Nonlinear Correction Method Research Articles

A method for automatic correction of drift-distorted SPM images

A method for automatic correction of drift-distorted surface images obtained using a scanning probe microscope is developed. For the case of slowly varying drifts, simple linear transformations describing the observed distortions are constructed. One or two pairs of counter-scanned images (CSIs) are used as initial data. A system of linear equations is solved by finding the coordinate of the same surface feature in each CSI. The solutions obtained, i.e., linear transformation coefficients, are used to correct drift-induced distortions in horizontal and vertical planes. Two nonlinear drift correction methods are proposed, which provide a better accuracy in comparison with the linear correction method. The developed method can be used in feature-oriented scanning of the surface.

SU-FF-T-228: A Integrated Approach to Improve Accuracy of Film Dosimetry in TPS Verification

Purpose: To eliminate negative impacts in film measurement system, which adopt commercially availabe scanner as digitizer, and diminish film's inherent over-response to low energy scatter photons, an integrated approach is proposed to improve total accuracy of film dosimetry. Method and Materials: The system is composed of EDR2 radiographic film, polystyrene phantom, auto-processor and ArtixScan 2020 Scanner. A wavelet packet filtering method combining with mid-value filtering is employed to eliminate interference-pattern artifacts, grains drift and high frequency noise, which usually produced by laser scanner based on CCD in film digitizing process and have random characters. In order to reconstruct the original OD image, point-spread function (PSF) is used to deconvolve transmission gray data. Besides calibrating for OD-Dose translation, the approach also integrates a nonlinearity correction method to scanner with Kodak step wedge film to correct the nonlinearity and inconsistency of the detectors' response to film's gray. To reduce film's inherent loverresponse to low energy, a set of coefficients of EDR2 film for Co-60 λ rays in polystyrene phantom is calculated through MC simulation and used to correct film dose in TPS's verification for rotating gamma system. The results from 0.015 cm3 PTW ion chamber is obtained and used to be the reference. Results: Trial validation experiment shows this approach has better linearity, higher sensitivity of OD-Dose response, and excellent agreement (SSD <5% in 21 test points) with those from ionization chamber at corresponding planes in phantom. Conclusion: This approach has a potential capability in clinicl to eliminate artifacts and noises in film digitizing process, and then significantly improve total accuracy of film dosimetry. To remove its over-response, the key is to acquire the appropriate correction coefficient for various buildups through experiment or MC simulation, both needing collaboration with other research groups interested.

Evidence of reduced measurement uncertainties from an FTIR instrument intercomparison at Kiruna, Sweden

We report the results of an intercomparison of vertical column amounts of HCl, HF, N 2O, HNO 3, CH 4, O 3, CO 2 and N 2 derived from the spectra recorded by two ground-based FTIR spectrometers operated side-by-side using the sun as a source. The procedures used to record spectra and derive vertical column amounts followed the format of previous instrument intercomparisons organised by the Network for Detection of Stratospheric Change (NDSC), but the level of agreement achieved was significantly better than for previous intercomparisons. For most gases the differences were typically 1% or less, with at least one of the five datasets showing no statistically significant difference between the results from different instruments. Principal exceptions were HNO 3 and CO 2 when measured on the Mercury Cadmium Telluride (MCT) detectors. For these gases differences of between 2% and 3% were more typical. We present evidence that these larger differences are due to the effects of detector non-linearity and show that by applying an established non-linearity correction method the typical level of agreement can be improved to better than 1% for these gases. We suggest that the improved level of agreement achieved during this intercomparison is indicative of the current state of the art within the NDSC infra-red working group and is a result of improved understanding of the importance of critical alignment parameters and newly developed techniques to characterise the spectrometers’ performance.

Investigations into the Effects of Human Activities on the Hydrological Cycle in the Yellow River Basin

The Yellow River is the origin of Chinese Nation. The water shortage problem has become so serious in recent years that the social and economy development of the basin has been greatly affected. Investigation into and study of the effects of human activities on hydrological cycle in the Yellow River Basin has very important value to rational allocation, optimized regulation, and effective protection of water resources in the basin. The research principle and method is the natural-artificial dual evolution mode of hydrological cycle. A quantitative analysis was conducted starting from a typical sub-basin in the middle reach of the Yellow River Basin: the Wuding River Basin. Empirical hydrological cycle formulae for the Wuding River are tested to reflect dynamic variation of basin vegetation/land cover. A trend of non-linearity of hydrological cycle in the Wuding River is observed. The principle of the natural-artificial dual evolution mode of hydrological cycle was then applied in the whole Yellow River Basin. The reason for the variation of the hydrological cycle is investigated under natural-artificial driving forces. Results show that natural force takes a main role in evolution of hydro-logical cycle in the source region of the Yellow River Basin. Then as the Yellow River flows downstream, artificial driving forces by human activities such as reservoirs, water and soil conservation measures, and water withdrawal and diversion become more and more important in the evolution of hydrological cycle. The method of nonlinear correction to hydrological cycle is introduced and applied in the Yellow River Basin.

Removal of EPI Nyquist ghost artifacts with two‐dimensional phase correction

Odd-even echo inconsistencies result in Nyquist ghost artifacts in the reconstructed EPI images. The ghost artifacts reduce the image signal-to-noise ratio and make it difficult to correctly interpret the EPI data. In this article a new 2D phase mapping protocol and a postprocessing algorithm are presented for an effective Nyquist ghost artifacts removal. After an appropriate k-space data regrouping, a 2D map accurately encoding low- and high-order phase errors is derived from two phase-encoded reference scans, which were originally proposed by Hu and Le (Magn Reson Med 36:166-171;1996) for their 1D nonlinear correction method. The measured phase map can be used in the postprocessing algorithm developed to remove ghost artifacts in subsequent EPI experiments. Experimental results from phantom, animal, and human studies suggest that the new technique is more effective than previously reported methods and has a better tolerance to signal intensity differences between reference and actual EPI scans. The proposed method may potentially be applied to repeated EPI measurements without subject movements, such as functional MRI and diffusion coefficient mapping.

Methodology to obtain accurate sea surface temperature from locally received NOAA-14 data in the Canary-Azores-Gibraltar area

A methodology to obtain the sea surface temperature (SST) in the Canary-Azores-Gibraltar area has been developed. The final accuracy of the AVHRR-based SST retrievals depends both on the accuracy of the measured radiance and the accuracy of the SST retrieval algorithm that converts the measured radiance into sea surface temperature. The procedure made in this framework consists of: (i) a radiance-based non-linearity correction method; (ii) an automatic procedure for the geometric correction, achieving accuracy to the order of the pixel; (iii) an improved algorithm for cloud detection, based on the method of the multiband thresholds; (iv) a new split-window function (SWF) to perform atmospheric correction in CANIGO area. This task has been accomplished by using the matchup data set of AVHRR brightness temperature (channel 4 and 5) and in situ SST data. The matchups were carefully screened from the HRPT scenes of all seasons in 1996-1998. The temporal and spatial coincidences are within 30 minutes and one pixel resolution, respectively. Coefficients of that algorithm are estimated from regression analysis using 60 co-located in situ and satellite measurements (matchups). Error analysis has shown that SST can theoretically be retrieved to within 0.38oC RMS.

Quasi-Center-Weighted PWM Multi-level LED Printhead with Non-linear Exposure Uniformity Correction

A Quasi-Center-Weighted PWM exposure scheme (with stretched bit) was created for a Multi-level LED printhead that reduces the exposure time difference between available exposure levels; thereby enabling better non-uniformity correction at very high printing speed. Also this technology still maintains the advantages of centered line with sharper text/graphics and the lower current spike (not all the pixels are turned on or turned off at the same time) of the regular Center-Weighted PWM system at the same time. Working together with a non-linear exposure non-uniformity correction method that obtains non-uniformity correction and gray level simultaneously, this system is shown to produce uniformity of &#x223C; 0.5% throughout the dynamic range of exposure of the multi-level printing system at high speed.

Piece-Wise Multiplicative Scatter Correction Applied to Near-Infrared Diffuse Transmittance Data from Meat Products

This paper presents a nonlinear scatter correction method, called piece-wise multiplicative scatter correction (PMSC), that is a further development of the multiplicative scatter correction (MSC) method. Near-infrared diffuse transmittance (NIT) data from meat and meat product samples were used to test the predictive performances of the PMSC and the MSC methods. With the use of PMSC, the prediction errors, expressed as the root mean square error of prediction (RMSEP), were improved by up to 36% for protein, up to 55% for fat, and up to 37% for water, in comparison to uncorrected data. The corresponding improvements by using PMSC compared to MSC were up to 22%, 24%, and 31% for protein, fat, and water, respectively.

A nonlinear correction method for orbit determination.

A nonlinear correction method for orbit determination.

More on nonlinear distortion correction

Further consideration is given to basic amplitude limitations which may apply to the complementary distortion method of nonlinear distortion correction. It is found, in disagreement with others, that points at which the differential gain is zero or infinite do not limit the amplitude over which complete correction is possible but that relative maxima, minima, gain zeros, and infinite-gain points in the characteristic do set limitations when the usual simply connected tandem configuration is employed. When the characteristic to be corrected is multiple valued or passes through points of zero or infinite gain within a given amplitude range, a multiply connected correction circuit must be used for perfect correction of distortion over the amplitude range in question.