Depth Response Curve Research Articles

Robust time-domain phase shift structured illumination microscopy based on intensity correction

SIM techniques based on synchronous phase shift and vertical scanning have been proposed for fast and precise three-dimensional (3D) measurement. These methods are also named as time-domain phase shift (TSIM) method. In these methods, the envelope of light intensity depth response (IDR) curve is extracted to achieve the 3D map. However, when this method is applied in rough surface or complex environment, the imaging noise and background intensity variation will severely affect the shape of IDR which brings difficulties in envelope detection and causes large measurement errors. In this paper, we propose an improved TSIM (ITSIM) technique to enhance the measurement accuracy and robustness of TSIM. In this technique, the modulation distribution of each image is first calculated by a global frequency analysis algorithm, and the modulation depth response curve (MDR) of each pixel can be obtained. These MDR curves are then multiplexed with the corresponding IDR curves to correct the shape of the IDR curves. Finally, the envelope of the corrected IDR curve is detected to accurately reconstruct the 3D shape. The proposed method can effectively resist the intensity fluctuation and imaging noise, and thus can improve the measurement accuracy compared with the conventional TSIM. The experiments performed on standard step sample show that the root mean square error of TSIM and ITSIM is 8.5nm and 21.2nm, respectively, justifying the feasibility of proposed ITSIM.

Biaxial structured illumination microscopy with high measurement accuracy based on product processing

Structured illumination microscopy (SIM) has been established for non-fluorescent three-dimensional (3D) measurement with nanometer resolution. In SIM, a narrower full width at half maximum (FWHM) of contrast depth response (CDR) curve indicates a higher measurement resolution and accuracy. In this paper, we propose a biaxial structured illumination microscopy based on product processing (BPSIM) to achieve a high resolution and accurate reconstruction. In this method, two CCDs placed in biaxial optical paths are utilized to capture signals. After that, through conducting a multiplication operation on these two signals, a product CDR (PCDR) with narrow FWHM is achieved. Further, the peak position of PCDR for each pixel is extracted to realize 3D measurement. Owing to narrow FWHM of PCDR, an enhanced measurement accuracy and resolution can be obtained. The measurement error of step sample achieved by SIM and BPSIM is 14.5 nm and 8.7 nm respectively, justifying the proposed method can realize an improved accuracy. The simulations are also performed to demonstrate the feasibility of proposed method, indicating the potential to be applied in high precision measurement.

Vegetation Response to Groundwater Variation in Arid Environments: Visualization of Research Evolution, Synthesis of Response Types, and Estimation of Groundwater Threshold.

Groundwater depth is an important environmental factor affecting vegetation growth and landscape dynamics in arid environments. This study applied a science mapping approach to visualize the development of groundwater-vegetation-related research, synthesized the vegetation response to changes in groundwater depth, and analyzed the change rate of the response curve to identify the groundwater threshold that is essential to conserve the groundwater-dependent terrestrial ecosystems. These ecosystems emerged as a research hotspot due to climate change, groundwater overexploitation, and the recognition of these ecosystems’ importance for sustainable development. There are two main types of response functions of vegetation to changes in groundwater depth—monotone and bell-shaped functions—among which the monotone function includes linear, curvilinear, and stepwise response. The shape of a response curve is mainly determined by the combined effects of oxygen stress, salinization, and water stress; oxygen stress and salinization dominate in shallow groundwater depth, while water stress dominates in deep groundwater depth. On a non-linear vegetation metric—groundwater depth response curve, the change rate analysis method is effective to identify the breakpoint that can be taken as a candidate threshold of groundwater depth. The results will add insight into the intellectual structure of the groundwater-vegetation interactions and provide practical reference for groundwater resource management, ecological conservation, and sustainable development in arid environments.

Accurate surface profilometry using differential optical sectioning microscopy with structured illumination.

A differential optical sectioning microscopy with structured-illumination (DOSM-SI) with enhanced axial precision is explored in this paper for three-dimensional (3D) measurement. As the segment of data on the linear region of the contrast depth response curve (CDR) is very sensitive to variation of the height information, the DOSM-SI introduces a new CDR2 with an axial shift to intersect the linear region of the CDR1, which is achieved by using two charge-coupled detectors (CCDs) in the optical path. The CCD1 is located on the imaging plane and the CCD2 is displaced from the imaging plane. The difference between the CDR1 and CDR2 for each pixel is defined as the differential depth response curve (DCDR). Further, the zero-crossing point of the DCDR for each pixel is accurately extracted using the line-fitting technique, and finally, the sample surface can be reconstructed with a high resolution and precision. Since the slope around the zero-crossing point of the DCDR is apparently larger than that of near the focal position, an enhanced resolution and precision can be realized in DOSM-SI. The experiments and theoretical analysis are elaborated to demonstrate the feasibility of DOSM-SI.

Parallel detection experiment of fluorescence confocal microscopy using DMD.

Parallel detection of fluorescence confocal microscopy (PDFCM) system based on Digital Micromirror Device (DMD) is reported in this paper in order to realize simultaneous multi-channel imaging and improve detection speed. DMD is added into PDFCM system, working to take replace of the single traditional pinhole in the confocal system, which divides the laser source into multiple excitation beams. The PDFCM imaging system based on DMD is experimentally set up. The multi-channel image of fluorescence signal of potato cells sample is detected by parallel lateral scanning in order to verify the feasibility of introducing the DMD into fluorescence confocal microscope. In addition, for the purpose of characterizing the microscope, the depth response curve is also acquired. The experimental result shows that in contrast to conventional microscopy, the DMD-based PDFCM system has higher axial resolution and faster detection speed, which may bring some potential benefits in the biology and medicine analysis. SCANNING 38:234-239, 2016. © 2015 Wiley Periodicals, Inc.

Large-area three-dimensional profilometer based on digital micromirror device

The single pinhole scanning confocal microscope is suffering from scanning speed. This paper studies a large-area profilometer with multiple virtual pinholes. A digital micromirror device comprised of millions of micromirrors generates multiple virtual pinholes which are utilized for parallel scanning. The key parameters affecting the measurement can be configured conveniently by the digital micromirror device controller. The working principles of a digital micromirror device base confocal microscope have been analyzed and a setup has been built up. Tomographic images are acquired and the depth response curves are extracted. A structured silicon sample is measured and three-dimensional results have been reconstructed. The system repeatability is better than 60 nm.

Comparing one- and two-dimensional EMI conductivity inverse modeling procedures for characterizing a two-layered soil

Apparent electrical conductivity (σa) measured with electromagnetic induction (EMI) instruments is used widely as a proxy to map lateral variations in soil properties. To account for the vertical changes in soil properties, EMI inversion techniques have been developed. Improvements in EMI sensing instrumentation allow simultaneous recording of σa measurements with different depth responses, facilitating 1D and 2D inversions. In this study, different inversion procedures of EMI data were evaluated on their effectiveness to characterize the depth of the interface between two contrasting soil layers, as well as their respective conductivities. A 1D-laterally constrained inversion procedure was compared with a non-constrained, robust 1D-inversion procedure. Both procedures make use of low induction number (LIN)-approximated depth response curves and provided similar results, although calibration with soil data was essential to attribute absolute values to the inversion data. Aforementioned 1D procedures were then compared to a procedure wherein the full solution of Maxwell's equations, which describe the electromagnetic signal response into the soil, is applied. All approaches rendered similar results. This shows that despite their limitations, the cumulative approximations of the EMI signal response can be used as a valuable and effective alternative to the full solution of Maxwell equations within EMI inversion procedures, especially when the measurements are mainly situated within the LIN measurement range. In a final step, 2D inversions of the EMI data were compared to 2D-inverted electrical resistivity tomography (ERT) data. The general patterns of the resulting inverted soil models were largely comparable and consistent with the observed soil information. To conclude, the different inversion procedures revealed analogous results which were largely comparable and consistent with the soil information. However absolute values could impossibly be obtained without any prior knowledge about the vertical distribution of the soil model. Therefore, the implementation of a thorough calibration based on soil observations was essential to guide the inversion results to a realistic outcome.

Parallel large-range scanning confocal microscope based on a digital micromirror device

A multi-point parallel large-range confocal microscope was designed and developed based on a digital micromirror device (DMD). Operated with specific patterns, the DMD can transform a single light source into multiple beams. The DMD functions as a virtual pinhole array and takes the place of traditional pinholes to realize parallel lateral scanning The DMD based confocal system can achieve parallel scanning in the case of ensuring axial resolution with high axial resolution. In that way, it can not only increase the inspection speed, but also safeware control the key parameters of the system, such as pinhole size and geometry. Interference patterns duo to reflections at the inner surfaces of the beamsplitter cube were eliminated, and a transverse scanning strategy was developed. In order to characterize the system, the depth response curves were acquired and finally the three-dimensional images of the target object was successfully reconstructed with a uncertainty of about 0.5%.

Full-field chromatic confocal surface profilometry employing digital micromirror device correspondence for minimizing lateral cross talks

Full-field chromatic confocal surface profilometry employing a digital micromirror device (DMD) for spatial correspondence is proposed to minimize lateral cross-talks between individual detection sensors. Although full-field chromatic confocal profilometry is capable of enhancing measurement efficiency by completely removing time-consuming vertical scanning operation, its vertical measurement resolution and accuracy are still severely affected by the potential sensor lateral cross-talk problem. To overcome this critical bottleneck, a DMD-based chromatic confocal method is developed by employing a specially-designed objective for chromatic light dispersion, and a DMD for lateral pixel correspondence and scanning, thereby reducing the lateral cross-talk influence. Using the chromatic objective, the incident light is dispersed according to a pre-designed detection range of several hundred micrometers, and a full-field reflected light is captured by a three-chip color camera for multi color detection. Using this method, the full width half maximum of the depth response curve can be significantly sharpened, thus improving the vertical measurement resolution and repeatability of the depth detection. From our preliminary experimental evaluation, it is verified that the ±3σ repeatability of the height measurement can be kept within 2% of the overall measurement range.

Electrical Conductivity Depth Modelling with a Multireceiver EMI Sensor for Prospecting Archaeological Features

ABSTRACTMultiple apparent electrical conductivity (ECa) measurements with an electromagnetic induction (EMI) sensor frequently reveal analogue patterns caused by conductive features in the soil. A procedure was proposed to highlight different archaeological anomalies based on combinations of the simultaneous ECa measurements with the DUALEM‐21S instrument. After selection of a 3.5 ha study site, 0.79 ha has been recorded by archaeological excavation. Since the majority of the archaeological features were found between the plough layer and 1.0 m below the soil surface, a set of four equations were developed to model the EC within that predefined depth interval. This set of four equations employed the four depth response curves specific to the four DUALEM‐21S coil configurations. The modelled conductivity between 0.5 and 1.0 m () showed a larger variability across the archaeological features than the raw EC data. To quantify the added value of this modelled conductivity, and measured ECa were compared with the rasterized map of the archaeological traces. Finally, the map proved to be better able to distinguish between the archaeological features and the ‘empty’ background. This technique allowed the highlighting of vague anomalies in the simultaneous DUALEM‐21S ECa measurements. Copyright © 2011 John Wiley & Sons, Ltd.

Biogenic emissions of CO2 and N2O at multiple depths increase exponentially during a simulated soil thaw for a northern prairie Mollisol

The fate of carbon (C) and nitrogen (N) belowground is important to current and future climate models as soils warm in northern latitudes. Currently, little is known about the sensitivity of microbial respiration to temperature changes at depths below 15 cm. We used whole-core (7.6 cm dia. × 90 cm) laboratory incubations to determine if temperature response quotients (Q10) for CO2 and N2O varied with depth for undisturbed prairie while plants were senescent and clipped at the surface. We collected intact soil cores from an undisturbed prairie in central North Dakota and uniformly subjected them to freezing (5 to −15 °C) and thawing (−15 to 5 °C). We measured rates of CO2 and N2O emissions at 5 °C temperature increments at 0, 15, 30, 45, 60, and 75 cm depths. During freezing, active and sterilized core emissions occurred only between 0 and −10 °C. During thawing, a simple first-order exponential model, E = αeβT, fit observed CO2 and N2O emissions (R2 = 0.91 and 0.99, respectively). Parameter estimates for β were not significantly different across depths for CO2 and for N2O (Q10 = 4.8 and 13.7, respectively). Parameter estimates for α (emissions when temperature is 0 °C) exponentially declined with depth for both gases for similar depth-response curves. Stepwise regressions of soil properties on α parameter estimates indicated emissions of CO2 and N2O at 0 °C during thawing were positively correlated (R2 > 0.6) with soil porosity. Results indicate pedogenic properties associated with depth may not necessarily influence temperature response curves during thawing but will affect emissions at 0 °C for both CO2 and N2O.

Radiochromic film spectroscopy of laser-accelerated proton beams using the FLUKA code and dosimetry traceable to primary standards

AbstractA new approach to spectroscopy of laser induced proton beams using radiochromic film (RCF) is presented. This approach allows primary standards of absorbed dose-to-water as used in radiotherapy to be transferred to the calibration of GafChromic HD-810 and EBT in a 29 MeV proton beam from the Birmingham cyclotron. These films were then irradiated in a common stack configuration using the TARANIS Nd:Glass multi-terawatt laser at Queens University Belfast, which can accelerate protons to 10–12 MeV, and a depth-dose curve was measured from a collimated beam. Previous work characterizing the relative effectiveness (RE) of GafChromic film as a function of energy was implemented into Monte Carlo depth-dose curves using FLUKA. A Bragg peak (BP) “library” for proton energies 0–15 MeV was generated, both with and without the RE function. These depth-response curves were iteratively summed in a FORTRAN routine to solve for the measured RCF depth-dose using a simple direct search algorithm. By comparing resultant spectra with both BP libraries, it was found that the effect of including the RE function accounted for an increase in the total number of protons by about 50%. To account for the energy loss due to a 20 µm aluminum filter in front of the film stack, FLUKA was used to create a matrix containing the energy loss transformations for each individual energy bin. Multiplication by the pseudo-inverse of this matrix resulted in “up-shifting” protons to higher energies. Applying this correction to two laser shots gave further increases in the total number of protons, N of 31% and 56%. Failure to consider the relative response of RCF to lower proton energies and neglecting energy losses in a stack filter foil can potentially lead to significant underestimates of the total number of protons in RCF spectroscopy of the low energy protons produced by laser ablation of thin targets.

Mapping depth-to-clay using fitted multiple depth response curves of a proximal EMI sensor

As an alternative for the depth response approximations based on the theoretical Maxwell's equations, a procedure was proposed to fit depth response curves for different coil configurations. A 39 ha study area was selected in the Belgian loess belt, where loess material was situated on a Tertiary substrate. A survey with the DUALEM-21S electromagnetic induction instrument was carried out to map the depth-to-clay ( z clay). The depth response curves were fitted both for the vertical and perpendicular coil configurations using 85 depth observations of z clay. The resulting depth response curves R( z clay) were: R p, s ( z clay ) = 0 .8135 ⋅ e -1 .4131 ⋅ z clay s for the perpendicular coil configuration (with s as the intercoil spacing) and R v, s ( z clay ) = 0 .9802 ⋅ e -0 .8102 ⋅ z clay s for the vertical coil configuration. A set of 4 equations based on the developed depth response functions was used to model z clay at each of the 209 400 measurement points. These z clay predictions were validated using geo-electrical imaging. With two multi-electrode resistivity arrays, z clay was 1D-inverted at 95 locations along two transects, assuming a two-layered soil system. A coefficient of determination of 0.95, with a root mean-squared estimation error of 0.22 m, was found between the predicted and 1D-inverted depths. This procedure allowed the accurate 3D-reconstruction of the paleolandscape before the deposition of the loess. Flow lines were modelled on this paleosurface, revealing past or subsurface stream patterns not visible on the present relief.

Comparison of Electromagnetic Induction and Direct Sensing of Soil Electrical Conductivity

Apparent profile soil electrical conductivity (ECa) can be an indirect indicator of a number of soil physical and chemical properties. Commercially available ECa sensors can be used to efficiently and inexpensively develop the spatially dense data sets desirable for describing within‐field spatial soil variability in precision agriculture. The objective of this research was to compare ECa measurements from a noncontact, electromagnetic induction–based sensor (Geonics EM38)1 to those obtained with a coulter‐based sensor (Veris 3100) and to relate ECa data to soil physical properties. Data were collected on two fields in Illinois (Argiudoll and Endoaquoll soils) and two in Missouri (Aqualfs). At 12 to 21 sampling sites in each field, 120‐cm‐deep soil cores were obtained for soil property determination. Depth response curves for each ECa sensor were derived or obtained from the literature. Within a single field and measurement date, EM38 data and Veris deep (0–100 cm depth) data were most highly correlated (r = 0.74–0.88). Differences between ECa sensors were more pronounced on the more layered Missouri soils due to differences in depth‐weighted response curves. Correlations of ECa with response curve–weighted clay content and cation exchange capacity were generally highest and most persistent across all fields and ECa data types. Significant correlations were also seen with organic C on the Missouri fields and with silt content. Significant correlations of ECa with soil moisture, sand content, or paste EC were observed only about 10% of the time. Data obtained with both types of ECa sensors were similar and exhibited similar relationships to soil physical and chemical properties.

Comparison of Electromagnetic Induction and Direct Sensing of Soil Electrical Conductivity

Apparent profile soil electrical conductivity (ECa) can be an indirect indicator of a number of soil physical and chemical properties. Commercially available ECa sensors can be used to efficiently and inexpensively develop the spatially dense data sets desirable for describing within-field spatial soil variability in precision agriculture. The objective of this research was to compare ECa measurements from a noncontact, electromagnetic induction–based sensor (Geonics EM38)1 to those obtained with a coulter-based sensor (Veris 3100) and to relate ECa data to soil physical properties. Data were collected on two fields in Illinois (Argiudoll and Endoaquoll soils) and two in Missouri (Aqualfs). At 12 to 21 sampling sites in each field, 120-cm-deep soil cores were obtained for soil property determination. Depth response curves for each ECa sensor were derived or obtained from the literature. Within a single field and measurement date, EM38 data and Veris deep (0–100 cm depth) data were most highly correlated (r = 0.74–0.88). Differences between ECa sensors were more pronounced on the more layered Missouri soils due to differences in depth-weighted response curves. Correlations of ECa with response curve–weighted clay content and cation exchange capacity were generally highest and most persistent across all fields and ECa data types. Significant correlations were also seen with organic C on the Missouri fields and with silt content. Significant correlations of ECa with soil moisture, sand content, or paste EC were observed only about 10% of the time. Data obtained with both types of ECa sensors were similar and exhibited similar relationships to soil physical and chemical properties.

Effects of source coherence and aperture array geometry on optical sectioning strength in direct-view microscopy.

Laser sources offer a possible solution to the problem of low light throughput in direct-view microscopes (DVMs). However, coherent source DVMs have been shown to suffer from problems such as increased sidelobes in the depth response because of coherent cross talk between neighboring apertures. We explore theoretically how source coherence affects the depth responses of DVMs by employing various aperture spacings and number of apertures. We show that, contrary to expectation, closely spaced apertures can result in decreased full width at half-maximum of the depth response curve. We explain this as an effect of destructive interference when cross talk between neighboring apertures occurs. Using apertures arranged in a square grid as an example, we move on to show that the use of aperture arrays that consist of regularly arranged apertures can accentuate the problematic sidelobes of the depth response. We show that arranging pinholes in a rectangular grid rather than a square grid can improve the optical sectioning strength significantly. Finally, by examination of the depth responses corresponding to the infinite-pinhole-array limit, we make some general statements about source coherence and the characteristics of arrays that are likely to perform well.

Proton dosimetry in bone using electron spin resonance

We have studied the ESR response of proton-irradiated ( in vitro) bone. The ESR response as a function of proton ( E = 105 MeV) dose to bone was linear from 0 to 50 Gy and similar to the photon ( E = 6 MV) dose response. The ESR depth response (Bragg) curve was depressed as compared to a depth-response curve determined with a parallel plate ionization chamber (PPIC). There was a short-term ESR signal fade in the Bragg peak region, likely attributable to the organic component in bone. We are continuing to investigate these latter two effects.

A simple and fast numerical method for the computation of daily totals of crop photosynthesis

Gaussian integration provides an accurate, fast and flexible method to calculate instantaneous or daily crop photosynthesis. The three-point method combines accuracy and speed, and it is so flexible that a depth or time dependent photosynthetic response curve can be easily introduced. Because of this efficiency it is an excellent method to be used in a subroutine in larger crop growth models.