Device for measuring soil organic carbon by concentrated laser induced combustion

Abstract

A device comprising a main body defining two independent conduits, an intake conduit and an exhaust conduit. The intake conduit and the exhaust conduit meet in a soil port for receiving a soil sample. The device comprises an air pump to produce an airflow in the conduits. An igniter comprising a laser emitter emits a laser pulse and an optical arrangement concentrates the laser pulse on the soil port. A sensing unit measures characteristics of the soil sample, including carbon dioxide on the the conduits and the amount of light reflected by the soil sample. A controller starts the pump, so an airflow passes through the conduits, and adjust the laser pulse based on soil reflectance, so that the laser pulse has a power level and a duration just enough to induce a combustion of the soil sample on the soil port, while simultaneously collects data measurements from the sensing unit.

Description

[0001] DEVICE FOR MEASURING SOIL ORGANIC CARBON BY CONCENTRATED LASER INDUCED COMBUSTION

[0002] FIELD

[0003] The present disclosure pertains to the field of measuring soil properties. It particularly relates to a device and a method for measuring soil properties in particular organic carbon using a concentrated laser to induce combustion.

[0004] BACKGROUND

[0005] Carbon farming involves agricultural activities inducing the removal of atmospheric carbon dioxide (CO2) through soil organic carbon sequestration. By applying soil regenerative farming techniques to agriculture, agroforestry, and livestock management, as well as through reforestation and peatland restoration, there is enormous potential for Earth’s soils to remove CO2 from the atmosphere, sequestering it for long periods of time.

[0006] One of the challenges facing soil regeneration efforts is accurately measuring current soil organic carbon stocks and monitoring these stocks after implementing soil regenerative techniques.

[0007] Traditionally, several laboratory methods such as dry combustion, loss on ignition, wet combustion, Walkley-Black, and others have been used to measure soil organic carbon (SOC).

[0008] The current most favored SOC measurement method in carbon farming projects is laboratory dry combustion, following standard EN 15936. However, having to rely on field soil samples to be sent to the laboratory is both expensive and slow. This introduces a significant cost penalty for carbon farming projects needing to establish a soil carbon baseline and then having to execute follow up sampling campaigns for project monitoring, reporting and verification purposes.

[0009] To reduce the cost and lead time of SOC measurement, several field soil carbon measurement techniques and devices have been proposed and tested.

[0010] At the moment, the state of the art mainly provides the following techniques: diffuse reflectance spectroscopy (DRS), laser induced breakdown spectroscopy (LIBS) and inelastic neutron scattering (INS). Amongst these field soil carbon measurement techniques, the most popular and economical one is DRS in the VIS-NIR spectrum. This technique involves illuminating the soil in the visual and near infrared range and analysing the soil's diffuse reflectance using a spectrometer. Although VIS-NIR DRS has the lowest cost among the currently available field SOC sensors, it is still significant.

[0011] One common drawback of the current field soil carbon measurement techniques is that they require calibration involving the processing of large amounts of data and they must be recalibrated for each new type of soil and region.

[0012] The present disclosure addresses these shortcomings and obtains further advantages in several embodiments.

[0013] SUMMARY

[0014] It is an object of the present invention a device for measuring soil organic carbon according to claim 1.

[0015] According to several embodiments soil carbon can be measured in a less expensive way. In particular, the need for recalibration when measuring new soil types and / or regions can be avoided.

[0016] The present invention allows inducing soil organic carbon combustion using concentrated laser energy. In contrast to laser induced breakdown spectroscopy (LIBS), which uses very intense (in the order of megawatts) but very short (in the order of nanoseconds) laser pulses to induce the breakdown of matter, decomposing it into plasma, and then analyses plasma emissions to identify elements in the soil, the proposed invention applies a new technique that uses lower power (in the order of hundreds of watts, typically from 100 to 900 W) but longer pulses (in the order of milliseconds, typically from 50 to 900 ms) of higher energy (in the order of tens of joules, typically from 20 to 80 J) to induce the combustion of soil organic carbon. An increase in CO2 content of an airstream passing over the induced combustion to estimate the carbon content of soil can be thus detected.

[0017] Advantageously, the technique proposed by the present invention can be adjusted to energy levels high enough to induce combustion of soil organic carbon (SOC) but not high enough to burn soil carbonates, being able to differentiate organic from total carbon without having to rely on chemical removal of carbonates.

[0018] According to several embodiments, a volume of soil being combusted may be estimated, thereby avoiding the need for separate subsample processing for bulk density estimation.

[0019] By measuring the amount of CO2 generated by soil organic carbon combustion, there is no need to rely on indirect techniques based on signature recognition, as is the case with DRS, LIBS or INS, the increase in exhaust CO2 being directly proportional to soil organic carbon content. Embodiments according to the present invention allows estimating the volume of soil being combusted, thereby avoiding the need for separate subsample processing for bulk density estimation. By measuring the amount of CO2 generated by soil organic carbon combustion, there is no need to rely on indirect techniques based on signature recognition, as is the case with DRS, LIBS or INS, the increase in exhaust CO2 being directly proportional to soil organic carbon content.

[0020] Embodiments of the device may include a battery, a controller, a laser driver, a motor driver, an igniter, an intake air filter, an exhaust air pump, and a main body.

[0021] In several embodiments of the device, a main body may include an intake manifold, an exhaust manifold, an exhaust pipe, an inner tube or inner duct and an outer tube or outer duct. The intake manifold is connected to the inner tube and the intake air filter. The exhaust manifold is connected to the outer tube and an exhaust pipe. The exhaust pipe is connected to an exhaust air pump. Each manifold includes several air sensors. The exhaust pipe contains an airflow sensor. The outer tube has an end stop at its bottom. This end stop is designed to lie flat on the soil at the bottom of a hole previously made into the ground using an auger of similar diameter to that of the outer tube. The end stop has a central orifice, a soil port.

[0022] In several embodiments of the device, a light detector such as a photodiode is mounted on the end stop to measure soil reflectance at the wavelength of emitting laser diodes.

[0023] In several embodiments of the device, an igniter may include a laser diode array and several optical stages concentrating and shaping the emitted laser radiation. The laser diode array includes a plurality of laser diodes arranged on a regular pattern, like a square or hexagonal grid, or any other suitable regularly spaced pattern, on the same plane. Each laser diode emission is collimated using a primary optical stage, either constituted of individual microlenses or a micro-lens array, placed at a convenient distance from the individual emitters, creating a compound collimated beam. Such compound collimated beam is then concentrated using a secondary converging optical stage, for instance a plano-convex lens. A third diverging optical stage, for instance a plano-concave lens, having a focal point coincident with the secondary optical stage, narrows and focuses the concentrated beam coming from the secondary optical stage at a specified focal plane distance. This narrower concentrated light beam passes through a light port on an intake manifold and into an inner tube of a main body, being the focal axis and plane of an igniter optical system adjusted to be coincident with a soil port at the bottom of an outer tube end stop of the main body.

[0024] In several embodiments of the device, a main body includes an inner tube connected to an intake manifold, admitting air from the environment through a filter mounted on the intake manifold intake. Air ingested by the device is conducted through an intake pipe including a CO2 sensor, a barometer, a RH sensor, and an air temperature sensor. Air passes from this intake pipe to the intake manifold, and from this to the inner tube to the bottom of the device, where it gets in contact with the soil through the soil port at the outer tube end stop. A concentrated light pulse passing through an intake manifold light port, through the inner tube and finally through the outer tube end stop soil port, is focused on the soil at the bottom of a ground hole, inducing the combustion of soil carbon. Air passing over the combusting soil surface is ingested by the passage between the outer and inner tubes. The cavity between the two tubes is communicated with an outer exhaust manifold, and air is conducted through an exhaust pipe including a second set of CO2, barometer, RH and air temperature sensors, together with an exhaust airflow sensor.

[0025] In several embodiments of the device, air at an exhaust is extracted by an air pump, creating in this way a continuous airflow which passes from the device intake to the exhaust through the soil being combusted at the bottom of the outer tube.

[0026] An electronic controller, with processing capabilities, either an embedded computer or microcontroller, reads signals from the several sensors (intake CO2, P, RH, T and exhaust CO2, P, RH, T and airflow) and controls the laser diode array through a laser diode driver and an air pump through a motor controller.

[0027] In several embodiments of the device is portable and the controller, the laser driver and the motor driver are powered by a battery.

[0028] A possible device operation may include the following steps:

[0029] 1) The operator, using an auger or a similar device, drills a hole into the ground to the desired soil measurement depth, the ground hole having the same diameter as the device outer tube.

[0030] 2) The operator handles the device and inserts its outer tube into the ground hole until the outer tube's end stop lies flat on the bottom of the hole.

[0031] 3) The operator initiates a measurement sequence by pressing a button on the device.

[0032] 4) The device executes a measurement sequence.

[0033] 5) Sensor data is retrieved and processed to estimate the soil carbon content.

[0034] 6) The results are displayed and / or logged by the controller.

[0035] A measurement sequence may typically include:

[0036] 1) Fire a very short laser pulse at low power.

[0037] 2) Read signal from photodiode measuring soil reflection. 3) Calculate soil reflectance.

[0038] 4) Start air pump.

[0039] 5) Based on P / RH / T intake data and soil reflectance, calculate required power level and pulse length to induce soil combustion.

[0040] 6) Start reading CO2 and P / RH / T intake sensors and CO2, P / RH / T, and airflow exhaust sensors.

[0041] 7) Adjust pump power until the desired airflow level is attained.

[0042] 8) Fire ignition laser pulse with previously calculated power level and length.

[0043] 9) Keep airflow level constant by closed loop control of air pump. Simultaneously log sensor data until intake and exhaust C02 levels equalize.

[0044] 10) Stop air pump.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the present invention with now be described, by way of example, with reference to the accompanying drawings in which:

[0047] FIG 1 shows an isometric view of an embodiment of the device.

[0048] FIG 2 shows an exploded isometric view of an embodiment of the device.

[0049] FIG 3 is a detailed upside-down isometric view of the igniter.

[0050] FIG 4 is an exploded upside-down isometric view of the igniter.

[0051] FIG 5 is an exploded upside-down isometric view of the concentrator.

[0052] FIG 6 is an isometric view of the main body.

[0053] FIG 7 is an exploded isometric view of the main body.

[0054] FIG 8 Figure 8 depicts a side view of an embodiment of the device.

[0055] FIG 9 shows a wireframe side view of an embodiment of the device.

[0056] FIG 10 depicts a schematic section view of an embodiment of the device and its working principle.

[0057] FIG 11 depicts a schematic section view of the invention showing its main electrical and electronic components.

[0058] FIG 12 is a block diagram of an architecture showing interconnected components of an embodiment of the device.

[0059] Numerals used:

[0060] 100 Device.

[0061] 10 Igniter.

[0062] 11 Divergent lens. 12 Igniter body.

[0063] 20 Concentrator.

[0064] 21 Lens holder.

[0065] 22 Convergent lens.

[0066] 23 Concentrator body.

[0067] 24 Collimator lens.

[0068] 24a Collimator lens array.

[0069] 25 Laser diode.

[0070] 25a Laser diode array.

[0071] 26 Heat spreader.

[0072] 27 Heat sink.

[0073] 30 Intake filter.

[0074] 50 Main body.

[0075] 51 Intake.

[0076] 52i, 52e CO2 sensor.

[0077] 53i, 56e P / RH / T sensor.

[0078] 54 Intake manifold.

[0079] 55 Light port.

[0080] 56 Exhaust manifold.

[0081] 57 Outer tube.

[0082] 60 Stop.

[0083] 58 Airflow sensor.

[0084] 59 Exhaust.

[0085] 61 Intake pipe

[0086] 62 Exhaust pipe

[0087] 68 photodiode

[0088] 67 Inner tube

[0089] 70 Air pump.

[0090] 81 Controller

[0091] 82 Battery

[0092] 83 Motor driver

[0093] 84 Laser driver

[0094] 88 Sensing unit DETAILED DESCRIPTION

[0095] Various embodiments are discussed in detail below. Yet it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways of making and using and do not delimit the scope of the invention. It will be apparent to those of skill in the art that variations may be applied to the devices, computer programs and / or methods.

[0096] FIG 1 illustrates an isometric view of a device 100 and FIG 2 illustrates its corresponding exploded isometric view, where the following parts are shown: an igniter 10, a main body 50, an intake filter 30 and an air pump 70. As can be appreciated, the device 100 is compact and portable, suitable for in-field use.

[0097] FIG 3 details in an upside-down isometric view the igniter 10 and FIG 4 is an exploded upside-down isometric view of the igniter 10. The igniter 10 includes a concentrator 20, an igniter body 12, and a divergent lens 11. The igniter body 12 has a conical shape, mounting the concentrator 20 at one end and the divergent lens 11 at its other end. The divergent lens 11 mount is airtight.

[0098] FIG 5 is an exploded upside-down isometric view of the concentrator 20. The concentrator includes a convergent lens 22, a concentrator body 23, a lens holder 21, a collimator lens array 24a, a laser diode array 25a, a heat spreader 26, and a heat sink 27.

[0099] The laser diode array 25a is composed by multiple laser diodes 25 arranged on a regular pattern, mounted on the heat spreader 26.

[0100] The collimator lens array 24a is made of individual collimator lenses 24 mounted on a common glass substrate. Alternatively, the collimator lens array 24a can be moulded on a single piece of glass. Alternatively, the collimator lens array 24a can be substituted with individual collimator lenses mounted on each laser diode.

[0101] FIG 6 is an isometric view of the main body 50 and FIG 7 is an exploded isometric view of the main body 50. They are described together. The main body 50 includes an intake manifold 54, an exhaust manifold 56, an exhaust pipe 62, an inner tube 67, and an outer tube 57 with an end stop 60.

[0102] The intake manifold 54 has an intake port 51 at one side, connecting with an intake filter 61, and an exhaust port 59 at its bottom, connecting with the inner tube 67. Several air sensors 52, 53 are mounted inside the intake manifold 54, close to its intake port 51. At least, the following intake air sensors may be included: a sensor for measuring carbon dioxide (CO2) in air, a sensor for measuring relative humidity (RH), a sensor for measuring temperature (T) and a sensor for measuring static pressure (P). The three latter are represented as a combined P / RH / T sensor 53i in the figures.

[0103] A light port 55 on the top of the intake manifold 54 allows the passage of light coming from the igniter 10. Airtight joints on the divergent lens mount and at the interface between the igniter 10 and the intake manifold 54 impede air to leak through the light port 55.

[0104] The exhaust manifold 56 has an intake port on its bottom (not shown), connected to the outer tube 57, and an exhaust port (not shown) at one side, connected to the exhaust pipe 62. The exhaust manifold 56 is mounted below the intake manifold 54 with an airtight joint and has a port on its top allowing the passage of the inner tube 67 through it. Several air sensors are mounted inside the exhaust manifold 56, close to its exhaust port. Similarly to the intake manifold, at least, the following intake air sensors may be included: a sensor for measuring carbon dioxide (CO2) in air, a sensor for measuring relative humidity (RH), a sensor for measuring temperature (T) and a sensor for measuring static pressure (P). The three latter are represented as a combined P / RH / T sensor 53e in the figures.

[0105] The exhaust pipe 62 connects the exhaust manifold 56 with the air pump (not shown). The exhaust pipe 62 includes an airflow sensor 58. The inner tube 67 and outer tube 67 are concentric, the outer tube 57 having a larger diameter than the inner tube 67, creating a conduit or passage therebetween. The outer tube 57 reaches further than the inner tube 67, creating a gap below the inner tube 67. The outer tube 57 has an end stop 60 at its bottom. This end stop 60 has a soil port 65 at its centre, and a light detector, for instance a photodiode 68 mounted in such a way that light reflected from the soil can illuminate its active surface. The soil port 65 must have a diameter slightly larger than that of the igniter beam (see FIGs 10-11) passing through it and impinging into the soil surface at the ground hole bottom. These manifolds 54 ,56, pipes 69, ports and tubes are arranged in such a way that they create two independent air conduits: an inner intake conduit, and an outer exhaust conduit. Both conduits meet at the bottom of the device 100, where the gap between the inner tube 67 and outer tube 57 allows the passage of air between a common region shared by the inner and outer conduits, just on top of the soil port 65 at the end stop 60 of the outer tube 57. Space below the inner tube 67, surrounded by the outer tube 57 and enclosed on its bottom by the outer tube’s end stop 60, and by soil blocking the soil port, forms a combustion chamber.

[0106] FIG 8 depicts a side view of device 100, FIG 9 shows a wireframe side view of device 100 and FIG 10 depicts a schematic section view of device 100 and its working principle. They are described together. As shown in previous figures, the main body 50 has a protruding outer tube 57 on its bottom. This is designed to be inserted into a ground hole, e.g., a ground hole made with an auger of similar diameter.

[0107] Divergent light beams emitted by laser diodes 25 in the laser diode array 25a are collimated by collimating lenses 24 in the collimating lens array 25a, creating a compound collimated beam. This compound collimated beam is concentrated by the convergent lens 22 into a convergent conic light beam 93. At the end of this convergent conic beam 93, the divergent lens 11 shapes the incoming concentrated radiation into a narrower beam 94, focusing it at the bottom of the ground sampling hole, this narrow beam consecutively passes through the intake manifold light port 54, the inner tube 67, and the soil port 65 at the end stop 60 of outer tube 57, impinging exposed soil and inducing its combustion.

[0108] Soil combustion is fed by an intake airstream passing consecutively though the intake filter 30, the intake manifold 54, and the inner tube 67, reaching the end of the outer tube 57 where a combustion chamber is formed.

[0109] Fumes from soil combustion are mixed with the intake stream 91 into an exhaust stream 92. The exhaust stream 91 passes consecutively though the outer tube 57, the exhaust manifold 56, the exhaust pipe 62 and the air pump 70, which forces and controls the airflow.

[0110] The amount of energy impinging the soil is determined by a laser driver 84, and therefore it is known, and thanks to the photodiode 68 at the end stop 60 measuring soil reflectance the amount of energy injected in the soil can be calculated.

[0111] Sensors at the intake manifold 54 and at the exhaust manifold 56 sense carbon dioxide (CO2), pressure (P), relative humidity (RH) and temperature (T) of the intake stream 91 and the exhaust streams 92. There is an additional airflow sensor 58 on the exhaust pipe 62.

[0112] By measuring the P, RH and T of the intake stream 91 and exhaust stream 92, the device 100 can estimate the humidity of the soil.

[0113] By measuring the difference in CO2 content between the intake stream 91 and exhaust stream 92, the device 100 can estimate the amount of CO2 generated by the combustion.

[0114] Considering the measured airflow, the amount of CO2 generated, the soil humidity and the amount of energy absorbed by the soil, the device 100 estimates the volume of soil having been combusted and the carbon content of this volume.

[0115] FIG 12 shows how the sensors, control and power components are interconnected. Thick arrows with void heads depict power flows. Thin arrows with solid heads depict signal and control flows.

[0116] The controller 81 is in the core of the device 100 and receives signals from several sensors grouped in a sensing unit 88: the intake CO2 sensor 52i, the intake P / RH / T sensor 53i, the exhaust CO2 sensor 52e, the exhaust P / RH / T sensor 53e, the exhaust airflow sensor 58 and the photodiode 68. Not all are essential in all cases. The

[0117] The controller 81 also reads a digital input from a trigger button 89 via an interface (not shown). The controller sends commands to a laser driver 84 and to a motor driver 83.

[0118] The laser driver 84 allows turning the laser diode array on / off and adjusting its power, thus it allows defining duration and power level of the laser pulse.

[0119] The motor driver 83 allows the adjustment of the air pump speed.

[0120] The battery 82 powers the laser driver 84, the motor driver 83, and the controller 81. The controller 81 is powered through a DC / DC converter or a similar device.

[0121] As an option, the controller 81 may be connected to a mobile phone, for instance using Bluetooth. An app in the operator’s mobile phone may be used to visualise data and / or upload data to the cloud, including localisation data obtained by the phone.

[0122] As an option, the controller 81 may be directly connected to internet using a cellular connection.

[0123] As an option, the device 100 may include a GNS receiver to record its location during the operation procedure.

[0124] As an option, the device 100 may include one or several cameras capturing images from the surroundings during the operation procedure, for reporting and verification purposes.

[0125] Before operating the device 100, it is necessary to bore a hole into the ground using an auger or a similar tool to the desired depth. The diameter of the ground hole should be equal to or slightly larger than the diameter of the device's outer tube.

[0126] The operator inserts the outer tube into the ground hole until the end stop contacts the bottom. The operator should allow the device to rest its weight on the soil at the bottom of the hole, compressing the soil under the outer tube’s end stop. The compression of the soil surrounding the soil port creates a relatively airtight seal at the base of the device, effectively preventing any air, except from the designated intake airstream, from entering the combustion chamber.

[0127] - When ready, the operator presses the trigger button to initiate a measurement sequence. The controller executes a measurement sequence, among other operations, controlling the light pulses through the laser driver and the stream airflow level thought the motor controller driving the air pump, and simultaneously recording a dataset of sensor measurements. The controller processes the dataset obtained during the measurement sequence and generates a soil organic carbon content estimate.

[0128] The results may be displayed to the operator and / or stored in the controller nonvolatile memory.

[0129] Here it follows a detailed description of an example of measurement sequence:

[0130] The controller starts the sequence by firing a short and low power laser pulse. The objective of this initial low energy light pulse is to estimate the soil reflectance, and not to induct the soil combustion.

[0131] - Light from the concentrated beam impinges the soil surface below the soil port. Depending on soil reflectance, part of this light is reflected.

[0132] - By measuring the amount of light reaching the photodiode active surface, the controller estimates the amount of light that has been reflected. Assuming a non- specular soil reflection, the photodiode sensor active area can be considered to be part of a hemisphere having a radius equal to the distance from the sensor surface to the soil port centre. Calculating the area of this hemisphere and dividing it by the photodiode sensor active area, a factor is obtained that multiplied by the amount of radiation detected by the photodiode can be extrapolated into the amount of reflected light from the soil.

[0133] In parallel, the controller activates the air pump by sending a command to the motor driver.

[0134] The controller starts reading the intake and exhaust air sensors, obtaining and logging at least the following data: Intake CO2 air content from Intake CO2 sensor, Intake air pressure from intake P sensor, Intake air relative humidity from intake RH sensor, Intake air temperature from Intake T sensor, Exhaust CO2 air content from exhaust CO2 sensor, Exhaust air pressure from exhaust P sensor, Exhaust air relative humidity from exhaust RH sensor, Exhaust air temperature from exhaust T sensor, and Stream airflow level from exhaust airflow sensor. At this step S52 the airflow through the device should be ramping up.

[0135] The controller adjusts the air pump power in a closed control loop, using the airflow sensor at the exhaust pipe as feed-back signal and sending commands to the motor driver to adjust the air pump speed. Its objective is to attain a desired airflow level and stabilise it, for instance by using a PID algorithm. - When the desired airflow level is attained and stable, the controller uses the estimated soil reflectance and the intake air data (CO2 content, air pressure, relative humidity and temperature) to determine the power level and the length of the ignition laser pulse.

[0136] - Using these parameters of power and pulse length, the controller will send a command to the laser driver that will trigger an ignition laser pulse. The concentrated laser beam will impinge at the soil surface within the soil port, at the bottom of the device device, inducing the combustion of organic carbon contained within a very shallow soil layer, liberating CO2, water vapour and other gases which get mixed with the air stream from the intake conduit, and are exhausted through the exhaust conduit.

[0137] The increase of CO2 and water vapour content will be measured by the exhaust sensors.

[0138] The controller keeps the desired airflow level until the sensed CO2 content at the intake and exhaust streams equalize, implying that the combustion has finished when the difference is below a threshold.

[0139] Then, the controller will stop the air pump and halt the recording of sensor data.

[0140] Here it follows a description of how the controller processes the data to obtain a soil carbon content estimate:

[0141] The amount of energy absorbed by the soil during the ignition pulse is estimated using the following simple formulas: energy injected = laser power * pulse length energy absorbed = energy injected - energy reflected

[0142] The controller uses differential analysis and integration of the CO2, P, RH, and T intake and exhaust measurement data to estimate the amount of CO2 and water vapour (H2O) liberated during the soil combustion episode.

[0143] Based on the liberated amount of CO2 and H2O, a proprietary algorithm is used to estimate soil humidity. Alternatively, a soil humidity sensor could be used.

[0144] Based on the estimated soil humidity, soil thermal conductivity is estimated.

[0145] Based on the amount of energy absorbed and the estimated soil thermal conductivity, the controller estimates the combusted soil volume.

[0146] Based on the liberated amount of CO2, the amount of combusted soil organic carbon is estimated.

[0147] SOC density = combusted SOC / combusted soil volume A possible formula to calculate soil reflectance:

[0148] Eabs = Epulse * (1 - R)

[0149] Eabs = Ereq

[0150] Epulse= Ereq / (1 - R)

[0151] Wherein: Eabs is energy absorbed by soil; Epulse is energy of the pulse; Ereq is energy required to provoke combustion of organic carbon; R is soil reflectance.

[0152] Once Ereq is calculated, length of pulse can be obtained:

[0153] Ereq= Wlaser * Tpulse

[0154] Tpulse= Ereq / Wlaser

[0155] Wherein:

[0156] Tpulse is pulse length (duration).

[0157] Wlaser is laser power emission.

[0158] Further measurement considerations and methodology:

[0159] To properly assess carbon stocks, it is normally required to take measurements at different places and depths, being a very common practice in carbon farming projects to consider a maximum sample depth of 30 cm. Ideally, to assess the carbon stock of a given field, several measurements should be taken at different points within the field and at several standard depths. For instance, taking measurements for each ground hole and three different depths of 10, 20 and 30 cm. Following this method, for each measurement point, the device operator should proceed in the following way:

[0160] Using an auger, bore a ground hole 10 cm deep.

[0161] Take a first device measurement at 10 cm depth.

[0162] Using an auger, deepen the ground hole a further 10 cm.

[0163] Take a second device measurement at 20 cm depth.

[0164] Using an auger, deepen the ground hole a further 10 cm.

[0165] Take a third device measurement at 30 cm depth.

[0166] A conservative estimate of the total carbon stock for the given field would be given by the following formula: average SOC density = (average SOC density at 10 cm + average SOC density at 20 cm + average SOC density at 30 cm) / 3 field SOC stock = average SOC density * field area * 0.3 m Many modifications will be apparent to those skilled in the art without departing from the scope of the appended claims.

Claims

We claim1. A device (100) for measuring soil organic carbon comprising: a main body (50) configured to be inserted into a ground hole, the main body (50) defining two independent conduits, an intake conduit for conveying an intake airstream (91) and an exhaust conduit for conveying an exhaust airstream (92), wherein the intake conduit and the exhaust conduit meet in a soil port (65), wherein the soil port (65) is an opening for exposing a soil sample at the surface of the bottom of the ground hole, an air pump (70) configured to produce the intake airstream (91) and the exhaust airstream (92) in the conduits; a sensing unit (88) configured to measure characteristics of the soil sample and of intake and exhaust airstreams, the soil sensing unit comprising: a carbon dioxide sensor (52i) configured to measure carbon dioxide on the intake conduit, a carbon dioxide sensor (52e) configured to measure carbon dioxide on the exhaust conduit, and a light detector (68) configured to measure the amount of light from a laser pulse reflected by the soil sample; an igniter (10) comprising a laser emitter configured to emit at least one laser pulse of an adjustable energy and an optical arrangement for concentrating the laser pulse on the soil port; a controller (81) configured to: start the air pump (70), control the laser emitter (25, 25a) by adjusting energy of the laser pulse to be emitted based on soil reflectance, wherein the soil reflectance is calculated from data of the light detector (68) from a previous laser pulse, so that the laser pulse is emitted to induce a combustion of the soil sample on the soil port (65), collect and process data measurements from the sensing unit (88) to obtain carbon dioxide information of the soil sample.

2. The device according to claim 1, wherein the igniter (10) and the intake conduit are arranged so that the laser pulse is transmitted via at least part of the intake conduit to the soil port (65).

3. The device according to claim 1 or 2, wherein the sensing unit (88) further comprises, for each intake and exhaust conduits, at least one of the following sensors: a relative humidity sensor, a temperature sensor, a static pressure sensor, and / or an airflow sensor (58) for measuring air flow in the exhaust conduit, wherein the controller (81) controls the air pump (70) for producing a continuous air flow.

4. The device according to any of claims 1 to 4, wherein the main body (50) comprises an inner tube (67) for defining at least part of the intake conduit, and an outer tube (57) located outside the inner tube (67) for defining therebetween at least part of the exhaust conduit, wherein the outer tube (57) protrudes further than the inner tube (67), creating a gap below the inner tube (67) to form the soil port.

5. The device according to claim 4, wherein the main body (50) comprises an intake air filter (30) mounted on the inner tube (67) configured to filter air from the environment.

6. The device according to any of claims 1 to 5, wherein the laser emitter comprises an array (25a) of laser diodes (25) arranged on a regular pattern and configured to emit a combined laser beam.

7. The device according to claim 6, wherein the focal axis and plane of the optical arrangement is adjustable to be coincident with the soil port (65).

8. The device according to claim 6 or 7, wherein the optical arrangement comprises: a collimator lens (24) placed at a distance from the emitters for creating a compound collimated light beam; a convergent lens (22) for concentrating the collimated light beam; a divergent lens (11) for focusing the concentrated light beam on the soil port.

9. The device according to any of claims 1 to 5, wherein the main body (50) further comprises: an intake manifold (54) connected to the inner tube (67) and the intake air filter (), andan exhaust manifold (56) connected to the outer tube (57) and to an exhaust pipe (62), wherein the exhaust pipe (62) is connected to the air pump (70).

10. The device according to claim 9, wherein the intake manifold (54) comprises a light port (55) for the concentrated light beam passing therethrough and into the inner tube (67) for reaching the soil port.

11. The device according to any of previous claims 1 to 10, wherein the controller (81) is configured to receive an instruction from a trigger button (89) so the following sequence is performed: firing a first laser pulse having a first energy with the laser emitter; reading data from the light detector regarding light reflected from the soil sample; calculating soil reflectance; starting the air pump (70); calculating based on intake data and soil reflectance, required power and length of a second laser pulse to induce soil combustion, wherein the energy of first laser pulse is lower than the energy of second laser pulse, wherein the intake data is obtained from the relative humidity sensor, the temperature sensor and the static pressure sensor.

12. The device according to any of claims 1 to 11, further comprising a motor driver (83) and a laser driver (84) to cooperate with the controller (81), so the controller (81) instructs the laser driver (84) to turn the laser emitter on / off and to adjust its power by defining length and power of the laser pulse, and so the controller (81) instructs the motor driver (83) to adjust the speed of the air pump (70).

13. The device according to any of claims 3 to 12, wherein, to obtain carbon dioxide information of the soil sample, the controller is configured to perform one or more of the following operations: estimating the amount of energy absorbed by the soil during the second pulse based on the energy of the laser pulse inducing combustion and the energy reflected, estimating the amount of carbon dioxide water vapor liberated during soil combustion based on the intake data and exhaust data of carbon dioxide, pressure, relative humidity and temperature,instructing the soil humidity sensor to measure or estimating soil humidity based on the liberated amount of carbon dioxide and water, estimating soil thermal conductivity based on soil humidity, estimating the combusted soil volume based on the amount of energy absorbed and the estimated soil thermal conductivity, estimating the amount of combusted soil organic carbon based on the liberated amount of carbon dioxide, estimating soil organic carbon density based on combusted soil volume and liberated carbon dioxide volume, stopping the air pump (70) based on a comparison of the intake data and exhaust data of carbon dioxide.

14. The device according to any of claims 1 to 13, wherein the controller (81) is configured to communicate with a user device, so the controller (81) sends carbon dioxide information to be displayable on the user device and / or receives a triggering instruction to start measuring.

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