Flat Index Research Articles

Radio spectral index distribution of SDSS-FIRST sources across optical diagnostic diagrams

Context. The empirical relations between supermassive black holes and their host spheroids point towards the crucial role of galactic nuclei in affecting the properties of their hosts. A detailed understanding of how the activity of a galactic nucleus regulates the growth of its host is still missing. Aims. To understand the activity and the types of accretion of supermassive black holes in different hosts, it is essential to study the radio-optical properties of a large sample of extragalactic sources. In particular, we aim to study the radio spectral index trends across the optical emission line diagnostic diagrams to search for potential (anti)correlations. Methods. To this goal, we combined flux densities from the radio FIRST survey at 1.4 GHz (with the flux density range 10 mJy ≤ F1.4 ≤ 100 mJy) for 396 SDSS sources at intermediate redshift (0.04 ≤ z ≤ 0.4) with the Effelsberg radiotelescope measurements at 4.85 GHz and 10.45 GHz. The information about the optical emission-line ratios is obtained from the SDSS-DR7 catalogue. Results. Using the Effelsberg data, we were able to infer the two-point radio spectral index distributions for star-forming galaxies, composite galaxies (with a combined contribution to the line emission from the star formation and AGN activity), Seyferts, and low ionization narrow emission region (LINER) galaxies. Conclusions. While studying the distribution of steep, flat, and inverted sources across optical diagnostic diagrams, we found three distinct classes of radio emitters for our sample: (i) sources with a steep radio index, high ionization ratio, and high radio loudness, (ii) sources with a flat radio index, lower ionization ratio, and intermediate radio loudness, (iii) sources with an inverted radio index, low ionization ratio, and low radio loudness. The classes (i), (ii), and (iii) cluster mainly along the transition from Seyfert to LINER sources in the optical diagnostic (Baldwin, Phillips & Telervich; BPT) diagram. We interpret these groups as a result of the recurrent nuclear-jet activity.

A hillslope based digital soil mapping approach, for hydropedological assessments

Urban sprawl and the accompanying development is set to increase pressure on the hydrological system. In turn, the hydrology of an area affects the infrastructure. Hydropedology, can assist to sustainably manage the infrastructure-hydrology interaction. Even though the hillslope scale is accepted as ideal for hydropedological assessments, regional soil maps have been used when hydropedology assessments were undertaken for larger areas. This study uses a hillslope based approach within a digital soil mapping method to conduct a hydropedological assessment for a large (12,000 ha) urban area under developmental pressure within Johannesburg, South Africa. One hundred and thirty-three hillslopes within the study area were delineated and mean and standard deviation of terrain attributes were calculated for each hillslope. Based on these values, the conditioned Latin hypercube sampling (cLHS) method was used to select 30 hillslopes on which soil observations would be made, in a transect, at the surveyor's discretion. A hydropedological soil map was created with the multinomial logistic regression algorithm and the 142 soil observations made. The soil map attained an acceptable 69% validation point accuracy and a Kappa value of 0.59, and was used to create a hillslope conceptual hydrological response map. The chi-square test and QQ-plots indicated that the cLHS selected hillslopes represented the hillslopes of the study site well, but the observations only represented some of the terrain attributes well. Despite the range of the observation dataset covering at least 98.7% of the pixels for the multi resolution index of valley bottom flatness (MRVBF), topographic wetness index (TWI) and altitude above channel network layers, their site distribution differed statistically from that of the observation distribution. The hillslope based survey approach allowed for an acceptable soil map to be created, while allowing for hillslope based hydropedological interpretations to be made. The “cost” for the hillslope based approach was that the distribution of some covariates for the observations differed from their distributions over the entire site.

Correlation between flat feet and body mass index in primary school students

Body mass index is one of the indicators used to detect body weight and nutritional status. Excessive weight in children can affect the occurrence of flat feet compared with children who have normal weight. Flat feet is a foot structure disorder that does not form the medial arch. The aim of this research is to know the relationship between body mass index and flat feet in elementary school children at Xaverius 1 Palembang. This is an analytical-observational research with a cross-sectional design. The subjects of this research are 70 students of elementary school at Xaverius 1 Palembang and collected by using stratified random sampling proportionally. The research was conducted in October 2017. Data analysis was performed by Chi-Square test on SPSS application. The category of body mass index was classified into overweight/obese and not-overweight. In the category of overweight/obese, there are 24 (80%) people were positive flat feet and 6 (20%) normal people. In the category of not-overweight, there are 7 (17.5%) people were positive flat feet and 33 (82.5%) normal people. The result of the bivariate analysis showed that there was a significant relationship between body mass index and flat feet (p = 0,000) with PR value of 4.571, that is overweight/obese people risk 4.5 times for flat feet compared to people who were notoverweight.

CHANG-ES. XX. High-resolution Radio Continuum Images of Edge-on Galaxies and Their AGNs: Data Release 3

Abstract The CHANG-ES galaxy sample consists of 35 nearby edge-on galaxies that have been observed using the VLA at 1.6 and 6.0 GHz. Here we present the third data release of our sample, namely, the B configuration 1.6 GHz sample. In addition, we make available the band-to-band spectral index maps between 1.6 and 6.0 GHz, the latter taken in the matching resolution C configuration. The images can be downloaded from https://www.queensu.ca/changes. These are our highest-resolution images (≈3″), and we examine the possible presence of low-luminosity active galactic nuclei (AGNs) in the sample, as well as some in-disk structure. New features can be seen in the spectral index maps that are masked in the total intensity emission, including hidden spiral arms in NGC 3448 and two previously unknown radio lobes on either side of the nucleus of NGC 3628. Our AGN detection rate, using only radio criteria, is 55%, which we take as a lower limit because some weaker embedded AGNs are likely present that could be revealed at higher resolution. Archival XMM-Newton data were used to search for further fingerprints of the AGNs in the studied sample. In galaxy disks, discrete regions of flat spectral index are seen, likely due to a thermal emission fraction that is higher than the global average.

Uncovering Red and Dusty Ultraluminous X-Ray Sources with Spitzer

Abstract We present a mid-infrared (IR) sample study of nearby ultraluminous X-ray sources (ULXs) using multiepoch observations with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. Spitzer/IRAC observations taken after 2014 were obtained as part of the Spitzer Infrared Intensive Transients Survey. Our sample includes 96 ULXs located within 10 Mpc. Of the 96 ULXs, 12 have candidate counterparts consistent with absolute mid-IR magnitudes of supergiants, and 16 counterparts exceeded the mid-IR brightness of single supergiants and are thus more consistent with star clusters or non-ULX background active galactic nuclei. The supergiant candidate counterparts exhibit a bimodal color distribution in a Spitzer/IRAC color–magnitude diagram, where “red” and “‘blue” ULXs fall in IRAC colors [3.6] – [4.5] ∼ 0.7 and [3.6] – [4.5] ∼ 0.0, respectively. The mid-IR colors and absolute magnitudes of four “red” and five “blue” ULXs are consistent with those of supergiant B[e] (sgB[e]) and red supergiant (RSG) stars, respectively. Although “blue,” RSG-like mid-IR ULX counterparts likely host RSG mass donors; we propose that “red” counterparts are ULXs exhibiting the “B[e] phenomenon” rather than hosts of sgB[e] mass donors. We show that the mid-IR excess from the “red” ULXs is likely due to thermal emission from circumstellar or circumbinary dust. Using dust as a probe for total mass, we estimate mass-loss rates of M ˙ ∼ 1 × 10 − 4 M ⊙ yr−1 in dust-forming outflows of red ULXs. Based on the transient mid-IR behavior and its relatively flat spectral index, α = −0.19 ± 0.1, we suggest that the mid-IR emission from Holmberg IX X-1 originates from a variable jet.

Facial flatness indices: application in orthodontics.

Facial flatness indices have been used in anthropology to discern differences among populations. They were evaluated on skulls from around the world.Aims(1) to evaluate the use of facial flatness indices in orthodontics and (2) to assess their variation among malocclusions, age and sex.Materials and MethodsA total of 322 cone beam computed tomography radiographs were digitized and three facial indices (frontal, simotic and zygomaxillary) along with three transverse distances (fmo1–fmo2, zma1–zma2 and n1–n2) were assessed and compared between different groups.ResultsThe zygomaxillary index was increased in Class II (32.6 ± 0.42; p < 0.001) and decreased in Class III malocclusions (29.4 ± 0.66; p < 0.001) compared to Class I (31.18 ± 0.3; p < 0.001). The frontal and nasal flatness are not characteristic features of any of the sagittal malocclusions. Facial flatness indices did not differ between males and females and between growing and non-growing patients.ConclusionThe position of subspinale point (A point) forward or backward relative to the zygomaxillary width is a factor of assessment of facial flatness. The zygomaxillary index could be helpful in weighting proportionally the width of the maxilla (expansion) relative to its sagittal position in Class II and Class III malocclusions.

Detailed Characterization of a Lenster—A mm-Wave Flat Lens

We perform detailed free-space measurements of a previously published metal-mesh thin flat gradient index lens using a vector network analyzer. Direct measurements of the transmission and phase of the lens are made over the frequency band of 75–220 GHz, including off-axis performance. Beam patterns at 110 and 160 GHz show good agreement with the Airy pattern expectation and demonstrate its relative broadband performance. We also show that the beam profiles are not affected when it is rotated by ±6° with the receiver demonstrating its usability under nonnormal illumination.

Pebble Morphometric Study of the Ogwashi-Asaba Formation at Ubakala and Environs in Southeastern Nigeria

Pebble morphometric study was carried out for the Ogwashi-Asaba Formation so as to understand its paleodepositional environment. The three axes; the long (l), the intermediate (i) and the short (s) were measured for the two sets of one hundred and forty (140) and one hundred and fifty (150) pebbles collected from two outcrops of the Ogwashi-Asaba Formation. Pebble form indices such as Maximum Projection Sphericity (MPSI), coefficient of flatness (FR %), elongation ratio (ER) and oblate-prolate (OP) index were computed from these measurements. Roundness was estimated using Sames image sets. The mean values of the pebble form indices ranges from 49.78 to 52.02 for coefficient of flatness (FR %). 0.71 to 0.73 for sphericity, 2.60 t0 3.53 for oblate-prolate index, and 0.66 to 0.69 for elongation ratio. The calculated indices are suggestive of fluvial sedimentation for the Ogwashi-Asaba Formation. Bivariate plots of coefficient of flatness (FR %) versus maximum projection sphericity index (MPSI) and plots of sphericity (MPSI) versus oblate-prolate index (OP) are also indicative of fluvial origin. Scatter plots of roundness versus elongation ratio shows that 100% of the pebbles are in a littoral field. Plots of bivariate parameters such as simple skewness versus simple standard deviation, and second moment skewness versus second moment standard deviation suggests the Ogwashi-Asaba Formation as a product of the fluvial depositional processes. Keywords: Niger Delta Basin, Ogwashi-Asaba Formation, Pebble morphometry, Pebble Form indices. DOI : 10.7176/JNSR/9-6-06 Publication date :March 31 st 2019

Predicting soil types and soil properties with limited data in the Uasin Gishu Plateau, Kenya

Digital soil mapping (DSM) approaches can be used to create new soil maps or enhance existing maps, particularly in areas where only general soil maps are available. In this study, we utilized a knowledge-based inference soil mapping approach to develop a first-generation digital soil map for part of the Uasin Gishu Plateau in western Kenya. We calculated the following environmental covariates from the Shuttle Radar Topographic Mission (SRTM) 30 m digital elevation model (DEM): slope gradient, multi-resolution valley bottom flatness index (MrVBF), multi-resolution ridgetop flatness index (MrRTF), topographic position index (TPI), elevation, and profile curvature. These covariates were then used along with existing soil information and expert knowledge from soil scientists familiar with the area to produce new raster-based maps of soil types, effective soil depth, soil moisture storage capacity and soil drainage class. The soil type maps predicted using clustering analysis and fuzzy logic methods showed good agreement with field observations based on the overall accuracy values. The fuzzy logic map performed slightly better (kappa coefficient (k) = 0.68; overall accuracy = 0.76) than the map based on clustering analysis (k = 0.59; overall accuracy = 0.68). The accuracy for the effective soil depth fuzzy logic map was higher (R2 = 0.56; RMSE = 11; ME = 1.1) compared to the existing soil map (R2 = 0.34; RMSE = 27; ME = 8). Seven major soil types occur in the study area: Ferralsols, Nitisols, Gleysols, Luvisols, Acrisols, Cambisols and Regosols, according to the World Reference Base soil classification system. This study generated detailed and improved predictions of soil types and properties at 30 m grid resolution. These maps should be more useful for soil, crop and land use management decisions than existing maps.

Cellular-phone-based computer vision system to extract shape properties of coarse aggregate for asphalt mixtures

A new computer-vision cellular-phone-based methodology and scheme was developed to determine the shape properties (Flatness Index, Elongation Index and Roundness Index) of coarse aggregate particles. This scheme utilizes cellular phones images and image processing techniques (IPT) in determining the coarse aggregate particles shape properties. This methodology compared with the conventional methods, which need special laboratory technicians and are time consuming was faster and more accurate procedure. Fifty coarse aggregate particles were collected and their shape properties were measured manually (using caliper and AutoCAD) then computed using image processing procedure. To compute these shape properties using image processing, special data acquisition method was designed and implemented. The aggregate particles were arranged on a grid of an apparatus designed specifically for this task, and mapped by the cellular phone from two views; top view and side view. Then cellular phones images were analyzed with ImageJ software.

Polarised structures in the radio lobes of B2 0258+35

Context. The contribution of active galactic nuclei to the magnetisation of the Universe can be constrained by knowing their duty cycles, jet and magnetic field morphologies, and the physical processes dominating their interaction with the surrounding environment. Aims. The magnetic field morphology and strength of radio lobes of AGN has an influence on the mechanisms for the propagation of cosmic rays into intergalactic space. Using the source B2 0258+35 we want to investigate the interaction of its radio lobes with the surrounding environment and examine the underlying physical effects. Methods. Published H I and radio continuum data at λ21 cm were combined with newly reduced archival Westerbork Radio Synthesis Telescope polarisation data at the same wavelength to investigate the polarised emission in the radio lobes of B2 0258+35. We assumed energy equipartition between the cosmic rays and the magnetic field to calculate their pressure and investigate the physical processes leading to the detected emission. Results. We detected a unique S-shaped diffuse polarised structure. The lobes have a pressure of p = 1.95 ± 0.4 × 10−14 dyn cm−2. The calculated total magnetic field strengths are low (Beq = 1.21 ± 0.12 μG). We observe depolarisation in the northern lobe, which might originate from the H I-disc in the foreground. In addition we see an anti-correlation between the pressure and the fractional polarisation along the S-shaped structure. Therefore we consider magnetic draping and magnetic field compression as possible effects that might have created the observed S-shape. Conclusions. Our results suggest that magnetic draping can be effectively used to explain the observed polarised structures. This is likely due to the combination of a relatively low magnetic field strength, enabling super-Alfvénic motion of the rising lobes (with MA = 2.47 − 3.50), and the coherency of the surrounding magnetic field. Moreover, the draped layer tends to suppress any mixing of the material between the radio lobes and the surrounding environment, but can enhance the mixing and re-acceleration efficiencies inside the lobes, providing an explanation for the average flat spectral index observed in the lobes.

Assessment and monitoring of land degradation in the northwest coast region, Egypt using Earth observations data

This study assesses the spatial and temporal distribution of land degradation hotspots and their driving forces in the northwest coast of Egypt (NWC) based on MODIS-Enhanced Vegetation Index (EVI) and Tropical Rainfall Measuring Mission (TRMM) satellite rainfall data, using time series analysis and binomial logistic regression methodologies. The time series analyses of rainfall TRMM data across 2001–2016 proved the inter-annual rainfall variability through northwest coast of Egypt. Year 2016 was the most wet year with ∼690 mm/year and year 2010 is the most dry one with 89 mm/year with a trend line of 150 to 300 mm. Negative trends in vegetation degradation occurred across 2001–2016 in 28–37% at NWC, Dabaa and Matrouh, but only in 13% at Barrani Areas with improvement of vegetation cover ranged between 5 and 15% at NWC, Dabaa and Matrouh and increased to 38% at Barrani. The reclassified RESTREND-human induced rainfall adjusted map gives land degradation hotspots up to about 37% of the NWC area across 2001–2016, while 27% responded to land improvement measures. About half of the land degradation area (16%) and about one tenth (9%) of the land improvement areas are statistically significant. Spatial logistic regression modeling ranked the factors influencing land degradation dynamics in Matrouh subarea in decreasing order as: elevation, slope, range land, vegetation index, negative change in vegetation index, bare land, mid-slope position, and multi resolution ridge top flatness index .

Evaluation of three-dimensional particle shape index from projected two-dimensional image

Traditionally, the shape of a three-dimensional (3D) particle is inferred from a single parameter called the aspect ratio (AR) that is evaluated from a collection of projected two-dimensional (2D) images of the 3D particle. While this approach could offer an estimate of the particle shape, it is likely that a single parameter is insufficient to describe the 3D shape characteristics of a particle. Conventionally, the shape of a 3D particle can be described by two parameters: the elongation index (EI) and the flatness index (FI), defined as the length ratios of different principal dimensions. This paper presents a novel approach that can be used to evaluate the EI and FI of 3D particles based on their projected 2D images. The novelty of this proposed method is that the distribution of the AR is considered rather than only the mean value. The performance of the algorithm is examined using numerically generated ellipsoids and real sand particles scanned using microfocus X-ray computed tomography. The results appear promising and the plausible combinations of the EI and FI of the 3D particles can be obtained.

A search for hypercompact H iiregions in the Galactic Plane

We have carried out the largest and most unbiased search for hypercompact (HC) HII regions. Our method combines four interferometric radio continuum surveys (THOR, CORNISH, MAGPIS and White2005) with far-infrared and sub-mm Galactic Plane surveys to identify embedded HII regions with positive spectral indices. 120 positive spectrum HII regions have been identified from a total sample of 534 positive spectral index radio sources. None of these HII regions, including the known HCHII regions recovered in our search, fulfills the canonical definition of an HCHII region at 5 GHz. We suggest that the current canonical definition of HCHII regions is not accurate and should be revised to include a hierarchical structure of ionized gas that results in an extended morphology at 5 GHz. Correlating our search with known ultracompact (UC) HII region surveys, we find that roughly half of detected UCHII regions have positive spectral indices, instead of more commonly assumed flat and optically thin spectra. This implies a mix of optically thin and thick emission and has important implications for previous analyses which have so far assumed optically thin emission for these objects. Positive spectrum HII regions are statistically more luminous and possess higher Lyman continuum fluxes than HII regions with flat or negative indices. Positive spectrum HII regions are thus more likely to be associated with more luminous and massive stars. No differences are found in clump mass, linear diameter or luminosity-to-mass ratio between positive spectrum and non-positive spectrum HII regions.

Quantifying the Reflectance Anisotropy Effect on Albedo Retrieval from Remotely Sensed Observations Using Archetypal BRDFs

The reflectance anisotropy effect on albedo retrieval was evaluated using the Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution functions (BRDFs) product, and archetypal BRDFs. Shortwave-band archetypal BRDFs were established, and validated, based on the Anisotropy Flat indeX (AFX) and time series MODIS BRDF over tile h11v03. To generate surface albedo, archetypal BRDFs were used to fit simulated reflectance, based on the least squares method. Albedo was also retrieved based on the least root-mean-square-error (RMSE) method or normalized difference vegetation index (NDVI) based prior BRDF knowledge. The difference between those albedos and the MODIS albedo was used to quantify the reflectance anisotropy effect. The albedo over tile h11v03 for day 185 in 2009 was retrieved from single directional reflectance and the third archetypal BRDF. The results show that six archetypal BRDFs are sufficient to represent the reflectance anisotropy for albedo estimation. For the data used in this study, the relative uncertainty caused by reflectance anisotropy can reach up to 7.4%, 16.2%, and 20.2% for sufficient, insufficient multi-angular and single directional observations. The intermediate archetypal BRDFs may be used to improve the albedo retrieval accuracy from insufficient or single observations with a relative uncertainty range of 8–15%.

Evaluation Method for Effective Coastal Repair in Moon Bay, Yingkou, China

ABSTRACT Zhang, M.; Sun, Z.; Sun, J.; Suo, A., and Ashraf, M.A., 2018. Evaluation method for effective coastal repair in Moon Bay, Yingkou, China. In: Ashraf, M.A. and Chowdhury, A.J.K. (eds.), Coastal Ecosystem Responses to Human and Climatic Changes throughout Asia. To evaluate the effect of coastal beach engineering, coastal geomorphic changes before and after repairs were monitored. A comprehensive coast repair index (CCRI), beach repair index (BRI), and tidal flat repair index (TRI) were established to evaluate the effects of coastal reparation. All three indices were calculated and graphed based on GIS. This study's coast (Moon Bay, Yingkou, China) was divided into 12 units to apply evaluation methods for the effect of coastal repair engineering. Results show this evaluation method can effectively determine the overall results of coastal repair engineering in Moon Bay. The CCRI was above 0.70 in middle units 6, 7, 8, and 9, while a range of 0.60–0.699 was calculated for west units 1, 2, 3, and 5. Th...

O2iJoin: An Efficient Index-Based Algorithm for Overlap Interval Join

Time intervals are often associated with tuples to represent their valid time in temporal relations, where overlap join is crucial for various kinds of queries. Many existing overlap join algorithms use indices based on tree structures such as quad-tree, B+-tree and interval tree. These algorithms usually have high CPU cost since deep path traversals are unavoidable, which makes them not so competitive as data-partition or plane-sweep based algorithms. This paper proposes an efficient overlap join algorithm based on a new two-layer flat index named as Overlap Interval Inverted Index (i.e., O2i Index). It uses an array to record the end points of intervals and approximates the nesting structures of intervals via two functions in the first layer, and the second layer uses inverted lists to trace all intervals satisfying the approximated nesting structures. With the help of the new index, the join algorithm only visits the must-be-scanned lists and skips all others. Analyses and experiments on both real and synthetic datasets show that the proposed algorithm is as competitive as the state-of-the-art algorithms.

Highly Efficient Dielectric Optical Incoupler for Quantum Well Infrared Photodetectors

In this letter, we propose a highly efficient all-dielectric optical incoupler for a quantum well infrared photodetector (QWIP) operating in the very long wavelength infrared regime from 14 to $16~\mu \text{m}$ . The microstructure is comprised of a thin top-contact/QWs/bottom-contact semiconductor layer sandwiched by a germanium layer drilled with periodic holes and a flat low-refractive index substrate. By exploiting the waveguide mode, the dielectric optical incoupler can convert infrared radiation efficiently into the QWs layer with strong infrared absorption for QWs at the specific wavelength of 14.9 $\mu \text{m}$ , of which the absorption increases 7.5-fold compared with an isotropic active region without any designed framework. More importantly, a large electrical field component ( $E_{z}$ ) normal to the plane of QWs can be obtained with a large value of coupling efficiency ( $\eta$ ) of $\vert \text{E}_{z} \vert ^{2}$ reaching up to 1.4. A slight dispersion (over 40°) and weak polarization dependence of the guided mode supported by the dielectric incoupler might be beneficial to high-performance infrared photodetectors.

The influence of spatial resolution on the angular variation patterns of optical reflectance as retrieved from MODIS and POLDER measurements

Multiangle remote sensing plays a central role in the development of algorithms for the retrieval of various surface biophysical parameters that are influenced by the reflectance anisotropy. Surface reflectance anisotropy is characterized by the Bidirectional Reflectance Distribution Function (BRDF). Within the past decade, space-borne multiangle observations acquired by the MODerate resolution Imaging Spectroradiometer (MODIS) sensor (which has a gridded spatial resolution of 500 m) and by the POLarization and Directionality of Earth Reflectances (POLDER) sensor (which has a spatial resolution of 6 × 7 km) have been used for a wide variety of global applications. However, it is necessary to fully understand the variability inherent in the surface BRDF information as retrieved from MODIS and POLDER at these two spatial resolutions to optimize their use. In this study, we make use of extensive POLDER Bidirectional Reflectance Factors (BRFs) selected from the entire archive of the POLDER BRDF database and standard MODIS BRDF parameter products (MCD43A1, Collection V005) that were geolocated within the same spatial extents as the POLDER data. The variability in surface BRDF is characterized by investigation of three BRDF model parameters as retrieved from MODIS and POLDER and a comprehensive index indicating the variations in the primary dome-bowl BRDF patterns (the anisotropic flat index (AFX)). The principal information content contained in these BRDF data is characterized by the general BRDF shapes (the BRDF archetypes) that account for >90% of the total variance in these BRDF data. A hotspot-revised BRDF model is used directly on top of the retrieved model BRDF parameters to capture the hotspot effect associated with these BRDF parameters. The main findings of this study show that the variability in surface BRDF, as extracted from the MODIS and POLDER datasets, shares six reciprocal BRDF archetypes. However, the 500-m MODIS BRDF data can uniquely capture some additional extreme BRDF shapes mainly due to the data's finer pixel scales. These original findings are very important, because subsequent albedo retrievals can be significantly impacted by the use of BRDFs of different resolutions. This study provides evidence concerning the influence of spatial resolution on angular variation patterns of optical reflectance as retrieved from the MODIS and POLDER BRDF products.

Topographic Controls on Soil Nutrient Variations in a Silvopasture System

Core Ideas Topographic variation influenced soil nutrient distribution in a silvopasture system. High‐resolution digital maps of soil nutrients were generated. Terrain attributes identified topographic functional units as management zones. Level of soil nutrients in topographic functional units were different. Topography plays a crucial role in spatial distribution of nutrients in soils; however, studies to quantify topographic influence on soil nutrient distribution from a silvopasture system are mostly lacking. To address this question, a 4.3‐ha silvopasture site in northwest Arkansas was selected and a total of 51 topsoil (0–15 cm thickness) samples were collected and analyzed for primary (total N [TN], P, K), secondary (Ca, Mg, S), and micronutrients (Fe, Zn, Cu, Mn, B, Na). Topographic information was acquired from 12 terrain attributes derived from a 1‐m digital elevation model. The prediction model was based on random forest. Results showed TN, S, and P were best predicted, whereas Cu, Ca, and Mn had the lowest prediction performance. Levels of S, Ca, Zn, Fe, and TN increased with SAGA wetness index, valley depth, flow accumulation, and multi‐resolution valley bottom flatness index. Normalized height and slope height were positively related to Na but negatively to B and Cu distribution. Aspect had a positive influence on P and Mg concentrations. Based on terrain attributes, the study site could be divided into four topographic functional units (TFU), namely A, B, C, and D; TFU A had the highest nutrients present, whereas TFU B had the lowest P, K, Zn, Cu, Fe, and Ca but highest Na content. However, Mn, Mg, and B did not vary among TFUs. This study affirmed topographic influences on soil nutrient distribution, and the resulting continuous soil nutrient maps are useful for fine‐tuning production systems through optimum nutrient and pasture management.