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1、Remote Sensing遥 感Remote SensingLast Lecture Absorption features Vegetation Soils Rocks and minerals Water, ice and snow ConclusionsLast Lecture EMR which has interacted with matter will be deficient in some wavelengths, due to absorption processes occurring at atomic or molecular scales These absorp
2、tion features create distinctive “spectral signatures” for different Earth surface types These can be exploited by “multispectral” remote sensing methods for mapping and monitoring purposesRemote SensingRemote Sensing地表任一点反射的电磁波被分解为若干个波段，每个波段有一个反射率Remote Sensing反射率的大小用灰度表示，并被转换成数字信号，通常是28（0-255）5040
3、30201000.40.60.70.81.3REFLECTANCE(%)Wavelength (micrometers)Visible0.5Near IRGrassGREENBLUEGREENREDBLUEGREENREDNEAR IRNear IRBand PlacementBand DisplayBand 1Band 2Band 3Band 4Band 5Band 7BLUEGREENREDNEAR IRSHORTWAVE IRMID-WAVE IRNEAR IRColor Theory All colors created from additive primary colors: Re
4、d Green Blue Complementary colors: Magenta YellowYellow CyanRedGreenBlueMCYWBlackMultispectral DisplayBLUEGREENREDNEAR IRSHORTWAVE IRMID-WAVE IRLONGWAVE IR1Landsat TM Band234576Band Combination =742 (LANDSAT)Color Guns =Band Composite Output =Band 3Visible RedBand 2Visible GreenBand 1Visible BlueInd
5、ividual Landsat BandsApplied to Color GunsResulting ImageBand 4Near InfraredBand 3Visible RedBand 2Visible GreenIndividual Landsat BandsApplied to Color GunsResulting ImageAVRIS Hyperspectral CubeAirborne Visible/Infrared Airborne Visible/Infrared Imaging Spectrometer Imaging Spectrometer 224 spectr
6、al channels 224 spectral channels 400 2500 nm spectral 400 2500 nm spectral resolution, resolution, 20 meter ground 20 meter ground resolution.resolution.Brine Shrimp pondBrine Shrimp pondSensingSensor arrayLens225214199198202176 Each “cell” recorded as a “digital number” (DN) or “brightness value”
7、Measures amount of EM radiation The brighter the signal, the higher the value.PixelsEach cell is called a “picture element”, or pixelEach pixel represents a single brightness value for a specific geographical area225 204 188 146214 198 169 152202 200 178 162i columnsj rowsi x j = 4 x 4 = 16 pixels11
8、4 109 101 97Sensor Properties Spatial resolution Spectral resolution/# bands Radiometric resolution Temporal resolutionSource: NASASpatial Resolution Measure of the smallest angular or linear separation between 2 objects that can be resolved by the sensor In practice, sensor systems nominal spatial
9、resolution is the dimension in meters (or feet) on the ground projected instantaneous field of view (IFOV) Generally, smaller spatial resolution greater the resolving power of the sensor systemSpatial ResolutionIKONOS4mLandsat30mDOQ0.5m Space Imaging(cont.) Spatial ResolutionUseful rule: To detect a
10、 feature, the spatial resolution of the sensor system should be less than the size of the feature measured in its smallest dimension.Spectral ResolutionNumber and size of the bands which can be recorded by the sensor nominal spectral resolution Coarse sensitive to large portion of ems contained in a
11、 small number of wide bands Fine sensitive to same portion of ems but have many small bandsGoal finer spectral sampling to distinguish between scene objects and featuresMore detailed information about how individual features reflect or emit em energy increase probability of finding unique characteri
12、stics that enable a feature to be distinguished from other features.Spectral Resolution the SPECTRAL resolution defines the range of light stored in the image A black and white photograph stores a visible light; it has one channel that stores the light for 0.4 to 0.7 micrometers A natural color imag
13、e stores reflected red, blue and green light in different channels; e.g. 0.45 - 0.52 mm for blue, 0.52 - 0.60 mm for green and 0.63 - 0.69 mm for red A LANDSAT image contains 7 channnels as described above that store reflected light other than visible light. A HYPER-SPECTRAL image contains hundreds
14、of channels. E.g. A hyperspectral image that collects visible light may divide the visible light range into 300 channels, each channel containing a narrow range of wavelengths. Spectral Resolution/# Bands100s of BandsHyper-spectralNIRSWIRLW IRSWIRBand 2.53-.62Band 3.63-.69 Band 1.45-.52VisibleBand 4
15、.79-.90Band 51.55-1.75Band 72.08-2.35Band 610.4-12.4Near IRSWIRLWIR1000s of BandsUltra-spectralMulti-spectralSpectral Resolution/# BandsRadiometric Resolution the RADIOMETRIC resolution defines the range of values that an individual pixel can have Refers to the sensitivity of the sensor to incoming
16、radiance. Typical digital images have a range of values from 0 255 (a total of 256 possible values). An image that just has black or white pixels would only store 0 (black) or 1 (white). RADAR images have range from 0 to 4.3 x 109. Radiometric ResolutionTemporal Resolution How often the remote sensing system records imagery of a particular area.Examples Landsat 18 days SPOT 26 daysTemporal Resolution2752 Km at the Equator185 KmOrbit 1, Day 1Orbit 2, Day 1Orbit 1, Day 8Orbit 2, Day 8LandsatTrade-
