topographic effects on remotely sensed imagery
DESCRIPTION
Topographic Effects on Remotely Sensed Imagery. Changes in topography result in irregularly illuminated areas and in variations in light reflection geometry. Remotely sensed data should be corrected for topographic effects, accounting for actual incidence angles. Surface Normal. - PowerPoint PPT PresentationTRANSCRIPT
• Changes in topography result in irregularly illuminated areas and in variations in light reflection geometry.
• Remotely sensed data should be corrected for topographic effects, accounting for actual incidence angles.
Topographic Effects on Remotely Sensed Imagery
Z = sun zenith angleI = angle of incidence
Surface Normal
Statistical-Empirical Correction for Topographic Effects
Illumination: cos(i) = cos(e) cos (z) + sin(e) sin (z) cos (Øs - Øn)
i = angle of incidencee = surface slopez = solar zenith angleØs = solar azimuth angleØn = surface aspect
Observed radiance: LOBS = b + m cos(i)
Corrected radiance: LCOR = LOBS - m cos(i) - b + LOBS, avrg
LOBS = observed radiance (actual terrain)
LCOR = corrected radiance (normalized, horizontal surface)
m, b = regression coefficients
} at time of satellite overpass
10715 ground referencepoints (natural forest)
b = 74.9m = 54.1(band 4)
Observed Radiance: LOBS = b + m cos(i)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
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Corrected Radiance: LCOR = LOBS - b - m cos(i) + LOBS,avrg
10715 ground referencepoints (natural forest)
b = 74.9m = 54.1(band 4)
cos(i)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
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Digital Elevation Model
1200-12501250-13001300-13501350-14001400-14501450-15001500-15501550-16001600-16501650-17001700-17501750-18001800-18501850-19001900-19501950-20002000-20502050-21002100-21502150-22002200-22502250-23002300-2350
(m.a.s.l.)
DEM-based aspect (degrees.) DEM-based slope (degrees.)
Color composite original bands 742 Color composite corrected bands 742
USC Original Composite 742 USC Corrected Composite 742
Mitch Langford’sclassification
Unknown clusters
BNBPPNBPBDPCPNMSCCCTFQCNCIYUPRQPNCMRMCRAPNE
Cluster 1Cluster 2Cluster 3Cluster 4Cluster 5Cluster 6Cluster 7
Airphotography-based land use USC corrected composite 453
Cluster 1Cluster 2Cluster 3Cluster 4Cluster 5Cluster 6Cluster 7
Mitch Langford’s classification USC corrected composite 453
Conclusions
1 Satellite imagery of mountainous regions should be corrected for topographic effects before using any further.
2 The statistical-empirical correction method using DEM-derived information proved to be effective and easy.
3 The spatial resolution of imagery (30 m) may be insufficient to identify many small plots with different land cover.
4 Image correction and classification can be further improved by using better ground reference information.