1/17/14%1%Introduction to Remote Sensing Lecture objectives • Motivation for learning about remote sensing • Introducing the basic concepts • Historical development of remote sensing • Example applications1/17/14%2%What is remote sensing? ‘The measurement or acquisition of information of some property of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object or phenomenon under study’ ASPRS definition The ‘recording device’ is usually a sensor on a satellite, aircraft, or on the ground/sea. The ‘object’ or ‘phenomenon’ could be on the Earth’s surface or in the atmosphere, or out in space. Contrast with in-situ measurements. Why do we care? • Wide use across many scientific fields • Big employment area for graduates • Global change is topical (e.g., climate, environment) • Strengths: synoptic, global, all-weather, all-terrain, safe, cheap (after initial investment), non-destructive, change detection • Weaknesses: calibration/validation needed, initial high cost/risk, high data rates/volumes, indirect1/17/14%3%What is being detected? • Electromagnetic (EM) radiation • Day – reflected and emitted • Night – emitted • Contrast with other geophysical techniques (e.g., acoustic, seismic) Electromagnetic waves • Electric field (E) • Magnetic field (M) • Perpendicular and travel at velocity, c (3x108 ms-1) • Characterized by wavelength (λ), frequency and energy1/17/14%4%Electromagnetic spectrum Longer wavelength Lower frequency Lower energy Shorter wavelength Higher frequency Higher energy Infrared EM radiation • Wave and particle interpretation • The basic ‘particle’ of EM radiation is the photon • Fundamental processes: • Emission – the ‘birth’ of photons • all bodies above absolute zero emit EM radiation • Absorption – the ‘death’ of photons • Scattering – the ‘life’ of photons • directional changes – reflection, refraction1/17/14%5%Passive vs. active systems • Passive: measures naturally occurring radiation • Active: Radar (radio), Lidar (visible light) The instrument (sensor) Imaging vs. non-imaging1/17/14%6%Sensor components • Collector • Optics • Detector • Filters • Calibration source • Signal processor • Antenna • Power Remote sensing platforms • Satellites: polar-orbiting, equatorial, geostationary • Spacecraft: space shuttle, space station, rockets • Aircraft (‘suborbital’): manned and unmanned (UAVs) • Airborne: balloons, kites • Ground-based1/17/14%7%NASA Global Hawk Unmanned Aerial Vehicle (UAV) Atmosphere Nadir view Sun Solar occultation Limb view Satellite viewing geometry – passive systems Geostationary1/17/14%8%The four resolutions of remote sensing • Spatial • Temporal • Spectral • Radiometric • Trade-offs between these – systems usually optimize one at the expense of another The four resolutions of remote sensing (1) • Spatial resolution: high, medium, moderate, low • Smallest area that can be discerned in an image • Determined by altitude and Instantaneous Field of View (IFOV) of sensor1/17/14%9%The four resolutions of remote sensing (2) Temporal resolution Shortest revisit time of a sensor High (minutes-hours), Medium (days), Low (weeks) Geostationary: 1-15 minutes High spatial resolution sensor - 2 weeks http://www.youtube.com/watch?v=jgrllVs2DDw The four resolutions of remote sensing (3) Spectral resolution The ability of a sensor to define fine wavelength intervals Multi-spectral (3-15 channels) to hyperspectral (200+ channels) Reflectance1/17/14%10%The four resolutions of remote sensing (4) Radiometric resolution Sensitivity to small differences in emitted or reflected energy 16 bit = 65536 quantization levels Remote sensing process Statement of problem • What information do we want? • Spectral/spatial/temporal resolution needed? • Useful wavelength region? Data collection Data analysis Presentation of information Reflectance of vegetation in Visible – SWIR region1/17/14%11%Remote sensing problems are inverse problems An understanding of how electromagnetic radiation interacts with matter provides the ‘tracks’ exploited by remote sensing applications Atmospheric windows1/17/14%12%History of Remote Sensing • First aerial photo credited to Frenchman Felix Tournachon in Bievre Valley, 1858. • Boston from balloon (oldest preserved aerial photo), 1860, by James Wallace Black. Remote sensing milestones • 1800: Discovery of infrared (IR) light by Sir William Herschel • 1801: Discovery of ultraviolet (UV) light by Johann Wilhelm Ritter • 1839: Beginning of the practice of photography • 1847: Fizeau and Foucault show IR shares properties with visible light • 1850-1860: Photography from balloons • 1873: Theory of electromagnetic (EM) energy developed by James Clark Maxwell • 1909-1910: Photography from airplanes: Wright takes first aerial movie • 1914-1918: World War I: aerial reconnaissance • 1920-1930: Development and initial applications of aerial photography and photogrammetry (spatial measurements from photographs) • 1929: Robert Goddard launches first instrumented rocket • 1930-1940: Development of radars in Germany, the UK and USA • 1939-1945: World War II: applications of non-visible portions of the EM spectrum; acquisition and interpretation of aerial photos1/17/14%13%Remote sensing milestones • 1950-1960: Military research and development; Cold War espionage • 1956: Robert Colwell’s research on crop disease detection with IR photos • 1957: Launch of first Earth-orbiting satellite (Sputnik-1) • 1962: Cuban Missile Crisis (use of aerial photography) • 1960-1970: First use of the term ‘remote sensing’ – TIROS weather satellite (April 1960) – Apollo Program photos and observations from space • 1970-1980: Rapid advances in digital image processing; computer age – 1972 Launch of Landsat 1 (ERTS); first Earth Observation satellite for scientific use – 1973 Skylab observations from space – First UV satellite sensors (ozone monitoring) • 1980-1990: Landsat 4 sensor (new generation); French SPOT Earth Observation satellites; development of hyperspectral sensors •