FR2460475A1 - In-situ measurement of moisture evaporation from vegetation - using various parameter sensors with outputs fed to data acquisition and computer system - Google Patents

Abstract

The evaporation of moisture from vegetation is measured on location in order to determine the watering requirements. An energy meter (1) is attached to a horizontal telescopic support (7) on a pylon (8) in order to measure the net amount of radiation on a particular site. A heat flow meter (2) measures heat in the ground and temp. and humidity sensors (3) together with carbon dioxide sensors (5) measure various characteristics from vertical supports (14). The sensor outputs are transmitted via an electronic transmission unit (81) to a measuring centre in a trailer (82) where a data acquisition system and computer determine the required results.

Description

The present invention relates to devices for determining "in situ" the evapotranspiration of a plant cover by the energy balance method and the mass flux density of carbon dioxide.

The "in situ" study of the evapotranspiration of a cultivated area is very useful in agriculture.

In fact, it makes it possible to determine the water needs of a crop as well as its biological and energy state.

This study can be carried out for the duration of the growth of a particular type of crop or during a pre-determined period to study its own needs.

In addition, the multiplication of measurements on several cultivated areas makes it possible to determine the evapotranspiration of a region or of a particular site.

The method offering the most ease for this study is the method of energy balance put into practice for many years.

It consists in measuring by means of sensors a certain number of parameters such as the net radiation (RN) the heat flow in the soil o, the temperature and water vapor concentration gradients AT and QC, to determine by calculation the heat flow between the surface considered and the atmosphere and the latent heat flow due to evaporation or condensation of water at the level of the ground surface.

This last parameter is none other than actual evapotranspiration which cannot be calculated without first determining the heat flow between the surface considered and the atmosphere.

The net radiation, the heat flux in the ground as well as the temperature and water vapor concentration gradients are respectively measured by a balance meter, a flux meter and by the psychrometric method.

These different sensors are grouped together in a measurement installation or site linked to a computer group allowing quantified data to be obtained.

To this end, the installation and the devices used for the "in situ" determination of the tevapotranspiration of a plant cover by the energy balance method comprising a set of sensors such as, for example, balance meters, flow meters, psychrometer. - very, thermometric probes and sampling system C02 measuring respectively values such as the net radiation, the heat flow in the soil, the humidity of the air, the temperature of the soil, the rate of carbon dioxide and transmitting these different values are characterized by an electronic central unit comprising a data acquisition system and a management and calculation computer. essentially in what it comprises a gantry comprising at least two parallel vertical uprights joined by a high crosspiece between which and on which is mounted vertically movable by any means a sliding frame on the vertical uprights which receives two sets of at least one psychometer.

According to another characteristic of the invention, the sets of psychrometers are respectively mobile on a fixed vertical column of the mobile frame by means of cylinders which are preferably pneumatic cylinders connected by a circuit supplied by a compressed air generator, each cylinder being controlled by a direction reverser.

According to another characteristic of the invention, each group of psychrometers is guided by at least one rolling member carried by its support fixed at the end of the cylinder rod and movable on the column, which cooperates with the corresponding vertical upright of the movable frame. .

According to yet another characteristic of the invention, psychrometers consisting of a cylindrical body receiving a wick wetted from one or two lateral or lateral reservoirs and a probe are characterized in that the cylindrical body is divided into two segments coaxial, one of which receiving the wick has a synthetic ring pierced with orifices arranged opposite which pass the ends of the wick and that on the one hand the bottom of the tank or tanks is provided with a boss cylindrical tubular blocking in wedge in the corresponding orifice of the ring by means of an elastic member and that on the other hand the segment of tube receiving the exile probe segment of tube receiving the wick are fixed by wedging in the ring by means of 'internal elastic organs therein.

Other advantages and characteristics of the invention will appear on reading the description below of a preferred embodiment given by way of nonlimiting example and illustrated by the accompanying drawings in which.

- Figure 1 is a schematic view showing in elevation
the installation object of the invention set up on a site
extent to which the mobile canteen comprising the groups
of calculation and generators were for the simplification of the drawing
close to the gantry.

- Figure 2 is an elevational view of the movable frame carrying the
groups of psychrometers.

- Figure 3 is a partial sectional view of Figure 2 shown
feeling the fixation of a group of psychrometers on the column
fixed mobile frame.

- Figure 4 shows in perspective a group support of
psychrometers.

- Figure 5 shows in plan view the rolling member of
supports of Figure 4 cooperating with the movable frame.

- Figure 6 shows an exploded view in isomated perspective
stick of a psychrometer.

- Figures 7. 8. 9. show the diagram of the pneuma circuit
actuator tick actuating the psychrometers during
of the different operating phases.

- Figures 10.11 show the mobile and towable box
comprising the control elements of the installation and the
data calculation means.

- Figure 12 is a general diagram of the operation of a system
for automatic measurement of plant cover evapotranspiration
pem the energy balance method.

As shown in the installation (fig. 1) according to the invention consists of one or more series of sensors such as balance meters 1, flux meters 2, psychrometers 3 temperature probes 4 and C02 analyzer 5, each measuring a parameter, transmitted to an electronic control unit 6 for calculating the evapotranspiration of one or more measurement sites
The balance meter 1 of a known type measures the net radiation of the site, that is to say the algebraic sum of the radiation of solar origin of the radiation specific to the atmosphere, and of the radiation specific to the ground and the vegetation towards the zenith.

The balance meter 1 is fixed in a removable manner at the end of a horizontal pole 7 carried by a vertical pylon 8 provided with a base 9.

The pole 7, preferably telescopic and or removable for later storage, is provided with a pylon attachment member.

This member is for example constituted by a threaded rod axially aligned with the pole passing right through the pylon 8 and cooperating with a locking nut.

To adjust the height of the balance meter above the plant cover, the pylon 8 can be provided with a series of transverse orifices called to cooperate with the fixing member of the pole 7.

The vertical pylon a is constituted by a series of tubular modules fitted removably into one another, and is held vertically by metal cables.

Preferably, the pylon 8 is capped at the top end of a screed on which the cables are connected.

The base 9 of the pylon 8 is constituted by tubular elements forming a cross and whose longitudinal axes are located in the same plane.

To facilitate storage, the base can be easily separated from the pylon 8.

The pole 7 is advantageously provided with a case 10 for connecting the electrical wires of the balance meter 1.

The purpose of the flowmeter 2 of a known type is to measure the heat flow in the ground.

it is placed about a few centimeters from the surface to avoid any deformation of the flow lines.

In addition, to avoid significantly modifying the evaporation between the ground surface and the sensor, the latter may be porous.

Psychrometers 3 measure the differences in air temperature dTA and wet temperature bTH between two different levels
Z and Z + tu, as well as the temperature differences between aTA and iTH and a reference temperature T.0.

This reference temperature can advantageously be that of the ground at a depth at least equal to a few tens of centimeters, for example 50 cm.

This last parameter is measured by the thermoprobe 4 of a type known to those skilled in the art.

For the measurement of ATA and TH between levels Z and Z + nZ the psychrometers are movable in height between the levels mentioned.

In addition to limit the risk of errors when measuring the different parameters, the psychrometers ent an alternating movement, that is to say that those which were at level Z + ssZ pass at level
Z while those who were at this level go to level Z + at.

To this end, the psychrometers preferably four in number are mounted two by two between the uprights of a gantry 11 on a reversing frame 12 adjustable in height and carrying the members for reversing the position of the psychrometers 3.

The gantry 11 is provided with means for holding in position constituted for example by a set of ropes 13 anchored to the ground and for viewed from tensioning means.

This gantry consists of two vertical uprights 14 each provided with a base 15 and joined at their upper end by a horizontal crosspiece 16.

The vertical uprights 14 are constituted by modular tubular elements of preferably circular cross section, nested one inside the other in a removable manner.

The bottom modular element of each upright fits into the base 15. This base consists of a vertical tube of circular cross section, secured to at least two horizontal elements preferably perpendicular to each other.

The vertical tube of the base receives the low modular element of the upright and the horizontal elements are directed towards the outside of the gantry in order to increase its support surface.

The uprights 14 are kept at a distance by the end crosspiece 16.

This horizontal crosspiece is constituted by a tube of circular cross section extended at each end and at right angles by a tubular element fitting into a modular element high by an upright.

At each end this crosspiece is provided with a means of fixing the ropes.

This means is advantageously constituted by a metal plate welded at the end of the cross-member and provided with a transverse orifice for the passage of a ring for attaching the cables.

Between the uprights 14 of the gantry 11 is mounted the reversing frame 12 adjustable in height to 8 adapt to the height of the vegetation of the measurement site.

The chassis 12 is made up of two vertical uprights 17 joined by two transverse and horizontal cross members 18 and 19.

The uprights 17 of the same dimensions in metal or the like consist of a U-shaped cross-section whose wings are turned towards the inside of the chassis and are parallel to its plane.

The lower cross member 18 is in the form of a metal section of U-shaped cross section, the wings of said section are advantageously turned downwards and are parallel to the plane of the chassis.

The outer face of the web of the cross member 18 receives at each end the bottom of the vertical uprights 17.

These amounts are fixed to this crosspiece by welding or other methods or devices known to those skilled in the art.

The upper cross member 19 also consists of a metal section of U-shaped cross section, the wings of which are directed downward and are parallel to the plane of the chassis.

It is assembled to the uprights 17 rigidly, for example by welding, and this connection is reinforced by gussets fixed on the one hand to the cross-member 19 and to each upright 17.

The tavers 19 and 18 are longitudinally extended at each end by sliding means 20 of the reversing frame on the uprights 14 of the gantry 11.

These means each consist of a guide, preferably metallic, in two or more parts integral with one another by blocking members.

This guide is provided with a median cylindrical orifice for the passage of the uprights 14 of the gantry 11.

The crosspieces 19 and 18 of the reversing frame 12 are joined by two vertical tubular columns 21, of preferably circular cross section.

These two columns are respectively located on either side of the vertical vertical axis of the chassis 12.

Along each column slides a support 22 carrying two psychrometers 4.

The support 22, preferably made of metal, is in the form of a
U provided with two arms 23 parallel to the plane of the chassis and extending the plane of the core of said 11 respectively on either side of the column 21 as shown in FIG. 4.

The horizontal and parallel wings 24 each have a cylindrical orifice 25 in which is engaged a ring 26 preferably self-lubricating mounted on the column 21. The wings 24 of each support 22 are held at a distance by a tubular spacer 27, of section cylindrical straight engaged on column 21.

Each arm 23 of each support 22 carries at least one vertical fixing lug 28 of a psychrometer 3.

This psychrometer is in the form of a hollow cylinder containing a device 29 for measuring the dry temperature TA and a device 29 A for measuring the wet temperature TH.

These devices 29 and 29A each consist of either a platinum probe, a constantan copper thermocouple, a thermistor, a transistor type probe.

The platinum probe 29 is in the form of a rod ending in a point. This probe engages radially in the cylindrical body of the psychrometer.

The platinum probe 29A is also in the form of a
stick extended at right angles by a point.

This probe as shown in section view following F is available.
dried in a cylindrical cross member 29 B housed in the body of the shrink
chrometer and diametral to this one.

This crosspiece is provided with a passage opening for the point of
the 29 A probe.

this axial point to the body of the pslchrometer through
a humidifying organ such as cigarette paper, cooperates
with a wick of textile 30 passing diametrically through the body of the
psychrometer.

The ends of this wick each bathe in a liquid such
water contained in a side tank 31.

These tanks are supplied with water by means of a flexible 32 re
linked to a reserve 33 provided with a breather 34.

This breather has a radial hole 34A which by its position
allows you to adjust the water level in the tanks
terals.

This reserve is fixed by means of a fixing lug 35 to the sup
port 22.

It is easy to understand that a single reserve per support is enough to
lie the tanks 31 of the two psychrometers 3.

According to a particular embodiment of the invention, the
cylindrical body of the psychrometer which receives the wick 30 is a
metallic tubular element pierced on the same diameter by two ori
which receives a ring made of a synthetic material 36 of which
a shoulder 37 is also pierced with two orifices 38 of passa
wick age. These orifices with a diameter greater than that of the
drill bit receive a tubular cylindrical boss 39
produced by machining or any other means on the bottom of each
tanks 32 and offset relative to their axis which facilitates
the establishment of said tanks.

Preferably, the tubular cylindrical bosses have
one or more grooves which receive one or more elas organs
ticks which can be O-rings for sealing and
blocking 40. The reservoirs 31 are made of a synthetic material
transparent tick and are closed by a cover with elastic O-ring seal 41 through an orifice through which passes the conduit 32 for water supply.

The front part 42 of the ring which projects in front of the metallic tubular element 43 is provided with a first elastic member which can have an O-ring 44 in a first internal groove which cooperates with the blocking of the metallic tubular element 43 and a second resilient member which can other an O-ring 45 in a second groove in front of the previous one which cooperates in locking with a second tubular element 46 receiving the probe 29 and coaxial with the first. The reservoir 34 is also made of transparent synthetic material.

The psychrometer is also fitted with an electric fan 29C controlled by electronic regulation.

The purpose of this fan is to ensure that air passes through the psychrometer neither too fast nor too slow so as not to influence the measurement of the dry temperature TA and the wet temperature
TH.

The upward or downward vertical movement of the psychrometers between the levels Z and Z + A Z is caused by two jacks 47 and 48 each receiving a support 22. The jacks 47 and 48 can be pneumatic or hydraulic jacks. The cylinders 47 and 48 are fixed vertically on the upper cross member 19 of the reversing frame 12 and their rod 49 is fixed on one of the wings 24 of the support 22 by means of organs known to those skilled in the art.

To guide their descent, one of the arms 23 of each support 22 is extended by a metal plate 50 provided at the end with a rotating rolling member 51 in an upright 17 of the inverting chassis 12.

According to a preferred embodiment the axis of rotation of the rolling member is horizontal and parallel to the plane of the reversing frame as shown in FIG. 5. In FIGS. 7.8. And 9 is shown a pneumatic cylinder control circuit which is composed by a compressed air pressure source 52 with a conditioning group 53, two distributors 54 and 55.

The conditioning group 53 of the known type is composed of a filter, a pressure regulator with a pressure gauge and a lubricator intended to charge the compressed air with oil to lubricate the various pneumatic members.

This conditioning group 53 is connected by a pipe 56 to the pneumatic distributor 54 electrically controlled and provided with five orifices 57.58.59.60.61 and the drawer of which can occupy two distinct positions.

The air brought in through line 56 is introduced through port 57 into distributor 54 and out through port 59.

From the orifice 59 it passes through a line 62 connected to the orifice 63 of the distributor 55 of the same type as the previous one. The compressed air leaves the distributor 55 through the orifice 64 and is brought by a pipe 65 to the front chamber 66 of the actuator 47 and causes the retraction of its rod 49 and therefore the vertical upward movement of the first group of psychrometer to reach the level Z + OZ, The air contained in the rear chamber 67 of the actuator 47 is expelled via a pipe 68 towards the orifice 69 of the distributor 55 from which it exits through the orifice 70. From this orifice 70 the air is brought by a pipe 71 to the rear chamber 72 of the actuator 48 and causes the exit of its rod 49 and therefore the vertical downward movement of the second group of psychrometers to come to level Z.

The air contained in the front chamber 73 of the actuator 48 is expelled through a pipe 74 connected to the orifice 60 of the distributor 54 and is expelled through the orifice 61 into the atmosphere.

The reverse movement is obtained by the action on the pilot of the distributor 54 which causes the change of position of the drawer of this distributor in FIG. 8.

To adjust the speed of their ascent or descent, the lines 65.

68.71 and 74 are each provided with a restriction provided with means for varying the air flow and in parallel with a non-return valve.

This change in position is controlled by the electronic central unit 6 at a regulated rate, for example every two minutes to limit errors on the calculation of evapotranspiration and on the heat flow exchanged between the surface considered and the atmosphere.

In addition, to indicate to the central unit the final positions of the psychrometers, the uprights of the chassis 12, which are fitted with position indicator devices such as relays actuated by the rolling member 51 of each support 23.

To adjust the movement of the psychrometers, each column 22 can be fitted with a stop provided with a clamp as shown in FIG. 2.

The compressed air introduced through the orifice 57 of the distributor 54 exits therefrom through the orifice 60. Via the line 75 it is introduced into the front chamber 73 of the actuator 48 which causes the rod 49 to re-enter and therefore the rise to level Z + Z of the two psychrometers carried by said rod. The air contained in the rear chamber 72 of the actuator 48 is introduced into the rear chamber 67 of the actuator 47 via the pipes 71 - 68 and the distributor 55.

The air contained in the front chamber 66 is then expelled via the lines 65 and 62 into the variable-rate atmosphere.

The different psychrometers are calibrated by setting them to a predetermined Z level before measurement.

For this only the pilot of the distributor 55 is actuated manually which causes the exit of the rod 49 of the jack 47. To adjust the c8te Z of the psychrometers the movable casing 12 is advantageously adjustable in height by a device cooperating through a transmission with the upper cross member 19 of said chassis.

This device is fixed laterally to the gantry 11 and on one of its legs 15. it consists of a winch 75 with brake of known type on the drum of which is fixed and wound a cable 76 which cooperates with two pulleys 77.78 rotating mounted at the top of the gantry on the cross 16.

One of the pulleys 77 is mounted tangent to the median axis of the gantry and the end of the cable which passes through a pulley 79 of a lifter 80 of the cross member 19 of the movable frame of the psychrometers is fixed to the cross member 17 of the gantry so that by rotation of the winch drum we control the lowering or raise it from the frame.

The carbon dioxide flow from the measurement site is calculated from the carbon dioxide gradient between levels Z and Z + ss AZ.

For this determination, the measurement site is equipped with sampling devices transmitting the information collected to a gas analyzer.

The different information from the sensors is transmitted by cable to the central measurement unit 6, where it will be operated by means of electronic transmission devices placed in a box 81 fixed to one of the uprights of the gantry 12.

This case 81, preferably waterproof and presurized, is provided with a protective cover provided with a roof with at least two slopes.

This roof is preferably provided with one or more openings to keep the case at room temperature.

This central unit 6 is advantageously arranged in a box 82 provided with running gear and a trailer hitch to be brought in close proximity to the measurement site.

Electronic devices include a multiplexing device, a low level axplifier, a digital analog conversion device, serial transmission logic and a measurement bridge.

These electronic devices make it possible to simplify the transmission of data to the central measurement unit and making it possible to increase the possible distance between the measurement site and the said central unit.

The electronic central unit and the electronic devices are connected by a cable provided with three shielded two-wire lines ensuring respectively the transmission of the information given by the sensors to the electronic central unit, the transmission of information from the electronic central unit 6 to the measurement site and the power supply electronic and electrical equipment.

This supply of electrical energy can be provided by the network or by a set of accumulator batteries arranged in a box and delivering a voltage of a few tens of volts.

According to another embodiment, the data are transmitted to the electronic central unit by optical fiber.

The electronic control unit is made up of data acquisition and a management and calculation computer. The data acquisition records every two minutes, that is to say at each new position of the psychrometers, the parameters measured by the various sensors.

This data acquisition can be provided for the subsequent processing of the data with a known type of belt perforator.

The two successive values of each parameter are then averaged by the computer which then calculates the heat flow exchanged between the surface considered and the atmosphere and evapotranspiration.

These different parameters calculated every two minutes are stored for the calculation of the hourly and daily average of the four terms of the energy balance, that is to say the net radiation, the heat flux in the ground, the flux heat exchanged between the surface considered and the atmosphere and evapotranspiration.

These different results are then recorded on a printer.

The datalogger as described can process one or more sites at the same time.

For this, this power station receives information from several series of sensors and calculates the average values of the four terms of the energy balance alternately for each of the sites.

The interior of the box 82 is provided with two enclosures 83 and 84 separated by a transverse partition 85.

The enclosure 83 is provided with a series of shelves supported by consoles for the storage of the various organs of the electronic central unit, of the carbon dioxide analyzer and of the electric energy generators.

In addition, this enclosure can also be provided with means ensuring a constant temperature, for example a fan 86.

The enclosure 83 is provided with storage compartments for the various devices equipping the measurement site (gantry element, etc.) and a compressor provided with its tank and its drive member constituted for example by a motor electric.

The purpose of this compressor is to supply compressed air to the pneumatic devices previously described.

The installation as described may also also be provided with watering or irrigation devices for the plant cover.

This or these devices such as a solenoid valve or the like are controlled by the electronic control unit by means of one or more power circuits known to those skilled in the art.

In addition, this installation makes it possible to study the behavior of nature in micro climates or the disturbances brought about by in
industrialization of a region, for example disturbances due to thermal power plants.

The installation and the devices used for the "in situ" determination of the evapotranspiration of a plant cover by the energy balance method according to the invention can receive arrangements and variants in the field of technical equivalents without going beyond the scope of this patent.

Claims (1)

 CLAIMS NS  R1 / Installation and devices used for the determination  "in situ" of the evapotranspiration of a plant cover by the  energy balance method comprising a set of sensors  such as, for example, balance meters, flumeters, psychrnmeters,  thermal probes and carbon dioxide sampling systems  measuring values such as radiation respectively  net, the heat flow in the soil, the humidity  air, soil temperature, carbon and trans gas levels  putting these different values to a central electronic com  carrying a data acquisition system and a computer  management and calculation characterized in that the installation  includes a portal frame made up of at least two parallel uprights  leles united by a high crosspiece inside which and  on which is mounted vertically movable by any means a  sliding frame on the vertical uprights which receives two sets  of at least one psychrometer. R2 / Installation according to claim 1 characterized in that the  sets of psychrometers are respectively mobile on a colon  fixed of the mobile frame by means of a jack, each jack being  controlled by a direction reversal device. R3 / Installation according to claim 1 and claim 2  characterized in that the cylinders are controlled by a circuit  pneumatic powered by a compressed air generator. R4 / Installation according to claim 1 and each of the claims  tions 2 and 3 characterized in that each of the psy groups  chrometers is guided by at least one bearing member worn  by its support, fixed at the end of the cylinder rod and movable on  the column which cooperates with the corresponding vertical upright  of the mobile frame. R5 / Installation according to claim 1 comprising psychro  meters consisting of a cylindrical body receiving, a wick hu  midified from one or two lateral or lateral tanks  and a probe characterized in that the cylindrical body is  divided into two segments, one of which receives the wick  synthetic ring pierced with orifices arranged opposite by  which pass the ends of the wick and that the bottom of  each tank made of transparent synthetic material is  with a tubular cylindrical boss through which the m  che which comes to jam in jamming dens correspon  in the ring. R6 / Installation according to claim 1 and claim 5  characterized in that the tube receiving the wick and the tube re  the probe are fixed by wedging in the ring at  means of internal elastic organs thereof. R7 / Installation according to claim 5 characterized in that the  Psychrometer probes are platinum probes.  R8 / Installation according to claim 1 caractirisSe in that the  data transmission to the electronic control unit is  carried out by two-wire cable.  R9 / Installation according to claim 1 characterized in that the  data transmission to the electronic control unit is  made by optical fiber.  R10 / Installation according to claim 1 characterized in that the  portal frame consists of removable elements. R11 / Installation according to claim 1 and claim 10  characterized in that the electronic control unit and its power supply  station, the compressed air generator and all the aces  are carried by a towable box with a box  elements for the tubular elements of the gantry.