1What is Remote Sensing?Remote sensing is the science and art of obtaining information about a target through the analysis of data acquired by a device that is not in contact with the object, area, or phenomenon under investigation.Remote sensing is with us every dayEyes: we see thing around and sometimes far away from us. We even identify them as clouds, birds, and planes. Why can we see? Because of the sunlight reflected into our nerve cells in the retina. What’s special for our eyes is that we only see a narrow range ofsolar radiation within a large spectrum.Camera: Except we were born with a pair of most sophisticated remote sensing device, eyes, many of us have a remote sensing device, camera.Bats: emit microwaves and collect the reflected wave for navigation (the same way Radar works) In both examples above, the medium that carry the information is the Electromagnetic Radiation. Using various sensors, we can collect the electromagnetic radiation in any portion of the spectrum. Based on the source of energy, remote sensing can be broken into two categories:Passive Remote Sensing: The source of energy collected by sensors is either reflected solar radiation (e.g. human eye) or emitted by the targets (thermal camera).Active Remote Sensing: The source of energy collected by sensors is actively generated by a man-made device. For example, radar, lidar.Two Types of Remote SensingElectromagnetic Radiation from the Sun2Landsat 7 ETM+ Spectral BandsThe number of bands and the width of spectrum that each sensor covers arereferred to spectral resolutionU-2 AircraftA high altitude aircraft (U-2) was built to collect information over thesoviet territory. U-2 flies at 70,000 ft beyond the range of surface-to-air missiles and aircraft at that time. U-2 provided tremendousamount of information about the Soviet Union during to 1950’s and 1960’sU-2 remains to be a valuable means of collected information remotely,today. 1. President Bush used it during Gulf War in 19912. President Clinton used it in the war in Bosnia in 1998-1999.The Missile CrisisIn October 14, 1962, President Kennedy ordered high altitude U-2reconnaissance flights over western Cuba which identified the deployment of Soviet missiles which was only 90 miles from USmainland. President Kennedy then initiated a naval blockade of Cuba. This is now known as missile crisis in history. Figure 3-8 a of JensenThis photograph was shown to President Kennedy on Oct. 16, 1962 by US topphoto interpreter A. C. Lundahl.3Satellite Remote Sensing—Landsat 7Sun-synchronous orbit:Satellite always crossed theequator at precisely the samelocal time.Swath Width and Field of View185 kmField of View175kmsceneLandsatSatellite ground track705kmSpatial ResolutionPixel size=(30x30m)Temporal ResolutionThe shortest time needed to repeat a ground track4What is Digital Remote Sensing? Digital remote sensing literally means that the remotely sensedproducts are digits or numbers other than filmsInformation on the film: Information recorded on a film is essentially the amount of reflected sun light back into space fromthe ground surface. Different ground object reflect differentamount of energy leading to a different extent of exposure onthe film. The developed photos is the printed version of sun lightreflected from the target. The interpreter has to extract informationbased on the shape, size, tune, texture to identify targets.101030255301030301. Space is covered continuouslywith cells.2. Each cell has one numberindicating the amount of energy received from the cell3. The cell is called pixel (picture element)4. The size of the pixel is the spatial resolution sensorDigital Images1010302510301020151010302553010303030140153030122040Multispectral remotely sensed dataEach band will generate a layer of remotely sensed data, usuallywith the same cell (pixel) size. For Landsat satellite, we will have6 layers of data corresponding to the 6 bands.5Color Arithmeticred+green=yellowgreen+blue=cyanred+blue=magentaHow to Make Photos with Numbers?redbluegreenwhiteyellowblackcyanmagentaColor SpaceVegetation InformationNormalized Difference Vegetation IndexdNIRdNIRRRRRNDVIReRe+−=NDVI: [-1.0, 1.0]Often, the more the leaves of vegetation present, the bigger theContrast in reflectance in the red and near-infrared spectra.6Phenology from AVHRRFeb 27-Mar 12Jul 17-Jul 30Aug 14-Mar 27Jun 19-Jul 2Apr 24-May 7Nov 6-19Orbit: 705 km, Time to cross equator: 10:30 a.m. sun-synchronous, near-polar, circularSensor Systems: Across Track Scanning Radiometric resolution: 12 bitsTemporal resolution: 2 daysSpatial Resolution:250 m (bands 1-2)500 m (bands 3-7)1000 m (bands 8-36)Design Life: 6 yearsMODISMODISBands7Monitoring forest firePre-forest firePost-forest fireBurned area identified from spaceThis is the image from MODIS showing the wide sediment plumeof Yangtze River as it runs into theEast China Sea. Yangtze River,originating from the Himalayans, isthe longest river in China (6380km),the third longest in the world afterthe Amazon, and the Nile. Theworld largest dam, the Three GorgesDam, is now being built in Sichuanprovince. Due to deforestation in theupper reaches of the river, manyfear that the river will become thesecond Yellow River in China.Color, size, and tone are all helpful to identify the severity and extension of soil erosionLand-Ocean InteractionsSea Surface Temperature8This is MODIS image shows temperature of Gulf Stream. The current stretches from theGulf of Mexico up the East Coast of the United States and departs from North AmericaHeading across the Atlantic to British Isles. This warm current creates a moderate Northern European climate.Warm core ringsrotate clockwiseCold core ringsrotate counter clockwiseGulf StreamSpectral Properties of Water with AlgaeAlgae is the primary plant in the ocean that absorbs CO2, in the meantime initiatethe food chain in the ocean. It is very important to understand its spatial and temporal dynamics.Phytoplankton bloom inthe Black Sea. MODISband 1 (red), 4 (green)and 3 (blue)9Remote Sensing of CloudsCloud types from MODIS: pink: cold high level snow and ice clouds; neon green: low levelwater clouds. Different cloud types reflect and emit radiant energy differently.Remote Sensing of SnowIn the visible spectrumclouds and snow lookvery similar. Thus, it isdifficult to separate them with human eyes.But they are very different in the mid-infrared.10A massive iceberg, one of the largest ever observed, broke off the Ross Ice