GEOG/GEOL 4093/5093 11. REMOTE SENSING1.1.1. Definitions• Collection of information about an object without coming intophysical contact• Measurements can be made fromgroundaircraftsatellite• Remote sensing is a technique to gather information• The information is carried by electromagnetic radiation• Remote sensing is the quantitative analysis of digitalinformation• Image interpretation from hard copies is a subject of the past• Additional skills are needed in digital image analysis(computer programming, image display tools, statistics, ..)• With satellite remote sensing global change issues can beaddressed by monitoring regional and global changes• Scientist in various fields - biology, climatology, geology,atmospheric science, chemistry, oceanography, and more -are needed for this interdisciplinary workGEOG/GEOL 4093/5093 21.2.1. Meteorology profiling of atmospheric temp. and water vapor measuring wind velocity1.2.2. Oceanography measurements of sea surface temperature mapping ocean currents1.2.3. Glaciology mapping motion of sea ice and ice sheets determining the navigability of the sea1.2.4. Geology identification of rock types location of geological faults and anomalies1.2.5. Agriculturemonitoring the extend and type of vegetationmapping soil types1.2.6. Hydrology assessing water resources forecasting melt water run-off from snow1.2.7. Disaster controlwarning of sand and dust storms, floodingmonitoring of pollution1.2. APPLICATION OF REMOTE SENSINGGEOG/GEOL 4093/5093 31.3. CLASSIFICATION OF SYSTEMSGEOG/GEOL 4093/5093 41.4.1. Classification of EM waves1 µm = 10-6 m1 nm = 10-9 m1Å = 10 -10 m1.4. THE ELECTROMAGNETIC SPECTRUMGEOG/GEOL 4093/5093 51.4.2. EMR used in remote sensingDiagram shows those parts of the EM spectrum which isimportant in remote sensing.The letters (K,X,S) are used to denote parts of the microwavespectrum (radar engineers)The lower graphs shows the atmospheric transmission of theEMR versus wavelength (log-scale)GEOG/GEOL 4093/5093 61.5.1. Electromagnetic Radiation (EMR)• Form of energy transport in free space• A harmonic wave can be described according to the Maxwellequations:ω = angular frequency (2πν) (ν =c/λ) k = wave number (2π/λ)1.5.2. Generation of EMR• EMR is generated by transformation of energy from otherforms, such as:1. Kinetic heat (friction)2. Chemical visible (molecular excitation)3. Electrical radio frequency (dipole antenna)4. Magnetic microwave (electron tube)1.5. PROPERTIES OF ELECTROMAGNETIC RADIATIONEx= Eo cos(ω t-kz)GEOG/GEOL 4093/5093 7EM WAVE PROPERTIES• Electric and magnetic fields are orthogonal to each other• Waves travel through space at the velocity of light• Speed of light: c = 300,000 kms-1Distance t for light Polar orbiting satellite 1,000 km 0.003 s Geostationary satellite 34,000 km 0.11 s Moon 384,000 km 1.28 s Sun 149.6 Mio km 8.5 min Diameter of our galaxy 100,000 ly Andromeda galaxy 2.2 Mio ly1.5.3. Frequencies and wavelengthsThe product of wavelength and frequency is a constant:λ = distance of separation between two wave peaksν = number of wave peaks passing in a given time c = speed of lightν λ = cGEOG/GEOL 4093/5093 8EM WAVE PROPERTIES1.5.4. Polarization• The orientation of the electric field is termed polarization andis important in discussing the operation of remote sensingsystems.vertical polarization (V): electric vector is perpendicular to the plane of incidencehorizontal polarization (H): electric vector is parallel to the plane of incidence• Radiation from the sun is unpolarized (at random)• Man made sources (laser, radar) have polarized radiationExample: polarization filterGEOG/GEOL 4093/5093 9EM PARTICLE PROPERTIES• EM energy is transferred in discrete units (photons)• Radiant energy (Q of I photon) is proportional to the frequency(ν) h = Planck's constant = 6.626 10-34 Js1 µm = 10-6 m1 nm = 10-9 m1.5.5. Spectral Radiance (Planck's law)ALL BODIES WHOSE TEMPERATURE ARE ABOVEABSOLUTE ZERO (0 K = -273.2 C) EMIT RADIATION(German Physicist – Nobel Price 1918)• Heat energy transformed into radiant energyBasic law for radiationmeasurements in allspectrah = Planck's constant k = Bolzmann constant T = Degree Kelvin (273.15 + °C) [K] e = 2.71• For isotropic radiation:Q = h ν [J])11)(2()(/52−=kTchehcLλλλ∫=Ω=πλπφλλ2)(cos)()( LdLMGEOG/GEOL 4093/5093 101.5.6. Stefan-Bolzmann law (TIR)• The total emitted energy over the whole spectrum isproportional the physical temperatureThe total outgoing radiation for all wavelengths is (Unit: W m-2)σ = Stefan-Bolzmann constant = 5.669 10-8 W m-2 K-41.5.7. Blackbody• Object that absorbs and emits 100% of radiation• Does not exist in nature• Emissivity would equal one1.5.8. Graybody• Object that reflects part of the incident radiation• Emissivity is smaller than one4403244152)( TThckdLL δπλλ ===∫∞L = ε σT4GEOG/GEOL 4093/5093 111.5.9. EmissivityEmissivity describes the actual absorption and emissionproperties of real objects, or gray bodies.Emissivity is wavelengths dependentEmissivity = emittance from gray body / by emittance fromblackbodyEmissivity establishes the radiant temperature Trad of an object two objects have the same kinematic temperature (Tkin),but Trad will be unequal Trad = ε1/4 Tkin⇒ ε = (Trad/Tkin)4GEOG/GEOL 4093/5093 12BLACKBODY AND GRAYBODYSpectral emissivity and spectral emittance as a function ofwavelengthsGEOG/GEOL 4093/5093 131.5.10. Wien's displacement law a = 2898 µm KSun's peak wavelengths: 2.88 103/ 6000° = 0.48 µmEarth's peak wavelengths: 2.88 103/ 300° = 9.6 µmSpectral radiant emittance of a blackbody at varioustemperatures. Note the change of scales between the twographs.λmax T = constant = aGEOG/GEOL 4093/5093 141.6. DEFINITION OF RADIATION QUANTITIESGEOG/GEOL 4093/5093 15Spectral Region Wavelengths Percent ofµm total EnergyGamma and X rays <0.01Far UV 0.01-0.2 0.02Middle UV 0.2-0.3 1.95Near UV 0.3-0.4 5.32Visible 0.4-0.7 43.5Near IR 0.7-1.5 36.8Middle IR 1.5-5.6 12.0Far IR 5.6-1000 0.41Microwave >1000Radio Waves >1000,000For terrestrial remote sensing the most important source is thesun• EM from ultraviolet - visible - infrared• (max) = 0.47 µmThe surface temperature of the earth is 300° K• (max) shifted to longer wavelengths (9.7 µm)In remote sensing• 2.5