurs when the water level is low enough for "islands" to appear. I would assume that under normal conditions the water level is high enough that there are no islands. If depth0 is the minimum depth where there are no islands, then the volume at any time is ((depth - depth0)*area + volume0). volume0 can be measured by first emptying the paddy and letting the resulting puddles dry out, and then adding a measured amount of water back into the paddy until there are no islands.
Would GPS provide you with enough true detail? Are the bottoms of these paddies so uniform and smooth that you can interpolate a bottom with sufficient accuracy? Would people walking or machines moving around in them leave footprints deep and plentiful enough to account for a lot of volume that might not get accounted for?
I guess that the idea that all of California's rice goes to make Budweiser is an urban legend. It is seems Costco and others sell California rice for regualar use.
But there are certainly some growers that do supply Budweiser with their whole crop, send the straw to chicken farms, and bring back the waste to fertilize. One of the growers was a good friend and quite happy with the arrangement.
+++++++++++
Getting to the bottom of it all.
There is a real question of what you mean by 'the bottom' of a rice paddy. The top layer seems to be mostly silt that actually holds the rice plant. But under than is a harder layer that planters or machines that plant the rice walk on.. it also seems to be the water barrier. It could be an underlying strata of clay in some cases.
Rice consumes about 3 times the water than growing wheat requires. But supposedly, the actual amount of water that contributes to growth is about the same as wheat. The other 2/3 is used in the process of flooding the field in preparation for planting.
+++++++
Every rice paddy I looked at seems perfectly level. The flooding process seems to work along with a grading process where the farmers might drag a long board across the field to level the mud. It looks level, but nobody is bothering with a surveyor's transist to make sure. The main thing is that the paddies have an intricate layout for maximizing the use of water during the irrigation and the abilty to redirect water when there is too much or too little.
Phil,
Thanks for the tip about Rhino. That is what they'll have to do, app-specific interpolation between the points and compute the volume under that surface. Peano curve, too many turns!!
George,
They assure me they can start the measurements early in the morning when there is no wind. However, you know how that goes in practice. I like the hungry ducks! Not to mention the organic fertilizer for the rice. California rice fields are a haven for water birds, elsewhere too. Tor just posted a photo, and he commented about the heron's spiky feet not sinking in too deep.
Dave and ElecticAye
Interesting idea about taking a photo may in IR as the paddy fills or even after it is full. It will have a slight slope, less than 0.01% and less than that variation in smoothness.
Dave, yes, you'd think they would simply have to measure the volume of water they put in until there are no more islands, and given the surface area that gives them your depth0. That might work if the substrate is already saturated. I wonder what other factors might preclude that. Irrigation systems can easily measure volume flow.
The only thing that is cooler than rice fields in Japan, is the Daio Wasabi Farms. These are a 'must see' if you can. And the wasbi ice cream is great as well. I would love to get another visit to Japan soon.
As their head explodes, some might take issue with, "Wasabi root is often grated and eaten as spice. It provides excellent mild flavor to Japanese cuisine. "! I like it myself, and know how to pace it!
Kwinn, I like the idea of using the high torque motor from an electric screwdriver, for a proto anyway. Do you, and robot and watercraft builders, have other suggestions about motors and about bushings and housings to keep them dry? Assuming that it is a wheeled vehicle.
I'd like to pitch my idea again, combined with points Dave Hein has made and the aerial ideas.
Since there should be no "islands" in the paddy at its lowest level of 4cm the body of water is contiguous.
The use of a pressure transducer to determine the height of the water above the sensor combined with the area of the body can get you ballpark height. Averages and what not for slopes on the floor can be used.
To get the area of the body send a quad up with a camera and use ground based scale markers for an image that can be used to calculate the area.
Correlate pressure and temperature for density of the fluid, use height and area for volume.
After that dose with a mild dye or other compound that can be used as a volumetric ratio check and adjust the calculated value for volume accordingly.
Tracy,
In regards to protecting motors in a wet environment, I like the magnetic drive solution. In this case motor is enclosed and wheels etc driven with magnetic coupling thru the case.
Jim
I once made a snow depth "sensor" from a painted pole and the optical line sensor (parallax 28317) by measuring the length not covered I was able to determine snow depth. it seems to me that a similar method could be used in a rice patty. Stick a bunch of poles in the patty and do the measuring optically and transmit the resulting measurements via a wireless link.
I think this could become an interesting case study in the pragmatics of design and deployment of a technical solution.
On the one hand, the device or devices have to easy to use, cost effective, and durable. On the other hand, all the variables that affect precision have to be identified.
Meanwhile, I have been enjoying the link to the live camera of the Japanese Alps and the Matsumoto Samurai Castle.. during daytime hours. (Right now these show almost nothing.)
@Ray0665
That... is actually a brilliant solution. Much easier than measuring the water depth each and every time. Do it once, when you stick the poles into the bottom (which can as well be done when the field is still dry). After that you simply look at where the waterline is on the stick. As Loopy and some others noted, rice paddies are not that uneven and you shouldn't need more than a few poles to have good enough coverage.
That gets back to the starting point, the way they do it now. Two guys walk around and take some 50 measurements with a gaging stick, and from that come up with a volume. Or one guy makes one measurement at what he considers a representative location, and that's it, simple, area times depth. Trouble is, the estimate is often +/-50% off due to variations of the bottom contour in the shallow water. I appreciate all the comments and ideas, and it has raised a lot of questions and doubts that I really need to run by the people who want to do this project. For one thing, I don't really know how they have decided that it is +/-50% off. Was that by dilution tests? By metering the incoming irrigation water? What is the gold standard?
How many poles would be good enough coverage? I don't know. Ask Mr. Nyquist. Highest contour frequency lower than the distance constant of the poles or the wheels of the paddy wagon. Undoubtedly overkill, with a few assumptions. I suppose each pole would be driven in right to its zero mark at ground level, so each pole would indicate its local depth. It might not be possible to leave poles in place, due to machinery in use.
The survey from the air is interesting. A time lapse showing which areas fill first and then up to the final islands might give a contour map, provided the shallow water behaves itself and really finds a level rather than sticking here and there.
I really wonder if the actual cause of the 50% error is not identified properly.
In a rice paddy, you have a layer of soft mud over a hard bottom that can actually hold quite a bit of water. I am still not clear if that layer is affecting the readings. But if it is, it should not be a +/- variation... it would be consistent in one direction.
That's why you need to know the volume at the point when the water just covers all the islands, which can be determined by measuring the amount of water used to fill an empty paddy to that point. Measure the depth at that point, and then anything above that is just depth*area. The depth measurement point doesn't even need to be in the paddy. It can be somewhere along the perimeter, where a PVC pipe connects to the paddy.
EDIT: If you want to make sure that the water absorbed in the mud is accounted for, the volume0 measurement may taken over a period of several days. This would require accounting for evaporation and/or rain. This could be done by having a container filled with water where you could measure the change in level due to evaporation or rain. I've used this method to determine if the slowly dropping level in my swimming pool was due to evaporation or a leak. However, if the paddy is very leaky this method wouldn't work.
Well, an 'empty' or 'dry' rice paddy might be a perfect starting point. But in the real world, I have doubts that the soil can ever be perfectly dry or the paddy has no retained water. Rice depends on the soft muddy overburden of muck to stand up straight when first planted. It is very different from a corn or a wheat field that is seeded as it is a transplant process.
In other words, I don't see any means of getting a good starting point for many of the proposals.. The best way might be to have a 'tracer' of some sort mixed in with the chemical treatment that could verify that the right concentration has been reached. If the concentration is too low... add more chemical. If too high, drain off some into another field and dilute with fresh water.
I also wonder if the treatment actually is failing because it only involves the paddy and not the surrounding embankments. The snails can be everywhere.. including the embankments and in the irrigation canals.
Have you ever tried to get rid of aquatic snails in an aquarium once they take over? It is quite a challenge to do so without killing all the fish or at least transferring the fish to a holding tank while you dump the tank and start over.
The survey from the air is interesting. A time lapse showing which areas fill first and then up to the final islands might give a contour map, provided the shallow water behaves itself and really finds a level rather than sticking here and there.
Excellent point. If there are mounds with recesses, the recesses will not fill until the mounds are breached. Then they will fill suddenly. So those recesses will be entirely missed in any inferred contour map.
It's not as if you're filling the paddy uniformly from above, as in a rainstorm, but more likely from one corner with a hose.
The starting point is to start with a paddy that is full of water. Empty out the water. Then refill the paddy and measure the amount of water needed to fill it. The tricky part is to account for the low parts where water puddles after it is empty. That might be accomplished running hoses out to the puddles to empty them, or by using areal photography and determining an "average" level for each of the puddle to compute the remaining volume.
In southeast Texas, don't know about rest of the U.S., rice is planted by airplane. The field is flooded then a plane spread the seeds. Field size is hundreds of acres, an order of magnitude greater than the 4 hectare paddy under consideration. There was one farmer when I was growing up, 50 years ago, that used a seed drill like those used for planting wheat. Just saw a picture of planting by plane on the Cal Rice site.
John Abshier
PS When I was in Vietnam (1970-71) I was struck by how similar the area between Saigon and the Cambodian border was to the coastal plain of southeast Texas. The farming methods were at opposite ends of the capital-labor axis.
It figures Texas would have rice paddies 10x bigger than anywhere else! USDA figures say Arkansas is the U.S. largest producer, followed by California, Louisiana, Mississippi, Missouri and Texas. But the U.S.A produces only 2% of the world's rice.
I wondered about that 7 second video on the Calrice web site, an airplane moving so fast over a paddy that its hard to imagine it was dropping seed. My understanding is that rice is first seeded at high density in nursery beds, and then transplanted as healthy seedlings with 4 or 5 leaves to the paddy. It is the paddy they want to gage, just before transplanting occurs.
Transplantation is what I saw in Vietnam and have seen in pictures from other parts of Asia usually in small paddies. But when I was growing up (my grandfather lived across the road from a rice field) planes were used for seeding, fertilizing, and spreading herbicides. I don't get back to that part of Texas often. Many farmers in the area have moved from rice to soybeans.
................................However, just about any ultrasound concept is that xmtrs have a dead zone of approx. 30cm.
I was tempted to measure the depth of water in a tank using a speaker and microphone as an oscillator. In theory the feedback frequency should be inversely proportional to the distance between the water and the speaker/microphone. Unfortunately there was a time constraint on the project so I had to pass on the idea. Have to revisit the idea some time.
I wonder if a similar idea would work for measuring depth. One approach would be similar to the speaker/microphone measurement of the frequency of oscillation, the other would be to sweep the transmitted frequency, mix it with the reflected frequency that is received, and use the resulting frequency to calculate the depth.
Ultrasound was my first thought too, either using MHz as in medical imaging, and/or using phase measurement or a standing wave (resonance) rather than time for an echo pulse. Sound travels 4.33 times faster in water than it does in air, and the wavelength is therefore 4.33 times longer. Take a water depth of 4cm. 1484m/s / 0.04m = 37.1kHz to a full wavelength. In air that would be 343 / 0.04 = 8.575 kHz. The inverse problem necessary for medical imaging is awful, however, in this case the substrate to 1st approx. is a simple hard(?) plane. Both the top and bottom surfaces are huge impedance mismatches, so a strong standing wave is to be expected.
I was wondering what to use as a transducer. I happened to have 25kHz sealed piezo air transducers left over from another project. That is the kind in a teflon-coated aluminum case, and the piezo element is bonded to the inside face, which resonates like a drumhead matched to the piezo. Resonance of those things is very sharp with very little response at other frequencies.
Yesterday I put a couple of them as a quick experiment in water in a tub about 4cm deep, and found a strong resonance at 38.5kHz. Wow, nothing at 25kHz. The surprising thing was that there were strong resonances to be found all the way up to 300kHz. It stands to reason in a way. The impedance match from the piezo to the dense water is much better than it is to the thin air.
At these short distances, if you use two transducers, be sure to include the distance between them in your depth computations. This tripped me up with an ultrasonic project I'm working on. 'Couldn't figure out why stuff that was really close was reading further away than it should. D'oh!
No, I tried it at the end of the day and had to get home for dinner. Really crude. Transducers in alligator clips hanging face down over the edge of the plastic tub. One transducer to the signal generator and scope H-sync, and the receiving xducer to channel A of the 'scope. I'll make a little raft and be more scientific about it and use a larger tub with anechoic side walls to simulate a bigger pond. Good point about the longer signal path, Phil, but it's not there yet. A lot was going on with the signal. A barely imperceptible ripple in the water surface caused quite large fluctuations on the 'scope.
Interesting problem. I've been doing some work with Senix ultrasonic sensors in Vermont. The ones I have give a very good, easily calibrated analog signal with trip points, adjustable filtering as well.
What I picture is a wheel (picture a wheelbarrow with a bicycle wheel) with sensor suspended out in front at known distance from the bottom of the wheel. The water level is somewhere in between. Some sort of visual feedback lets the operator keep the sensor interface level. Maybe a gimbal or even gyro. The operator would move across the field, automatically taking readings coordinated to gps. The sensor would indicate the biggest distance if the wheel rises on the subsurface and the smallest distance if the wheel enters a low spot.
Could use wireless from the field device back to the guy on shore so only one researcher gets wet at a time.
Comments
But there are certainly some growers that do supply Budweiser with their whole crop, send the straw to chicken farms, and bring back the waste to fertilize. One of the growers was a good friend and quite happy with the arrangement.
+++++++++++
Getting to the bottom of it all.
There is a real question of what you mean by 'the bottom' of a rice paddy. The top layer seems to be mostly silt that actually holds the rice plant. But under than is a harder layer that planters or machines that plant the rice walk on.. it also seems to be the water barrier. It could be an underlying strata of clay in some cases.
Rice consumes about 3 times the water than growing wheat requires. But supposedly, the actual amount of water that contributes to growth is about the same as wheat. The other 2/3 is used in the process of flooding the field in preparation for planting.
+++++++
Every rice paddy I looked at seems perfectly level. The flooding process seems to work along with a grading process where the farmers might drag a long board across the field to level the mud. It looks level, but nobody is bothering with a surveyor's transist to make sure. The main thing is that the paddies have an intricate layout for maximizing the use of water during the irrigation and the abilty to redirect water when there is too much or too little.
Thanks for the tip about Rhino. That is what they'll have to do, app-specific interpolation between the points and compute the volume under that surface. Peano curve, too many turns!!
George,
They assure me they can start the measurements early in the morning when there is no wind. However, you know how that goes in practice. I like the hungry ducks! Not to mention the organic fertilizer for the rice. California rice fields are a haven for water birds, elsewhere too. Tor just posted a photo, and he commented about the heron's spiky feet not sinking in too deep.
Dave and ElecticAye
Interesting idea about taking a photo may in IR as the paddy fills or even after it is full. It will have a slight slope, less than 0.01% and less than that variation in smoothness.
http://welcome.city.matsumoto.nagano.jp/contents03+index.id+15.htm
Kwinn, I like the idea of using the high torque motor from an electric screwdriver, for a proto anyway. Do you, and robot and watercraft builders, have other suggestions about motors and about bushings and housings to keep them dry? Assuming that it is a wheeled vehicle.
Since there should be no "islands" in the paddy at its lowest level of 4cm the body of water is contiguous.
The use of a pressure transducer to determine the height of the water above the sensor combined with the area of the body can get you ballpark height. Averages and what not for slopes on the floor can be used.
To get the area of the body send a quad up with a camera and use ground based scale markers for an image that can be used to calculate the area.
Correlate pressure and temperature for density of the fluid, use height and area for volume.
After that dose with a mild dye or other compound that can be used as a volumetric ratio check and adjust the calculated value for volume accordingly.
In regards to protecting motors in a wet environment, I like the magnetic drive solution. In this case motor is enclosed and wheels etc driven with magnetic coupling thru the case.
Jim
On the one hand, the device or devices have to easy to use, cost effective, and durable. On the other hand, all the variables that affect precision have to be identified.
Meanwhile, I have been enjoying the link to the live camera of the Japanese Alps and the Matsumoto Samurai Castle.. during daytime hours. (Right now these show almost nothing.)
And we do have a live camera of an active rice field for anyone that cares to observe.
http://tanbo-art.com/tanbo/ <++ the live camera of an active rice field.
http://yamagatakanko.com.e.db.hp.transer.com/log/?l=281817
http://youkoso.city.matsumoto.nagano.jp/special3_index-id_74-htm
http://www.city.matsumoto.nagano.jp/live/livecamera.html
That... is actually a brilliant solution. Much easier than measuring the water depth each and every time. Do it once, when you stick the poles into the bottom (which can as well be done when the field is still dry). After that you simply look at where the waterline is on the stick. As Loopy and some others noted, rice paddies are not that uneven and you shouldn't need more than a few poles to have good enough coverage.
-Tor
How many poles would be good enough coverage? I don't know. Ask Mr. Nyquist. Highest contour frequency lower than the distance constant of the poles or the wheels of the paddy wagon. Undoubtedly overkill, with a few assumptions. I suppose each pole would be driven in right to its zero mark at ground level, so each pole would indicate its local depth. It might not be possible to leave poles in place, due to machinery in use.
The survey from the air is interesting. A time lapse showing which areas fill first and then up to the final islands might give a contour map, provided the shallow water behaves itself and really finds a level rather than sticking here and there.
In a rice paddy, you have a layer of soft mud over a hard bottom that can actually hold quite a bit of water. I am still not clear if that layer is affecting the readings. But if it is, it should not be a +/- variation... it would be consistent in one direction.
EDIT: If you want to make sure that the water absorbed in the mud is accounted for, the volume0 measurement may taken over a period of several days. This would require accounting for evaporation and/or rain. This could be done by having a container filled with water where you could measure the change in level due to evaporation or rain. I've used this method to determine if the slowly dropping level in my swimming pool was due to evaporation or a leak. However, if the paddy is very leaky this method wouldn't work.
In other words, I don't see any means of getting a good starting point for many of the proposals.. The best way might be to have a 'tracer' of some sort mixed in with the chemical treatment that could verify that the right concentration has been reached. If the concentration is too low... add more chemical. If too high, drain off some into another field and dilute with fresh water.
I also wonder if the treatment actually is failing because it only involves the paddy and not the surrounding embankments. The snails can be everywhere.. including the embankments and in the irrigation canals.
Have you ever tried to get rid of aquatic snails in an aquarium once they take over? It is quite a challenge to do so without killing all the fish or at least transferring the fish to a holding tank while you dump the tank and start over.
Excellent point. If there are mounds with recesses, the recesses will not fill until the mounds are breached. Then they will fill suddenly. So those recesses will be entirely missed in any inferred contour map.
It's not as if you're filling the paddy uniformly from above, as in a rainstorm, but more likely from one corner with a hose.
-Phil
John Abshier
PS When I was in Vietnam (1970-71) I was struck by how similar the area between Saigon and the Cambodian border was to the coastal plain of southeast Texas. The farming methods were at opposite ends of the capital-labor axis.
I wondered about that 7 second video on the Calrice web site, an airplane moving so fast over a paddy that its hard to imagine it was dropping seed. My understanding is that rice is first seeded at high density in nursery beds, and then transplanted as healthy seedlings with 4 or 5 leaves to the paddy. It is the paddy they want to gage, just before transplanting occurs.
John Abshier
One such company http://www.airmartechnology.com/2009/survey/product-results.asp has submersible devices to play with.
However, just about any ultrasound concept is that xmtrs have a dead zone of approx. 30cm.
I was tempted to measure the depth of water in a tank using a speaker and microphone as an oscillator. In theory the feedback frequency should be inversely proportional to the distance between the water and the speaker/microphone. Unfortunately there was a time constraint on the project so I had to pass on the idea. Have to revisit the idea some time.
I wonder if a similar idea would work for measuring depth. One approach would be similar to the speaker/microphone measurement of the frequency of oscillation, the other would be to sweep the transmitted frequency, mix it with the reflected frequency that is received, and use the resulting frequency to calculate the depth.
I was wondering what to use as a transducer. I happened to have 25kHz sealed piezo air transducers left over from another project. That is the kind in a teflon-coated aluminum case, and the piezo element is bonded to the inside face, which resonates like a drumhead matched to the piezo. Resonance of those things is very sharp with very little response at other frequencies.
Yesterday I put a couple of them as a quick experiment in water in a tub about 4cm deep, and found a strong resonance at 38.5kHz. Wow, nothing at 25kHz. The surprising thing was that there were strong resonances to be found all the way up to 300kHz. It stands to reason in a way. The impedance match from the piezo to the dense water is much better than it is to the thin air.
-Phil
Interesting problem. I've been doing some work with Senix ultrasonic sensors in Vermont. The ones I have give a very good, easily calibrated analog signal with trip points, adjustable filtering as well.
What I picture is a wheel (picture a wheelbarrow with a bicycle wheel) with sensor suspended out in front at known distance from the bottom of the wheel. The water level is somewhere in between. Some sort of visual feedback lets the operator keep the sensor interface level. Maybe a gimbal or even gyro. The operator would move across the field, automatically taking readings coordinated to gps. The sensor would indicate the biggest distance if the wheel rises on the subsurface and the smallest distance if the wheel enters a low spot.
Could use wireless from the field device back to the guy on shore so only one researcher gets wet at a time.
Cheers,