Patent Description:
Measuring the moisture content of materials such as surface soils using cosmogenic neutron detection is known in the art. Cosmic rays continually bombard the Earth and penetrate into materials at the land surface, including soil, atmosphere, water, man-made structures, vegetation, and the like. Inside these materials, cosmogenic highenergy (><NUM> MeV) neutrons collide with matter and produce fast (<<NUM> MeV) cosmogenic neutrons. These neutrons interact with matter in reactions called neutron scattering that lead to the gradual decrease of neutron energies and eventually to the removal of neutrons from the environment. Hydrogen is by far the most efficient element in scattering neutrons. Therefore, moisture content of the soil through which neutrons have traveled can be inferred from the measured neutron flux, which is inversely correlated with soil moisture content. This principle has been used to develop a cosmogenic neutron soil moisture measuring method widely accepted around the world.

However, there are limitations to this method. At any given location near the land surface, neutrons are present that have interacted with the land surface material anywhere from the near field (within meters of the location) to the far field (or wide-area, hundreds of meters from the location). This reduces the accuracy of measurements by introducing a disproportionate amount of signal to the detector, as the local intensity of cosmogenic neutrons may not reflect average water content of the material over this broad region.

Additionally, neutron detectors must be calibrated. Calibration of cosmogenic neutron probes is typically done by comparing neutron measurements with independently obtained soil moisture to obtain calibration parameter No (neutron intensity that would be measured above a completely dry soil). Independent soil moisture is obtained by collecting a large number (typically <NUM>, prescribed by Zreda et al. , <NUM>) of soil samples within the hectometer-sized footprint and measuring soil water content by the gravimetric (oven drying) method. This is a difficult, time-consuming and expensive process. Additionally, it does not work in soils with stones, as sample collection is difficult, in areas with rock outcrops, and in areas with organic litter covering soil.

A sensor according to the preamble of claim <NUM> and according to the preamble of claim <NUM> are known from <CIT>.

Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.

The invention relates to a sensor as defined in claim <NUM> and a method as defined in claim <NUM>.

Embodiments of the present disclosure provide a wide area cosmogenic neutron sensor for detecting moisture within a measurement surface. Briefly described, in architecture, one embodiment of the sensor, among others, can be implemented as follows. A neutron detector is positionable above a measurement surface, wherein a moderator material is positioned around at least a portion of the neutron detector to form a moderated neutron detector. A neutron shield is positioned around a portion of the moderated neutron detector, whereby the neutron shield substantially covers an entirety of a bottom of the moderated neutron detector, wherein the neutron shield is positioned to interact with cosmogenic neutrons propagating to the bottom of the moderated neutron detector, thereby substantially blocking fast, epithermal, and thermal cosmogenic neutrons propagating to the bottom of the moderated neutron detector from reaching the moderated neutron detector, and wherein the neutron shield is not positioned on at least a top side of the moderated neutron detector. A stand structure holds the moderated neutron detector and the neutron shield in a position a spaced vertical distance above the measurement surface with the bottom side of the moderated neutron detector facing the measurement surface. Wide area cosmogenic neutrons propagating from the measurement surface travel through an air space before arriving at the moderated neutron detector.

The present disclosure can also be viewed as providing a wide area cosmogenic neutron sensor for detecting moisture within a measurement surface. Briefly described, in architecture, one embodiment of the sensor, among others, can be implemented as follows. A neutron detector is positionable above the measurement surface, wherein a first moderator material is positioned around only a portion of the neutron detector to form a moderated neutron detector. A second moderator material is positioned along a bottom of the moderated neutron detector, the second moderator material being separate from the first moderator material. A neutron shield is positioned along the bottom of the moderated neutron detector, whereby the neutron shield substantially covers an entirety of the bottom of the moderated neutron detector, wherein the neutron shield is positioned to interact with cosmogenic neutrons propagating to the bottom of the moderated neutron detector, thereby substantially blocking fast, epithermal, and thermal cosmogenic neutrons propagating to the bottom of the moderated neutron detector from reaching the moderated neutron detector, and wherein the neutron shield is not positioned on at least a top side of the moderated neutron detector. A stand structure holds the moderated neutron detector and the neutron shield in a position a spaced vertical distance above the measurement surface with the bottom side of the moderated neutron detector facing the measurement surface. Wide area cosmogenic neutrons propagating from the measurement surface travel through an air space before arriving at the moderated neutron detector.

The present disclosure can also be viewed as providing a method for detecting wide area cosmogenic neutrons for use in detecting moisture within a measurement surface. In this regard, one embodiment of such a method, among others, can be broadly summarized by the following steps: positioning a neutron detector above the measurement surface, wherein a moderator material is positioned around at least a portion of the neutron detector to form a moderated neutron detector; placing a neutron shield around a portion of the moderated neutron detector, whereby the neutron shield substantially covers an entirety of a bottom of the moderated neutron detector, whereby the neutron shield is positioned to interact with cosmogenic neutrons propagating to the bottom of the moderated neutron detector, thereby substantially blocking fast, epithermal, and thermal cosmogenic neutrons propagating to the bottom of the moderated neutron detector from reaching the moderated neutron detector, and wherein the neutron shield is not positioned on a top side of the moderated neutron detector; and spacing the moderated neutron detector a spaced vertical distance about the measurement surface with a stand structure, whereby the bottom side of the moderated neutron detector faces the measurement surface, whereby wide area cosmogenic neutrons propagating from the measurement surface travel through an air space before arriving at the moderated neutron detector.

Detectors that can be used for measuring the intensity of cosmogenic neutrons near the land surface have been known for decades (Knoll, <NUM>), and dedicated sensors for measuring soil moisture have been around for approximately ten years (Zreda et al. , <NUM>, <NUM>). Such sensors, which we call Cosmogenic Neutron Sensors (CNS), measure the local intensity of neutrons in an energy band that is dictated by the design of the sensor. An unmoderated, or bare, thermal neutron detector is sensitive to thermal neutrons having a median energy of <NUM> eV. Adding a plastic moderator around the thermal neutron detector shifts the energy sensitivity of the thermal neutron detector to neutrons having higher energies. An energy band may be selected to optimize the ability of the sensor to detect neutrons that have maximum sensitivity to water in the material near the surface. The standard CNS (Zreda et al. , <NUM>) has <NUM> of plastic surrounding the bare detector. It measures neutrons in energy band <NUM> eV to <NUM> eV, which is sensitive to hydrogen content.

The intensity of cosmogenic fast neutrons displays a complex spatial pattern around the neutron measuring device, with contributions that vary with direction and distance. The current neutron sensors count neutrons coming from all directions and distances and produce a single integral value of neutron intensity; the directional and distance information is lost in the integration process. That measured value is converted to an integrated value of soil moisture by means of a calibration function.

The distance that contributes <NUM>% (<NUM>-e-<NUM>) of neutrons counted is considered the effective measurement range of a cosmogenic sensor, or its "footprint". The physical spatial neutron distribution that reflects the probability of a measured neutron originating from the material at a given distance is called the spatial sensitivity function of the neutrons. In the very common case of radial symmetry, the function is referred to as the radial sensitivity function. When the cosmogenic method for measuring soil moisture was developed, its developers determined from neutron transport modeling that the radial sensitivity function follows exponential decay with distance (Desilets and Zreda, <NUM>; "conventional" in <FIG>). But recent modeling results (Köhli et al. , <NUM>; Schrön et al. , 2017b), as well as our own field measurements, suggest a different radial sensitivity that can be approximated by doubleexponential functions.

<FIG> are graphs showing the radial sensitivity functions for conventional and revised models of cosmogenic soil moisture probes. The normalized horizontal weight for the conventional model is shown in broken lines, while the normalized horizontal weight for the revised model is shown in solid lines. The boundaries of fractional contribution <NUM> are indicated below the curves in both <FIG>. The conventional radial sensitivity function of Desilets and Zreda (<NUM>) is an exponential curve, and the revised radial sensitivity function of Schrön et al. (2017b) is a double exponential curve. <FIG> shows that both conventional and revised models are similar at radial distances greater than <NUM> meters. <FIG> shows that the models are very different at shorter distances from <NUM> meters to about <NUM> meters.

In <FIG>, the boundaries of fractional contribution <NUM> indicate that, up to a distance just under <NUM> meters, the neutron contribution to the total measurement of a CNS is about <NUM>%. Thus, the neutrons that come from short distances contribute a large fraction of the total measured neutron intensity, thereby interfering with wide-area measurement. In <FIG>, the boundaries of fractional contribution <NUM> indicate that another <NUM>% of the neutrons in the total measurement come from distances less than <NUM> meters, while another <NUM>% comes from distances between that point and about <NUM> meters.

Critically, the contribution to the total neutron count is not uniform within the footprint, with a large proportion coming from the first few meters around a detector. This important fact was not well understood among the community of CNS experts. The ability separately to measure local and wide-area neutrons would represent a powerful improvement to the CNS technique. However, such measurement discrimination is impossible with the currently-used cosmogenic soil moisture measuring devices, as they are not capable of discerning which neutrons have contributed to the total measurement.

<FIG> is an illustration of the neutron sources incident upon a neutron detector <NUM>. A neutron detector <NUM> is shown oriented above a measurement surface <NUM>. In use, the measurement surface <NUM> may be the ground, construction, a body of water, and the like. Neutrons are incident upon the detector <NUM> from overhead, from the wide area below the detector <NUM>, and from the local area below the detector <NUM>.

The measured neutron intensity contains neutrons coming directly from above the detector <NUM>, also called overhead neutrons <NUM>. These overhead neutrons <NUM>, when corrected for the effects of solar activity, atmospheric pressure, latitude and longitude, and other conditions, constitute a constant background in all measurements. They have no history of interactions with soil water, and are therefore generally undesirable. Removal of overhead neutrons <NUM> may decrease the noise, and thus improve the sensitivity and accuracy of the neutron sensor <NUM> to changes in soil moisture. This in turn improves the signal-to-noise ratio and increases the dynamic range of the CNS method.

The measured neutron intensity also contains a significant amount of neutrons coming from areas below the detector <NUM> that are several meters or hectometers away from the detector <NUM>, also called wide area neutrons <NUM>. Although the area enclosed within less than <NUM> radius around the detector contributes approximately one-third to the total number of neutrons measured, a significant remainder of the detected neutrons are wide area neutrons.

The measured neutron intensity also contains a significant amount of neutrons coming from areas below the detector <NUM> that are near the detector <NUM>, also called local area neutrons <NUM>. The neutrons coming from below the detector <NUM> can distort the measurement of wide area average moisture value.

This is important for at least two reasons. First, an accurate measurement of a wide area measurement surface should minimize the local area neutrons <NUM>. If wide-area measurement is desired, the neutrons coming from below should be reduced or substantially eliminated. Second, an accurate measurement of a local area measurement surface should minimize the wide area neutrons <NUM>. High sensitivity to local area neutrons <NUM> can be used to measure near-field (within meters) soil moisture. However, because far-field neutrons (those beyond a few meters from the detector <NUM>) contribute approximately <NUM>% to the total neutrons measured, they have to be blocked if near-field measurement is desired.

Furthermore, the neutrons coming from below and above the detector <NUM>, <NUM> make up approximately <NUM>% of the measured total neutrons, although this number depends on soil moisture and other local conditions. The remaining ~<NUM>% are wide area neutrons <NUM> coming from the sides from distances between a few meters and a few hectometers. These numbers represent average distributions of neutrons coming from above, below, and to the side of the detector <NUM>. There may be some directional overlapping of neutrons from any direction. For example, a portion of neutrons <NUM> may not hit the detector <NUM> from above, but may enter from the side. A portion of neutrons <NUM> may hit the detector <NUM> from above rather than from the side. This representation of neutrons <NUM>, <NUM>, and <NUM> and their directions with respect to the detector <NUM> merely indicates that neutrons are probabilistically likely to come from these respective directions. Given these distributions, the ability preferentially to select these neutrons is desirable, even required, for proper wide-area measurement of soil moisture.

<FIG> is an illustration of the prior art cosmogenic neutron sensor <NUM>. The moderated cosmogenic neutron sensor <NUM> of the prior art may include a hydrogen-sensitive neutron detector <NUM>. The hydrogen-sensitive neutron detector <NUM> may include a thermal neutron detector surrounded by a neutron moderator, as shown in <FIG>. The neutron moderator may be made from a moderating material, such as polyethylene, that makes the thermal neutron detector sensitive to epithermal neutrons in a desired energy range. The signal from hydrogen-sensitive neutron detector <NUM> may be transmitted via a cable <NUM> to electronic modules and data logger <NUM>. A power supply <NUM> may provide power to the hydrogen-sensitive neutron detector <NUM>. As shown in <FIG>, above, the prior art cosmogenic neutron sensor <NUM> may receive neutrons from overhead, from a wide area, and from a local area.

<FIG> is an illustration of exemplary prior art hydrogen-sensitive neutron detectors <NUM>, <NUM>, <NUM>. Hydrogen-sensitive neutron detector <NUM> includes a thermal neutron detector <NUM>, which is a gas proportional counter. Thermal neutron detector <NUM> may include a moderator <NUM> surrounding the thermal neutron detector <NUM>, with a space <NUM> in between. The space <NUM> may generally be a vacuum or an air-filled space. Hydrogen-sensitive neutron detector <NUM> includes a thermal neutron detector <NUM>, which is a lithium foil detector. Thermal neutron detector <NUM> may include a moderator <NUM> surrounding the thermal neutron detector <NUM>, with a space <NUM> in between. Hydrogen-sensitive neutron detector <NUM> includes a fast neutron detector <NUM>, which may be a scintillator detector. Other hydrogen-sensitive neutron detectors may be included the scope of this disclosure.

It should be noted that, in the drawings, areas shown with parallel line hatching indicate neutron shields. Areas shown with cross hatching indicate moderators. And areas shown with stippling indicate constant hydrogen materials.

<FIG> is an illustration of neutrons <NUM>, <NUM>, <NUM> impinging upon the prior art moderated cosmogenic neutron sensor <NUM>. Cosmogenic neutrons <NUM> propagate from space to objects and soil on earth. The cosmogenic neutrons <NUM> may become overhead neutrons <NUM>, which impinge upon the moderated cosmogenic neutron sensor <NUM> without interacting with any objects or soil. The cosmogenic neutrons <NUM> may interact with objects or hydrogen in soil and become wide area or local area neutrons <NUM>, <NUM>. Wide and local area neutrons <NUM>, <NUM>, along with overhead neutrons <NUM>, may propagate toward and impinge upon the moderated cosmogenic neutron sensor <NUM>, reaching the thermal neutron sensor <NUM> and causing a measurement to be made from all directions of the neutron sources. The moderated cosmogenic neutron sensor <NUM> may detect the total intensity of all neutrons impinging upon the cosmogenic neutron sensor <NUM>.

<FIG> is an illustration of a cosmogenic neutron detector <NUM> in accordance with a first exemplary embodiment of the present disclosure. The cosmogenic neutron detector <NUM> includes a hydrogen-sensitive neutron detector <NUM> orientable above a measurement surface <NUM>. A neutron shield <NUM> is positionable on the hydrogen-sensitive neutron detector <NUM>. The neutron shield <NUM> is positioned to interact with at least a portion of cosmogenic neutrons <NUM>, <NUM>, <NUM> propagating in a direction of the hydrogen-sensitive neutron detector <NUM>.

The hydrogen-sensitive neutron detector <NUM> may be any suitable type of neutron detector, including gas-proportional detectors with moderator, scintillation neutron detectors, semiconductor neutron detectors, and others. The hydrogen-sensitive neutron detector <NUM> may respond to energies between <NUM> and <NUM> MeV, or any subrange thereof. The hydrogen-sensitive neutron detector <NUM> may be sized and shaped to detect cosmogenic neutrons over a desired area or with a desired sensitivity. The hydrogen-sensitive neutron detector <NUM> may include a moderator to make the hydrogen-sensitive neutron detector <NUM> sensitive to a desired range of neutrons. The hydrogen-sensitive neutron detector <NUM> may detect neutrons from all directions without discrimination.

The term "neutron detector" <NUM> in this disclosure may refer to any suitable type of hydrogen-sensitive neutron detector, with or without a moderator, as some neutron sensors do not require moderated neutrons. For ease of representation in the drawings, the neutron detector <NUM> may generally be shown as a box. However, the box is a diagrammatic representation only; the neutron detector <NUM> may actually include one or more tube detectors, sheet detectors, or moderators.

The neutron detector <NUM> is orientable above a measurement surface <NUM>. The neutron detector <NUM> may be oriented in any suitable direction, whether vertically or horizontally, depending on the desired use. The measurement surface <NUM> may be an area or surface below the cosmogenic neutron sensor <NUM> of any size, elevation, and material. In one example, the measurement surface <NUM> may be an area of land having dirt, soil, rocks, water, urban construction, or some combination thereof. The measurement surface <NUM> may have a local area, a wide area, and an intermediate area. The local area may be a portion of the measurement surface <NUM> located immediately below the physical footprint of the neutron detector <NUM>, and often, the radial location below and within several meters of the cosmogenic neutron sensor <NUM>. In one example, the local area may be located within <NUM>, meter, <NUM>, meters, <NUM>, meters, <NUM>, meters, or greater of the cosmogenic neutron sensor <NUM>. The wide area may be a portion of the measurement surface <NUM> located further away from the cosmogenic neutron sensor <NUM>. In one example, the wide area may begin where the local area ends, and may continue to the extent of the measurement surface. For instance, if, hypothetically, the local area is located within about <NUM> meters of the cosmogenic neutron sensor <NUM>, the wide area may begin at about <NUM> meters from the cosmogenic neutron sensor <NUM> and may continue until the end of the measurement area. The intermediate area may be a portion of the measurement surface <NUM> located between the local area and the wide area. For example, the intermediate area may include a portion of the local area and a portion of the wide area.

The neutron detector <NUM> may be oriented above the measurement surface <NUM> in use. Where the measurement surface <NUM> is generally land or water, this means that the neutron detector <NUM> may be positioned vertically or horizontally above the measurement surface <NUM>. This may cause overhead neutrons <NUM> to propagate toward the cosmogenic neutron sensor <NUM> substantially from above, while local area and wide area neutrons <NUM>, <NUM> propagate toward the cosmogenic neutron sensor <NUM> substantially from below and from the sides, respectively.

The neutron shield <NUM> may be positionable on the neutron detector <NUM>. The shield <NUM> interacts with neutrons <NUM>, <NUM>, <NUM> propagating in a direction of the neutron detector <NUM> by causing them to be substantially blocked. This may prevent the neutrons <NUM>, <NUM>, <NUM> from reaching the neutron detector <NUM>. For the purposes of this disclosure, "interact" means to prevent a neutron from reaching the neutron detector <NUM> in the measurable energy range. Therefore, when the shield <NUM> interacts with the neutrons <NUM>, <NUM>, <NUM> propagating in a direction of the neutron detector <NUM>, the shield <NUM> causes those neutrons to either fail to reach the neutron detector <NUM>, or to fail to reach the neutron detector <NUM> with a measurable strength, which, in the field of neutron detector, is equivalent to preventing them from reaching the neutron detector <NUM>. In this way, the neutrons that interact with the shield <NUM> are blocked or prevented from being detected by the neutron detector <NUM>.

The shield <NUM> may be made from any suitable material for slowing or reflecting neutrons, such as a plastic like high density polyethylene (HDPE) or ultra-high molecular weight polyethylene (UHMW). Various combinations of a neutron moderator such as HDPE and neutron filter such as cadmium can act as the neutron shield as well.

The shield <NUM> may be positioned to interact with at least a portion of cosmogenic neutrons <NUM>, <NUM>, <NUM> propagating in a direction of the neutron detector <NUM>. Depending on use, a user may wish to shield the neutron detector <NUM> from neutrons propagating from one or more sources or directions. For example, a user wishing to measure only the local area neutrons <NUM> may wish to shield the neutron detector <NUM> from wide area and overhead neutrons <NUM>, <NUM>. A user wishing to measure only wide area neutrons <NUM> may wish to shield the neutron detector <NUM> from local area and overhead neutrons <NUM>, <NUM>. A user wishing to measure only neutrons from an intermediate area may wish to shield the neutron detector <NUM> from a portion of local area neutrons <NUM> and a portion of wide area neutrons <NUM>. A user wishing to reduce the noise floor of the cosmogenic neutron sensor <NUM> may wish to shield the neutron detector <NUM> from overhead neutrons <NUM> in combination with other shielding patterns.

The location and sizing of the shield <NUM> may be dependent on the size of the neutron detector <NUM>, the height of the detector above the measurement surface <NUM>, the size of the measurement surface <NUM>, or some combination thereof. In one example, a shield <NUM> positioned to interact with local area neutrons <NUM> may be located below the neutron detector <NUM> and may be at least the size of the lower side of the detector <NUM>. In one example, the shield <NUM> may extend past the lower side of the detector <NUM> to interact with neutrons from a greater distance away. For wide area sensing, the shield <NUM> may be somewhat larger than the lower side of the detector <NUM>. The size of the shield <NUM> below may influence what percentage of neutrons from below are blocked. In another example, a shield <NUM> positioned to interact with wide area neutrons <NUM> may cover the sides of the neutron detector <NUM> not facing the measurement surface <NUM>. In another example, a shield <NUM> positioned to interact with overhead neutrons <NUM> may be located above the neutron detector <NUM> and may be at least the size of the upper side of the detector <NUM>. In one example, the shield <NUM> may extend past the upper side of the detector <NUM> to interact with neutrons from a greater angle above the detector <NUM>.

<FIG> shows the shield <NUM> interacting with neutrons from many different potential sources. Cosmogenic neutrons <NUM> propagate down from space and toward the measurement surface <NUM>. Overhead neutrons <NUM> reach the shield <NUM> and are slowed or deflected when interacting with the shield material. Cosmogenic neutrons <NUM> that reach the measurement surface <NUM> interact with hydrogen in the surface material and propagate upward toward the cosmogenic neutron sensor <NUM>. Wide area neutrons <NUM> and local area neutrons <NUM> reach the shield <NUM> and are slowed or deflected when interacting with the shield material. In one example, neutrons that do not interact with the shield <NUM> reach the moderator and the neutron detector <NUM> and are counted. In this way, only neutrons from particular and desired sources are detected by the cosmogenic neutron sensor <NUM>.

The feasibility of a shield <NUM> has been confirmed by field experiments and neutron transport modeling over areas with contrasting water content. One of the experiments was a transect across a water tank surrounded by soil obtained using a standard moderated detector shown in <FIG> and <FIG> followed by the cosmogenic neutron sensor shown in <FIG>, below. The results, shown in <FIG>, below, show that the standard detector is highly sensitive to local neutrons, and thus is not a good wide-area detector, whereas the detector with neutron shield below has a much reduced sensitivity to local neutrons and thus is a good wide-area detector. Other operating examples are discussed below.

The cosmogenic neutron sensor <NUM> may include additional electronic components, such as a power source, communications interface, control hardware, and the like. For portable detectors <NUM>, the power source may be a battery or solar power. The communications interface may allow a user to collect and retrieve neutron data from the cosmogenic neutron sensor <NUM>. The communications interface may include communications hardware, such as data ports, antennas, and the like, and may be accessed by wired or wireless communication. The control hardware may allow a user to operate and troubleshoot the device.

<FIG> are illustrations of cosmogenic neutron sensors <NUM> in accordance with a first exemplary embodiment of the present disclosure.

<FIG> shows a cosmogenic neutron sensor <NUM> with a wide area configuration. Neutrons <NUM> propagating from a local area below the cosmogenic neutron sensor <NUM> are blocked from reaching the neutron detector by a shield <NUM>, while wide area neutrons <NUM> and overhead neutrons <NUM> reach the neutron detector.

<FIG> shows a cosmogenic neutron sensor <NUM> with a wide and local area configuration. Neutrons <NUM> propagating from overhead are blocked from reaching the neutron detector by a shield <NUM>, while wide area nueutrons <NUM> and local area neutrons <NUM> reach the neutron detector.

<FIG> shows a cosmogenic neutron sensor <NUM> with a wide area and noise reduction configuration. Neutrons <NUM>, <NUM> propagating from overhead and from a local area below the cosmogenic neutron sensor <NUM> are blocked from reaching the neutron detector by a shield <NUM>, while wide area neutrons <NUM> reach the neutron detector.

<FIG> shows a cosmogenic neutron sensor <NUM> with a local area and noise reduction configuration. Neutrons <NUM>, <NUM> propagating from overhead and from a wide area below the cosmogenic neutron sensor <NUM> are blocked from reaching the neutron detector by a shield <NUM>, while local area neutrons <NUM> reach the neutron detector.

<FIG> is an illustration of a wide area cosmogenic neutron sensor <NUM>, in accordance with the first exemplary embodiment of the present disclosure. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM>. The neutron detector <NUM> may be orientable above a measurement surface <NUM>. A neutron shield <NUM> may be positioned to interact with cosmogenic neutrons propagating from a local area of the measurement surface <NUM> below the neutron detector <NUM>. <FIG> shows a cross-sectional illustration of the cosmogenic neutron sensor <NUM>. The neutron detector <NUM> is oriented above a measurement surface <NUM>. The neutron shield <NUM> is positioned on the neutron detector <NUM> at a bottom side of the detector <NUM>. In one example, the neutron shield <NUM> may be made from HDPE and may be about <NUM> centimeters in thickness. In the example shown in <FIG>, the neutron shield <NUM> covers the entirety of the bottom side of the detector <NUM> and extends outward past the neutron detector <NUM>. This may provide shielding from the local area of the measurement surface <NUM> that is both directly below the neutron detector <NUM> and somewhat farther away. In another example, the neutron shield <NUM> may be smaller, covering only the bottom side of the detector <NUM>.

This exemplary cosmogenic neutron sensor <NUM> may allow a user to measure only cosmogenic neutrons propagating from overhead and from a wide area of the measurement surface <NUM>. This may allow the cosmogenic neutron sensor <NUM> higher sensitivity to wide area measurements, as the substantial contribution of neutrons from the local area of the measurement surface <NUM> will not be measured due to the neutron shield <NUM>. In operation, this wide area-type cosmogenic neutron sensor <NUM> may be used at some height above the measurement surface <NUM> so as to detect neutrons from a broad area of the measurement surface <NUM>.

<FIG> is an exemplary transect graph <NUM> of neutron intensity measured using the prior art moderated cosmogenic neutron detector and the cosmogenic neutron sensor <NUM> of <FIG>. The two sensors were used to measure neutron intensity over a local area while being moved over a land measurement surface, over a water measurement surface, and back over a land measurement surface. The results of the prior art moderated cosmogenic neutron detector are shown with circular plot points as a function of position, while the results of the cosmogenic neutron sensor <NUM> of <FIG> are shown with square plot points as a function of position. The space between lines <NUM> indicates where the measurement surface was water. The space outside of lines <NUM> indicates where the measurement surface was land. The plot for the prior art sensor shows that it is sensitive to local area neutrons, and therefore shows a large change at the boundary between the water and the dry land. This is because the local area neutron contribution from a water measurement surface is lower than the local area neutron contribution from a land measurement surface. In contrast, the plot for the cosmogenic neutron sensor <NUM> shows no statistically relevant sensitivity to local neutrons. The neutron intensity count remains nearly constant as the cosmogenic neutron sensor <NUM> moves from land to water and back to land.

<FIG> is an illustration of a local area cosmogenic neutron sensor <NUM>, in accordance with the first exemplary embodiment of the present disclosure. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM> having a thermal neutron detector <NUM> inside. The neutron detector <NUM> may be orientable above a measurement surface <NUM>. A neutron shield <NUM> may be positioned to interact with cosmogenic neutrons propagating from an area above the neutron detector <NUM> and a wide area below the neutron detector <NUM>. The neutron shield <NUM> is positioned on the neutron detector <NUM> to shield the neutron detector <NUM> everywhere except for the bottom side of the detector <NUM>. In one example, the neutron shield <NUM> may be made from HDPE and may be about <NUM> centimeters in thickness. In the example shown in <FIG>, the neutron shield <NUM> covers the entirety of the detector <NUM> except for the bottom side of the detector <NUM>. This includes a top side of the detector and horizontal sides of the detector. This may provide shielding from overhead and wide areas of the measurement surface <NUM>.

This exemplary cosmogenic neutron sensor <NUM> may allow a user to measure only cosmogenic neutrons propagating from a local area of the measurement surface <NUM>. This may allow the cosmogenic neutron sensor <NUM> higher sensitivity to local area measurements, as the substantial contribution of neutrons from the wide area of the measurement surface <NUM> and neutrons from overhead will not be calculated due to the neutron shield <NUM>. In operation, this local area-type cosmogenic neutron sensor <NUM> may be used at a short height above the measurement surface <NUM> so as to detect neutrons from a specific surface area of the measurement surface <NUM>.

<FIG> is an exemplary transect graph <NUM> of neutron intensity measured using the prior art moderated cosmogenic neutron detector and the cosmogenic neutron sensor <NUM> of <FIG>. The feasibility of this cosmogenic neutron sensor <NUM> was confirmed by field experiments and neutron transport modeling over areas with contrasting water content. One was a transect across a water tank sunken into soil in which the prior art moderated detector was used, followed by the cosmogenic neutron sensor <NUM>. As a control, the cosmogenic neutron sensor <NUM> was also used over the same soil area without the water tank present. The space between lines <NUM> indicates where the measurement surface was water, while the space outside lines <NUM> indicates where the measurement surface was land. The circle plot points show the baseline neutron intensities obtained by the cosmogenic neutron sensor <NUM> before the tank was installed. They indicate uniform soil moisture conditions along the land-water transect. The triangle plot points show measurements made with the cosmogenic neutron sensor <NUM>. The cosmogenic neutron sensor <NUM> is sensitive to local neutrons and shows a change at the boundary between the water and the soil of nearly a factor of two. The square plot points show measurements made with the prior art moderated detector that sees both local neutrons and neutrons from far away. This is why the prior art moderated data show a smaller change between the water and the surrounding soil. The neutron contribution from far-away distances is greatly reduced by the cosmogenic neutron sensor <NUM>, which detects and measures predominantly local area neutrons.

With the cosmogenic neutron sensor <NUM> at the measurement surface, its measurement footprint is similar to the physical size of the detector or its physical footprint, e.g., the length and width spatial dimensions of the detector. In the example shown in <FIG>, this is approximately <NUM> meters. With the detector raised above the measurement surface, the measurement footprint increases significantly to the order of meters or tens of meters, depending on the height at which the cosmogenic neutron sensor <NUM> is placed. This is due to the fact that as the detector is raised above the measurement surface, the measurement footprint increases due to the increased angular area of neutron interaction below the detector, e.g., where the higher the detector is raised, a greater number of neutrons arriving on angular paths can be detected.

The results show that the prior art detector is capable of measuring only a small portion of the contrast between water and land, and thus is not a good local area detector. In contrast, the cosmogenic neutron sensor <NUM> has a much increased sensitivity to local neutrons and thus is a good small-area detector. This shows a much improved performance of the cosmogenic neutron sensor <NUM> with the neutron shield <NUM> around the entire detector <NUM> except at the bottom surface <NUM> in measuring local area neutrons. This measurement is substantially less affected by the wide area neutrons than measurements made with the prior art moderated detector. Essentially, the cosmogenic neutron sensor <NUM> measures substantially only the neutrons shown in <FIG>.

<FIG> is an exemplary graph <NUM> of a calibration function measured using the cosmogenic neutron sensor of <FIG>. The cosmogenic neutron sensor <NUM> was used to measure neutron intensity over solid surfaces with different soil water contents. The results were then normalized to the results of measured neutron intensity over water located in the same area, as in <FIG>. The resultant curve was generally a match to the calibration curve of a standard prior art cosmogenic neutron sensor.

The feasibility of the cosmogenic neutron sensor to measure moisture across the full range of values, from dry soil to water, has been demonstrated by measurements over numerous sites with water content variable between a few percent by volume and <NUM> % (water), assessed independently by taking soil samples, drying them in an oven, and computing water content from the water loss by drying. The results show a clear correlation between known soil water content and the neutron intensity, thus showing the feasibility of the detector.

<FIG> is an exemplary illustration of a wide area calibration site. To calibrate a wide area cosmogenic neutron sensor <NUM>, such as the one discussed in <FIG>, above, a local area cosmogenic neutron sensor may be used to sample the moisture content in a number of local areas <NUM> - <NUM> within the wide area. The moisture content of the local areas <NUM> - <NUM> may be averaged or otherwise processed in order to calibrate the wide area cosmogenic neutron sensor <NUM>. This is discussed further in <FIG>, below.

<FIG> is an illustration of a cosmogenic neutron sensor <NUM> with an overhead neutron shield <NUM>, in accordance with the first exemplary embodiment of the present disclosure. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM>. The neutron detector <NUM> may be orientable above a measurement surface <NUM>. A neutron shield <NUM> may be positioned to interact with cosmogenic neutrons propagating from an area above the neutron detector <NUM>. The neutron shield <NUM> is positioned on the neutron detector <NUM> to shield the neutron detector <NUM> from a top of the detector <NUM>. In one example, the neutron shield <NUM> may be made from HDPE and may be about <NUM> centimeters in thickness. In the example shown in <FIG>, the neutron shield <NUM> covers the entirety of the top of the detector <NUM> and extends further horizontally past the top of the detector <NUM>. This may provide shielding from overhead neutrons. In one example, the neutron shield <NUM> may only cover the top of the detector <NUM> without extending further, depending on the intended use of the cosmogenic neutron sensor <NUM>.

This exemplary cosmogenic neutron sensor <NUM> may allow a user to measure only cosmogenic neutrons propagating from local and wide areas of the measurement surface <NUM>. This may allow the cosmogenic neutron sensor <NUM> higher sensitivity to these measurements, as the substantial contribution of neutrons from overhead will not be calculated due to the neutron shield <NUM>. Essentially, the unimportant neutrons contributing to the noise of the detector <NUM> may be blocked.

<FIG> is an exemplary graph <NUM> of the neutron intensity as a function of neutron shield thickness measured using the cosmogenic neutron sensor <NUM> of <FIG>. Four neutron shields <NUM> of increasing thickness were tested. The greatest decrease in neutron intensity is shown using shields of up to about <NUM> centimeters thick. Thus, a thickness of about <NUM> or more centimeters may be sufficient to block a reasonable number of overhead neutrons from reaching the neutron detector <NUM>.

<FIG> are illustrations of wide area cosmogenic neutron sensors <NUM>, <NUM>, in accordance with the first exemplary embodiment of the present disclosure.

<FIG> shows a cosmogenic neutron sensor <NUM> for detecting wide area neutrons. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM>. The neutron detector <NUM> may be orientable above a measurement surface <NUM>. Neutron shields <NUM>, <NUM> may be positioned on the neutron detector <NUM>. Upper neutron shield <NUM> may be positioned to interact with cosmogenic neutrons propagating from an area above the neutron detector <NUM>. Lower neutron shield <NUM> may be positioned to interact with cosmogenic neutrons propagating from a local area below the neutron detector <NUM>. The neutron shields <NUM>, <NUM> are positioned on the neutron detector <NUM> to shield the neutron detector <NUM> at a top and bottom of the detector. In one example, the neutron shield <NUM> may be made from HDPE and may be about <NUM> centimeters in thickness. In the example shown in <FIG>, the neutron shields <NUM>, <NUM> cover the entirety of the top and bottom of the neutron detector <NUM> and extend further horizontally past the neutron detector <NUM>. This may provide shielding from overhead neutrons and local area neutrons below the neutron detector <NUM>. In one example, the neutron shields <NUM>, <NUM> may only cover the top and bottom of the neutron detector <NUM> without extending further, depending on the intended use of the cosmogenic neutron sensor <NUM>.

<FIG> shows a cosmogenic neutron sensor <NUM> modified to weigh less than the cosmogenic neutron sensor <NUM> of <FIG>. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM>. The neutron detector <NUM> may include a neutron detector <NUM> and a moderating material located around a portion of the neutron detector <NUM>. The moderating material, or moderator, may be positioned to moderate cosmogenic neutrons propagating from a wide area of the measurement surface <NUM> below the neutron detector <NUM>. Portions of the neutron detector <NUM> that will be shielded may not have the moderating material in order to reduce the detector <NUM>'s weight. The neutron detector <NUM> may be orientable above a measurement surface <NUM>. Neutron shields <NUM>, <NUM> may be positioned on the neutron detector <NUM>. The neutron shields <NUM>, <NUM> may be cadmium or a like material, and the size of the shields <NUM>, <NUM> may cover only the top and bottom of the neutron detector <NUM>. This may allow the cosmogenic neutron sensor <NUM> to be smaller and more lightweight than the detector described relative to <FIG>.

<FIG> is an illustration of an intermediate area cosmogenic neutron sensor <NUM>, in accordance with the first exemplary embodiment of the present disclosure. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM>. The neutron detector <NUM> may be orientable above a measurement surface <NUM>. The cosmogenic neutron sensor <NUM> may have a neutron shield <NUM> on the neutron detector <NUM> and a neutron shield <NUM> below the neutron detector <NUM>. The neutron shield <NUM> on the neutron detector <NUM> may interact with neutrons propagating from overhead and from a portion of a wide area below the neutron detector <NUM>. The neutron shield <NUM> may interact with neutrons propagating from a portion of a local area below the neutron detector <NUM>. The bottom side of the thermal neutron detector <NUM> may not be directly covered by the neutron shield <NUM>, <NUM>. An air gap <NUM> may separate the neutron detector <NUM> and the lower neutron shield <NUM>. The neutron shield <NUM>, <NUM> may be positioned to allow cosmogenic neutrons propagating from an intermediate area of the measurement surface <NUM> below the neutron detector <NUM>, as the neutron shield elements <NUM>, <NUM> are spaced apart vertically. The neutron shield <NUM>, <NUM> reduces the local area neutron contribution, wide area neutron contribution, and overhead neutron contribution. However, neutrons propagating toward the neutron detector <NUM> from an intermediate distance are not blocked from hitting the detector <NUM>. The scale of observation can be controlled by changing the size of the air gap <NUM> between the lower neutron shield <NUM> and the upper neutron shield <NUM>, as well as by adjusting the sizes of the neutron shields <NUM>, <NUM>.

<FIG> is a flow chart showing a method for detecting cosmogenic neutrons, in accordance with the first exemplary embodiment of the present disclosure. It should be noted that any process descriptions or blocks in flow charts should be understood as representing modules, segments, portions of code, or steps that include one or more instructions for implementing specific logical functions in the process, and alternate implementations are included within the scope of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present disclosure.

Step <NUM> includes providing a neutron detector and a neutron shield positionable on the neutron detector. The neutron detector and neutron shield may be the same neutron detector and neutron shield described relative to <FIG>, above.

Step <NUM> includes orienting the neutron detector above a measurement surface. The measurement surface may be any desired measurement surface, including land, water, urban construction, and the like. The neutron detector may be oriented above the measurement surface by any suitable means. In one example, the neutron detector may be placed on a number of legs or a stand. In another example, the neutron detector may be a handheld device that is oriented above the measurement surface by a user of the device. In another example, the neutron detector may be attached to a vehicle, such as an automobile, airplane, or drone. The vehicle may hold the neutron detector above the measurement surface while also moving the neutron detector about the measurement surface. This may be particularly helpful for local area measurements made over a large area. In another example, the neutron detector may be attached to an aircraft, drone, satellite, tower, or tall building.

Step <NUM> includes positioning the neutron shield to interact with at least a portion of cosmogenic neutrons propagating in a direction of the neutron detector. The neutron shield may be positioned in one or more places on the neutron detector in order to interact with cosmogenic neutrons propagating from one or more particular directions. For example, the neutron shield may be positioned on a top or upper portion of the neutron detector in order to interact with overhead neutrons. The neutron shield may be positioned on a bottom or lower portion of the neutron detector in order to interact with local area neutrons propagating from below the neutron detector. The neutron shield may be positioned on or around a side portion of the neutron detector in order to interact with wide area neutrons propagating from below the neutron detector. The positions of the shields may be combined as well. A neutron shield may be positioned on a top portion of the neutron detector and a bottom portion of the neutron detector in order to interact with cosmogenic neutrons propagating from overhead and from a local area below the neutron detector. Only a portion of a side of the neutron detector may be covered by the neutron shield. Any other combinations and permutations of the neutron shield location may be considered within the scope of this disclosure.

Step <NUM> includes measuring a quantity of cosmogenic neutrons impinging upon the neutron detector. For stationary sensors, measurements may be made over the course of several minutes to one hour. For mobile sensors, measurements may be made over the course of several seconds to several minutes. Software may record the various measurements and process them to convert a neutron count rate to a moisture content value.

The method may further include any other features, components, or functions disclosed relative to any other figure of this disclosure.

<FIG> is an illustration of the cosmogenic neutron sensor <NUM> in use during calibration, in accordance with a second exemplary embodiment of the present disclosure. The cosmogenic neutron sensor <NUM> may be the local area-type detector discussed relative to <FIG>, above. The cosmogenic neutron sensor <NUM> may include neutron detector <NUM> having a neutron shield <NUM> positioned to interact with neutrons propagating from a wide area of the measurement surface <NUM> below the neutron detector <NUM>. In one example, the neutron shield <NUM> may also be positioned to interact with neutrons propagating from above the measurement surface <NUM> so as to decrease the noise of the cosmogenic neutron sensor <NUM>. Thus, the cosmogenic neutron sensor <NUM> may primarily measure the intensity of neutrons propagating from a local area below the neutron detector <NUM>.

The cosmogenic neutron sensor <NUM> may be calibrated by using the detector <NUM> to record specific measurements, then calculating a calibration curve. This is described further in <FIG>, below. <FIG> shows the cosmogenic neutron sensor <NUM> oriented above a first measurement surface <NUM>, which may be a body of water, as well as above a second measurement surface <NUM>, which may be a constant hydrogen content surface. The constant hydrogen content surface material may be one or more material with precisely engineered hydrogen content. For example, the material may be a combination of mineral grains mixed with water to achieve the specific hydrogen content. In another example, a material may be fabricated by combining particular amounts of mineral grains, for example, quartz sand, with amounts of HDPE particles, to make a homogenous mixture that can be pressed or melted into a solid material. The hydrogen content of the material will remain constant over time; thus, the material can be used to calibrate the cosmogenic neutron sensor <NUM>. Multiple different materials representing a full range of hydrogen content or moisture content may be used to calibrate a cosmogenic neutron sensor <NUM> over the range.

<FIG> is a flow chart showing a method of calibrating a local area cosmogenic neutron sensor for soil moisture detection, in accordance with a second exemplary embodiment of the present disclosure. Traditionally, a calibration function for the standard cosmogenic soil moisture probe is obtained using measured neutron intensity and independently measured soil moisture to calculate a parameter. Two or more calibrations at different soil moisture values are needed to define the curve, and the calibration measurements must be performed by heating the samples in an oven and measuring the mass of water removed in order to obtain the moisture content of the soil. This can be an inconvenient, labor-intensive process. The method of calibrating a local area cosmogenic neutron sensor described herein allows calibration tests to be made and verified from within the cosmogenic neutron sensor. The objective of the method is to find the relationship between local area soil moisture and local area neutron intensity. In order to do that, neutron intensity may be measured at a number of local area sites with varying soil moisture contents or using a number of artificial materials with varying, but known, hydrogen content. The resulting calibration function may be of the form: N = f(SM), where N is neutron intensity, and f(SM) is a function of the soil moisture.

Step <NUM> includes providing a neutron detector and a neutron shield positioned to interact with cosmogenic neutrons propagating from a wide area of a measurement surface below the neutron detector. In one example, the neutron shield may also be positioned to interact with cosmogenic neutrons propagating from above the neutron detector. In other words, the cosmogenic neutron sensor may be a local area-type detector for measuring neutrons propagating toward the neutron detector from a local area below the detector.

Step <NUM> includes orienting the neutron detector above a first measurement surface. This may be done as described in <FIG>, above. The first measurement surface may generally be a body of water. The neutron detector may be oriented at a suitable height above the first measurement surface to make an accurate measurement.

Step <NUM> includes measuring the neutron intensity of the first measurement surface. The neutron intensity may be recorded and stored, either onboard the cosmogenic neutron sensor, or on connected memory. Step <NUM> may also include measuring the moisture content of the first measurement surface using an alternative method, such as oven drying, capacitive, resistive, core sampling method, and the like. This may provide verification for the measured neutron intensity of the first measurement surface as a function of the soil moisture. If the moisture content of the first measurement surface is already known - for instance, if the first surface is water or an artificial surface having a known moisture content - then using an alternative method to measure the moisture content of the first measurement surface may be redundant.

Step <NUM> includes calibrating a cosmogenic neutron sensor based on the measured neutron intensity of the first measurement surface and at least one additional data point. In one example, the at least one additional data point may be a measurement of the neutron intensity from at least a second measurement surface. The at least second measurement surface must be a different measurement surface than the first measurement surface. The second measurement surface may have a different moisture content from the first measurement surface. Third and subsequent measurements may have different levels of moisture content as well. The first and subsequent measurements of neutron intensity at the first and subsequent measurement surfaces may be correlated to first and subsequent moisture content values, either as described above or using other correlation methods. For instance, a first measurement may be correlated with a first moisture content value using an alternative measurement method. Subsequent measurements may be correlated with subsequent moisture content values using the same alternative measurement method. This may be repeated a number of times in order to provide a sufficient amount of data to define a calibration curve. The moisture content values may be used to define the calibration curve as a function of moisture content.

When the at least one additional data point is measured from at least a second measurement surface, calibrating may include measuring the neutron intensity of the at least second measurement surface. In one example, the first measurement surface may be a body of water, and a second measurement surface may be a constant hydrogen content surface. The body of water may provide a calibration measurement for a measurement surface with <NUM>% moisture content, while the constant hydrogen content surface may provide a calibration measurement for a measurement surface with a specific and known moisture content. Additional measurements may be made with constant hydrogen content surfaces of other specific and known moisture contents. For example, the first measurement may be with a surface having <NUM>% moisture content, while a second may be made with a surface having <NUM>% moisture content, and a third may be made with a surface having <NUM>% moisture content.

Calibrating may further include defining a calibration curve based on the first and at least second measurements. The calibration curve may be defined based on any suitable analytical techniques, depending on the number of measurements, the accuracy desired, and the intended use of the cosmogenic neutron detector. For example, regression analysis may be combined with the double exponential curve of the radial sensitivity function to calculate the calibration parameters of two or more measurements. The cosmogenic neutron sensor may be calibrated based on the defined calibration curve.

In one example, the at least one additional data point may be a known calibration curve for the cosmogenic neutron sensor. For instance, if a calibration curve is already known, then the cosmogenic neutron sensor may only require a single measurement of neutron intensity over a surface. The single measurement may be correlated to a moisture content value and fit to the known calibration curve, and the cosmogenic neutron sensor may be calibrated according the to fit.

In one example, the cosmogenic neutron sensor may be oriented on a soil surface, wherein the bottom of the cosmogenic neutron sensor touches the soil surface. The neutron intensity of the first measurement surface may be measured to a desired precision. The cosmogenic neutron sensor may be removed, and soil samples from the measured area may be collected at depths between <NUM> centimeters and <NUM> centimeters to allow for gravimetric water content measurements. At least one additional data point may be obtained from at least a second measurement. At least one of the additional data points may be a measurement made over a water surface. The moisture content of the soil samples may be determined by an alternative method. A calibration curve may then be defined based on the measurements of the neutron intensities and the corresponding measurements of the moisture content of the local areas.

<FIG> is a flow chart showing a method of calibration of a wide area cosmogenic neutron sensor for soil moisture detection, in accordance with the second exemplary embodiment of the present disclosure.

Step <NUM> includes determining at least two local area calibration functions, each determined by: providing a hydrogen-sensitive neutron detector and a neutron shield positioned to interact with cosmogenic neutrons propagating from a wide area of a measurement surface below the hydrogen-sensitive neutron detector; orienting the hydrogen-sensitive neutron detector above a first measurement surface; and calibrating a cosmogenic neutron sensor based on the defined measured neutron intensity of the first measurement surface and at least one additional data point to produce a local area calibration data point.

In one example, a local area cosmogenic neutron sensor may be used as described in steps <NUM>-<NUM>. The first measurement surface may be a local area portion of a wide area measurement surface. The at least one additional data point may be a measurement from a second surface, which may be a different local area having a different moisture content or a material having a known moisture or hydrogen content. Any additional measurements may be made from yet different local areas of the measurement surface. The at least one additional data point may alternatively be a known calibration curve for the cosmogenic neutron sensor. The cosmogenic neutron sensor may be calibrating based on the measured neutron intensity of the first measurement surface and the at least one additional data point. This may produce a local area calibration function.

The local area calibration function may be determined for at least two local area points. As shown in <FIG>, local area calibration functions may be determined from a number of local areas within a wide area to ultimately be measured.

Step <NUM> includes calibrating a wide area cosmogenic neutron sensor based on the at least two determined local area calibration functions and a weighting function. The wide area cosmogenic neutron sensor may be a wide area cosmogenic neutron sensor described herein, or it may be a prior art cosmogenic neutron sensor. In one example, the weighting function may include a spatial sensitivity function. The wide area calibration curve may be defined based on an average of the at least two local area calibration functions, as this may indicate the average moisture content over the wide area. This calibration curve may be used to calibrate a wide area cosmogenic neutron sensor for the wide area measurement surface.

In one example, the method may be performed using a local area cosmogenic neutron sensor and a wide area cosmogenic neutron sensor. The local area cosmogenic neutron sensor may be used to calibrate the wide area cosmogenic neutron sensor. The wide area cosmogenic neutron sensor may be placed above a first surface. In one example, this point may be the center of a wide area measurement surface. The wide area measurement surface may be a circular area roughly <NUM> meters in diameter. The wide area cosmogenic neutron sensor may be used to make a wide area measurement for the remaining duration of the method. The local area cosmogenic neutron sensor may be used to measure the neutron intensity, and subsequently, the moisture content, of a local area within the wide area measurement surface. A local area moisture content measurement may be made for a different local area within the wide area measurement surface. A number of local area measurements may be made in order to sufficiently compute an accurate and precise average soil moisture over the wide area measurement surface. In one example, this may be <NUM> or more local area measurements. Preferably, this will be at least <NUM> local area measurements, depending on the side of the wide area measurement surface.

The average wide area soil moisture may be determined from the local area measurements. The wide area cosmogenic neutron sensor may finish making the wide area neutron intensity measurement. An average neutron intensity for the wide area may be determined for the measurement interval. A calibration function may be determined based on the average local area moisture measurements and the average neutron intensity for the wide area. This calibration function may be weighted by a weighting function, which may be the spatial or radial sensitivity function.

In one particular example, a wide area cosmogenic neutron detector may be used to make a measurement. A local area cosmogenic neutron detector may be calibrated as discussed relative to <FIG>, above. The local area cosmogenic neutron detector may be used to measure neutron intensity at <NUM> sites within a <NUM> meter radius of the wide area cosmogenic neutron sensor. The local area neutron intensity measured at the <NUM> sites may be converted to moisture level values using the calibration function determined during the local area cosmogenic neutron detector calibration. A few grams of soil from each of the local area sites may be collected. A soil composite may be made by mixing <NUM>-<NUM> grams of each of the collected soil samples together to form a relatively homogenous mixture. The lattice water or hydrogen content of the soil composite may be measured. The soil organic carbon of the soil composite may be measured. The average moisture content may be determined from the above measurements. A calibration function for the wide area cosmogenic neutron sensor may be determined, and the sensor may be calibrated.

The usual calibration of such sensors involves taking numerous soil samples and measuring their hitherto unknown water content in the laboratory. The number of samples has to be sufficient to capture the spatial variability of soil moisture; Zreda et al. (<NUM>) suggested taking <NUM> samples. The samples are dried in laboratory oven and their water content is calculated from the difference between wet soil mass and its dry mass. The process is laborious, expensive and at many locations difficult or impossible to conduct because of the presence of stones or rock outcrops in the soil. The new example above uses the local area cosmogenic neutron sensor to replace sampling and processing of soil. The measured local neutron intensities taken at many points inside the wide area measurement footprint are combined to produce an average value over the wide area sensor's measurement footprint. That value is used to calculate the calibration parameters.

<FIG> is an illustration of a cosmogenic neutron sensor <NUM> having overhead and wide area cadmium neutron shields <NUM>, in accordance with the first exemplary embodiment of the present disclosure. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM>, which may be the same as the neutron detector <NUM> shown in <FIG>, above. Moderating material <NUM> may be positioned on the neutron detector <NUM> and at a bottom portion of the neutron detector <NUM>. The moderating material <NUM>, or moderator, may be positioned to moderate cosmogenic neutrons propagating from a local area of the measurement surface <NUM> below the neutron detector <NUM>. A cadmium neutron shield <NUM> may be positioned on the neutron detector <NUM> to interact with neutrons propagating from above the neutron detector <NUM> and from a wide area of the measurement surface <NUM> below the neutron detector <NUM>. The incorporation of a cadmium neutron shield <NUM> in place of additional moderating material <NUM> around the top and sides of the cosmogenic neutron sensor <NUM> may cause the cosmogenic neutron sensor <NUM> to weigh less than other examples discussed herein. This may be particularly useful for cosmogenic neutron sensors <NUM> for use in airplanes, drones, satellites, and other aerial vehicles, as a reduced payload may be required for the cosmogenic neutron sensor <NUM> to be able to be used with these vehicles.

This is a cadmium improvement of the prior art moderated detector discussed in <FIG>, above. The moderator that is on all sides of the detectors in <FIG> may be reduced to one moderator slab <NUM> placed below the neutron detector <NUM>, and surrounded by a cadmium sheet <NUM>. Epithermal neutrons coming from below enter the space enclosed by cadmium <NUM>, undergo moderation in the moderator <NUM> and become thermal neutrons that are counted by the neutron detector <NUM>. Epithermal neutrons coming from all other directions enter the space enclosed by cadmium <NUM>, reflect off the moderator slab <NUM>, become thermalized, and are counted by the neutron detector <NUM>. The main advantage of this example is a significant reduction of mass of the instrument, which is important in aerial neutron sensing using drones where payload is a limiting factor.

<FIG> is an illustration of a local area cosmogenic neutron sensor <NUM> with a neutron shield <NUM> and a cadmium foil layer <NUM>, in accordance with the first exemplary embodiment of the present disclosure. The cosmogenic neutron sensor <NUM> may include a neutron detector <NUM> oriented above a measurement surface <NUM>. A layer of cadmium foil <NUM> may be positioned around the neutron detector <NUM>, leaving a gap space <NUM>. The gap space <NUM> may contain air, or it may be a vacuum. A neutron shield <NUM> may be positioned on the layer of cadmium foil <NUM>. The cadmium foil and neutron shield <NUM>, <NUM> may be positioned to interact with neutrons propagating from overhead and from a wide area of the measurement surface <NUM> below the neutron detector <NUM>.

<FIG> is an illustration of a local area cosmogenic neutron sensor <NUM> with a skirt-style neutron shield <NUM>, in accordance with the first exemplary embodiment of the present disclosure. The local area cosmogenic neutron sensor <NUM> may include a neutron detector <NUM> positioned above a measurement surface <NUM>. A skirt-style neutron shield <NUM> may be positioned on the neutron detector <NUM> to interact with overhead and wide area neutrons. The sides of the neutron shield <NUM> may extend vertically below the neutron detector <NUM> toward the measurement surface <NUM>. This may enhance the neutron shield <NUM>'s effectiveness in blocking wide area neutrons by narrowing the cosmogenic neutron sensor <NUM>'s local area measurement footprint. In turn, the resolution of the cosmogenic neutron sensor <NUM> may be increased.

<FIG> are illustrations of a wide area cosmogenic neutron sensor <NUM>, in accordance with the first exemplary embodiment of the present disclosure.

With reference to <FIG> first, as shown, the wide area cosmogenic neutron sensor <NUM> includes a standard hydrogen sensitive neutron detector <NUM>, which is also referred to as a standard cosmogenic-neutron soil moisture sensor (CNS) <NUM>, or just `CNS <NUM>' for short. The CNS <NUM> includes a moderator material <NUM> surrounding a neutron detector <NUM>. The wide area CNS <NUM> also includes a generalized neutron shield <NUM> which is positioned below the CNS <NUM> and between the CNS <NUM> and the measurement surface <NUM>, such that the shield <NUM> covers or substantially covers all portions of the bottom side of the CNS <NUM>. The neutron shield <NUM> blocks neutrons emanating from a local region of the measurement surface <NUM> below the CNS <NUM> and shield <NUM> from entering the CNS <NUM>. However, this arrangement allows neutrons emanating from a wide area of the measurement surface <NUM> to enter the CNS <NUM> via the atmosphere. Therefore, this configuration is insensitive to local area neutrons and is sensitive to wide area neutrons. Together, the CNS <NUM> and the shield <NUM> are referred to as a wide area CNS <NUM>.

The neutron shield <NUM> may, in a nonlimiting example, be a hydrogenated moderating material such as paraffin, a plastic material such as HDPE or UHMW, or water. The purpose of the shield <NUM> is to block, not moderate, a population of neutrons. If a moderating material is used as a shield <NUM>, referred to as a moderating shield-which is distinct from a moderator-it must be of sufficient thickness that it not only moderates but substantially absorbs neutrons. A practical moderating shield of the type described here should be at least <NUM>, but it can be much thicker, such as greater than <NUM>. For a given material, at some predetermined thickness, adding additional material bulk will provide little additional shielding and will add unnecessary weight, which is not desired.

With the shield <NUM> positioned on the bottom side of the CNS <NUM>, the purpose of the shield <NUM> is to block neutrons in a local area below the CNS <NUM>. The shield <NUM> is generally positioned parallel to the plane of the measurement surface and generally extends laterally in two dimensions, e.g., along the length and width dimensions of the CNS <NUM>. The size of the neutron shield <NUM> in two dimensions, parallel to the measurement surface <NUM> may be varied from zero to a size much larger than the lateral extent of the CNS <NUM>. For instance, the shield <NUM> may be just as wide as the CNS <NUM>, twice or three times as wide as the CNS <NUM>, or have a spatial footprint which is otherwise the same size or wider than the CNS <NUM>. As the lateral size of the shield <NUM> increases relative to the size of the CNS <NUM>, the size of the local area of excluded or blocked neutrons increases. The size and shape of the shield <NUM> may depend upon the size, shape, and orientation of the CNS <NUM> and/or depend upon the size of the desired radial sensitivity function. As the shield <NUM> grows in size in the plane of the measurement surface <NUM>, it blocks neutrons from a larger local area of the measurement surface <NUM> to the CNS <NUM> and skews the radial sensitivity function to a larger size. To some extent, the shield <NUM> design may be chosen to produce wide area sensitivity of a varying amount.

In the depiction of <FIG>, the measurement surface <NUM> includes a land surface <NUM> which comprises a quantity of soil <NUM> having hydrogen atoms <NUM> therein. In other examples, the measurement surface <NUM> may include other settings for the measurement of neutrons, including water or liquid surfaces, vegetation, plants, substrates, or other locations. As shown in <FIG>, the CNS <NUM> with the shield <NUM> is supported in a position vertically above the measurement surface <NUM> with a stand structure <NUM>, which may include any type of mechanical or electro-mechanical device or components which are capable of holding the CNS <NUM> and shield <NUM> above the measurement surface <NUM>. In <FIG>, the stand structure <NUM> is depicted as simplistic columns which support the weight of the CNS <NUM> and shield <NUM>, but it is noted the stand structure <NUM> may include other supporting structures, such as scaffolding, cases, stands, land and/or air vehicles, human-carried structures such as backpacks, or any other structure. The CNS <NUM> is held a distance 'D' from the measurement surface <NUM>, where D can represent any distance, commonly one centimeter or greater, a few centimeters or greater, a meter or greater, or any other distance.

Due to the CNS <NUM> and the shield <NUM> located thereunder in the position described herein, i.e., covering the bottom wall of the CNS <NUM> but not covering the top face of the CNS <NUM>, and the CNS <NUM> being positioned a distance D above the measurement surface <NUM>, the CNS <NUM> is insensitive to neutrons in the local area of the measurement surface <NUM> positioned immediately below the CNS <NUM> and the shield <NUM>, and the adjacent locations which are below and lateral to the CNS <NUM> and the shield <NUM>. This area is collectively known as the `local area'. While the local area neutrons are blocked, the CNS <NUM> is preferentially sensitive to the neutrons which reach the CNS <NUM> through a path which does not intersect the shield <NUM>, which are referred to as `wide area' neutrons. These neutrons generally arrive from the surrounding atmosphere of the CNS <NUM> and may originate from a remote portion of the measurement surface <NUM> which is beyond the local area.

It is noted that the exact location and dimensions of the wide area relative to the local area may vary, depending on factors such as the size of the shield <NUM>, the value of distance D, and other factors. In general terms, the local area is commonly understood as the area immediately below the physical footprint of the CNS <NUM>, e.g., the length and width spatial dimensions of the CNS <NUM>, as well as the surrounding areas of the measurement surface which are below the CNS <NUM> and latterly offset from the physical footprint of the CNS <NUM>. In some cases, the local area may include an area of the measurement surface within a <NUM> meter radius of the CNS <NUM>, whereas in other cases, the local area may include a portion of the measurement surface within a <NUM> meter radius, a <NUM> meter radius, a <NUM> meter radius, a <NUM> meter radius, and/or a <NUM> meter radius, or greater, or any combination thereof.

The neutron shield <NUM> is capable of substantially blocking or shielding neutrons emanating from a local area of the measurement surface <NUM> in a wide range of energies up to and beyond the energy of fast neutrons. For instance, the shield <NUM> blocks neutrons with which it interacts, thereby preventing them reaching the CNS <NUM> in the measurable energy range. Relative to <FIG>, these neutrons blocked by the shield <NUM> include thermal neutrons (<NUM>. 5eV) <NUM>, epithermal neutrons (<NUM>. 5eV-1000eV) <NUM>, and fast neutrons (<NUM>,000eV or more) <NUM>. In contrast, the fast neutrons <NUM> and the epithermal neutrons <NUM> which originate from the wide area which do not intersect with the shield <NUM> can be received at the CNS <NUM>.

With reference now to <FIG>, it depicts a wide area cosmogenic neutron sensor <NUM> which is similar to the wide area CNS <NUM> of <FIG>. Accordingly, the description of the components and features of the wide area CNS <NUM> of <FIG> applies to the wide area CNS <NUM> of <FIG>, except as otherwise noted.

As shown in <FIG>, the wide area CNS <NUM> includes a variation in the shield <NUM> position relative to the wide area CNS <NUM> of <FIG>. As shown in <FIG>, the shield <NUM> is not only positioned on the bottom side of the CNS <NUM>, but a sidewall shield 2130A is also positioned along the sidewalls of the CNS <NUM>. While adjusting the size of the shield <NUM> in a wide area CNS <NUM> can modify the size of the excluded local area for the wide area CNS <NUM>, using sidewall shields 2130A along the sidewalls of the CNS <NUM> can also modify the excluded local area to which the CNS <NUM> is insensitive. The sidewall shields 2130A effectively make the local area larger, thereby restricting access from neutrons traveling laterally from reaching the CNS <NUM>. The sidewall shields 2130A may enhance the ability of the shield to preferentially block a population of neutrons emanating from a larger portion of the local area of the measurement surface <NUM>. A population of neutrons from a wide area preferentially enter the CNS <NUM> from above and are excluded by the sidewall shields 2130A.

It is noted that the height of the sidewall shields 2130A can vary from a height of just greater than <NUM> to the height of the CNS <NUM> itself, or even higher than the height of the CNS <NUM>. The height of the sidewall shields 2130A can modify the size of the excluded local area, thereby narrowing the wide area to which the wide area CNS <NUM> is sensitive, whereby taller sidewall shields 2130A tend to exclude neutrons from a larger local area than shorter sidewall shields 2130A. It is noted that this configuration using the sidewall shields 2130A can be applied to various geometries, including square, rectangular, or cylindrical neutron shield geometries, or others, all of which are considered within the scope of the present disclosure.

As shown in <FIG>, the wide area CNS <NUM> includes a variation in the height of the CNS <NUM> relative to the shield <NUM>. While the shield <NUM> remains a distance, Di, relative to the measurement surface <NUM>, as described relative to <FIG>, the CNS <NUM> is also positioned a distance, D<NUM>, above the shield <NUM>, such that the CNS <NUM> is spaced above the shield <NUM>. Distance D<NUM> is a distance which is greater than zero, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, cm or another distance. It is noted that the shield <NUM> may have a characteristic size scale in a plane parallel to the measurement surface <NUM>. For example, if the shield <NUM> has a square shape or square spatial footprint, then the side of the square may set a scale for its characteristic size. If the shield <NUM> is circular, then the diameter may define its characteristic size. If the shield <NUM> is rectangular, then the shorter side of the rectangle may define its smallest characteristic size. In the wide area CNS <NUM> of <FIG>, the height distance D<NUM> of the CNS <NUM> above the neutron shield <NUM> may vary from an amount greater than zero to an amount equal to three times the smallest characteristic size scale of the shield <NUM>.

Raising the CNS <NUM> above the neutron shield <NUM> may allow for continuous variation in the size of the excluded local area. For instance, the further the CNS <NUM> is raised above the neutron shield <NUM>, the size of the excluded local area will decrease. By selectively adjusting the height distance D<NUM> between the CNS <NUM> and the shield <NUM>, one can achieve the excluded local area size which they desire. Therefore, it allows the shape of the radial sensitivity function to be modified such that it includes more or less of the local area.

<FIG> depict a variation to the wide area cosmogenic neutron sensors <NUM>, <NUM>, and <NUM> of <FIG>, respectively. In particular, <FIG> depict the additional use of a thermal neutron shield <NUM>. In contrast to the wide area CNSs <NUM>, <NUM>, <NUM> of <FIG>, which are shown in standard form, i.e., without the use of a thermal neutron shield, the additional use of an external thermal neutron shield <NUM> improves the performance of the standard CNS by substantially blocking thermal neutrons <NUM> from entering the wide area CNS <NUM>, <NUM>, <NUM>. For a standard CNS, such as those shown in <FIG>, the moderator <NUM> surrounding the internal thermal neutron detector <NUM> is of such a thickness to optimize measurement of neutrons which are sensitive to hydrogen. In general, some population of thermal neutrons penetrates the moderator and is measured in the detector. This represents unwanted noise in the CNS. The addition of an external thermal neutron shield <NUM> substantially lowers this source of noise in the CNS <NUM>, <NUM>, <NUM> without reducing wanted signal from hydrogen-sensitive `fast' neutrons <NUM>.

In particular, the thermal neutron shield <NUM> acts like a filter by only blocking thermal neutrons <NUM> below the range of approximately 1eV, while allowing epithermal neutrons <NUM> above approximately 1eV to pass through. Thus, the thermal neutron shield <NUM> acts to block low energy neutrons below the range ~ 1eV without interacting with or otherwise affecting neutrons above ∼1eV. While different materials may be used as the thermal neutron shield <NUM>, an example of a thermal neutron shield <NUM> is cadmium metal which blocks neutrons with energy below <NUM> eV. Other suitable materials may include boron or gadolinium, or another material which blocks thermal neutrons below some energy level or energy level range. The size, thickness, number of layers, or other parameters of the material or materials used for the thermal neutron shield <NUM> may be varied, as dependent on the design of the local area CNS <NUM>.

The external thermal neutron shield <NUM> may be used with any of the configurations depicted in <FIG> to improve a standard CNS, and specifically, the function of the CNS, itself, without changing the measurement properties relative to the wide area versus local area of the wide area CNS <NUM>, <NUM>, <NUM>. Thus, the use of the external thermal neutron shield <NUM> may provide an improvement to the standard CNS that does not alter its intended function of the CNS. Such thermal neutron shields <NUM> provide a marginal improvement in the standard CNS instrument.

It is noted that the thermal neutron shield <NUM> may be positioned about an entirety of the CNS, as shown in <FIG>, or it may be positioned about a portion of the CNS, such as shown in <FIG>. For example, since the shield <NUM> is positioned along the bottom wall of the CNS in <FIG>, it may be possible to omit the thermal neutron shield <NUM> from the bottom wall of the CNS since the neutron shield <NUM> below will block all neutrons, including thermal neutrons. In <FIG>, since the shields <NUM> are positioned along the bottom wall and the sidewalls of the CNS, it may be possible to omit the thermal neutron shield <NUM> in these locations, or at least shorten the portions of the thermal neutron shield <NUM> which are positioned along the sides of the CNS.

It is noted that <FIG> are representative of various exemplary situations of using the thermal neutron shield <NUM> provided for clarity in disclosure, and that any configuration depicted may have all or any portion of its CNS's surfaces covered with a thermal neutron shield <NUM>. Since many thermal neutron absorbing materials are expensive, omitting the thermal neutron shield <NUM> from portions of the CNS where it is not needed may help reduce costs.

Turning next to <FIG>, these figures depict a variation of a wide area cosmogenic neutron sensor 2310A, 2310B, and 2310C which are similar to those previously described in <FIG> and <FIG>. Accordingly, the description of the components and features of the wide area CNS <NUM> of <FIG> and the CNSs in <FIG> apply to the wide area CNSs 2310A 2310B, and 2310C of <FIG>, respectively, except as otherwise noted.

The wide area CNS 2310A, 2310B, and 2310C of <FIG> may have portions of its moderator <NUM> and/or thermal neutron shield <NUM> omitted or replaced by other structures. For example, for the case of a neutron shield <NUM> which is made entirely of a moderating material or for which the top portion 2130B is made of a moderating material, it may be possible to omit the moderator <NUM> along the bottom of the CNS <NUM> to reduce the weight or cost of the wide area CNS 2310A, 2310B, and 2310C. For example, in <FIG>, a standard CNS <NUM> (depicted in <FIG>) has the bottom face of its moderator <NUM> removed where it is placed on top of a neutron shield <NUM>.

This configuration can be used when at least the top portion 2130B of the neutron shield <NUM>, which is adjacent to the CNS <NUM>, is made from a moderating material. In this configuration, the top portion 2130B of the shield <NUM>, which is a moderating material, replaces the bottom moderator face <NUM> of the standard CNS <NUM>. The top portion 2130B may be integral with the neutron shield <NUM> itself, or it may be a separate structure which is separated from the shield <NUM> with a layer in between. The removal of a lower moderator <NUM> from the CNS <NUM> reduces weight and may save costs due to the ability to use less moderating material <NUM> about the CNS <NUM> itself. The behavior of the wide area CNS 2310A is the same as that described in <FIG>.

<FIG> depicts a similar configuration of CNS 2310B, where both the moderator <NUM> and the thermal neutron shield <NUM> are omitted from the bottom surface of the CNS <NUM>. As previously discussed, the thermal neutron shield <NUM> improves the performance of the CNS <NUM> by blocking thermal neutrons from entering the detector which is considered to be noise in a standard CNS <NUM>, but it can be removed from the lower surface since the upper portion 2130B of the shield <NUM> and the shield <NUM> can reduce that noise.

<FIG> depicts a related configuration of CNS <NUM>0C, where a thermal neutron detector <NUM> is surrounded on the top and sides by a thermal neutron shield <NUM>. In this design, there is no thermal neutron shield <NUM> below the thermal neutron detector <NUM>, but the detector <NUM> and thermal neutron shield <NUM> are positioned on the neutron shield <NUM>. At least the top portion 2130B of the neutron shield <NUM> is made from a moderating material, and the top portion of the generalized shield is at least <NUM>" thick. The neutron shield <NUM> is able to block neutrons from below the shield <NUM> from entering the detector <NUM>. If the lower portion of the neutron shield <NUM> is made from a moderating material and has a thickness of <NUM> inches to <NUM> inches, or greater, then it is thick enough to substantially block neutrons.

The neutron shield <NUM> preferentially blocks hydrogen sensitive neutrons emanating from a local area below the thermal neutron detector <NUM>. Hydrogen sensitive neutrons <NUM> emanating from a wide area around the thermal neutron detector <NUM> are, preferentially, able to enter the detector <NUM> from above and from the sides. Hydrogen sensitive neutrons have kinetic energy well above the cutoff energy of the thermal neutron shield and they pass through it freely. They also pass around and through the thermal neutron detector <NUM>. Hydrogen sensitive neutrons <NUM>, <NUM> impingent upon the upper portion 2130B of the neutron shield <NUM> from a direction above the upper portion 2130B of the neutron shield <NUM> are moderated and experience forward and backward scatter. Some subset of these neutrons are thermalized and backscattered by the upper portion 2130B of the shield <NUM> and pass into the thermal neutron detector <NUM> where they may be detected. Thermal neutrons emanating from below the detector <NUM> are blocked by the neutron shield <NUM>. Thermal neutrons impinging upon the detector <NUM> from above and on the sides are blocked by the thermal neutron shield <NUM>. Thus, with this design, thermal neutron contamination is reduced in the detector <NUM>.

The detected hydrogen sensitive neutrons arrive, preferentially, from a wide area around the detectors <NUM> while local area neutrons are preferentially blocked by the shield <NUM>. It is noted that this configuration of the wide area CNS 2310C may have different sensitivity, in general, from the wide area CNS <NUM> described relative to <FIG>, since the wide area CNS 2310C of <FIG> has a very different moderator shape.

With <FIG>, it is noted that the upper portion 2130B of the shield <NUM> may be integrated into the shield <NUM> as a unitary structure, or it may be a separate structure which is affixed or attached to the shield <NUM>. It is also noted that the shield <NUM> may be positioned a spaced distance D above the measurement surface <NUM>, as described relative to <FIG>, or it may be positioned directly on the measurement surface <NUM>.

Claim 1:
A wide area cosmogenic neutron sensor (<NUM>) for detecting moisture within a measurement surface (<NUM>), the wide area cosmogenic neutron sensor comprising:
a neutron detector (<NUM>) positionable above the measurement surface (<NUM>), wherein a moderator material (<NUM>) is positioned around at least a portion of the neutron detector to form a moderated neutron detector (<NUM>),
a neutron shield (<NUM>) positioned around a portion of the moderated neutron detector (<NUM>), whereby the neutron shield (<NUM>) substantially covers an entirety of a bottom of the moderated neutron detector (<NUM>), wherein the neutron shield (<NUM>) is positioned to interact with cosmogenic neutrons (<NUM>, <NUM>, <NUM>) propagating to the bottom of the moderated neutron detector (<NUM>), thereby substantially blocking fast, epithermal, and thermal cosmogenic neutrons (<NUM>, <NUM>, <NUM>) propagating to the bottom of the moderated neutron detector (<NUM>) from reaching the moderated neutron detector (<NUM>), and wherein the neutron shield (<NUM>) is not positioned on at least a top side of the moderated neutron detector (<NUM>);
characterized by,
a stand structure (<NUM>) holding the moderated neutron detector (<NUM>) and the neutron shield (<NUM>) in a position a first spaced vertical distance (D<NUM>) above the measurement surface (<NUM>) with the bottom side of the moderated neutron detector (<NUM>) facing the measurement surface (<NUM>),
wherein the moderated neutron detector (<NUM>) is positioned a second spaced vertical distance (D<NUM>) above the neutron shield (<NUM>), wherein the second spaced vertical distance (D<NUM>) is greater than zero; and
wherein wide area cosmogenic neutrons (<NUM>, <NUM>, <NUM>) propagating from the measurement surface (<NUM>) travel through an air space before arriving at the moderated neutron detector (<NUM>).