Digital Image Processing: A Remote Sensing PerspectivePerspectiveFW5560Lecture 6Lecture 6Radiometric CorrectionRadiometric correctionRadiometric correctionImproving the accuracy of surface spectral reflectance or emittance. Would like to obtain measurements of absolute flihh’fM idreflectance or emittance at the earth’s surface. Must consider contributions and subtraction imposed by atmospheric components.pAlso consider gains and bias of the sensors themselves.Photon energy of 10-14 Wavelength in meters (m) Electromagnetic Spectrum and the Photon Energy of Visible Light4.0 gyvisible light in electron volts (eV) Photon wavelength in nanometers (nm) 10 Gamma and x-ray 10 -12 ultraviolet3.0 3.5 violet limit blue400 45010 -8 Sun Earth Ultraviolet 3.10 275ultravioletElectromagnetic Spectrum2.0 2.5 green limit yellow orange red450550 580 600 65010 -6 Visible 2.752.252.142.061.912.48green 500101.5 650Infrared 1.9110001.241.77 700red limitnear-infrared0.5 1.010 -2 Microwave and radio waves 30k0.041 far infrared0 10Radiant flux,Φ Concept of Radiant Flux Density Radiant Flux DensityThe concept of radiant flux density for an area on theIrradianceRadiant flux, Φ Radiant Flux Densitydensity for an area on the surface of the earth. Idi (E)iIrradiance E λ = Α Φ Irradiance (Eλ) is a measure of the amount of incoming energy in Watts m-2.Area, A Radiant flux, Φ Exitance (Mλ) is a measure of the amount of energy leaving Exitance in Watts m-2.M λ = Α Φ Area, ARadiance (LRadiance (Lλλ) is the radiant flux per unit solid angle leaving an ) is the radiant flux per unit solid angle leaving an tdd i i di ti it jtdtdd i i di ti it jtdextended source in a given direction per unit projected source area extended source in a given direction per unit projected source area in that direction and is measured in watts per meter squared per in that direction and is measured in watts per meter squared per steradiansteradian (W m(W m--2 2 srsr--1 1 ). We are only interested in the radiant flux in ). We are only interested in the radiant flux in certain wavelengths (Lcertain wavelengths (L) leaving the projected source area (A)) leaving the projected source area (A)certain wavelengths (Lcertain wavelengths (Lλλ) leaving the projected source area (A) ) leaving the projected source area (A) within a certain direction (within a certain direction (θθ) and solid angle () and solid angle (ΩΩ): ): ΦΦΦΦ Ω Ω LLλ λ = ______= ______ Α Α coscos θ θ Normal to Surface Radiant flux, Φ Concept of Radiance This is the most precise remoteThis is the most precise remotesensing radiometric measurement.sensing radiometric measurement.Side view fS θ of Source Area, A PjdS ASolid Angle, Ω Projected Source Area = L λ A Cos θ θ Ω A Cos θEnergy-matter Interactions in hA h hSdVarious Paths of Satellite Received Radiancethe Atmosphere, at the Study Area, and at the Remote Sensor DetectorTotal radiance at the sensorRemote sensor detectorLSSolar irradiance L LE90Þ0p TThe total radiance reaching Diffuse sky irradiance12Atmosphere θ0T θv T Edthe sensor is:irradiance L 13Atmosphere41,3,5θθ0 vIEdReflectance from study areaReflectance from neighboring area5()1study area, neighboring area,λ nrλ r()pdooovSLETETL++∆×=∆λθρπθλθλcos1Primary Focal Plane (PFP), where the silicon detectors for bands 1-4 and 8 are located. A portion of the scene energy is redirected from the PFP to theCold Focal PlanewherePFP to the Cold Focal Planewhere the detectors for bands 5, 7, and 6 are located. The spectral filters for Landsat 7 Handbookthe bands are located directly in front of the detectors.The Landsat 7 ETM+ instrument achieves its 185-kilometer cross-track ground swath by using a bi-directional scan mirror to traverse the instrument line-of-sight through a 15-degree cross-gggtrack field of view. On descending passes, the mirror alternately scans west-to-east (forward scan) and then east-to-west (reverse scan) The active Earthimaging portion of each scan lasts forscan). The active Earth-imaging portion of each scan lasts for, nominally, 60.743 milliseconds. During this time, the Landsat 7 spacecraft advances approximately 410 meters downtrack.An estimated 22 percent of any given scene is lost because of the SLC failure The maximum widthSLC failure. The maximum width of the data gaps along the edge of the image would be equivalent to fll li i tlone full scan line, or approximately 390 to 450 meters. The precise location of the missing scan lines will vary from scene to scene.Band-specific gap mask files are included with every Scan yLine Corrector (SLC)-off Level 1 Terrain (L1T) corrected standard productcorrected standard product. These ancillary data allow you to identify the location flli l ff db hGap Mask Legend Values:green=primary sceneof all pixels affected by the original data gaps in the primary SLC-off scene.green primary sceneblue = fill scene 1yellow = fill scene 2i k fill 3pyThe gap mask is provided as a series of individual band files in compressed (GZIP)pink = fill scene 3red = no data (not filled) files, in compressed (GZIP) GeoTIFF