T5-Radiometric Correction_2010_v1_3slides

T5-Radiometric Correction_2010_v1_3slides - Geography 333...

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1 Geography 333 Remote Sensing I Topic 5: Radiometric Correction 2 Readings This Topic: Chapter 2 (sensors) This Topic: Chapter 6 (Radiation Principles) – p 194-222 Next Topic: Chapter 8 – Image Enhancements (Geometric Corrections) 3 Outline Understanding digital numbers (DNs) Radiometric errors and sources of variance Sensor noise Scene illumination Atmospheric attenuation Image pre-processing summary: what to do and when to do it
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2 4 Image Processing The goal of image processing is to produce a corrected image that is as close as possible , both radiometrically and geometrically to the true radiant energy and spatial characteristics of the study area at the time of data acquisition. Internal and external errors must be identified to correct the RS data Radiometry : the field that studies the measurement of electromagnetic radiation, including visible light. 5 Internal Errors Internal errors are produced by the remote sensing system itself. They are generally systematic (predictable) and may be identified and then corrected based on prelaunch or in-flight calibration measurements. Example: line-striping in the image may be caused by a single detector that has become uncalibrated. In many instances, radiometric correction can adjust for detector miscalibration MODIS - Solar Dif user Stability Monitor 6 External Errors Usually introduced by phenomena that vary in nature through space and time. The most important external variables that can cause remote sensor data to exhibit radiometric and geometric errors are Atmosphere Terrain elevation, slope and aspect Some external errors may be corrected by relating empirical observations made on the ground (i.e. radiometric and geometric ground control points) to sensor system measurements.
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3 7 R adiometric correction R adiometric correction of remotely sensed data normally involves the processing of digital images to improve the fidelity of the brightness value magnitudes (as opposed to geometric correction which involves improving the fidelity of relative spatial or absolute locational aspects of image brightness values). The main purpose for applying radiometric corrections is to reduce the influence of errors or inconsistencies in image brightness values that may limit one's ability to interpret or quantitatively process and analyze digital remotely sensed images. radiometric errors and inconsistencies are often referred to as "noise", which could be considered any undesirable spatial or temporal variations in image brightness not associated with variations in the imaged surface. Source: ht p:/ www.cas.sc.edu/geog/rslab/Rscc/mod5/5-1/5-1.html 8 Terms and Relationships Radiance/Radiant flux : total amount of radiation (usually expressed for a specific wavelength) per unit area (Watts/m2) Irradiance: total amount of incoming radiation per unit area Exitance : total amount of outgoing (reflected, emitted) radiation per unit area Reflectance: ( hemispherical reflectance ): ratio of exitance to irradiance. a.k.a
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T5-Radiometric Correction_2010_v1_3slides - Geography 333...

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