2 Lecture Overview Introduction to electromagnetic waves What is remote sensing?Introduction to satellite imagery5 resolutions of satellite imageryImage display
3 Energy and Electromagnetic Waves Processes that produce or release energy emit electromagnetic wavesElectromagnetic waves can also come from objects that release energy previously absorbed from elsewhereFor Example:The sun is emitting heat, light, and many other types of electromagnetic waves that are produced through the process of fusionYou are also emitting electromagnetic waves right now as your body metabolizes calories and emits heat (infrared energy)So, if we could see infrared light, you would appear brighter than the wallCan you think of an example for emitting energy that was previously absorbed?
5 Electromagnetic Waves Wavelength ()f = frequency: The number of waves passing through a point within a unit time (usually expressed per second)EMR energy moves at the speed of light (c): c = f Energy () carried by a photon: = h f [h=Planck constant (6.62610-34 Joules*seconds)]The shorter the wavelength, the higher the frequency, and the more energy a photon carries.For example, ultraviolet rays are shorter than visible light so they have more energy and are more dangerous (sunburns)C stays constant (in a vacuum) so if the frequency (i.e., energy goes up) what must happen to the wavelength?
6 One micrometer (μm) = one millionth (10-6) of a meter ers)One micrometer (μm) = one millionth (10-6) of a meter
7 You may also see wavelength in nanometers: One nanometer (nm) = one billionth (10-9) of a meter
8 What makes objects a certain color? The color of an object is determined by how much energy it reflects from each wavelength in the visible light portion of the EM spectrum.Objects reflect some wavelengthsObjects absorb some wavelengthsObjects don’t interact with some wavelengths (i.e., the waves pass through the objects largely unaffected)ExamplesWhite objects reflect all wavelengths of lightBlack objects absorb all wavelengths of lightBlue objects reflect blue light and absorb red and green lightWhy is vegetation green?
9 Spectral SignaturesNote red edgeAs with color, different objects reflect different amounts of energy at other wavelengths
10 Remote SensingRemote sensors are devices that sense energy from a remote location (i.e., a device not in physical contact with what it is sensing)Remote sensing is the science of acquiring, processing and interpreting information/data collected by remote sensorsThe most common application of remote sensing is classificationDifferentiating land cover classes (e.g., water, pavement, vegetation)Differentiating subtleties within classes (e.g., tree species)
11 Remote SensingPassive - detect emitted/reflected energy from other sources (e.g., the sun)Satellite sensorsAir photosCamerasVideo recordersActive – emit energy and detect reflectionsSonarRadarLidar
12 Satellite ImageryDigital data is obtained by sensors on satellite platforms.
14 Spatial ResolutionThe area on ground represented by each pixel (i.e., raster cell size)There is a tradeoff between the image footprint (area captured by a single image) and spatial resolutionSome sensors have different spatial resolutions for different bandsExamplesAdvanced Very High Resolution Radiometer (AVHRR) ~ 1 kmLandsat Multispectral Scanner (MSS) – 79 mLandsat Thematic Mapper (TM) – 30 mIKONOS – 1 m panchromatic /4 m multispectral
15 Temporal ResolutionHow often a satellite can obtain imagery of a particular areaFor a fixed sensor (can only point straight down) this depends on:1) The number of days between overhead passes at the same location2) The swath width of the sensor (i.e. the footprint of the images produced)Temporal resolution is higher for sensors that can move/tilt (side-to-side), but views from angles introduce distortionExamplesLandsat - 16 daysAVHRR - dailyIKONOS - 1 to 3 days (sensor can tilt)
16 Spectral ResolutionThe specific wavelength intervals in the electromagnetic spectrum captured by each sensorDetermined by the number, spacing and width of sampled wavelength bandsHigher resolution results in more precision in representation of spectral signaturesHyperspectral imagery has very high spectral resolution (e.g., Aviris data has 220 bands)This makes a very detailed spectral signature, but the data are somewhat rare, expensive, and cumbersome to use
17 Radiometric Resolution The number of possible data values reported by the sensor (i.e., how sensitive the sensor is to changes in brightness of objects that it views)Range is expressed as a power (2n )8-bit resolution has 28 values, or 256 values Range is 0-25511-bit resolution has 211 values, or 2048 values Range isThe value in each pixel is called theDigital Number (DN)Brightness Value (BV)
18 View Angle ResolutionThe number of angles at which the ground objects are recorded by the sensorIt can be useful to view objects from multiple angles for stereoscopic analysesSome features reflect light differently in different directionsIsotropic vs. anisotropic reflectanceExampleThe Multi-angle Imaging SpectroRadiometer (MISR) sensor has 9 view angles
19 Resolution CaveatsSome remote sensing initiatives have multiple satellites/sensors, with later versions featuring improvements (i.e., better resolutions)E.g., Landsat MSS, TM, ETM+Some satellites have more than one sensor on them, so resolutions are associated with the sensors and not satellitesE.g., Earth Observing System (EOS) – 2 satellites that each contain MODIS, ASTER, etc. sensors
21 Landsat TM Spectral Resolution Wavelength (in micrometers)DescriptionBlue-green Green Red Near-IR Mid-IR Thermal Mid-IR
22 Spectral Signatures Complete Signature Landsat TM Signature Note the overall loss of detailThis is the case for hyperspectral imagery* TM bands 5, 6, & 7 aren’t on this graph
23 Spectral Regions – Landsat TM BAND 1 (Visible Blue)PANCHROMATICBLUEGREENREDNEAR IRSHORTWAVE IRMID-WAVE IRLONGWAVE IR0.40.50.60.71.13.05.014.0mmBlue Visible - Used for bathymetry - water penetration to about 50m in clear water. Necessary for a true color imageIlluminates Materials in ShadowsWater Penetration for BathymetrySoil / Vegetation DifferentiationDeciduous / Coniferous Differentiation
24 Band 1Band 1 is used with bands 2 and 3 to construct true color composites to assess a variety of features.
25 Spectral Regions – Landsat TM BAND 2 (Visible Green)mmWater Penetration for BathymetryClear and Turbid Water ContrastDiscrimination of Oil on WaterGreen Reflectance Peak ofHealthy VegetationBLUEGREENREDNEAR IRSHORTWAVE IRMID-LONGWAVE IR14.05.03.01.10.70.60.50.4PANCHROMATICGreen Visible - Peak chlorophyll reflectance band, used for vegetation analysis. Also bathymetry - water penetration to about 40m.
26 Band 2Band 2 is used with bands 1 and 3 to construct a true composite and bands 3, 4, and 7 to construct near and shortwave infrared composites to assess a variety of features.
27 Spectral Regions – Landsat TM BAND 3 (Visible Red)mmVegetation DifferentiationChlorophyll AbsorptionLimited Water Penetration forBathymetryBLUEGREENREDNEAR IRSHORTWAVE IRMID-LONGWAVE IR14.05.03.01.10.70.60.50.4PANCHROMATICRed Visible - Provides added value information to vegetation analysis.
28 Band 3Band 3 is used with bands 1 and 2 to construct true color composites and bands 4 and 2 to construct near infrared composites to assess a variety of features.
29 Spectral Regions – Landsat TM BAND 4 (Near Infrared)Vegetation AnalysisShoreline MappingLandcover DiscriminationmmBLUEGREENREDNEAR IRSHORTWAVE IRMID-LONGWAVE IR14.05.03.01.10.70.60.50.4PANCHROMATICNear Infrared - This is the primary band used to assess vegetation. Analysts can also assess camouflage detection and land water delineation using band 4.
30 Band 4Band 4 is used with bands 3, 5, 7 and 2 to construct near and shortwave infrared composites to assess a variety of features.
31 Spectral Regions – Landsat TM BAND 5 (Short-wave Infrared)1.55 – 1.75mmFire MappingDiscrimination of Oil on WaterMoisture Content of Soil andVegetationSnow / Cloud DifferentiationVegetation AnalysisBLUEGREENREDNEAR IRSHORTWAVE IRMID-LONGWAVE IR14.05.03.01.10.70.60.50.4PANCHROMATICShort-wave Infrared - Camouflage detection, change detection, vegetation analysis.
32 Band 5Band 5 is used extensively with bands 3, 4, 6, and 7 to construct shortwave and longwave infrared composites to assess a variety of features.
34 Band 6Landsat has the ability to sense EM radiation in the LWIR region using band 6. Unlike other TM bands, band 5 has a spatial resolution of 60 meters on Landsat 7(etm+) (120 meters on 4 & 5… TM)It can be useful for geologic mapping, vegetation classification, vegetation stress detection, soil moisture content, fire management, thermal pollution, and ocean current studies.Band 6 is used with bands 5 and 7 to construct infrared composites to assess a variety of features.There is also a landsat TM panchromatic band with 15 m resolution** The spatial resolution of Landsat TM band is ≠ that of the other bands
35 Spectral Regions – Landsat TM BAND 7 (Mid-wave Infrared)2.08 – 2.35 mmSolar Reflectance From Metal RoofsSmoke PenetrationDaytime Reflectance Mixed WithEmitted EM RadiationNighttime Emitted EM RadiationBLUEGREENREDNEAR IRSHORTWAVE IRMID-LONGWAVE IR14.05.03.01.10.70.60.50.4PANCHROMATICMid-wave Infrared.
36 Band 7Band 7 is used extensively with bands 2, 4, 5, and 6 to construct shortwave and longwave infrared composites to assess a variety of features.
37 Landsat Bands Band 1 Band 2 Band 3 BLUEGREENREDNEAR IRSHORTWAVE IRMID-LONGWAVE IRReview the differences in features between the bands.
38 Resolution Example AVHRR English Channel Spatial Resolution: 1 km (swath width = 2700 km)Temporal Resolution: dailySpectral Resolution: 5 bands (1 visible, 1 NIR, 1 mid-IR, 2 thermal)Radiometric Resolution: 8-bit (cells for each band)View Angle Resolution: 1 view angleEnglish Channel
39 Resolution Example SPOT 5 Palm Springs, CA Spatial Resolution: 20m, 10m, 2.5m (~ 60 km footprint)Temporal Resolution: 1 daySpectral Resolution: 5 bands (1 red, 1 green, 1 NIR, 1 mid-IR, 1 pan)Radiometric Resolution: 8-bit (cells for each band)View Angle Resolution: unlimited (movable sensor)20 = mid-IR10 = Red, Green, NIR2.5 = PanPalm Springs, CA
40 Resolution Example IKONOS Sydney Olympic Park Spatial Resolution: 4m, 1m (swath width ~ kmTemporal Resolution: 3-5 days (144 days for nadir)Spectral Resolution: 5 bands (1 red, 1 green, 1 blue, 1 NIR, 1 pan)Radiometric Resolution: 11-bitView Angle Resolution: unlimited (movable sensor)Sydney Olympic Park
41 Image Display Graphics display devices use three color guns Red, Green, BlueAll colors can be formed from various combinations of these 3 colors (which is why they’re used in CRT computer/TV screens)The brightness values (BV) to be displayed will often have an 8-bit range0 to 255In remote sensing, we assign one band to each color gun to give color to the image
42 Spectral Bands vs. Image Displayed For digital data the spectral bands of the imagery can be displayed in any wayFor example, red reflectance can be assigned to green light (on screen) or vice versaFeatures we see on screen are usually ≠ what we would see with our eyes in terms of colorThis is important because we can’t see in infrared etc., but we can still display this data by assigning it to a color that we can see
43 Image Display For a single band, the resultant color will be grayscale All three colors display the same value, so the colors are shades of grayBand 1Band 1Band 1Red color gunGreen color gunBlue color gun
45 Image DisplayFor a multi-band image, the resultant color will depend on which bands are assigned to which color gunsRed (3)Green (2)Blue (1)True Color Composite(321)Red color gunGreen color gunBlue color gunNear Infrared (4)Red (3)Green (2)False Color Composite(432)Red color gunGreen color gunBlue color gun
46 Color composite image Color Composite Image Band A Band B Band C Blue color gunGreen color gunRed color gun
47 Landsat TM Composites432743321The order of the numbers indicates the color gun attributed to the bands red, green, and blue color guns.The first number gets displayed using the red color gun and so on.For example, in a 432 composite band 4 (NIR) reflectance gets displayed as red, band 3 (red) reflectance gets displayed as green, and band 2 (green) reflectance gets displayed as blue.