Mapping of Bara Shigri Glacier, H. P. using
Digital Image Processing Techniques
Results
Digital Image Analysis
i) Spectral Properties
The radiance value along a transect of glacier have been calculated and plotted glacier pixel location fro snout area. This shows distinct variation of glacier features in band 4 and band 2 than the other bands.
The four bands of IRS LISS II data are studies in details specifically the histograms of the DN values. IRS LISS II is seven bit quantization level where the DN values are ranging from 0-127. in General, band 1 is affected by atmospheric scattering. The careful examination of radiance plot along a transect from snout to ablation area of glacier from snout to ablation are of the glacier indicate that band 2 and band 4 snow variation of different glacial ice. The false colour composite of band 4 in red, band 3 in green and band 2 in blue indicate that bluish colour in the snout area is due to the glacial melt. The clear demarcation of ablation zone and accumulation zone are not clearly discernible in the false colour composite.
ii) Image Rationing
IRS LSS II band 2 and band 4 have been selected for rationing based on the DN value and radiance analysis along a glacial transect. The variation of DN values of different glacial features are very less. Because of 7 bit different glacial features is not discernible clearly in the ration of band 2/band . The band 4 has been enhanced using linear stretch based on the histogram and the image has been transformed to 8 bit information (0-255). The enhanced band 4 and band 2 have been used as Normalised Difference Glacial Index (NDGI).
| NDGI = |
Band 4 - Band 2
--------------------
Band 4 + Band 2 |
The ratio output enhanced different glacial features, density slicing and colour look up table are generated depicting different glacial features in the DNGI image and areal statistics are calculated.
iii) Digital Terrain Model
The height contours and spot heights from survey of India toposheets have been digitized. The height values are interpolated for entire part of the area and Digital Elevation Model (DEM) has been generated using the software available with Regional remote Sensing Service Centre. The false colour composite of band 4 in red, band 3 in green and band 3 in blue has been draped over DEM. Similarly, the colour coded NDGI image has been draped over DEM. The altitude variation of different glacial features are also studied.
Discussion
The outputs generated using digital image processing techniques have been interpreted for various glacial features, bara shigri glacier is a compound glacier where more tributary glaciers are joining the main valley. The entire glacial watershed area has been studied and mapped for glacial features.
i) Accumulation Zone
the accumulation zone form the upper part of the glacier which has net mass gain each year. The accumulation zone is clearly seen best at the end of the summer melting season. It has brightest tone in all the spectral bands of IRS LISS II data. The accumulation zone is totally frozen ground with smooth surface. The upper accumulation zones features like bergschrund (tension cracks), firm are not clearly discernible in IRS LISS II data. In the lower part of the accumulation zone, crevasses are also no discernible due to their dimension and are commonly concealed by snow bridges. The extent of accumulation zones differentiated better in eh ratio image (NDGI).
ii) Equilibrium Line
The line separating accumulation zone and ablation zone, is the equilibrium lie. The equilibrium line is not clearly discernible in the false colour composite. The false colour composite with the histogram equilised stretch of band 4 in red, band 3 in green ad band 2 in blue show ablation zone and accumulation zone. The expedition carried out by WIHG in Chota Shigri Glacier Indicate that Equilibrium Line Altitude (ELA) is 4400 mts above MSL. The ELA in Chota Shigri glacier has been verified in normalized difference Glacial Index (NDGI) image. The ELA in Bara Shigri main glacier is found to be 5200 Mts above MSL. The mild variation of ELA in different small glaciers of the Bara Shigri glacial complex has been observed.
iii) Ablation zone
The ablation zone form the lower part of the glacier where net loss of mass is prominent. The lowest part of ablation zone is terminus where the ice is mixed with moraines. A ice mixed with moraines in the snout area is clearly discernible in Fig 4. The pattern in the snout area indicate that this glacier is fast receding.
Figure 4 Spectral Properties of Bara Shigri Glacier
Figure 5 Bara Shigri Glacier
iv) Mass Balance
The mass balance of the glacier can be determined accurately by field measurements of the accumulation zone measurements of the accumulation zone and ablation zone. The position of transition snow line at the end of the melting snow line at the end of the melting season becomes a useful indicator of the mass balance. A correlation exist between altitude of the transient snow line and the annual specific net balance. The long term trend of the mass balance of no surging glaciers can be judged qualitatively from the characteristics of the lower ablation zone. In the Bara Shigri glacier complex no surging behaviour is observed. The sharp pointing edge f the terminus, high ice cored lateral moraines of the Bara Shigri glacier is indicative of negative mass balance.
Conclusion
At the end of summer period, the transient snow line moves in the higher altitude and the glaciers would be exposed. The end of the September and October months are suitable for studying the glaciers using satellite data. The hybrid approach of digital enhancements of IRS data with elevation model can be used on operational made of glacial mapping.
Acknowledgements
The authors express their deep sense of gratitude to Shri K. Radhakrishnan, Director NNRMS-RRSSC for his support and constant encouragement. Thanks to scientist of RRSSC, Nagpur, who had participated in scientific discussions.
References
-
John A. Elson, glacial Geology, Remote Sensing in Geology, edited by Barly S. Siegal & alan e. Gillepie.
- Mayewsk, P.A and Jesahake, P.A (1979) Himalayan and Trns-Himalayan and glacier fluctuation since A.D 1812. Arctic and Alphien research 11 (3)
- Rawat B. R. S., Anil K. Mundepi and Surendra Kumar (1989), Mass balance, Surface lowering, velocity pattern and
variation in Chota districts (H. P.), National Meet on Himalayan Glaciology, 5-6, June 1989.
