ENR 3700 Final Study Guide
ENR 3700 Final Study Guide ENR 3700 (Environment and Natural Resources) Kaiguang Zhao
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This 12 page Study Guide was uploaded by Sophie_ on Friday April 29, 2016. The Study Guide belongs to ENR 3700 (Environment and Natural Resources) Kaiguang Zhao at Ohio State University taught by Dr. Kaiguang Zhao in Spring 2016. Since its upload, it has received 238 views. For similar materials see Introduction to Spatial Information for Environment and Natural Resources in Environmental Science at Ohio State University.
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Date Created: 04/29/16
ENR 3700 Study Guide – Know all associated definitions with these concepts. Lecture 1 – Syllabus What are geospatial technologies? Three major geospatial technologies 1. GIS - a computer based system to acquire, store, query, process, analyze, and display spatial data. Stands for Geographic Information System 2. GPS- Global positioning system 3. RS-Stands for Remote Sensing What is spatial/geospatial data? Its two components. Interpret the “geo” in “geospatial”. Geospatial data is any information/data with a direct or indirect reference to a specific location or geographic area Two components - Attribute and Location Location interpreted through a (x,y,z) coordinate system Geo - “earth” Concepts of spatial data layers to model multiple aspects of the real-world; Liebig's law of the minimum Law of minimum= Growth only occurs at the rate permitted by the most limiting factor. Lecture 2 – Defining locations What is a coordinate system? Its related nomenclature : coordinate ref system, spatial reference system, EPSG naming. A frame used to define the geographical entities using some coordinate values. EPSG naming - European Petroleum Survey Group → now common in all coordinate namings Contrasting models for the Earth’ shape (sphere, ellipsoid, geoid). Geoid-Represents earth’s surface as if it was caused by gravity alone, irregular surface with equal gravity, true shape of earth Datum- A mathematical model that standardizes the shape of the Earth. Ellipsoid: model to approximate the shape of geoid, many possible Know three common datums for USA (NAD27, NAD83, WGS84). Which is local and which are global? NAD27-local, NAD83- Global, WGS84-Global Know the relationships among geoid, datum and geographic coordinate system (lat/lon) Geoid becomes datum, datum then helps with geographic coordinate system -datum is a mathematical model that standardizes the shape of the earth (geoid), including ellipsoid, orientation, and point of origin -once datum is given, it can be divided into a graticular network of parallels and meridians which is used to define latitude and longitude coordinates with respect to the equator and prime meridian Differences between geographic and projected coordinate systems Geographic coordinate system (GCS)- Latitude and longitude, defined based on spherical coordinates Projected Coordinate System (PCS)- planar coordinate system, based on a projection that transforms spherical coordinates into flat, planar coordinates, linear units, makes it easier to compute spatial metrics and relationships, 3D to 2D Distortion by projection and the four characteristics being distorted 1 ENR 3700 Study Guide – Know all associated definitions with these concepts. It is impossible to directly spread a sphere onto a flat surface so distortions will always occur during projections Shape, area, distance, direction (S.A.D.D.) What are the two common PCS for the US? UTM: based on transverse mercator projection State plane coordinate system: set of coordinate systems for every state of USA, each state divided into cones Lecture 3 – Map, Scale, & Orientation Define cartography. the science, art, and technologies of making maps Map elements. Which elements are essential and what are optional? -Essential: title, distance or scale, direction/orientation, legend, sources of info, dates of data or production, coordinate systems/projection -Optional: neatlines, inset/locator maps Three representations of scale. Difference between large vs small scale Lexical (words), graphical (scale bar), representative (fraction) Small scale - not much detail, shows large features, small RF values (i.e. 1:1,000,000,000) Large scale - lots of detail, shows small features, large RF values (i.e. 1:100) Use of the scale formula to compute RF or lengths of interest RF=map length/actual length (unitless) Difference between azimuth and bearings. How do we represent each & convert? azimuth-comparable angles measured clockwise from due north (reading from 0 to 360 degrees, only use North as a reference) bearing-horizontal angles referenced to either north or south line, divided in quadrants N or S angle between 0 and 90 degrees) Difference between true and magnetic north. true north=direction from any point along a meridian towards the north pole magnetic north=directions given by the compass and other instruments that rely on the Earth's magnetic field Magnetic Declination and The agonic line magnetic declination- The difference between the true and magnetic north (magnetic north switches as time goes by) Agonic line- The line of zero declination i.e.where no correction is needed between magnetic north and true north (in the eastern part of the US, but moving west more every year) Lecture 4 – GIS and GIS Data Model What are GIS and its five components? 2 ENR 3700 Study Guide – Know all associated definitions with these concepts. a computer based system for capturing, storing, querying, processing, analyzing and displaying spatial data people, software, hardware, data, methods Know all about vector and raster data models, especially regarding the representation of pt, line and polygons • Vector- Geometric primitives (i.e. points, lines, polygons) are used to represent discrete features with a clear spatial location and boundary ; determined by the number of points during digitizing -point: represented by coordinate (x,y) -line connecting points • Raster- The study area divided into regular square cells (think shaded grids) ; determined by the size of the cells (smaller cells = more details), especially used in continuous fields such as elevation and precipitation -point: cell/pixel What is topology? Typical topology, and why is it important? -Topology- spatial relationships between geographic features. Identical, touching, contain, cover, overlap, disjoint, adjacency, proximity/distance, connectivity/direction Important because more basic way to categorize how cells/shapes are interacting What is metadata and why is it important? -Metadata- data/description that provides information about other data. It’s important because it helps you interpret other kinds of data Three common vector data format (Shapefile, Coverage, and Geodatabase)? Their differences -Shapefile- One shapefile can save only one type of feature class (e.g., point, lines, or polygons. Shapefile is a simple data format and stores only location and attribute data but not topology data (small) -Coverage- An integrated, homogeneous set of feature classes (pts., lines, polygons) stored together (topology explicitly stored) (medium) -Geodatabase- An object-oriented data management file system that is a collection of datasets, feature classes, object classes and relationship class. Ino separation between location and attribute data) (large) Lecture 5 – GIS Analysis Conversion between vector and raster Rasterizing - divide the areas into grids and fill those grids occupied by vectors → fill occupied pixels or fill as few pixels as possible Vectorizing - trace locations of filled pixels along boundaries → trace and link pixel centers or trace edges of pixels A general understanding of image segmentation Image segmentation-computer automatically aggregate pixels in raster images into vector-based objects 3 ENR 3700 Study Guide – Know all associated definitions with these concepts. Digitizing and potential problems Scale, topological errors (gap/undershoot), overshoot, spike, duplicate/mismatch, disconnection, measurement errors Raster analysis: DEM-based terrain and viewshed analysis, map algebra, merging DEM based terrain - Digital Elevation Model (terrain/topography), slope, aspect, hillshading Viewshed analysis - given a DEM, can determine where can be seen from location Map algebra - use math like expressions (i.e. operators and functions) to process raster layers Merging - combining multiple images/rasters into a single one Typical GIS and geoprocessing procedures: query, clip, intersection, dissolve,.. Query - selecting features based on attributes (from attribute data table) or location (based on spatial relationships) → can be used to produce maps of subsets of the data Buffer - rings drawn around features at a specified distance from said features Merge (Append) - combines features of an input theme with similar features from an adjoining theme to produce an output theme that contains the attributes and full extent of both themes Dissolve - aggregates features that have the same value based upon some attribute Clip/Mask - acts as a cookies cutter, attributes are not altered Intersection - cuts an input theme with the features from an overlay theme to produce an output theme with features that have attribute data from both themes What is georeferencing? What is ground control points? How to choose good GCPS -Georeferencing- converts scanned paper maps or ungeoreferenced images into spatially referenced data by adding spatial coordinate information -Ground control points- selected points used to relate a previously ungeoreferenced image to real world coordinates. - Well marked – you can see in both images or files. The more, the better. Evenly distributed – You will need a good distribution of points across an image) (See Lab4 handout). Lecture 6 – GPS What are GPS and its three segments? Global Positioning System - tells current location based on current lat and long coordinates or UTM coordinates plus elevation (x, y, z) ; is a space-based radio-navigation system consisting of a constellation of satellites, a network of ground stations, and receivers, which determines precise locations of any point on Earth Three segments- Satellites (24-32 of them), Control segment (ground stations), user segment (receivers, aka us and our handy dandy receiving tools like iPhones) What exactly can GPS tell us? How does it work? The triangulation/trilateration principle GPS tell us where exactly you are on the Earth. It works by finding the distance between the satellites and receivers, and the time it takes to travel between those points. Trilateration- Use satellites as reference positions via the concept of intersecting spheres Recap: satellites travel in predictable paths, GPS receivers programmed with general position of satellites, radio signals travel at constant speed and include time data that receivers compare to predicted time data, by determining time difference in predicted vs. actual signals x speed of light the distance to satellite is determined 4 ENR 3700 Study Guide – Know all associated definitions with these concepts. What are the sources of error when using a GPS? Satellite errors (clock, orbit, control), receiver clock errors, signal jamming, poor overhead visibility, atmospheric interference,multipath signals, selective availability, poor satellite geometry (DOP) What are DOP /PDOP? Know how to interpret DOPS. What is a good satellite configuration? PDOP- Positional dilution of precision → An indicator of the geometry of satellite constellation, accounts for both number of satellites available and their relative locations to each other How to get better GPS measurements? -Have a low DOP measurement, i.e. satellites need to be spaced out appropriately in the sky -adequate number of satellites -averaging over time -clear weather -minimize multipath error -use open sites -appropriate planning -use differential GPS What is DGPS, and how does it work? Differential GPS- DGPS uses one stationary and one moving receiver to help overcome the various errors in the signal → the stationary receiver must be located on a precisely known control point. Lecture 7 – Geospatial Applicati3ons Extrapolate what you learned from Lecture 7 and the 10 labs to articulate the potential utility of GIS using examples; for example, you should be able to use habitat suitability analysis as an example to describe the general flow of a typical GIS project (See Lab5’s handout and the supplied flow chart in Lab5b). --Find suitable habitat for rare plant species → gather spatial data (rivers, forests, soils) → GIS analysis modeling (query to select lowland forest, acidic soil, intersect and use raster calculator, clip and mask) → finalize data and make map g Metadata-descriptive information needed to make sense of your data Metadata includes publisher, date, file format, description, spatial references, its accuracy, index Tobler’s first law and Dangermond’s view on GIS applications • First law: Everything is related to everything else, but near things are more related than distant things - ..how profound.. • Dangemond’s quote: The application of GIS is limited only by the imagination of those who use it Lecture 8 – Intro to Remote Sensing What is RS? Typical RS systems (e.g., passive vs active, and different platforms). Remote sensing: the art and science of obtaining info about an object without being in direct contact with the object 5 ENR 3700 Study Guide – Know all associated definitions with these concepts. Passive sensors: record naturally occurring energy that is reflected or emitted from the terrain of interest Active sensors: transmit manmade electromagnetic energy and then record the amount of radiation that returns/reflects to the sensor system (radar, lidar, sonar) Different platforms include cameras, sensors, and satellites -imaging: acquire digital image of field of view with some info about how strength of signal varies in space continuously -non-imaging: acquire intensity/strength of signals over field of view of sensors, generally not visualized as spatially continuous images Four RS resolutions . • Spatial o The size of the field of view/ pixel. Eg. 10x10m • Temporal o How often the sensor acquires data eg. every 20 days • Spectral o The number and size of spectral regions the sensor records data. Eg blue, green, red, near-infrared, thermal infrared, microwave (Radar). Wavelength bands that sensor can capture. • Radiometric (measurement) o The sensitivity of detectors to small differences in electromagnetic energy What are electromagnetic radiation (See Fig1. in Lab 8’s handout) and its typical spectral region (i.e., ultraviolet, visible, near infrared, thermal infrared, microwave, and radio)? Ultraviolet - 10^-6 - 10^-m Visible - 10^-6.2- 10^-6.6 m Near infrared - 0.76- 90 um Thermal infrared - 700 nm – 1 mm Microwave - 10^-4 - 10^-1 Radio - 10^-1 - 10^3 -- What is NIR --Near infrared Know what a spectral signature is and the spectral signatures of vegetation, trees, soil, and water 6 ENR 3700 Study Guide – Know all associated definitions with these concepts. Spectral signature- Reflectance values or digital numbers of an object that are plotted over varying wavelengths Lecture 10 – Intro to Lidar What is LiDAR? Its difference from SONAR and RADAR. What are the four components of LiDAR? -Sonar is sound. Radar is radio waves. Lidar is light/laser. -light detection and ranging: computer-based 3D point sampling system that utilizes a laser ranging device coupled with a differential GPS and inertial measurement unit to determine X, Y, Z coordinates and reflection intensity of illuminated targets -The four components of LiDar is Laser Unit (ranging) + GPS +IMU + Computer. (Distance + position + direction + processing) Explain how lidar works. -It is a computer-based three-dimensional point sampling system that utilizes a laser ranging device coupled with Differential Global Positioning System (GPS) and an Inertial Measurement Unit (IMU) to determine X.Y,Z coordinates and reflection intensity of illuminated targets 1. Lidar sensing brings z dimension into remote sensing 2. A technology to resolve 3D structures of environments 3. Typical lidar are 3D POINT CLOUDS Lidar Principle: Laser Unit Laser ranging (time of flight) -range=speed* time /2 -Green or Near-infrared laser Lidar principle: GPS and IMU GPS: X,Y, and Z coordinates of lidar platform IMU: Inertial Measurement Unit -platform altitude: tilting, pitch and yaw 7 ENR 3700 Study Guide – Know all associated definitions with these concepts. -tells which direction the laser is shot at Lidar is a breakthrough in remote sensing of forests There are stationary and mobile platform lidar types What are the different types of LiDAR (especially discrete-return vs waveform)? Waveforms are the temporal trajectory of returned energy. Discrete return scanner is the most popular lidar system for ecosystem studies. Lidar pulses vs LiDAR returns. Explain meanings of first, intermediate, and last returns Lidar pulse= frequency of light emitted from lidar system Lidar returns= laser pulses emitted from a lidar system reflect from objects both on and above the ground surface. One emitted laser pulse can return as 1 or more returns Return for trees • First returns (canopy top, roof) • Intermediate return (inside canopies) • Last return (ground, root) Know how to derive DEM from LiDAR. Know the difference between DEM and DSM (digital surface model) Digital Surface Model: the top surface of features Digital elevation/terrain model: terrain (ground level), requires filtering out non-ground points - Give examples of typical lidar applications. Be able to explain why lidar often underestimates tree height LiDar often underestimates tree height because………………….lack of 8 ENR 3700 Study Guide – Know all associated definitions with these concepts. leaves? It has to do with the frequency the laser is emitted Applications: • Topography mapping (terrain and elevation) • geology . geomorphology • Urban planning, transportation, civil planning, power lines • Natural resources Lecture 11 Image Analysis The RGB color model and its use for image display -The RGB color model is an additive color model which red, green and blue light are added together in various ways to reproduce a broad array of colors. With the RGB model, multiband image can be displayed. What is image analysis or digital image processing? -computer-based processing of an image to aid in interpreting the image or deriving information from the image Image analysis provides: • image enhancement o Improve the appearance of imagery to assist in visual interpretation of analysis • image transformation o Manipulating multiple bands of imagery to create new bands according to some heuristics o QGIS implementation § Raster calculator • geometric correction o Remote sensing imagery typically exhibits geometric distortions that cause locational errors o One common source of error is from the varying ground resolution when the sensor scans across the track • atmospheric correction o To remove the effect and contamination of the atmosphere (eg. clouds) 9 ENR 3700 Study Guide – Know all associated definitions with these concepts. o Sunlight must pass through the earth’s atmosphere TWICE before it reaches the satellite o The atmosphere is made up of air molecules that can scatter and absorb sunlight o The scattering of light by air is wavelength dependent • image orthorectification o Orthorectification refers to the process that removes effects of relief displacement due to elevation variation, the sensors optical distortions, and the image’s geometric perspective. Image Enhancement : Contrast Stretching and Spatial Filtering; what is spatial frequency? • Contrast stretching: to increase the tonal distinction between various features in a scene. Contrast stretching expands the original input Digital Number (DN) values to make use of the total range of sensitivity output device • Spatial filtering: to enhance (or suppress) specific spatial patterns in an image. Spatial filters are designed to highlight or suppress specific features in an image based on their spatial frequency. • Low frequency: few changes in brightness value, relatively homogenous regions (crop fields/forest patches) • High frequency: brightness values change dramatically over short distances (boundaries between different fields (roads)Image Transformation: Band ratioing and Indices; • Image subtraction • Band ratio o To reduce the effects of environmental conditions (eg. difference in DN due to topographic slope and aspect, clouds, shadows, seasonal changes in sun illumination angle, etc) o To provide unique information useful in discriminating between features in scene, such as soil and vegetation • Normalized difference index o Normalized difference vegetation index (NDVI) is a simple yet powerful index indicating the amount of vegetation, leaf area, or the heaths of vegetation What are NDVI (also see lab8’s handout) and NDVI and their physical meanings? Which Landsat bands are used to compute the two spectral indices? (NDVI): the normalized difference vegetation index is a simple graphical indicator that can be used to analyze remote sensing measurements, typically but not necessarily from a space platform, and assess whether the target being observed contains live green vegetation or not. -BIR:band4 VIS: band3 NDWI: normalized difference water index, indicate availability of water -shortwave infrared: band5 -NIR: band4 Atmospheric corrections, geometric corrections, Image Orthorectification, and mosaicking AC: remove effect and contamination of the atmosphere GC: RS imagery typically exhibits geometric distortions that cause some locational errors. IO: refers to the process that removes effects of relief displacement. 10 ENR 3700 Study Guide – Know all associated definitions with these concepts. M: merging multiple images into a single image Lecture 12 Advanced topics What is geocoding and how does it work? How does telemetry work? Kernel-based Point density map (heatmap)? What is a network as well as its two components? Geocoding (linear referencing) is the process of spatially referencing point features based on the address of the feature and knowledge of an address range for a street network. Convert address to coordinates (eg. lat/lon, or UTM) • Principles of geocoding o Inputs § 1-Your address § 2-A reference road layer • Ways to accomplish geocoding o Google Earth o Online services o ArcGIS and ArcToolbox Radio telemetry for tracking animals/wildlife • Triangulation principle: observe a target from at least two locations to obtain bearings, that is, which direction it lies in • Radio telemetry is also in automatic towers o Simultaneous radiotracking from a number of fixed receiving stations o Cost-effective o Large data sets can be gathered in a short period of time Kernel Density map- point analysis • Kernel density map/ heat map o The density of points in the neighborhood of a pixel o Kernel size/Search radius is measured in meters Network Defined as a set of interconnected line entities, generally arcs, whose attributes share some common theme primarily related to flow (e.g. roads, transportation, pipelines, power lines) • Basic elements of a network o A network is a system of linear features (arc/link) connected at intersections (nodes) o Network arcs have direction § Undirected (two-way traffic- non-migration) § Directed (eg. one way traffic -migrational) • Problems for network analysis o Route selection/path finding (finding shortest or least-cost path) o Allocation o Accessibility analysis Spatial interpolation and the Kriging method. Spatial interpolation • Creating a surface based on values at isolated sample points • The sample points are locations where we collect data on some phenomenon and record the spatial coordinates 11 ENR 3700 Study Guide – Know all associated definitions with these concepts. • We use mathematical estimation to “guess what the values are in between those points. • Why do spatial interpolation? : field data are expensive to collect and can’t be collected everywhere • The premise for spatial interpolation is the first law of geography o “Everything is related to everything else, but near things are more related than distant things.” Kriging method, normally the best choice for an interpolation method • Kriging is an advanced geostatistical procedure that generates an estimated surface from a scattered set of points with z-values. Unlike other interpolation methods in the interpolation toolset, to use the Kriging tool effectively involves an interactive investigation of the spatial behavior of the phenomenon represented by the z-values What is photogrammetry? • Deriving 3D information from multiple photographs • The science of making measurements from photographs, especially for recording the exact position of surface points from multiple photographs 12
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