• 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

120

110

100

90

80

70

60

50

40

30

20 cos(i)

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

120

110

100

90

80

70

60

50

40

30

20

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.