JP2006308433A - Soil water moving speed deriving method and soil water moving speed measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for simply deriving a soil water moving speed at once while dispensing with considerable computer resources. <P>SOLUTION: This soil water moving speed deriving method is a method for deriving the moving speed of water in soil. Two temperature sensors 21 and 23 and a heater 22 are aligned in the order of the temperature sensor 21, heater 22, and temperature sensor 23, in a straight line along the moving direction of the water in the soil which is a measurement place, and two temperature measurement terminals 21 and 23 are aligned within a distance allowing them to sense heat conduction based on the ON-OFF of the heater 22. The thermal diffusion coefficient k (constant) previously measured of the relevant soil is used to find thermal flux V in the relevant soil based on expression (1) expressed in the form of differentiation. This thermal flux V and the heat capacity C<SB>s</SB>(constant) previously measured of the relevant soil are used to derive the moving speed of the water in the relevant soil based on expression (2). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a soil water movement speed derivation method and a soil water movement speed measurement apparatus, and more particularly, to a soil water movement speed derivation method and a soil water movement speed measurement apparatus capable of monitoring the water movement speed only at one measurement point. .

  In agriculture and environmental engineering, it is extremely important to know the speed of water movement in the soil. For example, in the field of agriculture, it is important to know whether fertilizers have been used effectively for growing crops or whether fertilizers have flowed into groundwater. Also, in the field of environmental engineering, if a pollutant leaks into the soil, whether the soil pollutant is moving or not, how many years will it take to reach the groundwater area? It is important to know.

  In order to measure the movement of water, conventionally, a speed deriving method based on Darcy's law in which probes are inserted at two locations separated by several tens of centimeters and multiplied by a hydraulic conductivity is known. In addition, a method based on a heat pulse method is known in which a heat pulse is emitted from a heater and a temperature rise and fall at a location several millimeters apart is measured to obtain a water velocity.

JP 2003-329625 A Y.mori, et al 'Multi-Functional Heat Pulse Probe for the Simultaneous Measurement of Soil Water Content, Solute Concentration, and Heat Transport Parameters' Published in Vadose Zone Journal 2: 561-571 (2003)

However, the conventional technique has the following problems.
That is, in most cases, the water in the soil flows from vertically upward to vertically downward, and in the method based on Darcy's law, it is necessary to insert at least one of the two probes in a deep place, which is troublesome. was there.

  In addition, this method has a problem in principle that the non-linearity and spatial variability of the hydraulic conductivity are strong, and the accuracy is not necessarily high whether the obtained numerical value is close to the true value.

  Further, the method based on the heat pulse method solves the above-mentioned problems, but requires a great amount of computer resources because the equation to be solved is an integral form expressed by Equation (3). There was a problem. That is, in order to obtain one solution (flow velocity at one measurement point), it is necessary to calculate for several minutes or more using dedicated software, and monitoring (immediate measurement) is practically impossible. was there. In particular, soil monitoring often needs to be evaluated at several tens of locations, and this problem becomes even more pronounced.

  This invention is made | formed in view of the above, Comprising: It aims at providing the method which can derive | lead-out the soil water movement speed instantly simply without requiring a great amount of computer resources.

  Moreover, it aims at providing the portable apparatus which can monitor the soil water moving speed simply.

In order to achieve the above object, the method for deriving the soil water movement speed according to claim 1 is a method for deriving the water movement speed J in the soil, and the direction of water movement in the soil as the measurement location The two temperature measurement terminals and the heat source terminal are placed on a straight line along the line, in the order of the temperature measurement terminal-the heat source terminal-the temperature measurement terminal, and within a distance in which heat conduction based on ON / OFF of the heat source terminal can be sensed. Two temperature measurement terminals are arranged, and the heat diffusion coefficient κ (constant) of the soil that has been measured in advance is used to obtain the heat flux V in the soil based on the expression (1) expressed in the differential form. Using the heat flux V and the heat capacity C _s (constant) of the soil that has been measured in advance, the water movement speed J of the soil is derived from Equation (2).

ただし、
Ｔ_ｕ：上流側温度測定端子の位置における温度
Ｔ_ｄ：下流側温度測定端子の位置における温度
ｘ_ｕ：上流側温度測定端子と熱源端子との間隔（定数）
ｘ_ｄ：下流側温度測定端子と熱源端子との間隔（定数）
ｔ ：時間
ｔ_０：熱源端子における熱の印加時間（定数）

However,
T _u : temperature at the position of the upstream temperature measurement terminal T _d : temperature at the position of the downstream temperature measurement terminal x _u : interval between the upstream temperature measurement terminal and the heat source terminal (constant)
x _d : Distance between the downstream temperature measurement terminal and the heat source terminal (constant)
t: time t ₀ : heat application time (constant) at the heat source terminal

ただし、
Ｃ_ｗ：水の熱容量（定数）

However,
C _w : heat capacity of water (constant)

In other words, the invention according to claim 1 can simplify the analytical expression so that it can be expressed in the differential form by arranging the terminals on a straight line along the direction of movement of the water, and the number of calculations is significantly reduced compared to the integral form. It becomes possible to make it. In addition,
C _s = c _s ρ _s + c _w ρ _w θ
C _w = c _w ρ _w
C _s and c _w represent the specific heat of the soil and the density of water, and ρ _s and ρ _w represent the density of the soil and the water, respectively (specific numerical examples will be described later). Further, θ is a moisture content per volume (volume moisture content) contained in the soil, and is a value that varies depending on the experimental situation. In addition, C _w is not safely be treated as a constant, because it is also required as a number of enclosed people in relation to C _s, there is no particular need to be aware of the moisture content of the soil in practice. Incidentally, the heat capacity C _s and the diffusion coefficient κ is a value obtained for each experiment.

Moreover, the soil water moving speed measuring device according to claim 2 is a device for measuring the water moving speed J in the soil, exposed to the outside, and in a straight line, the temperature measuring terminal-the heat source terminal-the temperature measuring terminal. A heat source terminal and two temperature measurement terminals arranged in this order, a heat source control unit for controlling the heat source terminal to generate heat for a predetermined time t ₀ , and a thermal diffusion coefficient κ (constant of the soil) measured in advance ) And the heat capacity C _s (constant) of the soil based on the equations (1) and (2) expressed in a differential format, And an output unit for outputting the calculated moving speed J.

  In other words, the invention according to claim 2 can simplify the analytical expression so that it can be expressed in the differential form by arranging the terminals on a straight line along the direction of movement of the water, and the number of calculations is significantly reduced compared to the integral form. Therefore, the part responsible for the analysis can be made into a chip, and the size including the control unit can be made small and portable.

  In the present application, for example, a plurality of temperature measurement terminals are provided in a direction perpendicular to the direction in which the temperature measurement terminal, the heat source terminal, and the temperature measurement terminal are aligned (for example, both sides across the straight line), and the water movement direction. It is also included in the description in the claims that “the temperature terminals are arranged on a straight line along the direction of movement of water” in the claims. This is because, in principle, only the movement direction is corrected, and this is equivalent to the present invention for calculating the speed J along the movement direction.

  According to the soil water movement speed derivation method of the present invention (Claim 1), by arranging terminals on a straight line in a direction along the water movement direction, the analytical expression can be simplified so that it can be expressed in a differential form, and an integral form Since the number of calculations can be remarkably reduced as compared with the above, it is possible to easily and immediately derive the soil water movement speed without requiring a large amount of computer resources.

  Moreover, the soil water movement speed deriving method of the present invention (Claim 2) can simplify the analytical expression so that it can be expressed in a differential form by arranging terminals on a straight line in the direction along the water movement direction. Since the number of calculations can be remarkably reduced as compared to the above, the portion responsible for the analysis can be made into a chip, and the size including the control unit can be made small and portable. Thereby, the soil water movement speed can be easily monitored.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a configuration example of a monitoring apparatus according to the present invention. As illustrated, the monitoring device 1 includes a probe unit 2, a cable unit 3, and an analysis display unit 4. The probe unit 2 is composed of terminals arranged on three straight lines. These are the temperature sensor 21, the heater 22, and the temperature sensor 23, respectively.

  A cable part 3 extends from the probe part 2, and a socket 31 that can be connected to the analysis display part 4 is formed at the other end of the cable part 3. The probe unit 2 and the cable unit 3 are embedded in the ground to be monitored, for example, 30 cm. The probe unit 2 is embedded in the ground so that the cylinder is horizontal, that is, the tips of the temperature sensor 21, the heater 22, and the temperature sensor 23 are aligned in the vertical direction. This is because, as will be described later, these terminals need to be arranged along the flow of water, but the Vadose Zone (the soil layer from the surface to the groundwater surface) including the underground In most cases, the water flow is vertical.

  The analysis display unit 4 includes a socket receiver 41 that is an insertion port of the socket 31, a display unit 42 that displays the moving speed of water, an analysis unit 44 that does not appear in the figure, a control unit 43, a power supply 45, Is provided. FIG. 2 is a block diagram showing a functional configuration of the monitoring apparatus 1 with the analysis display unit 4 as the center. The control unit 43 controls heat ON / OFF of the heater 22 via the cable unit 3. Further, the control unit 43 acquires temperature information from the temperature sensor 21 and the temperature sensor 23. The analysis unit 44 derives the moving speed of the water in the soil in which the probe unit 2 is embedded, from the heating time of the heater 22 driven by the control unit 43 and the acquired temperature information. The analytical calculation used for derivation will be described later. The obtained moving speed is displayed on the display unit 42.

  With such a configuration, it is possible to monitor the water movement speed at each measurement point in sequence by the measurer carrying only the analysis display unit 4 and connecting the socket 31 exposed to the ground from the measurement point. Depending on the mode of use, the analysis display unit 4 is connected to all measurement points, a recording unit is provided instead of the display unit 42, and the moving speed of water is measured periodically by the control unit 43. You may make it record on a recording part. This enables long-term monitoring (daily changes, seasonal changes).

  Next, the analysis unit 44 will be described. The inventors of the present application have found that an analysis method related to the moving speed of water, which has been conventionally expressed only in an integral form, can be expressed in a differential form when the monitoring apparatus 1 is used under a predetermined condition.

  Conventionally, V has been obtained by analyzing equation (3). However, when it is based on the one-point method, the reliability of the result may be low due to the influence of noise, or a better result by the optimized identification method. There was a problem that it took too much time to derive.

  That is, the inventors of the present invention conventionally replaced the method of analyzing the upstream and downstream temperature changes represented by Equation (3) with the temperature change of the upstream temperature sensor and the downstream temperature sensor. The present invention has been conceived based on the discovery that it is more advantageous for calculation both in terms of accuracy and calculation time to grasp each temperature change as a temperature change rate.

  Specifically, the inventors of the present application firstly formula (4) defining the change in the temperature Td of the downstream temperature sensor 23 and formula (5) defining the temperature change Tu of the upstream temperature sensor 21. Was time-differentiated to derive Equation (6) and Equation (7), and these were divided to arrive at Equation (1).

  As can be seen from the expression of equation (1), equation (1) does not depend on the heat q applied to the heater. In the past, the heat of the heater was calculated by accurately measuring the current flowing through the circuit and multiplying it by the resistance value of the heater. However, there are many cases where the applied heat quantity q cannot be measured accurately, which is a problem of the conventional method. It was the cause. In addition, even if the heat applied to the heater is accurately obtained electrically, the heat applied to the soil will actually differ if there is a heat loss in the heater structure, and the heat flux is calculated from the absolute value. In the conventional method (3), which must be done, it is assumed that the surrounding work including the heater is also perfect.

  On the other hand, regardless of heat loss, heat propagation centered on the heater can be assumed to be the same for upstream and downstream (apart from the influence of water flow). The inventors of the present application have made the idea of the present invention by making use of this assumption to the maximum and studying a method that does not require the grasp of the absolute value q.

  Next, a verification experiment using the monitoring device 1 was performed. In the verification, a multi-step outflow test was conducted, and the actual flow rate value was compared with the analysis result using the monitoring device 1.

  FIG. 3 is a diagram showing a schematic configuration of this experimental system. In a very simple way, this is a device that fills a cylindrical container with sand from the Tottori Dune, drops water from the top, and measures the water movement speed as an actual measurement value based on the amount of water dropped from the bottom. is there. A probe portion 2 is inserted into the cylindrical container so that the flow velocity can be calculated numerically separately. In addition, the result of having adjusted the time which drops a water droplet from the upper part, and measuring the amount dripped from the lower part (drainage amount) is shown in FIG. As shown in the figure, it was decided to drop mainly after 250 minutes, 500 minutes, 1000 minutes, and 1700 minutes from the start of the experiment. In addition, the time when the amount of drainage does not change is the time when the movement of water does not occur.

The distances between the temperature sensor 21 and the heater 22 and the temperature sensor 23 and the heater 22 in the probe unit 2 used were adjusted to 6.00 mm, and the heater heating time t ₀ was 8 seconds. . FIG. 5 is a diagram showing the change over time in the temperature difference between the upstream temperature sensor (temperature sensor 21) and the downstream temperature sensor (temperature sensor 22) before heating the heater. As shown in the figure, the temperature sensor on the downstream side shows a high peak because a lot of heat is efficiently propagated by the water flow.

In addition, the thermal diffusion coefficient κ of the soil in this experiment is 6.5 × 10 ⁻⁷ [m ² s ⁻¹ ], the specific heat c _s = 0.795 [Jg ⁻¹ K ⁻¹ ], filling The density ρ _{s is} 1.63 [g · cm ⁻³ ]. These numerical values were previously measured prior to the experiment. Further, c _w = 4.18 [Jg ⁻¹ K ⁻¹ ] was used as the specific heat of water, and ρ _w = 0.998 [g · cm ⁻³ ] was used as the density.

FIG. 6 is a diagram showing the relationship between the flow velocity measurement result (calculated value) by the monitoring device 1 and the actual measurement value with various dropping speeds. As can be seen from the figure, it was confirmed that the results of the monitoring device and the actual measurement values were very close in terms of absolute values. In other words, the monitoring device 1 has a water moving speed of at least 0.1 to 27 [m / day] (1.15 × 10 ^{−6 to} 3.13 × 10 ⁻⁴ [m / day). If it is in the range of s]), it can be said that the result is sufficiently reliable.

  The measurement result obtained by the monitoring apparatus 1 can be obtained in a few seconds, whereas the conventional method uses CPU = 2.4 GHz, RAM = 512 MB, and analysis-dedicated software MATCAD 11 (Mathsoft Engineering & Education (USA)). 2 to 3 minutes were required. Also from this point, it can be said that the monitoring device 1 is superior to the conventional method from the viewpoint of size, analysis time, and cost.

  Note that the above is an analysis in a so-called saturated system, that is, a system in which only water is filled between sediments. Similarly, it was confirmed that measurement was possible.

  By using the present invention, it is possible to know an efficient fertilization timing in agriculture and to evaluate an effective fertilization amount. Further, if the present invention is used, for example, contamination monitoring can be performed around a chemical factory.

It is the figure which showed one structural example of the monitoring apparatus of this invention. It is a block diagram showing the functional structure of the monitoring apparatus centering on the analysis display part. It is the figure which showed schematic structure of this experimental system. It is the figure which showed the mode of dripping in this experimental system. It is the figure which showed the time-dependent change of the temperature difference before a heater heating of an upstream temperature sensor and a downstream temperature sensor. It is the figure which showed the relationship between the flow velocity measurement result by a monitoring apparatus, and a measured value, shaking various dropping speeds.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Monitoring apparatus 2 Probe part 3 Cable part 4 Analysis display part 21 Temperature sensor 22 Heater 23 Temperature sensor 31 Socket 41 Socket receptacle 42 Display part 43 Control part 44 Analysis part 45 Power supply

Claims (2)

A method for deriving a movement speed J of water in soil,
Two temperature measurement terminals and a heat source terminal are placed on a straight line along the direction of movement of water in the soil, which is the measurement location, in the order of the temperature measurement terminal, the heat source terminal, and the temperature measurement terminal, and the heat source terminal is turned on and off. Line up two temperature measuring terminals within a distance that can sense heat conduction based on
Using the thermal diffusion coefficient κ (constant) of the soil that has been measured in advance, the heat flux V in the soil is determined based on the equation (1) expressed in the differential form,
Using this heat flux V and the heat capacity C _s (constant) of the soil that has been measured in advance, the water movement speed J of the soil is derived from Equation (2). Derivation method.

T _u : temperature at the position of the upstream temperature measurement terminal T _d : temperature at the position of the downstream temperature measurement terminal x _u : interval between the upstream temperature measurement terminal and the heat source terminal (constant)
x _d : Distance between the downstream temperature measurement terminal and the heat source terminal (constant)
t: time t ₀ : heat application time (constant) at the heat source terminal

C _w : heat capacity of water (constant) A device for measuring the speed of movement J of water in the soil,
A heat source terminal and two temperature measurement terminals that are exposed to the outside and arranged in the order of temperature measurement terminal-heat source terminal-temperature measurement terminal in a straight line;
A heat source controller that controls the heat source terminal to generate heat for a predetermined time t ₀ ;
Based on equations (1) and (2) expressed in a differential form using the thermal diffusion coefficient κ (constant) of the soil and the heat capacity C _s (constant) of the soil measured in advance, An arithmetic chip for calculating the water movement speed J;
An output unit for outputting the moving speed J calculated by the arithmetic chip;
An apparatus for measuring the rate of movement of soil water, comprising:

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