Evaluation of Different Topographic Corrections for Landsat TM Data by Prediction of Foliage Projective Cover (FPC) in Topographically Complex Landscapes

Sisira Ediriweera,Tim Danaher,Trevor Moffiet,Doland Nichols,Sumith Pathirana

doi:10.3390/rs5126767

Abstract

The reflected radiance in topographically complex areas is severely affected by variations in topography; thus, topographic correction is considered a necessary pre-processing step when retrieving biophysical variables from these images. We assessed the performance of five topographic corrections: (i) C correction (C), (ii) Minnaert, (iii) Sun Canopy Sensor (SCS), (iv) SCS + C and (v) the Processing Scheme for Standardised Surface Reflectance (PSSSR) on the Landsat-5 Thematic Mapper (TM) reflectance in the context of prediction of Foliage Projective Cover (FPC) in hilly landscapes in north-eastern Australia. The performance of topographic corrections on the TM reflectance was assessed by (i) visual comparison and (ii) statistically comparing TM predicted FPC with ground measured FPC and LiDAR (Light Detection and Ranging)-derived FPC estimates. In the majority of cases, the PSSSR method performed best in terms of eliminating topographic effects, providing the best relationship and lowest residual error when comparing ground measured FPC and LiDAR FPC with TM predicted FPC. The Minnaert, C and SCS + C showed the poorest performance. Finally, the use of TM surface reflectance, which includes atmospheric correction and broad Bidirectional Reflectance Distribution Function (BRDF) effects, seemed to account for most topographic variation when predicting biophysical variables, such as FPC.

Highlights

Operational mapping, monitoring of vegetation cover and vegetation cover changes are important applications of remotely sensed data
Landsat Thematic Mapper (TM) Foliage Projective Cover (FPC) based on the same set of images in the same study areas is shown as greyscale images, with bright for higher and dark for lower FPC
The Processing Scheme for Standardised Surface Reflectance (PSSSR) and Sun Canopy Sensor (SCS) corrections appeared to show a greater decrease in the three-dimensional relief effect, and the scenes look flat in the closed canopy of Border Range National Park (BRNP)

Summary

Introduction

Operational mapping, monitoring of vegetation cover and vegetation cover changes are important applications of remotely sensed data. The need for vegetation information over large areas has prompted the investigation of the relationship between ground measurement of vegetation cover metrics and vegetation indices from spectral reflectance measured by remote sensors. The common approach has been to correlate a ground measured vegetation cover metric with vegetation indices or image reflectance. Variation of measured reflectance by sensors caused by factors other than variation in vegetation cover modifies these relationships and reduces the accuracy of derived vegetation cover estimates. Topography can substantially affect the radiometric properties of remotely sensed data; the estimation of vegetation cover on complex topography creates unique challenges compared to vegetation cover on flat terrain. It would seem that topographic correction is a necessary step in radiometric correction of satellite imagery when used for vegetation mapping

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Discussion

Conclusion