Geog 380: Introduction to Remote Sensing PDF

Geog 380: Source: https://earth.nullschool.net Geospatial Communication Topic 09: Introduction to Remote Sensing © Geoffrey Hay (2023) Learning objectives By the end of this topic, a successful student will be able to: § Explain the wave and particle theory of EMR § Explain the different types...

Geog 380: Source: https://earth.nullschool.net Geospatial Communication Topic 09: Introduction to Remote Sensing © Geoffrey Hay (2023) Learning objectives By the end of this topic, a successful student will be able to: § Explain the wave and particle theory of EMR § Explain the different types of energy-matter interactions § Explain spectral reflectance curves § Explain how band selection and assignment in a RGB model produces different colour images GEOG 380 - Topic 09 2 Remote Sensing: Definition § “the science and art of obtaining information about an object, area, or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area, or phenomenon under investigation.” Fig 1.21; Lillesand et al. (2004) - Lillesand et al. (2004) GEOG 380 - Topic 09 3 What is Remote Sensing GEOG 380 - Topic 09 § What is remote sensing (4:20) 4 Electromagnetic Radiation (EMR) GEOG 380 - Topic 09 5 How is EMR generated? § § § § EMR from the sun is generated during thermonuclear fusion EMR is absorbed by an atom in the form of potential energy stored in the excited state of electrons EMR is given off when the electron “loses its excited state” More detail in GEOG 484 http://rushartsbiology.wikispaces.com/file/view/pp_quantum_theory_clip_image008_0002.jpg /171829367/pp_quantum_theory_clip_image008_0002.jpg GEOG 380 - Topic 09 6 Wavelength and Frequency § Wavelength Fig 1.2; Lillesand and Kiefer (1987) § Distance between crests (or troughs) of wave form § measured in micrometers (μm) or nanometers (nm) § Frequency § # of crests that pass a point per unit time (one second) § Usually measured in megahertz (MHz) or gigahertz (GHz) GEOG 380 - Topic 09 7 Wave Theory § EM waves are perpendicular to the direction of travel § Described by: speed of light = frequency (wavelength) or c = vl frequency = or speed of light wavelength wavelength = Where: speed of light frequency c = speed of light (3 x 108 m/s) v = frequency l = wavelength (l) GEOG 380 - Topic 09 8 Particle & Wave Theory § § § § EMR is transferred in discrete packets (photons or quanta) Moves as a wave, with frequency inverse to wavelength Relationship between frequency & quanta is: Where Q = hv § Q = energy of photon (Joules) § v = frequency of radiation § h = Planck constant (6.626 x 10-34 J·s) § Energy is directly proportional to frequency § High frequency (i.e., gamma rays, x-rays etc), high energy 9 http://www.examiner.com/images/blog/wysiwyg/image/powers(2).JPG The Power of Numbers GEOG 380 - Topic 09 10 http://www.earthlyissues.com/electro.htm Electromagnetic Spectrum GEOG 380 - Topic 09 11 Black Bodies § A theoretical object that completely absorbs all incident radiation, and emits the absorbed energy at the maximum possible rate as given by the Stefan Boltzmann law: Ml = sT4 Where: Ml is total emitted radiation T is temperature s is Stefan-Boltzmann constant (5.670373×10−8 W m−2 K−4) GEOG 380 - Topic 09 12 Blackbody Emission Spectra § Peak blackbody emittance given by: Wien’s displacement law: lmax = k/T Where: T = temperature k = constant § Short l hot § Long l cooler http://www.acs.org/content/acs/en/climatescience/energybalance/_jcr_content/articleConten t/columnbootstrap_0/column0/image_0.img.jpg/1374091014655.jpg GEOG 380 - Topic 09 13 Definitions § Radiant flux § Radiant energy per unit time (Joules/second) § Watts § Irradiance § Radiant flux that is incident on a surface § Watts/m2 § Radiant emittance or exitance § Watts/m2 § Radiance § Radiant flux leaving a surface within a given solid angle (steradian) topic for GEOG 484 GEOG 380 - Topic 09 14 RS Instruments and EMR http://www.answers.com/topic/electromagnetic-spectrum § Remote sensing instruments collect data across specific wavelengths, depending on the instrument’s purpose, platform, and technology GEOG 380 - Topic 09 15 https://www.semanticscholar.org/paper/The-Future-of-Earth-Observation-in-Hydrology.-Mccabe-Rodell RS Instruments and EMR § Remote sensing instruments collect data across specific wavelengths, depending on the instrument’s purpose, platform, and technology § From insitu (ground level) to 36,000Km away. GEOG 380 - Topic 09 16 EMR interactions with matter GEOG 380 - Topic 09 17 http://remote-sensing.net/concepts.html Material interactions GEOG 380 - Topic 09 18 Transmission & Refraction § Bending of light occurs when EMR is transmitted through matter § Index of refraction measures how much the speed of light/sound is reduced inside the medium § 1.0 vacuum § 1.002926 atmosphere § 1.33 water (1/1.33= 0.75% speed of light in a vacuum) § Wavelength dependent http://www.dkimages.com/discover/Home/Science/Physics-andChemistry/Sound-and-Light/Light-Waves/Light-Waves-023.html GEOG 380 - Topic 09 19 Atmospheric scattering § Similar to reflection, but unpredictable § Operates through absorption and re-radiation of radiation by atoms or molecules § When scattering occurs in a volume (as in the atmosphere), we specify three types: https://phys.org/news/2016-03-scientists-discuss-complexities-tiny-particles.html GEOG 380 - Topic 09 § Mie § Rayleigh § Non-selective 20 § Occurs when the particle are smaller (usually < 0.1 times) the wavelength § Caused mainly by gases in upper atmosphere GEOG 380 - Topic 09 http://www.963jackfm.com/lies-your-parents-told-you Rayleigh Scattering 21 § Occurs when particles are approximately same size as wavelength § Caused by dust, smoke, particulates in lower atmosphere GEOG 380 - Topic 09 http://en.wikipedia.org/wiki/File:Knysnasunset.jpg Mie Scattering 22 Non-Selective Scattering GEOG 380 - Topic 09 http://ed101.bu.edu/StudentDoc/current/ED101fa10/jenmks/cumulus.html § Occurs with particles many times greater in size than wavelength § Caused by water droplets, ice crystals in lower atmosphere § Non-selective with respect to visible wavelengths – i.e., all wavelengths scattered about equally 23 Absorption § Occurs when EMR is absorbed by material and converted into other forms of energy § Water vapour, CO2, oxygen, ozone, chlorophyll, minerals § Wavelength dependent: those not greatly affected called ‘atmospheric windows’ GEOG 380 - Topic 09 24 Absorption § In absorption, the frequency of the incoming light wave is at or near the energy levels of the electrons in the matter § Occurs when EMR is absorbed by materials and converted into other forms of energy (i.e., heat) § Water vapour, CO2, oxygen, ozone, chlorophyll, minerals – all absorb light/EMR § Wavelength dependent: those not greatly affected called ‘atmospheric windows’ GEOG 380 - Topic 09 25 Absorption bands and atmospheric windows Atmospheric Window GEOG 380 - Topic 09 http://book.bionumbers.org/how-much-energy-is-carried-by-photons-used-in-photosynthesis/ 26 Atmospheric Windows https://gisgeography.com/atmospheric-window/ A range of wavelengths over which there is relatively little absorption of radiation by atmospheric gases § Consider a slightly dirty window pane… most light goes through it. GEOG 380 - Topic 09 27 Reflectance § Re-radiation of photons in unison, in a layer approximately ½ wavelength deep § ‘Bouncing off’ a surface https://www.pinterest.ca/pin/554435404109091030/ GEOG 380 - Topic 09 § Measured as a ratio of the amount of radiation reflected to the amount received by the surface § Usually specified by wavelength 28 Specular Reflection § Incoming radiation is reflected in a single direction § Mirror-like reflectance from a ‘smooth’ surface http://micro.magnet.fsu.edu/primer/java/reflection/specular/index.html GEOG 380 - Topic 09 29 Diffuse Reflection § Incoming radiation is reflected across many angles § ‘Rough’ surface consisting of many specular planes http://micro.magnet.fsu.edu/primer/java/reflection/specular/index.html GEOG 380 - Topic 09 § Lambertian Surface: an ideal diffuse reflector. Such a surface has the same radiance when viewed from any angle. 30 Wavelength Dependence § A single surface can act ‘rough’ at one wavelength and ‘smooth’ at another § It is dependent on the relative size of the wavelength in question and the size of the “bumps” on the surface GEOG 380 - Topic 09 31 The basics of image acquisition GEOG 380 - Topic 09 32 “Active” Versus “Passive” § Active sensors carry their own source of EMR § Usually operate in low-energy or naturally-scarce regions of the spectrum § Passive sensors have no onboard source of EMR § Usually operate in the naturally-abundant visible and infrared portions of the spectrum GEOG 380 - Topic 09 33 Reflectance curves http://remote-sensing.net/concepts.html § Materials interact with EMR in different ways § An object’s pattern of reflectance across different wavelengths is called its spectral signature GEOG 380 - Topic 09 34 http://www.geog.ucsb.edu/~jeff/115a/lectures/cameras_films_filter/film_spectralcurves.jpg Fig 2-28; Sabins (1997) Leaf Structure and Reflectance GEOG 380 - Topic 09 35 Modified from Fig 1.5; Lillesand et al. (2004) TM Bands and Spectral Reflectance GEOG 380 - Topic 09 36 Fig 1.8; Lillesand et al. (2004) Conifers and Deciduous Trees GEOG 380 - Topic 09 37 Resolution in Remote Sensing GEOG 380 - Topic 09 38 Types of Resolution in Cartography § Spatial § How narrowly defined is a representation § Temporal § How often are observations taken § How long are the observations taken for § Attribute § How well defined is the attribute § e.g. precision of precipitation measurement § e.g. number of brightness levels in an image GEOG 380 - Topic 09 39 Resolution in Remote Sensing § Spatial § Spatial resolution: Size of the smallest recording unit OR smallest size of feature that can be mapped or measured § Roughly analogous to PIXEL SIZE in a raster database § Temporal § How often are observations taken § How long are the observations taken for – important factor § Radiometric § The precision the measurement – determines the bit depth § Spectral § Number of portions of the EM Spectrum that are differentiated GEOG 380 - Topic 09 40 Spatial resolution and imagery 0.5 m GEOG 380 - Topic 09 2.5 m 10 m http://geoeyemediaportal.s3.amazonaws.com/assets/images/gallery/ge1/hires/Rome_09_11_09.jpg 41 Spectral Resolution Modified from Fig 1.5; Lillesand et al. (2004) https://www.edmundoptics.com/knowledge-center/application-notes/imaging/hyperspectral-and-multispectral-imaging/ GEOG 380 - Topic 09 42 The Decimal System of Numbers § Consider the number 193 100’s 10’s 1’s 1 * 102 9 * 101 3 * 100 1 9 3 GEOG 380 - Topic 09 43 The Binary System of Numbers § Same concept, but with base 2 § Consider the base10 number 193 128’s 64’s 32’s 16’s 8’s 4’s 2’s 1’s 1 * 27 1 * 26 0 * 25 0 * 24 0 * 23 0 * 22 0 * 21 1 * 20 1 1 0 0 0 0 0 1 GEOG 380 - Topic 09 44 8-bit (1 byte) versus 16-bit (2 bytes) 0 1 2 3 254 255 GEOG 380 - Topic 09 = 00000000 = 00000001 = 00000010 = 00000011 … = 11111110 = 11111111 0 1 2 3 = 0000000000000000 = 0000000000000001 = 0000000000000010 = 0000000000000011 … 65534= 1111111111111110 65535= 1111111111111111 45 Common Raster Bit Depth § 8-bit integer = 1 Byte § Stores pixel vales ranging from 0-255 § Common for satellite imagery § Unsigned 16-bit integer § Stores values ranging from 0-65535 § Common for optical and radar imagery § Signed 16-bit integer – one bit is used for sign § Stores values ranging from -32767 – 32767 § Common for Digital Elevation Models § http://www.nasaimages.org/luna/servlet/view/all/w hat/Landsat+7?os=100&pgs=50&sort=Title%252CDa te GEOG 380 - Topic 09 32 and 64 bit real – has fraction component § Often referred to as single and double precision § Digital elevation models 46 “Space” in image analysis Observation Space (Image) Frequency Data Space (Histogram) Frequency Band 3 DN Data Space (Scattergram) Band 4 DN GEOG 380 - Topic 09 Band 4 DN 47 How we display imagery GEOG 380 - Topic 09 48 RGB Colour Model http://msdn.microsoft.com/enus/library/windows/desktop/aa511283.aspx http://printmail.oregonstate.edu/vocab-p-t § § Also called additive colour theory Full spectrum of colours created by combinations of additive primaries GEOG 380 - Topic 09 49 Multiband images - composites Modified from Fig 1.5; Lillesand et al. (2004) GEOG 380 - Topic 09 http://www.nasaimages.org/luna/servlet/view/all/what/Landsat+7?os=100&pgs=50&sort=Title%252CDate 50 RGB Images – White Pixel Image Channel 8 bit Channel 8 bit Channel 8 bit Channel GEOG 380 - Topic 09 255 255 255 Red Gun Image On Monitor Green Gun Blue Gun 51 RGB Images – Red Pixel Image Channel 8 bit Channel 8 bit Channel 8 bit Channel GEOG 380 - Topic 09 255 0 0 Red Gun Image On Monitor Green Gun Blue Gun 52 RGB Images – Cyan Pixel Image Channel 8 bit Channel 8 bit Channel 8 bit Channel GEOG 380 - Topic 09 0 255 255 Red Gun Image On Monitor Green Gun Blue Gun 53 RGB Images – Grey Pixel Image Channel 8 bit Channel Red Gun 127 8 bit Channel Image On Monitor Green Gun 127 8 bit Channel Blue Gun 127 GEOG 380 - Topic 09 54 RGB Colour Display 8-bit channel 8-bit channel 22 200 236 74 75 153 239 179 8-bit channel GEOG 380 - Topic 09 182 51 119 96 Red Gun Green Gun Blue Gun 55 24-Bit ‘True Colour’ Display http://vesta.astro.amu.edu.pl/Library/WWW/Tutorial1/graphics/display_primer.html GEOG 380 - Topic 09 56 Multiband images - composites Modified from Fig 1.5; Lillesand et al. (2004) GEOG 380 - Topic 09 http://www.nasaimages.org/luna/servlet/view/all/what/Landsat+7?os=100&pgs=50&sort=Title%252CDate 57 http://www.nasaimages.org/luna/servlet/view/all/what/Landsat+7 San Francisco Bay (TM 321èRGB) GEOG 380 - Topic 09 58 http://www.nasaimages.org/luna/servlet/view/all/what/Landsat+7 San Francisco Bay (TM 432èRGB) GEOG 380 - Topic 09 59 http://www.nasaimages.org/luna/servlet/view/all/what/Landsat+7 San Francisco Bay (TM 542èRGB) GEOG 380 - Topic 09 60 Summary § EMR interactions with matter are complicated and are the basis for remote sensing § Individual records of radiation (as grey scale scene images) can be combined in an RGB model to present the scene as coloured § These usually are not what humans perceive as colour so we must “relearn” what colour is in this context GEOG 380 - Topic 09 61