NL2033056B1 - Portable soil density meter - Google Patents
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- 239000002689 soil Substances 0.000 title claims abstract description 169
- 230000005855 radiation Effects 0.000 claims abstract description 138
- 239000000523 sample Substances 0.000 claims abstract description 116
- 238000001514 detection method Methods 0.000 claims abstract description 48
- 238000000034 method Methods 0.000 claims abstract description 25
- 230000008569 process Effects 0.000 claims abstract description 13
- 238000005259 measurement Methods 0.000 claims description 30
- 238000000342 Monte Carlo simulation Methods 0.000 claims description 20
- 238000001228 spectrum Methods 0.000 claims description 16
- 230000005251 gamma ray Effects 0.000 claims description 12
- 230000000694 effects Effects 0.000 claims description 9
- 238000012545 processing Methods 0.000 claims description 9
- 238000010183 spectrum analysis Methods 0.000 claims description 7
- 230000000149 penetrating effect Effects 0.000 claims 2
- 238000004088 simulation Methods 0.000 description 10
- 238000004891 communication Methods 0.000 description 6
- 230000035515 penetration Effects 0.000 description 6
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
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- 239000002245 particle Substances 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 238000011088 calibration curve Methods 0.000 description 2
- 238000001739 density measurement Methods 0.000 description 2
- 230000036541 health Effects 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
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- 239000004576 sand Substances 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 235000016639 Syzygium aromaticum Nutrition 0.000 description 1
- 244000223014 Syzygium aromaticum Species 0.000 description 1
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- 238000006243 chemical reaction Methods 0.000 description 1
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- 230000001419 dependent effect Effects 0.000 description 1
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- 238000000084 gamma-ray spectrum Methods 0.000 description 1
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- 230000003287 optical effect Effects 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 230000002285 radioactive effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- KEAYESYHFKHZAL-BJUDXGSMSA-N sodium-22 Chemical compound [22Na] KEAYESYHFKHZAL-BJUDXGSMSA-N 0.000 description 1
- 230000005236 sound signal Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
- G01N9/24—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by observing the transmission of wave or particle radiation through the material
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
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Abstract
Portable soil density meter, including: a probe (1) configured to be inserted into soil (S), the probe (1) having a gamma radiation source (3) arranged for emitting gamma radiation out of the probe and a gamma radiation detector (5) arranged for detecting incoming gamma radiation, the probe further including a radiation shield (4) located between the gamma radiation source (3) and the radiation detector (5), wherein during use -when the probe (1) is inserted into soil- the detector (5) detects soil background gamma radiation as well as backscattered gamma radiation that emanates from the source (3) of the probe (1y), wherein the detector (5) is configured to generate a detection signal associated with detected gamma radiation, wherein the density meter includes a signal processor (10) configured to process the detection signal for reducing a signal component that is associated with soil background radiation, resulting in a field bulk density and optionally a dry bulk density.
Description
P133366NL00
Title: Portable soil density meter
The invention concerns a portable soil density meter.
Soil (bulk) density is an important physical soil health indicator and generally used for assessing soil quality. For example, it can give indications about soil pore space for water and air, organic matter content, mineral content, and soil strength.
A standard method to determine soil density 1s based on taking small soil cores from different depths, and performing off-site laboratory work for taking core measurements. This method requires a soil pit.
Creating this soil pit is labour intensive and also the analysis of the core samples involves a lot of laboratory work.
The present invention aims to provide an improved soil density measuring technique, in particular such that soil density can be determined accurately, efficiently, in a straight-forward manner, on site (in the field).
To this aim, there is provided a portable soil density meter that is defined by the features of claim 1.
Advantageously, there is provided a soil density meter that includes a probe configured to be inserted into sail, the probe having a gamma radiation source arranged for emitting gamma radiation out of the probe and a gamma radiation detector arranged for detecting incoming gamma radiation, the probe further including a radiation shield located between the gamma radiation source and the radiation detector, wherein during use (when the probe is inserted into soil) the detector detects soil background gamma radiation as well as backscattered gamma radiation that emanates from the source of the probe, while the radiation shield prevents radiation from the source to reach the detector directly, wherein the detector is configured to generate a detection signal associated with detected gamma radiation, wherein the density meter includes a signal processor configured to process the detection signal for reducing a signal component that is associated with soil background radiation, the processing preferably resulting in a field bulk density. Also, for example, the processor can be configured to translate the processed detection signal into soil density, e.g. by a predetermined algorithm (as will be explained below).
It has been found that this device can provide surprisingly good measuring results of soil density (during operation). In particular, it has been found that this can be achieved using a source of low activity, for example using a Na-22 gamma radiation source having a maximum activity of 1 MBq (megaBecquerel). The source is preferably configured such that the source activity is lower than the local exemption level. Herein, the local exemption level can be defined as the exemption level as provided by “Radiation Protection and Safety of Radiation Sources: International Basic
Safety Standards”, General Safety Requirements Part 3, No. GSR Part 3,
IAEA, July 2014 (hips www: pubiaen org/MTCI/Pabtbheations/PDW/Pub1578 web-57265295 nd).
In that case, no particularly safety measures have to be taken by the device operator during operation, wherein the resulting portable meter can be operated as it is (1.e. the operator does not have to wear radiation shielding clothing or cloves or the-like, the probe does not have to be transported in a radiation shielding box, and does not have to be stored in a radiation safety bunker after use). During operation, the amount of background radiation can be relatively high compared to the amount of backscattered source radiation, due to the use of the low activity source.
Still, the signal processor of the portable soil density meter can process the detection signal for reducing the signal component that is associated with soil background radiation (in particular by subtracting that signal component), in order to provide an accurate soil density determination.
Various gamma ray sources can be used, e.g. a Na-22 (sodium 22) source, or differently.
The radiation detector can be configured to translate recorded gamma radiation (which includes both background radiation as well as backscattered source radiation) into a digital signal for further signal analysis (by the signal processor). It is preferred that the digital signal includes energy information (spectrum) of the detected radiation. It follows that the probe (e.g. the detector) can preferably determine the energy of the deposited radiation, and store the result in an energy spectrum that is transmitted to the signal processor. Various types of detectors can be applied, for example a scintillation counter (crystal, photomultiplier tube or silicon photomultiplier), as will be clear to the skilled person.
For example, the signal processor can be configured to processes the signal in order to correct for the contribution from background radiation.
It is preferred that the signal processor is configured to determine or estimate the signal component associated with soil background radiation, and subsequently to subtract the determined or estimated background radiation component from the initial signal. To that aim, e.g., the signal processor can be configured to discriminate between radiation emanating from the source and the background radiation based on a spectrum analysis (which can optionally be a full spectrum analysis).
Good results can be achieved in case the radiation source and the radiation detector are spaced-apart by a predetermined (optimized) distance
X, wherein the signal processor is configured to process the detection signal taking into account the predetermined distance X between the detector and the source. .It has been found that a predetermined, relatively short source- detector distance Xin the range of 1-15 cm can lead to good results, for example a range of 4-8 cm. It is preferred that the signal processor is configured to use a predetermined relation between soil density and an amount of backscattered radiation to determine soil density, wherein the relation has preferably been determined by Monte Carlo simulations, preferably in combination with calibration measurements.
In particular, said predetermined distance X between the detector and the source can be used in the Monte Carlo simulations. The simulations can predict the detector response as function of soil density (i.e. estimate the relation between the measured signal and the soil density).
The concept of using Monte Carlo simulations for simulating gamma-ray measurements in different geometries and the use of these simulation in the (subsequent) processing of gamma-ray measurements is known to the skilled person, see for example “Determination of correction factors for borehole natural gamma-ray measurements by Monte Carlo simulations, M. Maucec et al., Nuclear Instruments and Methods in Physics
Research Section A: Accelerators, Spectrometers, Detectors and Associated
Equipment, 6092-3), 194-204. hitps/dolorg/ 19.1016 numa, 2008 08 054, and also “Towards a global network of gamma-ray detector calibration facilities”, Marco Tijs et al., Exploration Geophysics, Volume 47, Issue 4, pp. 302-307, September 2016. The inventors have found that these Monte Carlo simulations, in particular the results of these simulations, can also be used by or as part of a portable soil density meter, in particular in combination with a low activity gamma ray-source, to provide sufficiently accurate soil density estimations within a relatively short measuring time period.
An input to the Monte Carlo simulations can include a model of the complete probe geometry, probe dimensions, probe materials, and soil densities, as well as the source position and the energy distribution of the source,
An output to the simulations can be an estimation of the energy spectrum that would be recorded in the simulated geometry.
It is preferred that the Monte Carlo simulations are also used to optimize the probe (during probe manufacturing), for example to determine an optimal configuration of the sensor/detector, for example a size of a detector crystal (if any), and/or to determine an optimal distance X between detector and source, in particular such that a relatively high signal component for backscattered radiation can be present in the detector signal.
In particular, Monte Carlo simulations can be applied to determine an optimal probe configuration where expected uncertainty in the detector’s count rate results in a minimum uncertainty in the derived density. Or in 5 other words, where the soil density has a maximum effect on the recorded count rate.
According to a preferred embodiment, the signal processor is configured to generate a detection result, based on the processed detection signal, indicating soil density, and for example to transmit the detection result to a user interface, for example a remote user interface and/or to a user interface of the probe. In addition or alternatively, the signal processor can include or be connected/coupled to a digital memory for storing the detection result, as will be appreciated by the skilled person. Optionally, a remote server can be provided to receive (and store) a detection result, wherein the probe and server can e.g. be configured to communicate with each other via a computer network (e.g. Internet) for transmitting detection results to the remote server.
The probe of the soil density meter can be configured in various ways. According to a preferred embodiment, the probe has an elongated soil penetration body, for example a tubular element, containing the source, detector and shield, a distal end of the body preferably having a tapered tip, and a proximal end of the body preferably having a gripping structure for example a lateral handle, for manually holding the probe. This provides good handleability and good soil penetration. The overall soil density meter as such can be relatively light-weight, for example having a mass less than 20 kg and preferably less than 5 kg (e.g. at most 2 kg), to be manually portable by a single person.
It is preferred that the soil density meter includes a moisture sensor, arranged to detect soil moisture, wherein the signal processor is configured to use a detection result of the moisture sensor and the processed detection signal of the radiation detector to determining a dry soil density.
In this way, dry soil density can be determined by the portable soil density meter.
Further, an aspect of the invention provided a method for measuring soil density. The method can utilize a soil density meter according the invention. Advantageously, the method includes: -(manually) inserting a probe into the soil; -emitting gamma radiation from the probe into the soil, by a gamma radiation source; - detecting, by a detector of the probe, soil background gamma radiation as well as backscattered gamma radiation that emanates from the source of the probe; -processing, by a signal processor, a radiation detection signal (of the detector) to correct for a signal component that is associated with the sol background radiation, thereby providing a processed detector signal; and -generating, by the signal processor, a soil density result based on the processed detector signal.
In this way, above-mentioned advantages can be achieved. For example, the soil density result is based on a predetermined relation between soil density and an amount of backscattered radiation, wherein the predetermined relation has preferably been determined by Monte Carlo simulations. It is preferred that initially, a probe calibration step is carried out on a sample with a known soil density (e.g. by immersing the probe in a volume of water or sand). The calibration can be carried out, in particular, for checking an initial soil density determination result based on the Monte
Carlo simulation results with a real measurement by the probe. It has been found that usually, the calibration step leads to a linear correction with a scaling factor in the range of 0.8-1.2.
In this application, the following definitions can be applied, in particularly regarding soil, moisture and respective densities.
Generally, soil is composed of solid particles of different sizes and different composition (minerals as sand and clay and organic matter). The number and size of pores vary considerably among soils exhibiting different organic matter content, texture, and structure. In this application, soil in particularly concerns soil that is located just below a top surface (e.g. a field surface), for example within 0 to 2 meter below ground surface level.
Following from https. www. britannica.com/iscience/soil, soil is the biologically active, porous medium that has developed in the uppermost layer of Earth’s crust.
Usually, soil contains water. The soil’s moisture content 1s the ratio between the volume of water to the total volume of soil and water.
The Field Bulk Density (fBD) is the ratio of the mass of solids to the bulk volume of the soil, which includes the moisture content and the pore space between the soil particles (= dBD + moisture content).
The Soil (dry) Bulk Density (dBD) is the ratio of the mass of oven- dried solids to the bulk volume of the soil, which includes the pore space between the soil particles.
The Specific Density (SD) is the is the ratio of the mass of oven- dried solids to the grain volume of the soil, which excludes the volume of the pores.
The probe is preferably manually portable, by a single person. For example, a weight of the probe is at most 20 kg and preferably at most 5 kg.
Similarly, a maximum dimension of the probe (e.g. a length) can be at most 2 meter, preferably at most 1.5 meter (e.g. about 1.3 m). Thus, the probe can be transported and handled with ease, by a single operator, to provide a relatively large number of field tests within a limited amount of time.
Further advantageous embodiments are described in the dependent claims. Examples of the invention are discussed in further detail in the drawings.
Figure 1 schematically depicts a partly opened side view of an example of a portable soil density meter;
Figure 2 depicts soil, to be measured;
Figure 3 depicts the example of Fig. 1 during operation in the soil of Fig. 2; and
Figure 4 depicts a graph of estimated count rate versus soil density.
In this application, similar or corresponding features are denoted by similar or corresponding reference signs.
Figure 1 shows a portable soil density meter, schematically, in partly opened side view. The portable soil density meter includes a probe 1 configured to be inserted into soil S (e.g. into a hole H that has been drilled in the soil S). The probe 1 has a (single) gamma radiation source 3 arranged for emitting gamma radiation out of the probe.
Also, the probe 1 has a gamma radiation detector 5 arranged for detecting incoming gamma radiation. The detector 5 can e.g. be located above the source 3 (as in the drawings) or below the source 3.
The probe further includes a radiation shield 4 located between the gamma radiation source 3 and the radiation detector 5. For example, the shield 4 can be located immediately next to the detector 5, and for example immediately next to the source 3 (so that a height of the shield 4 determines a distance X between the source 3 and the detector 5).
The shield 4 can be shaped in various ways, and preferably has a conical shape (se Fig. 1) which leads to improved detection results. In case of a conical shield 4, a cone top of the shield 4 is preferably located next to the source 3, whereas an opposite cone base can have a width (diameter) that 1s at least the same as a width (e.g. diameter) of the detector 5.
During use -when the probe 1 is inserted into soil- the detector 5 detects soil background gamma radiation as well as backscattered gamma radiation that emanates from the source 3 of the probe 1. The backscattered radiation is a measure of soil density (which can be a wet soil density in case the soil Sis moist, i.e. contains water). The radiation shield 4 is configured to prevent that radiation from the source reaches the detector directly. To that aim, e.g., the shield 4 extends transversally in the probe 1 and may have a width that corresponds to the width of the probe 1. For example, the shield 4 can be made of a piece of high-density material (e.g. Wolfram).
Preferably, the probe 1 has an elongated soil penetration body 1a, for example a tubular element, containing the source 3, detector 5 and intermediate shield 4 (with the detector 5 preferably being located at a distal location with respect to the source 3, 1.e. below or above the source 3 when the probe 1 is in a vertical operating position). A distal end of the body preferably has a tapered tip 1b. A proximal end of the body preferably has a gripping structure for example a lateral handle lc, for manually holding the probe. For example, the handle 1c can extend transversally with respect to a longitudinal direction of the (main) body 1a of the probe 1.
According to a preferred embodiment, a length of the elongated soil penetration body la can be at most 2 meter, for example at most about 1 meter. A width W or outer diameter (measured normally with respect to its longitudinal) direction of the elongated soil penetration body la can e.g. be at most 10 cm, for example a width W of 5 cm or less, e.g. about 3 em.
The detector 5 is configured to generate a detection signal associated with detected gamma radiation, wherein the density meter includes a signal processor 10 configured to process the detection signal for reducing (e.g. subtracting) a signal component that is associated with soil background radiation (indicated by arrows BR in Figure 3). For example, the detector can be a gamma ray spectrometer. For example, the detector 5 can include a scintillation crystal (e.g. made of CsI or Nal).
In particular, the detector can be configured to translate the recorded gamma radiation into a digital signal for further analysis. Gamma ray detection preferably includes determining the energy (spectrum) of the deposited radiation, and generating or storing (in a memory) the resulting energy spectrum, as will be clear to the skilled person.
It is highly preferred that the gamma radiation source 3 has a maximum activity of 1 MBq (in particular in case of a Na-22 source), so that the probe 1 can be manually operated without special precautions (i.e. without the operator having to carry a dedicated radiation dose detector and without the operator having to wear protective clothing and gloves). It is preferred that the gamma radiation source 3 is relatively small, e.g. having a volume less than 1 mm’.
The signal processor 10 can be configured in various ways, e.g. having suitable hardware and/or software executed by (the) hardware, for carrying out signal processor tasks. The probe 1 can include one or more communication lines (not shown), e.g. wired and/or wireless communication lines, for communicating signals (e.g. detection results) from the detector 5 to the signal processor 10. Also, the probe 1 can include a power source (e.g. a rechargeable battery, not shown) for electrically powering other probe components (such as the signal processor and detector).
The signal processor 10 can be configured to reduce the signal component associated with soil background radiation, wherein the signal processor is preferably configured to discriminate between radiation emanating from the source and background radiation based on a spectrum analysis.
Good results are achieved in case the radiation source 3 and the radiation detector 5 are spaced-apart by a predetermined distance X (for example a distance X that has been optimized using Monte Carlo simulations and/or using calibration measurements), wherein the signal processor 10 is configured to process the detection signal taking into account the predetermined distance X between the detector 5 and the source 3. For example, according to an embodiment it has been found that good results can be achieved in case the distance X is relatively, short, in particular in the range of 1-15 cm, for example a range of 4-8 cm (in particular 5-7 cm).
In particular, the signal processor 10 can be configured to use a predetermined relation between soil density and an amount of backscattered radiation (an example being indicated by arrow SR in Figure 3) to determine soil density, wherein the relation has preferably been determined by Monte Carlo simulations, preferably in combination with initial calibration measurements. Moreover, preferably, the signal processor 10 is configured to determine soil field bulk density (fBD), based on the detection signal.
For example, as will be clear to the skilled person, the overall geometry of the source-shield -detector system can determine a response of the measured signal to the soil density. The optimal configuration is preferably determined with Monte Carlo Simulations that calculate the response of the detector to changes in soil density. This approach is similar to the approach for calculating response curves for borehole measurements (Maucec et al., 2009).
According to an embodiment, the signal processor 10 is configured to generate a detection result, based on the processed detection signal, indicating soil density, and for example to transmit the detection result to a user interface, for example a remote user interface and/or to a user interface of the probe.
According to a further, advantageous, embodiment, the portable soil density meter includes a moisture sensor 8, arranged to detect soil moisture. Preferably, the moisture sensor 8 is located at or near the lower end of the probe 1, and/or near the gamma ray detector 5. The moisture sensor 8 can be connected to the signal processor 10 (e.g. via a suitable electric wiring or a wireless communication link), for providing a moisture detection result thereto. The signal processor 10 is preferably configured to receive and use a detection result of the moisture sensor 8 and the processed detection signal of the radiation detector 5 to determining a dry soil density (dBD). For example the moisture sensor 8 can be a capacitance-based moisture sensor (known per se), wherein the probe (e.g. the signal processor 10) can include or be provided with suitable moisture sensor calibration data to determine or calculate moisture or moisture content from a respective sensor signal.
Also, it is preferred that the probe has a depth measuring sensor 12, to detect probe penetration depth, and in particular to register a probe depth of each of the density (and moisture) measurements. The skilled person will appreciate that the probe depth detector 12 can be configured in various ways, for example, it can be a detector 12 that is part of the handle 1b and that is arranged to measures the detector’s height D above an opposite top soil level T (the height D being representative of the depth of the main body 1a in the soil S). The height detector 12 can include e.g. an optical detector (detecting a distance D between the handle 1b and an opposite field surface T), a laser detector, audio detector, draw wire detector, radar detector or the -like. The depth sensor 1 can be communicatively connected to the signal processor 10 (e.g. wired or wirelessly), to provide a detection result thereto.
Operation or use of the probe can involve a method for measuring soil density, including the steps: -inserting a probe 1 into the soil S, for example into a hole drilled in the soil S; -emitting gamma radiation (and preferably no other radiation) from the probe 1 into the soil S, by the gamma radiation source 3; - detecting, by the detector 5 of the probe 1, soil background gamma radiation as well as backscattered gamma radiation that emanates from the source 3 of the probe 1;
-processing, by a signal processor 10, a radiation detection signal (of the detector) to correct for a signal component that is associated with the soil background radiation, thereby providing a processed detector signal; and -generating, by the signal processor 10, a soil density result (i.e. field bulk density) based on the processed detector signal.
Further steps can include processing the measurements of soil moisture, and combining the soil moisture measurements with the measured field bulk density to determine dry bulk density (as will be explained below).
For example the soil density result can be based on a predetermined relation between soil density and an amount of backscattered radiation, wherein the predetermined relation has preferably been determined by Monte Carlo simulations.
During operation, preferably, the radiation detector translates recorded gamma radiation (which includes both background radiation BR as well as backscattered source radiation SR) into a digital signal for further signal analysis (by the signal processor 10). The digital signal can include energy or spectrum information of the detected radiation, in particular the energy spectrum, as will be appreciate by the skilled person.
During use, the signal processor 10 can reduce (preferably subtract) the signal component associated with soil background radiation.
To that aim, the signal processor 10 can discriminate between the radiation emanating from the source and background radiation based on a spectrum analysis. The discrimination can be made based on the results of the Monte
Carlo simulations (wherein the MC simulation results can be simulated standard spectra of four radionuclides, which can e.g. be stored in a memory of the signal processor).
As will be clear to the skilled person, in the process of full spectrum analysis, the measured spectrum is fitted with a set of so-called "standard spectra”, which are the responses of a specific radionuclide in the geometry as used during the measurement. In this case, the measured spectrum originates from the three radionuclides K-40, U-238 and Th-232 which are present in the soil as well as source radionuclides (e.g. Na-22) used in the density meter. The required standard spectra of these four radio nuclides can be determined using the Monte Carlo simulations, and can be stored in a memory of the probe or signal processor. See e.g. Hendriks, P.H., Limburg,
J., de Meijer, R.J., 2001. Full-spectrum analysis of natural gamma-ray spectra. J. Environ. Radioact. 53, 365-80.
For example, during operation, the detector 5 can generate an initial count rate, including counts for both background radiation as well as counts for backscattered source radiation. The processor 10 is configured to process this count rate (provided in said digital signal), generating a corrected count rate that only reflects the counts for backscattered source radiation (i.e. wherein counts that are associated with the soil radionuclides are removed), in particular using the Monte Carlo simulation information (in particular the simulated response spectra of the three soil radionuclides and the source radionuclides). Herein, the corrected count rate equals the recorded count rate minus the background count rate.
Subsequently, conversion from corrected count rate to soil density can be achieved (by the signal processor 10) by the calibration curve derived from the Monte Carlo simulations (see Figure 4).
For example, in the process of such calibration, the geometry of the probe can be an input parameter (and is fixed) of the simulations, wherein the density of the soil is used as a variable, wherein the simulation is carried out to determine the relation between densities of soil and output (count rate).
An example of a resulting calibration curve is depicted in Figure 4, showing graphs of estimated corrected count rate CR (%) versus field bulk density (kg/l) for three different detector-source distances X1, X2, X3, as determined by the afore-mentioned MC simulations. The curves show that the uncertainty in density is smallest for distance X2, whereas distance X3 will not lead to reliable results over the whole soil density range. Therefore, also, distance X2 is preferably selected as source-detector distance X of the probe during probe manufacture, and the respective curve X2 can be used by the probe’s processor 10 (the curve X2 e.g. being stored in a memory of the processor 10) for processing the detector results.
It has been found that in this way, good and reliable soil density measurements can be achieved, swiftly and in an operator friendly manner.
It is preferred that a detection result is provided to a probe operator, e.g. via a user interface UI of the probe itself and/or to a remote user interface (wherein the signal processor 10 can be configured to provide the soil density result to the user interface Ul via a suitable communication link, e.g. wired or wirelessly, and for example digitally). The user interface
UI can include a display for displaying probe information (e.g. a density detection result and/or a depth measurement result) to the operator.
Alternatively or additionally the user interface UI can be configured to provide such information via sound signals our voice generation. As an example, the user interface UI can be part of or mounted to the handle 1b of the probe. Also, the user interface may be embodied in a portable user device, e.g. a cell phone or tablet, that can be configured to wirelessly communicate with the signal processor 10 (e.g. via an optional communication means of the signal processor 10). A respective wireless communication protocol can e.g. be a commonly known WIFI protocol,
Bluetooth or-the like.
During operation, the following equation can for example be used (by the signal processor) to determine the soil density p: p=a*exp(b * C),
wherein a and b are calibration parameters (that can be determined from a combination of the Monte Carlo simulations and calibration measurements, see e.g. Figure 4), C is the corrected count rate after correcting for the background radiation and source decay. As will be known to the skilled person, source decay follows from the half-life and time difference between source calibration and the actual measurement by the probe, thus, the signal processor has appropriate information (i.e. a timer to determine the time difference, as well as the source calibration time) to calculate such source decay.
Besides, in case an optional moisture detector 8 is implemented, the signal processor can use a moisture detection result (received from that detector 8) to further process a soil density result to calculate dry bulk density.
Preferably, for each density measurement, a probe depth is provided, e.g. by the probe depth sensor 12. A respective probe depth can e.g. be stored (in a memory) and/or provided to an operator via the user interface UI.
It follows that the probe 1 can measure soil bulk density in the field. In particular, the probe 1 can measure backscattering of radionuclides emitted by a low active radioactive source mounted in the probe. As will be appreciated, the amount of backscatter is a measure of the field bulk density of soil. As follows from the above, during operation, the gamma-ray measurements can be corrected for background, measured simultaneously, based on analysis of the full spectrum (Hendriks et al., 2001). The relation between field bulk density and amount of backscattered radiation can be determined by said Monte Carlo simulations.
Soil bulk density is an important physical soil health indicator and generally used for assessing soil quality. The probe 1 can measure the backscatter of gamma radiation emitted from the (low-activity) source, which can be used without legislation. It is preferred that the probe 1 can measure up to 100 cm deep and, preferably only needs a hole H of at most 10 cm diameter, preferably at most 5 cm (e.g. 3 cm) diameter for such a measurement. With this probe 1, there is no need for a soil pit or any laboratory work to determine soil bulk density, the probe 1 can provide the measured densities directly during measurement in the field. This allows the soil scientist to gather more information in the vertical, as well as the horizontal scale. For example, a series of measurements can be performed at different depths in a single hole, to provide a vertical profile.
The probe system can be designed for easy operation in the field.
As follows from the above, before measurement, a small hole (e.g. about 30 mm diameter) can be drilled by a hand auger or other coring device, a depth
D of the hole e.g. being at most 2 meter (for example about 1 meter), measured from the top field surface. Preferably, the width or diameter of the hole H is the same as the width or diameter of the probe’s main body 1a so that the body la can snuggingly fit into the hole H.
The probe 1 can then be placed in the hole H up to the preferred depth. Guiding and fixing the position can be made easy using an optional guiding mount. The guiding mount (or guiding system) can include a horizontal support or disc placed on the soil surface, wherein the horizontal support has an extension (e.g. a vertical guiding element or sleeve) in line with the borehole through which the probe 1 can move vertically.
Optionally, a fixation device, e.g. a screw on the guiding system, can be provided for fixating the probe 1 with respect to the support (at least during a measurement period).
It is preferred that the probe 1 generates a depth measurement result during operation, for example during entry into the hole H. The measured depth can be provided to the operator via an afore-mentioned user interface. The user interface UI can assist in positioning the probe 1, e.g. by continuously displaying the actual depth (determined by the depth sensor 12).
During operation, the operator can initiate a soil density measuring, e.g. by control of the user interface Ul, after which the probe 1 starts a gamma ray detecting period, detecting the radiation and processing the detection results. A measurement can be automatically stopped by the probe 1 (e.g. by the signal processor), for example at or within 60 seconds from the start and preferably at about 30 seconds after the start, and provide a detection result (i.e. a field bulk density and optionally a dry bulk density) to the operator via the user interface UI. It has been found that within 30 seconds, a statistical accuracy of ~0.01g/cms3 can be achieved by the probe.
A shorter measurement period (i.e. less than 30 seconds) is possible, but will result in a lower accuracy.
It will be appreciated that for a correction to providing dry bulk density values, a model can be used that incorporates moisture measurements from an internal (e.g. capacitance-based) moisture sensor 8.
Optionally, data acquisition/storage of the detection results can be achieved, e.g. by the signal processor or another device (e.g. a n optional memory of the user interface UI). For example, at each measurement location the density can be determined at a series of depths. For each measurement location, the position 1s stored automatically using GPS (Global Positioning
System) data, that can be provided e.g. by an optional GPS system (which may be part of the probe 1 and/or of the user interface UI). Optionally, the probe 1 and/or user interface UI can be configured for transferring measurement data via a computer network, e.g. via Internet, for example in
CSV format by e-mail, Whatsapp, messaging or the-like.
While specific embodiments have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described in the foregoing without departing from the scope of the claims set out below.
For example, in the drawings, the detector 5 and processor 10 are depicted as separate components, but it will be clear that the detector and processor can be integrated with each other (e.g. providing a spectrometer).
Claims (15)
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| NL2033056A NL2033056B1 (en) | 2022-09-16 | 2022-09-16 | Portable soil density meter |
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| NL2033056A NL2033056B1 (en) | 2022-09-16 | 2022-09-16 | Portable soil density meter |
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