Exploring Spectral Index Band and Vegetation Indices for Estimating Vegetation Area

Visual analysis and transformation of vegetation indices have been widely applied in studies of vegetation density using remote sensing data. However, visual analysis is time intensive compared to index transformation. On the other hand, the index transformation from medium resolution imagery is not fully representative for urban vegetation studies. Meanwhile, the spectral range of high-resolution imagery is usually limited to visible wavelengths for the image transformation. Worldview-2 imagery provides a new breakthrough with a high spatial resolution and supports various spectral resolutions. This study aims to explore the spectral value of the Worldview-2 image index for estimation of vegetation density. Normalized indices were made for 56 band combinations and Otsu thresholding was implemented for the threshold selection to separate vegetation and non-vegetation areas. This thresholding was done by minimizing classes’ variances between two groups of pixels which are distinguished by system or classification. The image binarization process was performed to differentiate between vegetation and non-vegetation. For the accuracy testing, a total of 250 samples was produced by a stratified random sampling method. Our results show that the combination of indices from red channel, red-edge, NIR-1, and NIR-2 provides the best accuracy for semantic accuracy. Vegetation area extracted from the index was then compared with the results of the visual analysis. Although the index results in area difference of 2.32 m2 compared to visual analysis, the combination of NIR-2 and red bands can give an accuracy of 96.29 %

Identifying Ultra-Cool Dwarfs at Low Galactic Latitudes: A Southern Candidate Catalogue

We present an Ultra-Cool Dwarf (UCD) catalogue compiled from low southern Galactic latitudes and mid-plane, from a cross-correlation of the 2MASS and SuperCOSMOS surveys. The catalogue contains 246 members identified from 5042 sq. deg. within 220 deg. <= l <= 360 deg. and 0 deg. < l <= 30 deg., for |b| <= 15 deg. Sixteen candidates are spectroscopically confirmed in the near-IR as UCDs with spectral types from M7.5V to L9. Our catalogue selection method is presented enabling UCDs from ~M8V to the L-T transition to be selected down to a 2MASS limiting magnitude of Ks ~= 14.5 mag. This method does not require candidates to have optical detections for catalogue inclusion. An optimal set of optical/near-IR and reduced proper-motion selection criteria have been defined that includes: an Rf and Ivn photometric surface gravity test, a dual Rf-band variability check, and an additional photometric classification scheme to selectively limit contaminants. We identify four candidates as possible companions to nearby Hipparcos stars -- observations are needed to identify these as potential benchmark UCD companions. We also identify twelve UCDs within a possible distance 20 pc, three are previously unknown of which two are estimated within 10 pc, complimenting the nearby volume-limited census of UCDs. An analysis of the catalogue spatial completeness provides estimates for distance completeness over three UCD MJ ranges, while Monte-Carlo simulations provide an estimate of catalogue areal completeness at the 75 per cent level. We estimate a UCD space density of Rho (total) = (6.41+-3.01)x10^3/pc^3 over the range of 10.5 <= MJ ~< 14.9, similar to values measured at higher Galactic latitudes (|b| ~> 10 deg.) in the field population and obtained from more robust spectroscopically confirmed UCD samples.Comment: MNRAS accepted April 2012. Contains 30 figures and 11 tables. Tables 2 and 6 to be published in full and on-line only. The on-line tables can also be obtained by contacting the author

SPIDERS: Selection of spectroscopic targets using AGN candidates detected in all-sky X-ray surveys

SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV survey running in parallel to the eBOSS cosmology project. SPIDERS will obtain optical spectroscopy for large numbers of X-ray-selected AGN and galaxy cluster members detected in wide area eROSITA, XMM-Newton and ROSAT surveys. We describe the methods used to choose spectroscopic targets for two sub-programmes of SPIDERS: X-ray selected AGN candidates detected in the ROSAT All Sky and the XMM-Newton Slew surveys. We have exploited a Bayesian cross-matching algorithm, guided by priors based on mid-IR colour-magnitude information from the WISE survey, to select the most probable optical counterpart to each X-ray detection. We empirically demonstrate the high fidelity of our counterpart selection method using a reference sample of bright well-localised X-ray sources collated from XMM-Newton, Chandra and Swift-XRT serendipitous catalogues, and also by examining blank-sky locations. We describe the down-selection steps which resulted in the final set of SPIDERS-AGN targets put forward for spectroscopy within the eBOSS/TDSS/SPIDERS survey, and present catalogues of these targets. We also present catalogues of ~12000 ROSAT and ~1500 XMM-Newton Slew survey sources which have existing optical spectroscopy from SDSS-DR12, including the results of our visual inspections. On completion of the SPIDERS program, we expect to have collected homogeneous spectroscopic redshift information over a footprint of ~7500 deg$^2$ for >85 percent of the ROSAT and XMM-Newton Slew survey sources having optical counterparts in the magnitude range 17<r<22.5, producing a large and highly complete sample of bright X-ray-selected AGN suitable for statistical studies of AGN evolution and clustering.Comment: MNRAS, accepte

A deep WISE search for very late type objects and the discovery of two halo/thick-disc T dwarfs : WISE 0013+0634 and WISE 0833+0052

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedA method is defined for identifying late-T and Y dwarfs in WISE down to low values of signal-to-noise. This requires a WISE detection only in the W2-band and uses the statistical properties of the WISE multiframe measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space, we use a control sample of isolated non-moving non-variable point sources from the Sloan Digital Sky Survey (SDSS), and identify a sample of 158 WISE W2-only candidates down to a signal-to-noise limit of eight. For signal-to-noise ranges >10 and 8-10, respectively, similar to 45 and similar to 90 per cent of our sample fall outside the selection criteria published by the WISE team, mainly due to the type of constraints placed on the number of individual W2 detections. We present follow-up of eight candidates and identify WISE 0013+0634 and WISE 0833+0052, T8 and T9 dwarfs with high proper motion (similar to 1.3 and similar to 1.8 arcsec yr(-1)). Both objects show a mid-infrared/near-infrared excess of similar to 1-1.5 mag and are K band suppressed. Distance estimates lead to space motion constraints that suggest halo (or at least thick disc) kinematics. We then assess the reduced proper motion diagram of WISE ultracool dwarfs, which suggests that late-T and Y dwarfs may have a higher thick-disc/halo population fraction than earlier objects.Peer reviewe