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IAPRS & SIS, Vol.34, Part 7, "Resource and Environmental Monitoring", Hyderabad, India,2002 
A SIMPLE TECHNIQUE FOR THE REMOVAL OF VERTICAL COHERENT NOISE 
FROM LANDSAT THEMATIC MAPPER IMAGES 
Janet Nichol*, Vijay Vohora? 
* Department of Land Surveying and GeoInformatics, The Hong Kong Polytechnic University, Hunghom, Kowloon, Hong Kong 
Department of Earth Science, University of Hong Kong, Pokfulam Road, Hong Kong 
Commission VI, WG VI/A 
KEYWORDS: Landsat TM, signal-to-noise ratio, median filter, image enhancement 
ABSTRACT: 
A method is described for removal of a coherent pattern of vertical coherent noise observed on LANDSAT Thematic Mapper images 
over homogeneous water surfaces where the image signal is relatively weak. The noise is observable in all six visible wavebands of 
the sensor when linear contrast enhancement is applied to improve the visualisation of water quality parameters. Since the noise is 
serious enough to affect image interpretation and quantification of these parameters a simple method has been developed for the 
removal of the noise using a series of median filters. The results of the noise removal are presented in the form of quantification of 
the Signal-to-Noise ratio of the images before and after application of the removal procedures, and suggest a 3 times increase. 
1. INTRODUCTION 
Increasing concern about human activities in coastal regions 
has not been accompanied by the development of fine spatial 
resolution satellite sensing systems calibrated for water. 
Systems such as SeaWifs, MODIS and MERIS which are 
calibrated with a high Signal-to-Noise Ratio (SNR) over water 
are more suited to oceanographic applications due to their 
coarse spatial resolution. Therefore more detailed studies of 
coastlines and small water bodies still rely on sensors having 
relatively fine spatial resolution but a low SNR for water, such 
as SPOT and Landsat. 
In the case of LANDSATSs 4 and 5 Thematic Mapper, noise is 
present in the form of striping with a period of 16 lines, due to 
gain and offset differences between the 16-row detector scans. 
The noise is particularly visible over homogeneous surfaces 
such as clouds and water bodies. The magnitude of this noise 
has not been considered serious enough to warrant removal 
using histogram matching techniques during final product 
generation at the ground receiving station due to the large 
amount of processing time required (Poros and Petersen, 1985). 
Methods have been proposed for removing this 16" line 
banding, comprising radiometric equalisation and histogram 
matching, as well as various types of kernel-based filtering. 
These methods are not completely successful however, because 
the noise comprises both a high frequency component with a 
radiance variation of up to 5W.m2.ster. and a low frequency 
component with radiance variation of up to 15W.m2.ster and 
after conventional noise removal the latter is still apparent as a 
slow variation in image content over a period of approximately 
80 scan lines. 
This paper describes the effects of a type of vertical coherent 
noise (other than the 16-line banding) which is also present in 
LANDSAT TM images over homogeneous surfaces (Figure 1). 
This noise comprises coherent banding in a NNE-SSW 
direction, with an irregular phase shift between groups of lines. 
The period of the pattern is approximately 10-11 pixels and the 
amplitude is 1-2 counts. Although of the same magnitude as the 
16-line banding, it is not so readily apparent, due to its lack of 
linear continuity across the image. This vertical coherent noise 
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has not previously been described in the literature for the 
LANDSATS 4 and 5 TM sensors. 
  
  
  
   
  
  
   
   
   
   
  
  
   
  
   
  
  
  
   
   
  
   
  
   
   
   
   
  
  
   
    
  
   
    
  
  
  
  
  
  
  
  
  
  
  
Figure 1. Contrast enhanced LANDSAT TM image extract 9*6 
km showing boundary of a sediment plume offshore from the 
Batanghari River, Sumatra. The transect line refers to Figure 4 
However Murphy et al. (1985), evaluating the LANDSAT TM 
product received a the Canadian ground receiving station, 
identified a coherent noise pattern with maximum amplitudes of 
0.5 DN although the magnitude, period and spatial appearance 
of the noise was not described. The authors concluded that 
since Fourier transforms would be necessary to remove the 
noise, corrections should not be made at the receiving station. 
The vertical coherent noise discussed in the present paper is 
observable in all six visible wavebands of LANDSAT TM 
images, and is strong enough, to affect analysis results. It has 
been observed by the authors on many different TM images in 
coastal regions (eg. Ireland, Singapore, Malaysia, Indonesia,