Apparent Reflectance Research Articles

The nature of instructional effects in color constancy.

The instructions subjects receive can have a large effect on experimentally measured color constancy, but the nature of these effects and how their existence should inform our understanding of color perception remains unclear. We used a factorial design to measure how instructional effects on constancy vary with experimental task and stimulus set. In each of 2 experiments, we employed both a classic adjustment-based asymmetric matching task and a novel color selection task. Four groups of naive subjects were instructed to make adjustments/selections based on (a) color (neutral instructions); (b) the light reaching the eye (physical spectrum instructions); (c) the actual surface reflectance of an object (objective reflectance instructions); or (d) the apparent surface reflectance of an object (apparent reflectance instructions). Across the 2 experiments we varied the naturalness of the stimuli. We find clear interactions between instructions, task, and stimuli. With simplified stimuli (Experiment 1), instructional effects were large and the data revealed 2 instruction-dependent patterns. In 1 (neutral and physical spectrum instructions) constancy was low, intersubject variability was also low, and adjustment-based and selection-based constancy were in agreement. In the other (reflectance instructions) constancy was high, intersubject variability was large, adjustment-based constancy deviated from selection-based constancy and for some subjects selection-based constancy increased across sessions. Similar patterns held for naturalistic stimuli (Experiment 2), although instructional effects were smaller. We interpret these 2 patterns as signatures of distinct task strategies-1 is perceptual, with judgments based primarily on the perceptual representation of color; the other involves explicit instruction-driven reasoning. (PsycINFO Database Record

Testing the ice-water discrimination and freeboard retrieval algorithms for the ICESat-2 mission

The ICESat-2 mission will provide routine estimates of sea ice freeboard from profiles of surface heights acquired by its photon-counting lidar: the Advanced Topographic Laser Altimeter System (ATLAS). In this paper, we describe and test procedures devised to separate returns of ice from open water — a crucial step in the estimation of local sea levels for freeboard calculations. The two data sets used in these tests, one each from winter and summer, were acquired by a Multiple Altimeter Beam Experimental Lidar (MABEL) implemented to support pre-launch development of retrieval approaches. Our approach first identifies likely open water returns using surface photon and background count rates as proxy indicators of apparent surface reflectance. Since these measured rates are noisy estimates of expected reflectance, relative surface heights are used to refine the selection of the candidate sea surface samples. Results show that winter freeboard distributions are consistent with expected regional variability, and the nearly identical repeat-track freeboard distributions during summer show retrieval consistency. From coincident lidar coverage, variability of sea level samples identified in the MABEL and Airborne Topographic Mapper (ATM) lidar profiles are 1.6 cm and 2.6 cm, with the overall difference between the distributions at 0.00 ± 0.15 m. This demonstrates the viability of the algorithms. The parameters used in these procedures will serve as a baseline and as a guide for understanding algorithm reliability. It is expected that they will be adjusted post-launch to reflect the on-orbit performance of ATLAS.

GLORI: A GNSS-R Dual Polarization Airborne Instrument for Land Surface Monitoring.

Global Navigation Satellite System-Reflectometry (GNSS-R) has emerged as a remote sensing tool, which is complementary to traditional monostatic radars, for the retrieval of geophysical parameters related to surface properties. In the present paper, we describe a new polarimetric GNSS-R system, referred to as the GLObal navigation satellite system Reflectometry Instrument (GLORI), dedicated to the study of land surfaces (soil moisture, vegetation water content, forest biomass) and inland water bodies. This system was installed as a permanent payload on a French ATR42 research aircraft, from which simultaneous measurements can be carried out using other instruments, when required. Following initial laboratory qualifications, two airborne campaigns involving nine flights were performed in 2014 and 2015 in the Southwest of France, over various types of land cover, including agricultural fields and forests. Some of these flights were made concurrently with in situ ground truth campaigns. Various preliminary applications for the characterisation of agricultural and forest areas are presented. Initial analysis of the data shows that the performance of the GLORI instrument is well within specifications, with a cross-polarization isolation better than −15 dB at all elevations above 45°, a relative polarimetric calibration accuracy better than 0.5 dB, and an apparent reflectivity sensitivity better than −30 dB, thus demonstrating its strong potential for the retrieval of land surface characteristics.

Evaluation of Radiometric and Atmospheric Correction Algorithms for Aboveground Forest Biomass Estimation Using Landsat 5 TM Data

Solar radiation is affected by absorption and emission phenomena during its downward trajectory from the Sun to the Earth’s surface and during the upward trajectory detected by satellite sensors. This leads to distortion of the ground radiometric properties (reflectance) recorded by satellite images, used in this study to estimate aboveground forest biomass (AGB). Atmospherically-corrected remote sensing data can be used to estimate AGB on a global scale and with moderate effort. The objective of this study was to evaluate four atmospheric correction algorithms (for surface reflectance), ATCOR2 (Atmospheric Correction for Flat Terrain), COST (Cosine of the Sun Zenith Angle), FLAASH (Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes) and 6S (Second Simulation of Satellite Signal in the Solar), and one radiometric correction algorithm (for reflectance at the sensor) ToA (Apparent Reflectance at the Top of Atmosphere) to estimate AGB in temperate forest in the northeast of the state of Durango, Mexico. The AGB was estimated from Landsat 5 TM imagery and ancillary information from a digital elevation model (DEM) using the non-parametric multivariate adaptive regression splines (MARS) technique. Field reference data for the model training were collected by systematic sampling of 99 permanent forest growth and soil research sites (SPIFyS) established during the winter of 2011. The following predictor variables were identified in the MARS model: Band 7, Band 5, slope (β), Wetness Index (WI), NDVI and MSAVI2. After cross-validation, 6S was found to be the optimal model for estimating AGB (R2 = 0.71 and RMSE = 33.5 Mg·ha−1; 37.61% of the average stand biomass). We conclude that atmospheric and radiometric correction of satellite images can be used along with non-parametric techniques to estimate AGB with acceptable accuracy.

A divinização e humanização do perdão no imaginário popular religioso brasileiro

Some behavioral models are created by imagination and only in this have real existence, even if it is fictitious. These images of collective representation or ideas are internalized by man, who builds for himself value systems, beliefs, ideologies and religious experiences. Popular religious imagery establish then, from an apparent reflection, axioms of faith and behavior that become guidelines to the practical actions of life. An expression from the eighteenth century British poet and essayist Alexander Pope, To err is human, to forgive is divine , has become an absolute truth in the Brazilian popular religious imagery. In this article, it is approached the deification and humanization nexus of forgiveness. Why is it possible to understand the human potential for error, but, when it becomes necessary to apply forgiveness to one who makes the mistake, we deify forgiveness? From a reflection on the popular religious imagery - where to err is an activity innate to man and to forgive a gift exclusively divine - and the theological vision and relationship of Brazilians with God, it is sought to introduce the concept of forgiveness according to the text sacred to Christians, exposing the principle that to forgive is both a divine and human act. It also evokes the difficulties experienced in the act of forgiving in the relation of man with his equal, and the assistance provided through counseling.

Detection of molecular signatures of oral squamous cell carcinoma and normal epithelium - application of a novel methodology for unsupervised segmentation of imaging mass spectrometry data.

Intra‐tumor heterogeneity is a vivid problem of molecular oncology that could be addressed by imaging mass spectrometry. Here we aimed to assess molecular heterogeneity of oral squamous cell carcinoma and to detect signatures discriminating normal and cancerous epithelium. Tryptic peptides were analyzed by MALDI‐IMS in tissue specimens from five patients with oral cancer. Novel algorithm of IMS data analysis was developed and implemented, which included Gaussian mixture modeling for detection of spectral components and iterative k‐means algorithm for unsupervised spectra clustering performed in domain reduced to a subset of the most dispersed components. About 4% of the detected peptides showed significantly different abundances between normal epithelium and tumor, and could be considered as a molecular signature of oral cancer. Moreover, unsupervised clustering revealed two major sub‐regions within expert‐defined tumor areas. One of them showed molecular similarity with histologically normal epithelium. The other one showed similarity with connective tissue, yet was markedly different from normal epithelium. Pathologist's re‐inspection of tissue specimens confirmed distinct features in both tumor sub‐regions: foci of actual cancer cells or cancer microenvironment‐related cells prevailed in corresponding areas. Hence, molecular differences detected during automated segmentation of IMS data had an apparent reflection in real structures present in tumor.

Propagating Neural Source Revealed by Doppler Shift of Population Spiking Frequency.

The use of novel techniques with an unfolded hippocampus and penetrating microelectrode array to record and analyze neural activity has revealed the existence of a source of neural signals that propagates throughout the hippocampus. The source itself is electrically silent, but its location can be inferred by building isochrone maps of population spikes that the source generates. The movement of the source can also be tracked by observing the Doppler frequency shift of these spikes. These results have general implications for how neural signals are generated and propagated in the hippocampus; moreover, they have important implications for the understanding of seizure generation and foci localization.

Geospatial Estimation of above Ground Forest Biomass in the Sierra Madre Occidental in the State of Durango, Mexico

Combined use of new geospatial techniques and non-parametric multivariate statistical methods enables monitoring and quantification of the biomass of large areas of forest ecosystems with acceptable reliability. The main objective of the present study was to estimate the aboveground forest biomass (AGB) in the Sierra Madre Occidental (SMO) in the state of Durango, Mexico, using the M5 model tree (M5P) technique and the analysis of medium-resolution satellite-based multi-spectral data, and field data collected from a network of 201 permanent forest growth and soil research sites (SPIFyS). Research plots were installed by systematic sampling throughout the study area in 2011. The digital levels of the images were converted to apparent reflectance (ToA) and surface reflectance (SR). The M5P technique that constructs tree-based piecewise linear models was used. The fitted model with SR and tree abundance by species group as predictive variables (ASG) explained 73% of the observed AGB variance (the root mean squared error (RMSE) = 39.40 Mg·ha−1). The variables that best discriminated the AGB, in order of decreasing importance, were the normalized difference vegetation index (NDVI), tree abundance of other broadleaves species (OB), Band 4 of Landsat 5 TM (Thematic Mapper) satellite and tree abundance of pines (Pinus). The results demonstrate the potential usefulness of the M5P method for estimating AGB based in the surface reflectance values (SR).

Spatial interpolation quality assessment for soil sensor transect datasets

Near-ground geophysical soil sensors provide valuable information for precision agriculture applications. Indeed, their readings can be used as proxy for many soil parameters. On-the-go soil sensor surveys are, typically, carried out intensively (e.g., every 2m) over many parallel transects. Two types of soil sensors measurements are considered in this paper: apparent electrical conductivity (4 fields in California, USA) and reflectance (1 field in Italy). Two types of spatial interpolations are carried out, universal kriging (model-based) and inverse distance weighting (deterministic). Interpolation quality assessment is usually carried out using leave-one-out (loo) resampling. We show that loo resampling on transect sampling datasets returns overly-optimistic, low interpolation errors, because the left-out data point has values very close to that of its neighbors in the training dataset. This bias in the map quality assessment can be reduced by removing the closest neighbors of the validation observation from the training dataset, in a (spatial) h-block (SHB) fashion. The results indicate that, for soil sensor data acquired along parallel transects: (i) the SHB resampling is a useful tool to test the performance of interpolation techniques and (ii) the optimal (i.e., rendering the same errors of un-sampled locations between transects) SHB threshold distance (h.dist) for neighbor-exclusion is proportional to the semi-variogram range and partial sill. This procedure provides research scientists with an improved means of understanding the error of soil maps made by interpolating soil sensor measurements.

Quality Control Assessment of the Mission Airborne Carbon 13 (MAC-13) Hyperspectral Imagery from Costa Rica

. A data quality assessment of airborne hyperspectral imagery (HSI) from Mission Airborne Carbon 2013 (MAC13) is presented. Because data quality is fundamentally important for modeling landscape biophysical characteristics from HSI, this article presents an assessment related to spectral alignment, spectroradiometric calibration, and geocorrection for 2,700 km2 of imagery acquired with the CASI-1500 and SASI-644 systems (375 nm – 2523 nm, 2.5 m resampled pixel size). MODIS, in-situ and image-based estimations of aerosol optical depth are compared for calculations of visibility for atmospheric correction. Information content (dimensionality) across the 5 ecosystems and 2 developed areas are also compared to illustrate the benefit of the extensive spectral resolution of the data.New approaches to the offset corrections of the imagery improved the accuracy of the calibrated results (radiance and reflectance). Assessment of visibility values applied to the atmospheric correction adduced that apparent reflectance computed using in-scene modeled visibility produced the most similar results to ground spectra. Dimensionality analysis revealed increased information content for all ecosystems when both sensors were considered. While not every HSI issue can be completely compensated for, an appreciation of common artifacts allows users to make more informed decision about their impact on planned analysis.

Radiometric Calibration of a Dual-Wavelength, Full-Waveform Terrestrial Lidar.

Radiometric calibration of the Dual-Wavelength Echidna® Lidar (DWEL), a full-waveform terrestrial laser scanner with two simultaneously-pulsing infrared lasers at 1064 nm and 1548 nm, provides accurate dual-wavelength apparent reflectance (ρapp), a physically-defined value that is related to the radiative and structural characteristics of scanned targets and independent of range and instrument optics and electronics. The errors of ρapp are 8.1% for 1064 nm and 6.4% for 1548 nm. A sensitivity analysis shows that ρapp error is dominated by range errors at near ranges, but by lidar intensity errors at far ranges. Our semi-empirical model for radiometric calibration combines a generalized logistic function to explicitly model telescopic effects due to defocusing of return signals at near range with a negative exponential function to model the fall-off of return intensity with range. Accurate values of ρapp from the radiometric calibration improve the quantification of vegetation structure, facilitate the comparison and coupling of lidar datasets from different instruments, campaigns or wavelengths and advance the utilization of bi- and multi-spectral information added to 3D scans by novel spectral lidars.

Radiometric calibration of a dual-wavelength terrestrial laser scanner using neural networks

ABSTRACTThe Salford Advanced Laser Canopy Analyser (SALCA) is a unique dual-wavelength full-waveform terrestrial laser scanner (TLS) designed to measure forest canopies. This article has two principle objectives, first to present the detailed analysis of the radiometric properties of the SALCA instrument, and second, to propose a novel method to calibrate the recorded intensity to apparent reflectance using a neural network approach. The results demonstrate the complexity of the radiometric response to range, reflectance, and laser temperature and show that neural networks can accurately estimate apparent reflectance for both wavelengths (a root mean square error (RMSE) of 0.072 and 0.069 for the 1063 and 1545 nm wavelengths, respectively). The trained network can then be used to calibrate full hemispherical scans in a forest environment, providing new opportunities for quantitative data analysis.

Landslide investigations in the northwest section of the lesser Khingan range in China using combined HDR and GPR methods

In the northwest section of the lesser Khingan range, located in the high-latitude permafrost region of northeast China, landslides are a frequent occurrence, due to permafrost melting and atmospheric precipitation. High-density resistivity (HDR) and ground-penetrating radar (GPR) methods are based on soil resistivity values and characteristics of radar wave reflection, respectively. The combination of these methods, together with geological drilling, can be used to determine the stratigraphic distribution of this region, which will allow precise determination of the exact location of the sliding surface of the landslide. Field test results show that the resistivity values and radar reflectivity characteristics of the soil in the landslide mass largely differ from those of the soil outside the mass. The apparent resistivity values exhibit abrupt layering at the position of the sliding surface, with a sudden decrease in apparent resistivity. In addition, the radar wave shows strong reflection at the position of the sliding surface, where the amplitude of the radar wave exhibits a sudden increase. Drilling results indicate that the soil has high water content at the location of the sliding surface of the landslide mass in the study area, which is entirely consistent with the GPR and HDR results. Thus, in practice, sudden changes in apparent resistivity values and abnormal radar wave reflection can be used as a basis for determining the location of sliding surfaces of landslide masses in this region.

A study of changes in apparent ionospheric reflection height within individual lightning flashes

Ionospheric reflection heights estimated using the zero-to-zero and peak-to-peak methods to measure skywave delay relative to the ground wave were compared for 108 first and 124 subsequent strokes at distances greater than 100km. For either metric there was a considerable decrease in average reflection height for subsequent strokes relative to first strokes. We showed that the observed difference cannot be explained by the difference in frequency content of first and subsequent return-stroke currents. Apparent changes in reflection height (estimated using the peak-to-peak method) within individual flashes for 54 daytime and 11 nighttime events at distances ranging from 50km to 330km were compared, and significant differences were found. For daytime conditions, the majority of the flashes showed either decrease (57%) or non-monotonic variation (39%) in reflection height with respect to the immediately preceding stroke. With respect to the first stroke, 91% of the flashes showed monotonic decrease in height. For nighttime flashes, patterns in reflection height changes with respect to the immediately preceding stroke were as follows: 46% no change, 27% monotonic decrease, and 27% non-monotonic variation. When changes were measured with respect to the first stroke, 54% of nighttime flashes showed monotonic decrease and 46% no change. Ionospheric reflection height tends to increase with return-stroke peak current. The observed daytime effects can be explained by (a) the dependence of EMP penetration depth on source intensity, which decreases with stroke order, (b) additional ionization associated with elves, or (c) combination of (a) and (b) above.

New Spectral Fitting Method for Full-Spectrum Solar-Induced Chlorophyll Fluorescence Retrieval Based on Principal Components Analysis

The full-spectrum Solar-Induced chlorophyll Fluorescence (SIF) within the 650-800 nm spectral region can provide important information regarding physiological and biochemical activities in vegetation. This paper proposes a new Full-spectrum Spectral Fitting Method (F-SFM) for the retrieval of SIF spectra based on Principal Components Analysis (PCA). Using F-SFM, both the full-spectrum reflectance and SIF within the 650-800 nm region were modeled by PCA based on a training dataset simulated by the Soil Canopy Observation, Photochemistry and Energy fluxes (SCOPE) model, and the weighting coefficients of the principal components were estimated by the least-squares fitting method. An iterative process was employed to improve the accuracy of the estimation of the reflectance. In each iteration, the SIF spectra retrieved from the last run were removed from the total upwelling radiance to minimize the small contribution of the SIF to the apparent reflectance outside the absorption bands. Then, the F-SFM algorithm was tested using both simulated and field-measured data with different Spectral Resolutions (SRs) and Signal-to-Noise Ratios (SNRs). For data with an SR of 0.3 nm and without noise, the Relative Root Mean Square Error (RRMSE) was less than 14% within the spectral region that was studied, and the peak-value ratio (SIF735/SIF685) was accurately estimated with an RRMSE of 3.56%. In addition, the F-SFM algorithm proved less sensitive to the SR than the three-band Fraunhofer Line Discrimination (3 FLD) and improved FLD (iFLD) methods. In the case of the field spectral data with SRs of 3 nm and 0.3 nm, the double-peak shape and the diurnal variation trend of the SIF spectra could be reasonably reconstructed by F-SFM, and the retrieved SIF values at the O2-A and O2-B bands were consistent with those retrieved by 3FLD from data with a high SR (0.3 nm) and SNR (1000). Therefore, the F-SFM method can provide full-spectrum SIF information with high accuracy even at relatively low SRs and SNRs, and shows promise for use in applications involving the SIF shape information.

Easily fabricated 60 GHz WR15/MSL transition to measure apparent reflection coefficient of differentially fed patch antennas

A new procedure to measure the apparent reflection coefficient of differential patch antennas at 60 GHz is described. The measurement method makes use of two WR15/microstrip-line (MSL) transitions which are simple to realise. The experimental results are compared with simulated results. This comparison emphasises the limited effect of transition losses on measurement accuracy.

What visual illusions tell us about underlying neural mechanisms and observer strategies for tackling the inverse problem of achromatic perception.

Research in lightness perception centers on understanding the prior assumptions and processing strategies the visual system uses to parse the retinal intensity distribution (the proximal stimulus) into the surface reflectance and illumination components of the scene (the distal stimulus—ground truth). It is agreed that the visual system must compare different regions of the visual image to solve this inverse problem; however, the nature of the comparisons and the mechanisms underlying them are topics of intense debate. Perceptual illusions are of value because they reveal important information about these visual processing mechanisms. We propose a framework for lightness research that resolves confusions and paradoxes in the literature, and provides insight into the mechanisms the visual system employs to tackle the inverse problem. The main idea is that much of the debate and confusion in the literature stems from the fact that lightness, defined as apparent reflectance, is underspecified and refers to three different types of judgments that are not comparable. Under stimulus conditions containing a visible illumination component, such as a shadow boundary, observers can distinguish and match three independent dimensions of achromatic experience: apparent intensity (brightness), apparent local intensity ratio (brightness-contrast), and apparent reflectance (lightness). In the absence of a visible illumination boundary, however, achromatic vision reduces to two dimensions and, depending on stimulus conditions and observer instructions, judgments of lightness are identical to judgments of brightness or brightness-contrast. Furthermore, because lightness judgments are based on different information under different conditions, they can differ greatly in their degree of difficulty and in their accuracy. This may, in part, explain the large variability in lightness constancy across studies.

Structural and magnetic properties of RTiNO2 (R=Ce, Pr, Nd) perovskite nitride oxides

Neutron powder diffraction indicates that CeTiNO2 and PrTiNO2 crystallize with orthorhombic Pnma symmetry (Ce: a=5.5580(5), b=7.8369(7), and c=5.5830(4)Å; Pr: a=5.5468(5), b=7.8142(5), and c=5.5514(5)Å) as a result of a–b+a– tilting of the titanium-centered octahedra. Careful examination of the NPD data, confirms the absence of long range anion order in both compounds, while apparent superstructure reflections seen in electron diffraction patterns provide evidence for short range anion order. Inverse magnetic susceptibility plots reveal that the RTiNO2 (R=Ce, Pr, Nd) compounds are paramagnetic with Weiss constants that vary from −28 to −42K. Effective magnetic moments for RTiNO2 (R=Ce, Pr, Nd) are 2.43μB, 3.63μB, and 3.47μB, respectively, in line with values expected for free rare-earth ions. Deviations from Curie–Weiss behavior that occur below 150K for CeTiNO2 and below 30K for NdTiNO2 are driven by magnetic anisotropy, spin–orbit coupling, and crystal field effects.

Effect of glass fiber and crystallinity on light transmission during laser transmission welding of thermoplastics

Abstract In order to predict and optimize the contour laser transmission welding (LTW) process, it is important to understand how the laser energy behaves during transmission through the transparent part. In this study, transmission measurements were made on unreinforced and glass-fiber-reinforced amorphous and semi-crystalline thermoplastics at different thicknesses. Using the ratio of transmitted power to laser power, apparent absorption coefficients and apparent reflections were calculated. The results indicate that there is a linear relationship between the glass fiber volume fraction and the apparent absorption coefficient of reinforced polymers; similar effects were also observed for crystallinity. A simple model was developed to estimate apparent absorption coefficient of reinforced polymers as a function of composition. The apparent reflection increased with crystallinity due to increased back scattering. However, for glass-fiber-reinforced polymers, the apparent reflection displayed a more complex behavior.

Comments and responses to "Theoretical approaches to lightness and perception".

In a review of the brightness/lightness literature Kingdom (2011) noted that “Divided into different camps, each with its own preferred stimuli, methodology and theory, the study of LBT (lightness, brightness, transparency) is sometimes more reminiscent of the social sciences with its deep ideological divides than it is of the neurosciences”. Methodology and theory clearly separate our work from that of Gilchrist as described by Kingdom (2011). The similarity of the underlying problems, however, has led us to investigate the roots of these differences and to propose a framework to bridge the divide and advance the field (Blakeslee & McCourt, 2015). The common question for brightness/lightness research is how, and under what circumstances, is the visual system able to differentiate the physically invariant reflectance of a surface from its potentially changing illumination. The visual system lacks direct access to either quantity, being given only their product which determines the retinal luminance (intensity) distribution. The recovery of surface reflectance and illumination is thus an inverse problem with no algorithmic solution, and observers must therefore employ knowledge or prior assumptions (conscious or unconscious, learned or innate) about these variables to approximate a solution. We propose a framework for brightness/lightness research that resolves many of the confusions that have plagued communication between research groups (for details see Blakeslee & McCourt, 2015). The core ideas of this framework are that: 1) much of the confusion in the brightness/lightness literature stems from groups using different definitions of the central variables (brightness and lightness); 2) the term lightness, when defined simply as apparent reflectance, is underspecified with regard to illumination and is often used to refer to three independent and incomparable types of judgments. We discuss the above confusions and the false dichotomy between brightness and lightness research paradigms that they create, in relation to the preceding article (Gilchrist, 2015).