Maximum Detection Depth Research Articles

Shift-multiplexing complex spectral-domain optical coherence tomography

We propose and experimentally demonstrate a shift-multiplexing complex spectral-domain optical coherence tomography (shift-multiplexing CSD-OCT) method, in which the maximum detection depth of SD-OCT can be greatly extended by incorporating the shift-multiplexing of detection positions with CSD-OCT. The tomographic imaging with twofold or threefold microscopic slides as the target sample is performed. The experimental results show that the tomographic imaging with more uniform brightness and clarity for the different depth regions in a thick sample can be achieved by the shift-multiplexing CSD-OCT system. In particular, even while the sample’s depth is beyond the maximum imaging depth of CSD-OCT system, the tomographic imaging of this sample can still be realized by using the shift-multiplexing CSD-OCT method without the need for any replacement of the equipment, such as high spectral capacity grating or high resolution of CCD. The shift-multiplexing CSD-OCT system can perform the imaging with the optimization and less reduction of sensitivity for the deeper detection position in the sample.

Glimpse into the design of MRS instrument

ABSTRACTThe Magnetic Resonance Sounding method (MRS) was developed in the former USSR in the late 1970s. Nowadays, available MRS instruments are more compact and reliable, and enormous progress has been made in electronics, computers and materials. Therefore, we can hope that it may be possible to increase the maximum depth of water detection and to improve the resolution of the method by using a larger current in the loop. Quite naturally, the questions arise: what are the practical limits of the MRS method and how much should be transmitting power to get the maximum depth of investigation? In this paper, we analyse the depth of groundwater detection and the vertical resolution of the MRS assuming different loops and different power levels of the current generator. The originality of our approach consists of a joint analysis of the maximum depth of investigation using accept able loop voltage and the modifications in the instrument design necessary for the improvements. We show that even under very favourable conditions it would be difficult to get significant improvement in the depth of investigation using currently available instruments. For example, under favourable noise conditions when rocks have low electrical conductivity and are non‐magnetic, a 20 m thick water saturated sand layer can be detected at a depth of about 325 m using an existing instrument (4 kV of the loop voltage) with a 400 × 400 m2 square loop. A 20% increase in the detection depth (390 m instead of 325 m) requires more powerful electronic equipment (16 kV instead of 4 kV) thus rendering the MRS system larger and heavier. However, using a 16 kV instrument allows us to increase the resolution depth by about 80% (from 120 m to 215 m). When rocks are electrically conductive, the screening of the MRS signal limits the depth of investigation and allows for only minor improvements even with a much more powerful current generator.

Detectability of Absorption and Reduced Scattering Coefficients in Frequency-Domain Measurements Using a Realistic Head Phantom

Detection limits of the changes in absorption and reduced scattering coefficients were investigated using a frequency-domain near-infrared system in a realistic head phantom. The results were quantified in terms of the maximum detectable depth for different activation volumes in the range of 0.8–20 microliters. The non-linear relation between the maximum detectable depth and the magnitude of changes in the absorption coefficient conform well with the Born approximation to the diffusion equation. The minimal detectable changes in the reduced scattering coefficient measured in terms of the phase signal were found to be approximately twice as large as that of the absorption coefficient using the AC signal for the same volume and at the same depth. The phase delay, which can be used to quantify the fast neuronal optical response in the human brain, showed a linear dependence on the reciprocal of the reduced scattering coefficient, as predicted by the Rytov approximation.

Mapping gravel bed river bathymetry from space

Understanding river form and behavior requires an efficient means of measuring channel morphology. This study evaluated the potential to map the bathymetry of two clear‐flowing, shallow (<3 m deep) gravel bed rivers <60 m wide from 2 m‐pixel WorldView2 satellite images. Direct measurements of water column optical properties were used to quantify constraints on depth retrieval. The smallest detectable change in depth was 0.01–0.04 m and the maximum detectable depth was 5 m in green bands but <2 m in the near‐infrared; lower sensor radiometric resolution yields less precise estimates over a smaller range. An algorithm for calibrating a band ratioXto field measurements of depthdproved effective when applied to spectra extracted from images (R2= 0.822 and 0.594 for the larger and smaller stream, respectively) or measured in the field (R2= 0.769 and 0.452). This procedure also identified optimal wavelength combinations, but different bands were selected for each site. Accuracy assessment of bathymetric maps produced using various calibration approaches and image types indicated that: 1) a lineardvs.Xrelation provided depth estimates nearly as accurate as a quadratic formulation; 2) panchromatic and pan‐sharpened multispectral images with smaller 0.5 m pixels did not yield more reliable depth estimates than the original images; and 3) depth retrieval was less reliable in pools due to saturation of the radiance signal. This investigation thus demonstrated the feasibility, as well as the limitations, of measuring the bathymetry of clear, shallow gravel bed rivers from space.

Silica-coated super paramagnetic iron oxide nanoparticles (SPION) as biocompatible contrast agent in biomedical photoacoustics

In this study, we report for the first time the use of silica-coated superparamagnetic iron oxide nanoparticles (SPION) as contrast agents in biomedical photoacoustic imaging. Using frequency-domain photoacoustic correlation (the photoacoustic radar), we investigated the effects of nanoparticle size, concentration and biological media (e.g. serum, sheep blood) on the photoacoustic response in turbid media. Maximum detection depth and the minimum measurable SPION concentration were determined experimentally. The nanoparticle-induced optical contrast ex vivo in dense muscular tissues (avian pectus and murine quadricept) was evaluated and the strong potential of silica-coated SPION as a possible photoacoustic contrast agents was demonstrated.

Evaluating the potential for remote bathymetric mapping of a turbid, sand‐bed river: 1. Field spectroscopy and radiative transfer modeling

Remote sensing offers an efficient means of mapping bathymetry in river systems, but this approach has been applied primarily to clear‐flowing, gravel bed streams. This study used field spectroscopy and radiative transfer modeling to assess the feasibility of spectrally based depth retrieval in a sand‐bed river with a higher suspended sediment concentration (SSC) and greater water turbidity. Attenuation of light within the water column was characterized by measuring the amount of downwelling radiant energy at different depths and calculating a diffuse attenuation coefficient, Kd. Attenuation was strongest in blue and near‐infrared bands due to scattering by suspended sediment and absorption by water, respectively. Even for red wavelengths with the lowest values of Kd, only a small fraction of the incident light propagated to the bed, restricting the range of depths amenable to remote sensing. Spectra recorded above the water surface were used to establish a strong, linear relationship (R2 = 0.949) between flow depth and a simple band ratio; even under moderately turbid conditions, depth remained the primary control on reflectance. Constraints on depth retrieval were examined via numerical modeling of radiative transfer within the atmosphere and water column. SSC and sensor radiometric resolution limited both the maximum detectable depth and the precision of image‐derived depth estimates. Thus, although field spectra indicated that the bathymetry of turbid channels could be remotely mapped, model results implied that depth retrieval in sediment‐laden rivers would be limited to shallow depths (on the order of 0.5 m) and subject to a significant degree of uncertainty.

Utilizing a Magnetic Locator to Search for Buried Firearms and Miscellaneous Weapons at a Controlled Research Site*,†

Forensic personnel generally use basic all-metal detectors for weapon searches because of their ease of use and cost efficiency. For ferromagnetic targets, an alternative easy to use and low-cost geophysical tool is a magnetic locator. The following study was designed to demonstrate the effectiveness of a common, commercially available magnetic locator in forensic weapon searches by determining the maximum depth of detection for 32 metallic forensic targets and testing the effects of metallic composition on detection. Maximum depth of detection was determined for 16 decommissioned street-level firearms, six pieces of assorted scrap metals, and 10 blunt or bladed weapons by burying each target at 5-cm intervals until the weapons were no longer detected. As expected, only ferromagnetic items were detected; weapons containing both ferromagnetic and nonferromagnetic components were generally detected to shallower depths. Overall, the magnetic locator can be a useful addition to weapon searches involving buried ferromagnetic weapons.

Three-dimensional active imaging with maximum depth range

In traditional three-dimensional (3D) active imaging methods, the detection depth range is observed to increase linearly with the detection time, and the intensity information was not fully utilized. However, by encoding the relative values into pseudovalues, the intensity information was fully utilized, and we found the maximum detection depth range increases exponentially with the detection time. Furthermore, we present a 3D imaging system capable of exponentially expanding the detection depth range. A 3D scene reconstruction was undertaken with the targets placed at a distance of 600-1100 m. Experimental results indicate that the method expands the detection depth range exponentially without distance resolution loss as compared with the conventional method.

An under-ice Arctic geophysical exploration sonar system concept to resolve international territorial claims.

A consequence of the shrinking polar ice cap is the increased interest in commercial shipping. Therefore, several nations are surveying the continental slopes and Arctic basin to better define the political boundaries. Under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS), the boundary between territorial and international waters is defined where the sub-bottom basement extends l km from the seafloor. Therefore, icebreakers and air guns are currently implemented for deep sub-bottom profiling. However, there still remains older and thicker ice that leads to inaccessible areas for geophysical surveys from surface ships. Submarines can easily navigate below the Arctic ice, but a safer sound source must be identified to avoid air guns or explosives. An analytic formulation was developed to predict the maximum basement detection depth of an under-ice sound source. This formulation was implemented to compare candidate underwater transducers and impulsive sound sources. Results from this study will be presented with discussions on additional constraints affecting the selection process. A workable submarine system for defining territorial boundaries would also help increase our understanding of the Arctic environment and facilitate exploration for potential natural resources. [Funding provided via UAF sub-award under NOAA Grant No. NA09NOS4000262.]

Detecting buried metallic weapons in a controlled setting using a conductivity meter

Forensic personnel may face a daunting task when searching for buried weapons at crime scenes or potential disposal sites. In particular, it is common to search for a small firearm that was discarded or buried by a perpetrator. When performing forensic searches, it is recommended to first use non-invasive methods such as geophysical instruments to minimize damage to evidence and to the crime scene. Geophysical tools are used to pinpoint small areas of interest across a scene for invasive testing, rather than digging large areas throughout the site. Prior to this project, there was no published research that tested the utility of the conductivity meter to search for metallic weapons such as firearms and blunt and sharp edged weapons. A sample comprised of 32 metallic weapons including firearms, blunt and sharp edged weapons, and scrap metals was buried in a controlled setting to test the applicability of a conductivity meter for forensic searches. Weapons were tested at multiple depths and after data collection was performed for one depth, the weapons were reburied 5 cm deeper until they were no longer detected. Variables such as weapon size, burial depth, transect interval spacing (25 and 50 cm), and metallic composition were tested. All of the controlled variables influenced maximum depth of detection. For example, size was a factor as larger weapons were detected at deeper depths compared to smaller weapons. Metal composition affected maximum depth of detection as the conductivity meter detected items comprised of ferrous metals at deeper depths than non-ferrous metals. Searches for large buried items may incorporate a transect interval spacing of 50 cm but small weapons may be undetected between transects and therefore a transect interval spacing of 25 cm is recommended. Overall, the conductivity meter is a geophysical tool to consider when searching for larger-sized metallic weapons or to use in conjunction with an all-metal detector, particularly when searching for buried metallic evidence in obstructed areas.

SU‐GG‐I‐179: Ultrasound‐Image Guided Radiation Treatment with Amplitude‐Based Gating System

Purpose To employ the first step for implementing UltraSound (US) imaging during radiation treatment, perform real‐time, zero‐dose 4D target tracking and implement amplitude‐based gating. Treatment volume can be reduced by gating or synchronizing the treatment machine with US‐based 4D target tracking. Methods and Materials Varian IX2300 is to be used with NOMOS BAT system. Organ motion study is tested with an in‐house moving station, which is coupled with a geometric phantom. The B‐mode BAT system consisting of a PC, Ultrasound unit, and an articulated arm is employed. The system uses contour data from a patient's CT simulation in combination with positional information derived from the BAT's articulated arm for target localization. An additional computer system called the BAT Workstation is also used to create the BAT studies. US probe is set at 22 cm maximum detection depth and 8 cm focus point. Videos of target movements are recoded during delivery in slices of TIF format. Results For 19 patients, a total of 185 treatment isocenter alignments were performed. Averaged positional adjustments in each axis are between 2.6 mm to 4.2 mm. US image quality was studied to verify radiation effects on the US transducer. A small noise ratio can be induced when the radiation is on the US probe and fields. Signal to noise ratio is estimated as 25 dB. An in‐house program can easily eliminate the noise and track the target volume. This suggests target tracking is possible with US during radiation treatment. Conclusion UltraSound image can be used as target localization with similar accuracy as CBCT or other invasive technique as below 1 mm resolution. A small noise ratio can be induced when the radiation is on the US probe and fields, but can also be easily eliminated by software. Therefore, US image guided radiation therapy is achievable.

Development of a TOF-ERDA measurement system for analysis of light elements using a He beam

A time-of-flight ERDA (TOF-ERDA) measurement system has been developed for the analysis of light elements. He ions are used for the incident beam, and recoil light ions are detected with the system. The system consists of a time detector and a silicon detector, and energy and velocity of recoil ion are measured simultaneously. The depth resolution of 21.6 ± 2.2 nm (FWHM) has been obtained by an ERDA measurement of a thin carbon layer onto a silicon wafer using a 5.7 MeV He beam. The mass resolution is better than 1 for elements up to oxygen. Maximum detectable depth of carbon in a PET film is about 650 nm. An ERDA measurement of implanted carbon in a silicon wafer has been demonstrated.

Controlled research utilizing a basic all-metal detector in the search for buried firearms and miscellaneous weapons

Incorporating geophysical technologies into forensic investigations has become a growing practice. Oftentimes, forensic professionals rely on basic metal detectors to assist their efforts during metallic weapons searches. This has created a need for controlled research in the area of weapons searches, specifically to formulate guidelines for geophysical methods that may be appropriate for locating weapons that have been discarded or buried by criminals attempting to conceal their involvement in a crime. Controlled research allows not only for testing of geophysical equipment, but also for updating search methodologies. This research project was designed to demonstrate the utility of an all-metal detector for locating a buried metallic weapon through detecting and identifying specific types of buried metal targets. Controlled testing of 32 buried targets which represented a variety of sizes and metallic compositions included 16 decommissioned street-level firearms, 6 pieces of assorted scrap metals, and 10 blunt or bladed weapons. While all forensic targets included in the project were detected with the basic all-metal detector, the size of the weapon and surface area were the two variables that affected maximum depth of detection, particularly with the firearm sample. For example, when using a High setting the largest firearms were detected at a maximum depth of 55 cm, but the majority of the remaining targets were only detected at a maximum depth of 40 cm or less. Overall, the all-metal detector proved to be a very good general purpose metal detector best suited for detecting metallic items at shallow depths.

Detection Distances of Selected Radio and Acoustic Tags in Minnesota Lakes and Rivers

AbstractIn freshwater, the optimal choice between radiotelemetry or acoustic telemetry has often been unclear because the combined effects of tag power, conductivity, tag depth, and antenna type on radio tag detection distances have not been quantified. To enable more informed decisions regarding the best telemetry methods to use at particular study sites, we measured maximum detection distances of an acoustic tag and two different 48–49‐MHz radio tags over a wide range of conductivities, depths, and acoustic conditions in Minnesota lakes and rivers. Radio tag detection distances increased with increasing tag power, decreased with increasing conductivity, and generally decreased with increasing depth. Detection distances measured with a Yagi antenna were typically about double those measured with a loop antenna. Maximum detection distances of the radio tags were predicted by the equation logeR = 13.69 − 0.005771·C − 0.006575·D + 0.1044·P + 0.7275·A − 0.001302·C·D − 0.00008208·C·P (where R = maximum detection distance, m; C = surface conductivity, μS/cm, at ambient temperature; D = tag depth, m; P = tag output power, dB relative to 1 mW; and A = antenna type [1 = Yagi, 0 = loop]). Acoustic detection distances were less variable overall than radio detection distances but still differed substantially between and within water bodies. We saw no consistent relationship between acoustic detection distance and tag depth, but detection distance was negatively affected by ambient noise. Our model indicates that a 48–49‐MHz radio tag can be detected with a boat‐mounted Yagi antenna at a depth of 50 m or more if conductivity is low enough, but the maximum detection depth decreases drastically as conductivity increases. The equation above can be used to predict whether detection distances of radio tags similar to the ones we tested will be adequate for a particular study.

Reconstruction of a hidden topography by single AFM force–distance curves

Force–distance curves have been acquired with an Atomic Force Microscope on polymethyl methacrylate with embedded glass spheres. The glass spheres provide a stiff substrate with an irregular and complex topography hidden underneath a compliant and even polymer film. This situation is a special case of a mechanical double-layer, which we examined in detail in previous experiments. Up to now uniform and non-uniform polymer films on an even substrate were examined. The film thickness on each point of the sample surface was known and force–distance curves could be averaged in groups according to the film thickness. In this way we were able to develop a semi empirical approach which allows describing the shape of averaged force–distance curves depending on the Young’s moduli of the involved materials and on the film thickness. In this experiment we reconstruct a hidden topography, i.e., we determine the polymer thickness on each point of the sample by analyzing single force–distance curves with our semi empirical equation. The accuracy reached by this approach permits to obtain a reconstruction of the shape and position of the embedded particles limited by a maximum detection depth. Single curves are also analyzed qualitatively in order to locate areas where the adhesion at the polymer/glass interface is weak or the two phases are detached.

SHARAD radar sounding of the Vastitas Borealis Formation in Amazonis Planitia

Amazonis Planitia has undergone alternating episodes of sedimentary and volcanic infilling, forming an interleaved sequence with an upper surface that is very smooth at the kilometer scale. Earlier work interprets the near‐surface materials as either young, rough lava flows or ice‐rich sediment layers, overlying a basement comprising the Vastitas Borealis Formation and earlier Hesperian plains. Sounding radar profiles across Amazonis Planitia from the Shallow Radar (SHARAD) instrument on the Mars Reconnaissance Orbiter reveal a subsurface dielectric interface that increases in depth toward the north along most orbital tracks. The maximum depth of detection is 100–170 m, depending upon the real dielectric permittivity of the materials, but the interface may persist at greater depth to the north if the reflected energy is attenuated below the SHARAD noise floor. The dielectric horizon likely marks the boundary between sedimentary material of the Vastitas Borealis Formation and underlying Hesperian volcanic plains. The SHARAD‐detected interface follows the surface topography across at least one of the large wrinkle ridges in north central Amazonis Planitia. This conformality suggests that Vastitas Borealis sediments, at least in this region, were emplaced prior to compressional tectonic deformation. The change in radar echo strength with time delay is consistent with a loss tangent of 0.005–0.012 for the column of material between the surface and the reflector. These values are consistent with dry, moderate‐density sediments or the lower end of the range of values measured for basalts. While a component of distributed ice in a higher‐loss matrix cannot be ruled out, we do not find evidence for a dielectric horizon within the Vastitas Borealis Formation that might suggest an abrupt change from an upper dry layer to an ice‐rich lower deposit.

Non-destructive Inspection of Composites Using Step Heating Thermography

The article explores the use of step heating thermography for defect identification in glass fiber reinforced composites. Step heating methods have potential for increasing the maximum detectable defect depth as compared with pulse heating methods. Inspection of thick fiberglass composites containing flat-bottom holes and resistive embedded defects using step heating thermography is investigated using 1-D analytical models, axisymmetric finite element modes, and experimental methods. 1-D heat transfer models of embedded defects under step heating are developed based on results from previous research of pulse heating thermography. Finite element models are used to explore the range of validity of defect identification techniques based on correlation with 1-D analytical methods, and it is found that accurate results are obtained for a defect radius to thickness ratio greater than two. Experimental results demonstrate the validity of the 1-D models for high defect resistance cases. For low resistance defects, detection is more difficult due to reduction of signal strength. A simple procedure is proposed to simultaneously determine defect depth and thermal resistance from the early time surface temperature profile based a two-point correlation with one-dimensional resistive defect solutions.

Detection of buried ice and sediment layers in permafrost using multi-frequency Ground Penetrating Radar: A case examination on Svalbard

We use multi-frequency Ground Penetrating Radar (GPR) to detect and map buried relic glacier ice and sediments in permafrost. Old aerial photographs 1936–1990 are used to show the origin of a sediment covered ice body, and illustrate how it has been buried. Together with a newly exposed ice/sediment cliff, this serves as excellent ground truthing for the GPR data. Empirical GPR frequency dependent relations are established to quantify the loss of the signal power through the layer of sediment. The loss through ice is in comparison negligible. These relations indicate that the maximum ice pocket detection depth (for this sediment type), with the different GPR systems used, are 90, 150 and 200 ns for the 800, 500 and 200 MHz systems respectively. The electromagnetic (EM) wave velocities calculated from diffractions yield velocities ranging between 0.115–0.135 m/ns for the sediment and 0.15–0.17 m/ns for the ice. With the derived EM wave velocities, these Two-Way-Travel (TWT) times correspond to a depth of ∼ 6, 9 and 13 m respectively. This loss cannot be tested for the 200 and 500 MHz systems due to lack of such a deep sediment layer on top of the ice, but is consistent with the 800 MHz data.

A novel design of thermal anomaly for mammary gland tumor phantom for microwave radiometer.

Microwave radiometry is the spectral measurement technique of resolving electromagnetic radiation of all matters which temperature is above absolute zero. This technique utilizes the electromagnetic noise field generated by a thermal volume similar to a mechanism existing in biological tissues. One particular application of microwave radiometry is for analyzing temperature differentials of inside of human body to detect and diagnose some crucial pathological conditions. For the general evaluation of a microwave radiometer, we propose a new type of phantom containing a mammary gland tumor imitator by considering biological heat diffusion effects propagated by a real tumor. Theoretical researches of human tumor revealed the fact that temperature distribution of tissues around a tumor formed a Gaussian statistics. To comply with the physiological property of the real tumor, we built a mammary gland tumor imitator composed of two parts (pseudotumor and thermal anomaly) and observed its temperature distribution when it was placed inside a phantom. Our results showed that the thermal properties of tumor imitator well agreed with heat-transfer properties of a real tumor and the proportional linear relationship existed between the location of tumor imitator and the intensity of radiometer measurements. From this relationship, we could also estimate several parameters related with our phantom, such as the minimum detectable size and maximum detectable depth of a tumor imitator.

Nuclear magnetic resonance as a geophysical tool for hydrogeologists

The proton Magnetic Resonance Sounding (MRS) is a geophysical technique specially designed for hydrogeological applications. It is based on the principle of Nuclear Magnetic Resonance (NMR) and allows the non-invasive detection of free water in the subsurface. As with many other geophysical methods, MRS is site-dependent. Modeling results show that MRS performance depends on the magnitude of the natural geomagnetic field, the electrical conductivity of rocks, the electromagnetic noise and other factors. For example, the maximum depth of groundwater detection for currently available equipment can vary from 45 to 170 m depending on measurement conditions, although an average depth of investigation is generally considered to be about 100 m. The processing of MRS data can provide the depth, thickness and water content of aquifers. Based on the water content and the relaxation times T 1 and T 2* provided by MRS, in association with calibration using borehole pumping test data, it is possible to estimate the aquifer's hydrodynamic properties, namely permeability, transmissivity, and specific yield. In this aim, experience gained through NMR logging has been applied to MRS data interpretation and a comparison between the results of borehole pumping tests and those of MRS experiments reveals a good correlation. An example of an MRS survey in Saudi Arabia is presented. The study area is some 1.3 km 2 and underlain by an aquifer composed of fractured diorite. The results of 7 borehole pumping tests and 13 MRS measurements show good agreement.